WO2017130657A1 - X-ray ct device, method for setting imaging condition, and program for setting imaging condition - Google Patents

X-ray ct device, method for setting imaging condition, and program for setting imaging condition Download PDF

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Publication number
WO2017130657A1
WO2017130657A1 PCT/JP2017/000262 JP2017000262W WO2017130657A1 WO 2017130657 A1 WO2017130657 A1 WO 2017130657A1 JP 2017000262 W JP2017000262 W JP 2017000262W WO 2017130657 A1 WO2017130657 A1 WO 2017130657A1
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ray
shooting
imaging
map
feature
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PCT/JP2017/000262
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French (fr)
Japanese (ja)
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後藤　大雅
高橋　悠
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株式会社日立製作所
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Publication of WO2017130657A1 publication Critical patent/WO2017130657A1/en

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
    • A61B6/02—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
    • A61B6/03—Computerised tomographs

Definitions

  • the present invention relates to an X-ray CT apparatus, an imaging condition setting method, and an imaging condition setting program, and more particularly to an X-ray CT apparatus, an imaging condition setting method, and an imaging condition setting program for controlling an X-ray dose applied to a specific part of a subject.
  • the X-ray tube While rotating the X-ray tube around the body axis of the subject, the X-ray tube emits X-rays in the form of a fan beam or cone beam, the X-ray transmitted through the subject is detected by the detector, and the obtained projection
  • An X-ray CT apparatus that acquires a reconstructed image inside a subject by back projecting data is known.
  • the rotation angle of the X-ray tube is divided into a plurality of angle ranges, and the X-ray irradiation output is reduced in an angle range where the distance between the X-ray sensitive part and the X-ray focal point is close.
  • an X-ray CT apparatus for reducing the X-ray exposure dose at a site having high X-ray sensitivity is disclosed.
  • Patent Document 2 by moving the bed, moving the subject relative to the X-ray source, and arranging the center of the diagnostic target part at or near the imaging center, An X-ray CT apparatus that suppresses X-ray irradiation on a living tissue is disclosed.
  • the X-ray CT apparatus of Patent Document 2 is not considered at all about reducing the X-ray exposure dose for a part having high X-ray sensitivity. For this reason, when a region having high X-ray sensitivity is included in the imaging range, the X-ray exposure dose may not be sufficiently reduced only by placing the center of the diagnostic target region at or near the imaging center.
  • the present invention has been made in view of the above circumstances, and an object of the present invention is to more effectively reduce unnecessary X-ray exposure dose for a portion having high X-ray sensitivity.
  • the present invention provides the following means.
  • One aspect of the present invention includes an X-ray source that circulates around a subject on a bed, and an X-ray detector that detects a dose of X-rays irradiated from the X-ray source and transmitted through the subject,
  • a scanner that acquires projection data, a reconstruction calculation unit that acquires a reconstructed image based on the projection data, a shooting condition setting unit that sets shooting conditions when acquiring the projection data, and projection according to the shooting conditions
  • a shooting feature value map generation unit that generates a shooting feature value map that maps feature values as information indicating features of the reconstructed image generated when data is acquired, and displays the shooting feature value map on a display unit
  • An X-ray CT apparatus including a display control unit is provided.
  • 1 is an external configuration diagram showing an outline of an X-ray CT apparatus according to a first embodiment of the present invention.
  • 1 is a block diagram showing an outline of an X-ray CT apparatus according to a first embodiment of the present invention. It is explanatory drawing which shows an example of the display screen displayed on the display apparatus of the X-ray CT apparatus which concerns on the 1st Embodiment of this invention. It is explanatory drawing which shows an example of the display screen displayed on the display apparatus of the X-ray CT apparatus which concerns on the 1st Embodiment of this invention.
  • 5 is a flowchart showing operations from acquisition of a positioning image to generation of a reconstructed image in the X-ray CT apparatus according to the first embodiment of the present invention.
  • an X-ray CT apparatus it is explanatory drawing which shows the imaging
  • an X-ray CT apparatus it is explanatory drawing which shows the relationship between the imaging start angle of the X-ray source (X-ray generator), the imaging start position, and the X-ray source trajectory (trajectory) when performing an axial scan.
  • an X-ray CT apparatus it is explanatory drawing which shows the relationship between the imaging start angle of the X-ray source (X-ray generator), the imaging start position, and the track
  • an X-ray CT apparatus a subject placed on a bed is irradiated with X-rays in a fan beam or cone beam shape while rotating an X-ray source around a body axis, and a plurality of detection elements are formed in an arc shape. Imaging is performed by receiving X-rays that have passed through the subject with a detector disposed in the area. Normally, one shooting in the rotation direction is referred to as one view, and about 1000 shootings are performed per one rotation in the rotation direction.
  • the following methods are mainly known as scanning (imaging) methods for performing imaging while rotating the X-ray source in this way.
  • FIG. 7A An imaging method in which the bed moves in the body axis direction after imaging and repeats an axial scan, which is called spiral scan, helical scan, or spiral scan.
  • the bed moves at a constant speed in the body axis direction and the X-ray source becomes the subject.
  • An imaging method (FIG. 7A)
  • FIG. 7B an imaging method in which the bed reciprocates in the body axis direction and the X-ray source circulates around the subject in a spiral orbit ( FIG. 7C) and called variable pitch scan, the bed moves at a variable speed, and the X-ray source orbits around the subject in a spiral orbit.
  • Imaging method, and the like are known as the main scanning method that.
  • an imaging method performed without rotating the X-ray source an imaging method called a scanogram, in which the bed moves with the X-ray source fixed (FIG. 7D) is also known.
  • the X-ray CT apparatus when imaging is performed while rotating the X-ray source as described above, fan-shaped fan beam-shaped or conical cone-beam-shaped X-rays are emitted from the X-ray source.
  • the number (period) of irradiation with X-rays varies depending on the region of the subject. That is, for example, the number of times (period) of X-ray irradiation differs between the vicinity of the body axis center of the subject and the body surface of the subject.
  • the period during which X-rays are irradiated differs for each region (image position) of the subject.
  • the period during which X-rays are irradiated (the rotation angle width at which the pixel position is imaged) is longer at the rotation center position. That is, projection data that can be used for reconstruction is collected over many angular widths at the rotation center, but is collected from a small angular width at positions away from the rotation center. Therefore, as shown in FIGS.
  • the angular width (back projection phase width) of projection data that can be used for reconstruction is related to the pixel position and the bed movement speed, and X
  • the imaging redundancy at each position of the subject differs depending on the trajectory of the radiation source, and in general spiral scanning, dose unevenness of 1.5 to 2 times can occur depending on the position. The same applies to the image noise, and unevenness such as the image noise ratio map in the spiral scan shown in FIGS. 10 and 11 occurs.
  • the X-ray irradiation amount can vary 1.5 to 2 times depending on the trajectory of the X-ray source. Even if it is half, depending on the trajectory of the X-ray source, the dose may be doubled. That is, if the trajectory of the X-ray source is not taken into account, the X-ray exposure dose cannot always be reduced.
  • the trajectory of the X-ray source can change depending on the imaging start angle (position) of the X-ray source, as will be described below.
  • FIG. 12A shows the case where the image is taken from 250 degrees from the image taking start angle 0 degree and FIG. 12B is from the image taking start angle 180 degree.
  • a, b, and c show the positions of the subjects. ing.
  • FIG. 12A shows that the points a, b, and c are both irradiated with fan beam-shaped X-rays from the X-ray source and photographed for 250 degrees.
  • each pixel considering with a parallel beam, it is considered that the image is taken over 180 degrees at the point b and 270 degrees or more at the point c.
  • FIG. 12B shows that points a, b, and c are irradiated with fan beam-shaped X-rays from the X-ray source and imaged over 250 degrees as in FIG. 12A.
  • FIG. 12B when viewed from each pixel (considering a parallel beam), it is considered that the image is taken over 180 degrees at the point c and over 270 degrees at the point b.
  • the shooting time (shooting angle range with a fan beam) is the same, the angle range when viewed with a parallel beam is different for each pixel, and these relationships change according to the shooting start angle.
  • the trajectory of the X-ray source changes according to the imaging start angle. That is, it can be seen that the X-ray exposure dose of the subject, the noise distribution in the axial plane, and the temporal resolution distribution change according to the imaging start angle.
  • 13A and 13B show the relationship between the imaging start angle and the source trajectory.
  • the position where data is collected does not depend on the shooting start angle.
  • the angle range for shooting that is, the position where data is collected, changes according to the shooting start angle.
  • the body axis direction position of the X-ray source may be varied when imaging the same range of the subject. it can. Therefore, in the case of step scan, the angle range to be imaged can be changed by the body axis direction position of the X-ray source to be imaged in addition to the imaging start angle.
  • the X-ray exposure dose of the subject depends on the trajectory of the X-ray source, and the trajectory of the X-ray source varies depending on the scanning method, the imaging start angle, and the like. For this reason, in order to reduce the X-ray exposure dose for a part having high X-ray sensitivity, it is necessary to set imaging conditions such as an X-ray source trajectory including an imaging start angle in accordance with the scanning method.
  • the present invention aims to more effectively reduce the unnecessary X-ray exposure dose for a specific part of a subject such as a part having high X-ray sensitivity under such a background.
  • the X-ray CT apparatus 1 according to the present embodiment can be applied to, for example, a multi-slice CT apparatus, and for example, a rotation-rotation system (third generation) can be adopted as a scanning system.
  • a rotation-rotation system third generation
  • the X-ray CT apparatus 1 includes a scanner 10, an operation unit 20, and a bed 30.
  • the scanner 10 performs a scan process on the subject placed on the bed 30 in accordance with an instruction from the operation unit 20.
  • the scanner 10 includes an X-ray generator 5 as an X-ray source, a high voltage generator 6, an X-ray controller 7, a collimator 8, a collimator controller 9, a detector 11, a central controller 12, a scanner controller 13, and a bed.
  • a control device 14, a couch movement measuring device 15, a driving device 16, a preamplifier 17, and an A / D converter 18 are provided.
  • the X-ray generator 5 generates X-rays by the high voltage applied to the high-voltage generator 6 while circling around the subject placed on the bed by the driving device 16 to be described later. Irradiate.
  • the high voltage generator 6 supplies a high voltage to the X-ray generator 5 in accordance with a control signal from the X-ray controller 7.
  • the collimator 8 is controlled by the collimator control device 9 and controls an X-ray irradiation region irradiated by the X-ray generator according to a control signal from the collimator control device 9.
  • the detector 11 is disposed facing the X-ray generator 5, detects X-rays irradiated from the X-ray generator 5 and transmitted through the subject, and outputs the detection result to the preamplifier 17 as a current value.
  • a single-row detector or a multi-row detector can be applied.
  • the multi-row detector has an advantage that a plurality of single-row detectors are arranged in the direction of the rotation axis, and as a whole, a wider range than that of the single detector can be photographed.
  • the preamplifier 17 amplifies the detection result received from the detector 11 and outputs it to the A / D converter 18.
  • the analog current value amplified by the preamplifier 17 is converted into digital data, further LOG-converted, calibrated, and output as projection data to an arithmetic unit 22 described later.
  • the X-ray generator 5, the collimator 8, the detector 11, the preamplifier 17, and the like are arranged on a disk (not shown), and the X-ray generator 5 is driven around the subject by driving the disk by the driving device 16. It is designed to go around.
  • the scanner control device 13 controls the drive device 16 and the collimator control device 9 for driving the disk on which the X-ray generation device 5 as the X-ray source is mounted in accordance with a control signal from the central control device 12 described later.
  • the couch controller 14 controls the moving speed and the like of the couch 30 according to the control signal from the central controller 12.
  • the bed 30 is measured for movement speed and distance by the bed movement measuring device 15.
  • the central control device 12 controls the above-described X-ray control device 7, scanner control device 13, and bed control device 14 based on an instruction input from the operation unit 20.
  • the operation unit 20 performs operations by the user, generation of reconstructed images, display of images, and the like, and includes an input / output device 21 and an arithmetic device 22.
  • the input / output device 21 includes a display control device 23 for displaying on the display device 29 a reconstructed image generated by the arithmetic device 22 and a photographing feature amount map, which will be described later, an input device 24 for inputting photographing conditions and reconstruction conditions, It includes a storage device 25 that stores input conditions and images to be displayed.
  • a display device 29 that displays various images in accordance with instructions from the display control device 23 is connected to the display control device 23.
  • a display device such as a liquid crystal display can be applied, and as the input device 24, one or more of a mouse, a keyboard, a touch panel, and the like can be applied.
  • the storage device 25 a drive device such as a hard disk or various storage media can be applied.
  • Examples of photographing conditions input from the input device 24 by the user include a bed moving speed, tube current, tube voltage, and slice position.
  • imaging methods such as axial scan and spiral scan, imaging start angle, imaging range in the body axis direction, beam pitch, tube current, tube voltage, etc., and settings such as X-ray exposure control (AEC) are also performed. .
  • the reconstruction conditions input from the input device 24 by the user include, for example, a reconstruction method, an image slice thickness, a backprojection phase width, a view weight slope width, a region of interest, a reconstructed image matrix size, and a reconstruction filter function. And the position of the reference point.
  • the computing device 22 includes a reconstruction computing device 26 that generates a reconstructed image based on projection data collected by the scanner, an image processing device 27 that performs necessary image processing on the reconstructed image, and a reconstructed image.
  • a shooting feature value map generation device 28 that maps the shooting feature values is included.
  • the function of each device included in the arithmetic device 22 can be realized as software by a CPU (not shown) included in the arithmetic device 22 reading and executing a program stored in a memory such as a ROM in advance. Also, some or all of the operations executed by each device included in the arithmetic device 22 can be realized by ASIC (application specific integrated circuit) or FPGA (field-programmable gate array).
  • the reconstruction calculation device 26 can reconstruct the acquired projection data by various methods.
  • the reconstruction calculation device 26 can be reconstructed by a known method such as so-called fan beam reconstruction or so-called parallel beam reconstruction.
  • the backprojection phase range used for reconstruction is determined for each reconstruction pixel. They may be different or in the same range.
  • the image processing device 27 performs necessary image processing on the reconstructed image reconstructed by the reconstruction computing device 26 so that the reconstructed image is in an optimum form for display on the display device 29.
  • the shooting feature amount map generation device 28 maps feature amounts as information indicating the features of the reconstructed image generated by the reconstruction calculation device 26 when acquiring projection data according to the shooting conditions input to the input device 24. A photographed feature map is generated. Details of the shooting feature map will be described later.
  • the imaging process and the reconstruction process in the X-ray CT apparatus configured as described above are performed as follows.
  • a shooting start signal is generated and input from the operation unit 20 to the central controller 12.
  • the central control device 12 receives the input imaging start signal, and sends a control signal necessary for imaging to the X-ray control device 7, the scanner control device 13, and the bed control device 14, and starts imaging.
  • a control signal is transmitted from the X-ray controller 7 to the high voltage generator 6, a high voltage is applied to the X-ray generator 5, and the subject is irradiated with X-rays from the X-ray generator 5. Is done.
  • a control signal is transmitted from the scanner control device 13 to the drive device 16, and the X-ray generator 5, the detector 11, the preamplifier 17, etc. circulate around the subject 4 by rotating the disk.
  • the bed 30 on which the subject is placed moves still (normal scan) or translates in the body axis direction of the subject (spiral scan).
  • X-rays irradiated by the X-ray generator are limited in irradiation area by the collimator 6, absorbed (attenuated) in each tissue in the subject, transmitted through the subject, and detected by the detector 11.
  • the X-rays detected by the detector 11 are converted into current, amplified by a preamplifier 19, converted to digital data by an A / D converter 20, LOG converted, calibrated, and subjected to calibration as an arithmetic unit 22 as projection data. Is input.
  • the reconstruction calculation device 26 performs a reconstruction process based on the projection data input to the calculation device 32 to generate a reconstructed image.
  • the generated reconstructed image is stored in the storage device 25 and displayed as a CT image by the display device 29.
  • the image processing device 27 the image is displayed as a CT image by the display device 29.
  • the shooting feature amount map generation device 28 generates a shooting feature amount map in which feature amounts as information indicating features of the reconstructed image are mapped.
  • the generated reconstructed image is stored in the storage device 25 and displayed on the display device 29 as shown in FIGS.
  • the shooting feature amount map generation device 28 is information indicating the characteristics of the reconstructed image generated by the reconstruction calculation device 26 when acquiring projection data according to the shooting conditions input to the input device 24.
  • a shooting feature amount map in which the feature amount is mapped is generated.
  • the X-ray exposure amount when acquiring the projection data and the re-generation generated from the acquired projection data is defined as a feature amount.
  • the shooting feature value map generation device 28 maps this feature value, that is, generates a map expressed on the image as a shooting feature value map.
  • the imaging feature amount map for example, an irradiation dose ratio map, an image noise ratio map, a time resolution ratio map, a spatial resolution ratio map, and the like can be generated.
  • the shooting feature amount map generation device 28 generates a shooting feature amount map and displays it on the display device 29.
  • the shooting feature amount map generation device 28 acquires a positioning image, generates a shooting feature amount map corresponding to the positioning image, and displays it on the display device 29 together with the positioning image.
  • FIG. 3 and 4 show an example of the display screen of the display device 29.
  • FIG. 3 In the display screen shown in FIG. 3, an area for setting two shooting feature amount maps, a reconstructed image, and shooting conditions are displayed together with the positioning image.
  • FIG. 4 together with the positioning image, two imaging feature quantity maps having different cross-sectional directions, an area for setting imaging conditions, and an imaging start angle and imaging feature quantity (irradiation dose) which are one of the imaging conditions. , Graphs (curves) representing the relationship with image noise, time resolution) are displayed.
  • the user can grasp the X-ray exposure dose and the degree of noise from the imaging feature map.
  • the display device 29 by causing the display device 29 to display the imaging feature amount map together with the positioning image, the user grasps in which part of the subject an area where the X-ray exposure amount or noise increases may occur. can do.
  • an imaging feature map for example, an irradiation dose ratio map, an image noise ratio map, a temporal resolution ratio map, a spatial resolution ratio map, a body axis resolution ratio map, and the like can be used. Can be created.
  • the irradiation dose ratio map can be acquired, for example, by performing a back projection process using a tube current / time product (mAs) per view as a projection value. In this case, it can be expressed as the following formulas (1) and (2) using fan beam back projection.
  • DSRM is a dose ratio map
  • ⁇ is a view index in fan beam projection
  • ⁇ is a detector channel index in fan beam projection
  • ⁇ is a detector in fan beam projection.
  • N view is the number of views
  • mA is the tube current modulation function [mA] in the view direction
  • T scan is the scan speed [s]
  • ⁇ 1 is the back projection start view with the fan beam
  • ⁇ 2 is the fan beam
  • the backprojection end view at x, y, z is the pixel index.
  • image noise ratio map The image noise (SD) ratio map can be expressed as the following formulas (3) and (4) using, for example, fan beam back projection.
  • an image noise ratio map may be generated as shown in the following formulas (5) and (6).
  • an image noise ratio map may be created by actually measuring the volume image.
  • SDRM is an image noise ratio map
  • ⁇ is a view index in fan beam projection
  • ⁇ is a detector channel index in fan beam projection
  • ⁇ is a detector row in fan beam projection.
  • N view is the number of views
  • W f is a view weight function
  • mA is a tube current modulation function [mA] in the view direction
  • T scan is a scan speed [s]
  • G is logarithmically converted when creating a projection value.
  • Pe is the projection data of the subject estimated from the positioning image and the imaging data for positioning image
  • Pa is the projection data of the Bowtie filter and the X-ray filter obtained by Air cal imaging
  • ⁇ 1 backprojection startup view of a fan beam beta 2 backprojection ends view of a fan-beam
  • x, y, z are the pixel It is an index.
  • positioning imaging data and forward projection data of the obtained positioning image can be used as Pe.
  • a projection value estimated based on the object model obtained from the projection value distribution of the scanogram may be used as Pe.
  • This object model can be acquired by using a method of estimating the object shape from the scanogram by AEC or the like.
  • the time resolution ratio map (total time width map) can be obtained, for example, by weighted backprojection processing using the imaging time ⁇ T scan per view as a projection value, as shown in the following formula (7). it can.
  • the effective time width map when used, it can be obtained by performing weighted backprojection using the imaging time ⁇ T scan per view as a projection value, as shown in the following formula (8).
  • TRRM is a temporal resolution ratio map
  • ⁇ is a view index in fan beam projection
  • N view is the number of views
  • W f is a view weight function
  • T scan is a scan speed [s]
  • ⁇ 1 is back projection with a fan beam.
  • the start view, ⁇ 2 is the back projection end view with the fan beam, and x, y, and z are pixel indices.
  • the spatial resolution ratio map can be obtained, for example, by performing a weighted back projection process on the value of the beam width in the channel direction according to the distance from the X-ray generator as an X-ray source to the pixel. In this case, it can be expressed as the following formulas (9) and (10) using fan beam back projection.
  • SRRM is a spatial resolution ratio map
  • ⁇ is a view index in fan beam projection
  • ⁇ is a detector channel index in fan beam projection
  • ⁇ is a detector row in fan beam projection.
  • N view is the number of views [view]
  • W f is the view weight function
  • D sid is the source-detector element distance [mm]
  • L is the source-pixel distance [mm]
  • ⁇ dcs is the channel direction detection.
  • the element size [mm] ⁇ 1 is a back projection start view with a fan beam
  • ⁇ 2 is a back projection end view with a fan beam
  • x, y, and z are pixel indexes.
  • the body axis resolution ratio map can be obtained, for example, by performing weighted back projection processing on the value of the beam width in the body axis direction according to the distance from the X-ray generator as an X-ray source to the pixel. In this case, it can be expressed as follows using fan beam back projection.
  • ZRRM is a body axis resolution ratio map
  • ⁇ is a view index in fan beam projection
  • ⁇ is a detector channel index in fan beam projection
  • ⁇ is a detector array in fan beam projection.
  • N view is the view number [view]
  • W f is the view weight function
  • D sid is the source-detector element distance [mm]
  • L is the source-pixel distance [mm]
  • ⁇ drs is the column direction.
  • ⁇ 1 is a back projection start view with a fan beam
  • ⁇ 2 is a back projection end view with a fan beam
  • x, y, and z are pixel indexes.
  • an imaging feature map an example of a method for generating an irradiation dose ratio map, an image noise ratio map, a temporal resolution ratio map, a spatial resolution ratio map, and a body axis resolution ratio map has been described.
  • the feature amount map based on other feature amounts indicating the features of the image can be applied to the shooting feature amount map, and other known methods can be used for the above-described feature amount map generation method. Can be used.
  • the above-described shooting feature amount map is generated as a three-dimensional image, and when the positioning image is volume data generated by a spiral scan, it is preferably displayed in accordance with the display of the positioning image. At that time, the same cross section is displayed side by side, the shooting feature map is colored and displayed superimposed on the positioning image, the value for the position selected by the cursor is displayed by referring to the shooting feature map, the positioning image The average value, maximum value, and minimum value of a predetermined area such as a circle or rectangle can be calculated and displayed.
  • the imaging feature map may display a plurality of surfaces such as an axial surface.
  • a three-dimensional image that is a shooting feature map may be projected in the same direction as the scanogram shooting to create and display a scanogram of the shooting feature map.
  • a cross section that passes through the rotation center of the three-dimensional image that is the imaging feature amount map or a cross section that becomes the center of the subject may be displayed. The subject center cross section at this time can be estimated from the positioning image.
  • the arithmetic unit 22 including the imaging feature value map generation device 28 receives the imaging condition of the positioning image set by the user via the input device 24 (step S11), and the positioning image according to the imaging condition set. Is sent to the scanner 10 (step 12).
  • the setting of the imaging condition of the positioning image and the imaging of the positioning image can be performed by a known method. For example, scanogram imaging or low-dose spiral scanning can be applied.
  • the imaging conditions and reconstruction conditions in the actual imaging are set by the user based on the positioning image.
  • the arithmetic unit 22 receives the set various conditions via the input device 24 (step S13).
  • the image reconstruction method can be set as a reconstruction condition.
  • imaging conditions an imaging method such as an axial scan and a spiral scan, an imaging start angle, an imaging range in the body axis direction, a beam pitch, a tube current, a tube voltage, and X-ray exposure control (AEC) are also set.
  • AEC X-ray exposure control
  • the type of shooting feature value to be calculated is also selected in the shooting condition setting area 50.
  • the shooting feature value map generating device 28 In the next step S14, the shooting feature value map generating device 28 generates a shooting feature value map from the shooting conditions set and input by the user in the previous step S13. At this time, the shooting feature value map generation device 28 calculates the feature value according to any one of the above-described formulas (1) to (12) according to the type of the feature value selected in the previous step, and the shooting feature value map. And the generated shooting feature amount map is transmitted to the display control device 23. The display control device 23 causes the display device 29 to display a shooting feature amount map together with the positioning image.
  • the shooting feature amount map displayed on the display device 29 is confirmed, and an input of whether or not the user needs to change the shooting conditions is accepted via the input device 24 (step S15).
  • the arithmetic unit 22 receives a signal indicating that the shooting conditions are not changed from the input device 24, proceeds to the next step S16, and is set. An instruction is transmitted to the scanner 10 to perform the main photographing under the photographing conditions.
  • the arithmetic unit 22 receives a signal to change the shooting condition from the input device 24, returns to step S13, and accepts the input of the reset shooting condition. Then, the shooting feature value map generation device 28 creates a shooting feature value map again according to the reset shooting conditions (step S14).
  • the irradiation dose ratio is selected in the imaging condition setting region 50 by the user, and the imaging feature value map generation device 28 uses the irradiation dose as the imaging feature value map.
  • a ratio map is generated and displayed on the display device 29.
  • the user can grasp
  • the user adjusts the imaging start angle as an imaging condition so that X-ray irradiation to highly sensitive X-ray parts such as the spleen, the lens, and the thyroid gland is reduced.
  • the photographing start angle can be adjusted by a slide bar displayed on the display screen of the display device 29 as shown in FIG. 3, or can be directly designated by a user's manual input.
  • a variable pitch scan it may be adjusted to increase the bed moving speed in a highly sensitive X-ray sensitive region such as the spleen, the lens or the thyroid gland.
  • the X-ray exposure amount increases.
  • the position in the body axis direction of the X-ray generator 5 can also be adjusted so that the joint of imaging shifts from a portion having high X-ray sensitivity.
  • a tomographic image is generated by reconstructing the projection data collected by the main imaging performed in step S16, and displayed on the display device 29.
  • the imaging feature amount map selected by the user is displayed side by side with the tomographic image, the imaging feature amount map is colored and displayed over the tomographic image, or the cursor It is also possible to display the value for the position selected by referring to the shooting feature map, or to calculate and display the average value, maximum value, or minimum value of the area surrounded by a circle or rectangle on the positioning image.
  • the X-ray generator as an X-ray source is circulated around the subject by the scanner, and the X-ray dose irradiated from the X-ray generator and transmitted through the subject is detected by the X-ray detector.
  • the detected projection data is acquired, and the projection data is reconstructed by a reconstruction calculation device to obtain a reconstructed image.
  • imaging conditions for acquiring projection data are set according to the subject. Then, when projection data is acquired by the scanner according to the set shooting conditions, a shooting feature amount map is generated by mapping feature amounts as information indicating features in the obtained reconstructed image, and this is displayed on the display device. .
  • the feature amount of the generated reconstructed image can be presented to the user, and the user confirms the displayed imaging feature amount map to thereby display the reconstructed image in the reconstructed image.
  • the feature amount of the image can be grasped. Therefore, the user can set the imaging conditions again as necessary. For example, when it is desired to reduce the X-ray irradiation to the X-ray sensitive parts such as the spleen, the lens and the thyroid gland, The starting angle and the like can be adjusted. Thereby, the trajectory of the X-ray source is changed, and the X-ray exposure amount can be reduced by reducing the X-ray irradiation period for the site having high X-ray sensitivity.
  • an irradiation dose ratio map corresponding to the imaging start angle as an imaging feature amount map
  • the user can obtain an X-ray irradiation dose for a site of interest such as a site with high X-ray sensitivity of the subject. It can be determined whether it is appropriate.
  • the irradiation dose ratio map when the X-ray irradiation dose to a part having high X-ray sensitivity is large, the X-ray sensitivity is changed by changing the trajectory of the X-ray generator by changing the imaging start angle. The X-ray exposure dose for high sites can be reduced.
  • an imaging feature amount map to be generated and displayed by appropriately selecting any one of a time resolution ratio map, an image noise ratio map, etc., the image of interest has good image noise, time resolution, spatial resolution,
  • An imaging condition that can generate a reconstructed image having a desired imaging feature amount, that is, a tomographic image, in the region of interest can be set.
  • FIG. 7A shows the trajectory of the X-ray generator during normal scanning
  • FIG. 7B shows the trajectory of the X-ray generator during helical scanning.
  • the data obtained by the spiral orbit as shown in FIG. 7B is corrected to the circular orbit data as shown in FIG. 7A by using data interpolation, and then the filter correction two-dimensional backprojection is performed.
  • the degree of artifact is determined by the degree of discontinuity in the X-ray source locus, that is, the degree of artifact varies depending on the moving speed of the subject.
  • the present embodiment after the shooting conditions are set, when the projection data is acquired according to the shooting conditions set by displaying the desired shooting feature amount map and the reconstructed image is generated, the degree of the artifact is increased. You can present what will happen. Therefore, the user can reset the photographing conditions as necessary, and can improve the quality of the acquired reconstructed image.
  • the X-ray CT apparatus sets a region of interest, that is, a ROI (Region of Interest) in the positioning image, and optimizes a feature amount in the set ROI.
  • a region of interest that is, a ROI (Region of Interest)
  • the optimization refers to, for example, an average value, a maximum value, a minimum value, etc. as an index value for the imaging feature amount in the entire ROI, and the imaging conditions so that the index value related to the imaging feature amount is the best. It means to decide.
  • the imaging feature amount is an irradiation dose ratio
  • the imaging is performed such that an index value (average value, maximum value, integral value, etc. of the irradiation dose ratio) related to the irradiation dose ratio in the ROI is low. It can be optimized by determining the conditions.
  • the imaging condition is determined so that the index value (average value, minimum value, integral value, etc.) of the time resolution in the ROI becomes high. Can be optimized.
  • the imaging conditions are determined so that an index value (average value, minimum value, integrated value, etc.) of the spatial resolution ratio in the ROI is high. It can be optimized by doing.
  • the shooting feature value map generation device 28 generates a shooting feature value map based on the set shooting conditions and the ROI, and at the same time, sets the value of the shooting feature value corresponding to the ROI position for each shooting start angle. And a shooting start angle-feature amount curve is generated. Then, the shooting feature value generation device 28 automatically sets an appropriate shooting start angle as an optimum shooting condition from the shooting start angle-feature value curve.
  • the imaging feature value generation device 28 starts imaging so that the average value or integral value of the imaging start angle-feature amount curve corresponding to the ROI range is optimized from the imaging start angle-feature value curve. Determine the angle.
  • the positioning image acquisition method, imaging condition setting, and image reconstruction method can be appropriately selected from various methods.
  • the arithmetic device 22 including the imaging feature value map generation device 28 receives the imaging condition of the positioning image set by the user via the input device 24 (step S21), and the positioning image is obtained according to the imaging condition set. An instruction for photographing is transmitted to the scanner 10 (step S22).
  • the arithmetic unit 22 sets a region of interest in the positioning image set and input by the user in the input device 24 as the ROI 51. (Step S23).
  • shooting conditions and reconstruction conditions in the main shooting are set by the user based on the positioning image, and the arithmetic device 22 Accepts various set conditions via the input device 24 (step S24).
  • the shooting feature value map generation device 28 generates a shooting feature value map based on the set shooting conditions and ROI, and transmits the generated shooting feature value map to the display device 29.
  • the shooting feature value map generation device 28 calculates the value of the shooting feature value corresponding to the ROI position for each shooting start angle, and is a graph showing the relationship between the shooting start angle and the feature value. -Generate a feature curve.
  • the shooting feature amount map generation device 28 transmits the generated shooting start angle-feature amount curve to the display control device 23, and causes the display device 29 to display the shooting start angle-feature amount curve as shown in FIG.
  • the imaging feature amount a graph showing the relationship between the irradiation start, the image noise, and the time resolution with the imaging start opening angle is generated.
  • the shooting feature value map generation device 28 considers the priority for each of these three shooting start angle-feature value curves, and the value of the feature value to be prioritized is closest to the target value, that is, the best. Is calculated as a candidate and displayed on the display device 29. In the arithmetic device 22, when there is one candidate, the photographing start angle which is the candidate is automatically determined (step S26).
  • the shooting feature amount with the highest priority is determined.
  • the imaging start angle is determined so as to be the best within the ROI.
  • the shooting start angle with the second highest shooting feature value in the ROI is determined as a candidate. If there are a plurality of candidate shooting start angles even when the second highest priority shooting feature amount is used, the third highest priority shooting feature amount is the best shooting start angle in the ROI. Are determined as candidates.
  • the shooting feature amount is first set to be the best (maximum value) when it is 1 and is most defective (minimum value) when it is 0.
  • the shooting start angle is determined so that the sum of values obtained by multiplying each shooting feature value by the respective priority coefficient is the highest.
  • a value obtained by subtracting the shooting feature value from 1 Can be used as candidates for the imaging feature amount.
  • the shooting feature value map generation device 28 generates a shooting feature value map based on the previously input shooting conditions and the shooting start angle automatically determined in step S26, and displays it together with the positioning image. It is displayed on the device 29.
  • step S28 when it is determined that the user needs to change the shooting condition, and the arithmetic unit 22 receives a signal to change the shooting condition from the input device 24, the process returns to step S24 to reset the shooting condition by the user. Then, the input of the reset imaging conditions is accepted. Then, the shooting feature amount map generation device 28 calculates again the shooting start angle-feature amount curve according to the reset shooting conditions (step S25), and again determines the best shooting start angle (step S26). Then, a shooting feature amount map is created (step S27).
  • step S28 If it is determined in step S28 that the user does not need to change the shooting condition, the arithmetic unit 22 receives a signal indicating that the shooting condition is not changed from the input device 24, and proceeds to the next step S29 to set the set shooting condition. An instruction is transmitted to the scanner 10 so as to perform actual photographing under conditions. Then, by reconstructing the obtained projection data, a tomographic image as a reconstructed image is generated and displayed on the display device 29 (step S30).
  • the imaging feature amount in the case of the helical scan fluctuates with the period of the beam pitch in the body axis direction
  • the entire ROI may not be a desired imaging feature amount. Therefore, when the ROI body axis size is large, it is desirable to automatically correct the beam pitch in the ROI region using variable pitch scanning, and such information may be presented to the user. Alternatively, a correction candidate for the shooting condition may be proposed to the user.
  • the shooting start angle with the best feature amount is automatically determined by the calculation device from the shooting start angle-feature amount curve.
  • the present invention is not limited to this. Can be performed manually by a user who has confirmed the shooting start angle-feature amount curve.
  • the X-ray CT apparatus determines the imaging start angle in consideration of a plurality of feature amounts. Therefore, as shown in FIG. 4, priority coefficients indicating priorities to be considered are set for a plurality of feature amounts, and a shooting start angle-feature amount curve is created for each feature amount. Then, the shooting start angle is determined so that the value calculated from the product of the shooting feature value and the priority coefficient is the best.
  • one shooting start angle-feature amount curve obtained by combining a plurality of types of shooting start angle-feature amount curves based on the priority coefficient may be generated in consideration of the priority coefficient. The user can manually determine the shooting start angle based on the plurality of displayed shooting start angle-feature amount curves.
  • the synthesis of the shooting start angle-feature amount curve is performed as follows. For example, in the case where a plurality of shooting feature amounts are set and priority coefficients are set for the respective shooting feature amounts, first, each shooting feature amount is best when it is 1, and is lowest when it is 0. Thus, it is standardized in advance. After that, by creating a function of the sum of values obtained by multiplying each shooting feature value by the priority coefficient with respect to the shooting start angle, one shooting start angle-feature amount curve synthesized from a plurality of shooting start angle-feature amount curves is created. can do.
  • the X-ray CT apparatus determines an imaging start angle in consideration of feature quantities in a plurality of ROIs.
  • a plurality of ROIs are set in the positioning image, and an imaging start angle-feature amount curve at each ROI position is generated and displayed.
  • the candidate for the shooting start angle is determined so that the sum of the product of the feature amount with respect to the shooting start angle and the priority coefficient is the best based on the priority coefficient set in each ROI.
  • a shooting start angle-feature amount curve at each ROI position may be synthesized, and one obtained shooting start angle-feature amount curve may be used.
  • the fifth embodiment of the present invention will be described below.
  • the X-ray CT apparatus according to this embodiment is a so-called two-tube CT apparatus, and the imaging start angle is determined in consideration of the feature amount in the two-tube CT apparatus.
  • imaging system two sets of X-ray tube and detector pairs (imaging system) are arranged at different angles in the rotation direction (the difference between the two angles is ⁇ ) (imaging system A, imaging system).
  • System B In the two-tube CT, the imaging systems A and B rotate at the same speed, and the beam pitch at the time of spiral imaging is the same in each imaging system.
  • different X-ray filters can be used for the imaging systems A and B, and the X-rays output from the X-ray tubes can be made different.
  • a single tomographic image is generated by combining data obtained by the two imaging systems.
  • the X-ray filter and the imaging dose are different between the imaging systems A and B, and the trajectory of the X-ray generator at the time of spiral scanning is also different.
  • a feature amount map and a shooting start angle-feature amount curve are obtained.
  • two shooting feature value maps can be displayed separately, and from the viewpoint of improving visibility, a composite map obtained by adding the two shooting feature value maps is used. It is desirable to use it.
  • a shooting start angle-feature amount curve is also obtained from a composite map, or a combined curve obtained by adding two shooting start angle-feature amount curves is used. Then, this composite curve can be used when automatically determining the photographing start angle candidates.

Abstract

In order to more effectively reduce unnecessary X-ray exposure of a region having high X-ray sensitivity, the present invention provides an X-ray CT device provided with: an X-ray source surrounding the periphery of a subject on a bed; a scanner for acquiring projection data, the scanner including an X-ray detector for detecting the dose of X-rays radiated from the X-ray source and passed through the subject; a reconstruction computation unit for acquiring a reconstruction image on the basis of the projection data; an imaging condition setting unit for setting an imaging condition during acquisition of the projection data; an imaging feature value map generation unit for generating an imaging feature value map in which a feature value is mapped as information indicating a feature of the reconstruction image generated when the projection data are acquired in accordance with the imaging condition; and a display control unit for causing the imaging feature value map to be displayed in a display unit.

Description

Ｘ線ＣＴ装置、撮影条件設定方法及び撮影条件設定プログラムX-ray CT apparatus, imaging condition setting method, and imaging condition setting program
　本願発明は、Ｘ線ＣＴ装置、撮影条件設定方法及び撮影条件設定プログラム、特に、被検体の特定部位に照射するＸ線量を制御するＸ線ＣＴ装置、撮影条件設定方法及び撮影条件設定プログラムに関する。 The present invention relates to an X-ray CT apparatus, an imaging condition setting method, and an imaging condition setting program, and more particularly to an X-ray CT apparatus, an imaging condition setting method, and an imaging condition setting program for controlling an X-ray dose applied to a specific part of a subject.
　Ｘ線管を被検体の体軸回りに回転させながら、Ｘ線管からファンビーム又はコーンビーム状にＸ線を照射し、被検体を透過したＸ線を検出器により検出し、得られた投影データを逆投影することにより被検体内部の再構成画像を取得するＸ線ＣＴ装置が知られている。 While rotating the X-ray tube around the body axis of the subject, the X-ray tube emits X-rays in the form of a fan beam or cone beam, the X-ray transmitted through the subject is detected by the detector, and the obtained projection An X-ray CT apparatus that acquires a reconstructed image inside a subject by back projecting data is known.
　このようなＸ線ＣＴ装置では、診断部位の詳細な画像を取得しつつも、被検体に対するＸ線被曝線量を低減することが望まれている。 In such an X-ray CT apparatus, it is desired to reduce the X-ray exposure dose to the subject while acquiring a detailed image of the diagnostic site.
　例えば、特許文献１には、Ｘ線管の回転角度を複数の角度範囲に区分し、Ｘ線感受性の高い部位とＸ線焦点間の距離が近くなる角度範囲についてＸ線の照射出力を小さくすることによりＸ線感受性の高い部位のＸ線被曝線量を低減するＸ線ＣＴ装置が開示されている。 For example, in Patent Document 1, the rotation angle of the X-ray tube is divided into a plurality of angle ranges, and the X-ray irradiation output is reduced in an angle range where the distance between the X-ray sensitive part and the X-ray focal point is close. Thus, an X-ray CT apparatus for reducing the X-ray exposure dose at a site having high X-ray sensitivity is disclosed.
　また、特許文献２には、寝台を移動させてＸ線源に対して被検体を相対的に移動させ、診断対象部位の中心を撮影中心又はその近傍に配置させることにより、診断対象部位以外の生体組織に対するＸ線照射を抑制するＸ線ＣＴ装置が開示されている。 Further, in Patent Document 2, by moving the bed, moving the subject relative to the X-ray source, and arranging the center of the diagnostic target part at or near the imaging center, An X-ray CT apparatus that suppresses X-ray irradiation on a living tissue is disclosed.
特許第４５０９４９３号公報Japanese Patent No. 4509493 特開２００７－２６７７８３号公報JP 2007-267783 A
　しかしながら、上述した特許文献１のＸ線ＣＴ装置では、Ｘ線感受性の高い部位に照射されるＸ線被曝線量を低減するに際し、当該部位とＸ線焦点との距離を考慮するに留まる。すなわち、スキャン方式やスキャン方式に応じたＸ線源の軌道に起因する被検体へのＸ線被曝線量の変動について何ら考慮されていない。このため、単に、Ｘ線感受性の高い部位とＸ線焦点との距離が近くなる角度範囲についてＸ線の照射出力を小さくするだけでは、Ｘ線被曝線量の低減が十分でない場合がある。 However, in the X-ray CT apparatus of Patent Document 1 described above, when reducing the X-ray exposure dose irradiated to a site having high X-ray sensitivity, only the distance between the site and the X-ray focal point is considered. That is, no consideration is given to fluctuations in the X-ray exposure dose to the subject due to the scan method and the trajectory of the X-ray source according to the scan method. For this reason, simply reducing the X-ray irradiation output in the angular range where the distance between the X-ray sensitive part and the X-ray focal point is close may not be sufficient to reduce the X-ray exposure dose.
　また、特許文献２のＸ線ＣＴ装置は、そもそもＸ線感受性の高い部位についてのＸ線被曝線量を低減することについて何ら考慮されていない。このため、撮影範囲にＸ線感受性の高い部位が含まれる場合には、診断対象部位の中心を撮影中心又はその近傍に配置させるだけでは、Ｘ線被曝線量の低減が十分でない場合がある。 In addition, the X-ray CT apparatus of Patent Document 2 is not considered at all about reducing the X-ray exposure dose for a part having high X-ray sensitivity. For this reason, when a region having high X-ray sensitivity is included in the imaging range, the X-ray exposure dose may not be sufficiently reduced only by placing the center of the diagnostic target region at or near the imaging center.
　本発明は上記実情に鑑みてなされたものであり、Ｘ線感受性の高い部位について、無用なＸ線被曝線量をより効果的に低減することを目的とする。 The present invention has been made in view of the above circumstances, and an object of the present invention is to more effectively reduce unnecessary X-ray exposure dose for a portion having high X-ray sensitivity.
　上記課題を解決するために、本発明は以下の手段を提供する。 In order to solve the above problems, the present invention provides the following means.
　本発明の一態様は、寝台上の被検体の周囲を周回するＸ線源と、該Ｘ線源から照射され、前記被検体を透過したＸ線の線量を検出するＸ線検出器を含み、投影データを取得するスキャナと、前記投影データに基づいて再構成画像を取得する再構成演算部と、前記投影データを取得する際の撮影条件を設定する撮影条件設定部と、前記撮影条件に従って投影データを取得する場合に生成される再構成画像の特徴を示す情報としての特徴量をマッピングした撮影特徴量マップを生成する撮影特徴量マップ生成部と、前記撮影特徴量マップを表示部に表示させる表示制御部と、を備えたＸ線ＣＴ装置を提供する。 One aspect of the present invention includes an X-ray source that circulates around a subject on a bed, and an X-ray detector that detects a dose of X-rays irradiated from the X-ray source and transmitted through the subject, A scanner that acquires projection data, a reconstruction calculation unit that acquires a reconstructed image based on the projection data, a shooting condition setting unit that sets shooting conditions when acquiring the projection data, and projection according to the shooting conditions A shooting feature value map generation unit that generates a shooting feature value map that maps feature values as information indicating features of the reconstructed image generated when data is acquired, and displays the shooting feature value map on a display unit An X-ray CT apparatus including a display control unit is provided.
　本発明によれば、Ｘ線感受性の高い部位について、無用なＸ線被曝量をより効果的に低減することができる。 According to the present invention, it is possible to more effectively reduce the amount of unnecessary X-ray exposure for a site having high X-ray sensitivity.
本発明の第１の実施形態に係るＸ線ＣＴ装置の概略を示す外観構成図である。1 is an external configuration diagram showing an outline of an X-ray CT apparatus according to a first embodiment of the present invention. 本発明の第１の実施形態に係るＸ線ＣＴ装置の概略を示すブロック図である。1 is a block diagram showing an outline of an X-ray CT apparatus according to a first embodiment of the present invention. 本発明の第１の実施形態に係るＸ線ＣＴ装置の表示装置に表示される表示画面の一例を示す説明図である。It is explanatory drawing which shows an example of the display screen displayed on the display apparatus of the X-ray CT apparatus which concerns on the 1st Embodiment of this invention. 本発明の第１の実施形態に係るＸ線ＣＴ装置の表示装置に表示される表示画面の一例を示す説明図である。It is explanatory drawing which shows an example of the display screen displayed on the display apparatus of the X-ray CT apparatus which concerns on the 1st Embodiment of this invention. 本発明の第１の実施形態に係るＸ線ＣＴ装置において、位置決め画像の取得から再構成画像の生成までの動作を示すフローチャートである。5 is a flowchart showing operations from acquisition of a positioning image to generation of a reconstructed image in the X-ray CT apparatus according to the first embodiment of the present invention. 本発明の第２の実施形態に係るＸ線ＣＴ装置において、位置決め画像の取得から再構成画像の生成までの動作を示すフローチャートである。It is a flowchart which shows operation | movement from acquisition of a positioning image to the production | generation of a reconstruction image in the X-ray CT apparatus which concerns on the 2nd Embodiment of this invention. Ｘ線ＣＴ装置におけるスキャン方式の一例としてアキシャルスキャン方式を示す説明図である。It is explanatory drawing which shows an axial scan system as an example of the scan system in a X-ray CT apparatus. Ｘ線ＣＴ装置におけるスキャン方式の一例として螺旋スキャン方式を示す説明図である。It is explanatory drawing which shows a spiral scanning system as an example of the scanning system in a X-ray CT apparatus. Ｘ線ＣＴ装置におけるスキャン方式の一例としてシャトルスキャン方式を示す説明図である。It is explanatory drawing which shows a shuttle scan system as an example of the scan system in an X-ray CT apparatus. Ｘ線ＣＴ装置におけるスキャン方式の一例としてスキャノグラム方式を示す説明図である。It is explanatory drawing which shows a scanogram system as an example of the scanning system in a X-ray CT apparatus. Ｘ線ＣＴ装置において、螺旋スキャンを行った場合において寝台の速度が比較的遅い場合の体軸方向の撮影冗長性を示す説明図である。In an X-ray CT apparatus, it is explanatory drawing which shows the imaging | photography redundancy of a body-axis direction when the speed of a bed is comparatively slow when a helical scan is performed. Ｘ線ＣＴ装置において螺旋スキャンを行った場合において寝台の速度が比較的速い場合の体軸方向の撮影冗長性を示す説明図である。It is explanatory drawing which shows the imaging | photography redundancy of a body-axis direction in case the speed of a bed is comparatively high when a helical scan is performed in an X-ray CT apparatus. Ｘ線ＣＴ装置において、アキシャルスキャンを行った場合の体軸方向の撮影冗長性を示す説明図である。It is explanatory drawing which shows the imaging | photography redundancy of a body-axis direction at the time of performing an axial scan in an X-ray CT apparatus. Ｘ線ＣＴ装置において、ステップスキャンを行った場合の体軸方向の撮影冗長性を示す説明図である。It is explanatory drawing which shows the imaging | photography redundancy of a body-axis direction at the time of performing a step scan in an X-ray CT apparatus. Ｘ線ＣＴ装置において、螺旋スキャンを行った場合の画像ノイズ比マップを示す説明図である。It is explanatory drawing which shows the image noise ratio map at the time of performing a helical scan in X-ray CT apparatus. Ｘ線ＣＴ装置において、螺旋スキャンを行った場合の画像ノイズ比マップを示す説明図である。It is explanatory drawing which shows the image noise ratio map at the time of performing a helical scan in X-ray CT apparatus. Ｘ線ＣＴ装置において、Ｘ線源（Ｘ線発生装置）の撮影開始角度と撮影冗長性との関係を示し、特に、撮影開始角度が０度である場合を示す説明図である。In an X-ray CT apparatus, it is explanatory drawing which shows the relationship between the imaging start angle of an X-ray source (X-ray generator) and imaging redundancy, and shows especially the case where an imaging start angle is 0 degree | times. Ｘ線ＣＴ装置において、Ｘ線源（Ｘ線発生装置）の撮影開始角度と撮影冗長性との関係を示し、特に、撮影開始角度が１８０度である場合を示す説明図である。In an X-ray CT apparatus, it is explanatory drawing which shows the relationship between the imaging start angle of an X-ray source (X-ray generator) and imaging redundancy, and shows especially the case where an imaging start angle is 180 degree | times. Ｘ線ＣＴ装置において、アキシャルスキャンを行う場合のＸ線源（Ｘ線発生装置）の撮影開始角度、撮影開始位置、Ｘ線源の軌道（軌跡）との関係を示す説明図である。In an X-ray CT apparatus, it is explanatory drawing which shows the relationship between the imaging start angle of the X-ray source (X-ray generator), the imaging start position, and the X-ray source trajectory (trajectory) when performing an axial scan. Ｘ線ＣＴ装置において、螺旋スキャンを行う場合のＸ線源（Ｘ線発生装置）の撮影開始角度、撮影開始位置、Ｘ線源の軌道（軌跡）との関係を示す説明図である。In an X-ray CT apparatus, it is explanatory drawing which shows the relationship between the imaging start angle of the X-ray source (X-ray generator), the imaging start position, and the track | orbit (trajectory) of an X-ray source in the case of performing a helical scan.
　以下、本発明の実施形態の説明に先立って、Ｘ線ＣＴ装置におけるスキャン方式及びＸ線源の軌道について説明する。 Hereinafter, prior to the description of the embodiment of the present invention, the scanning method and the trajectory of the X-ray source in the X-ray CT apparatus will be described.
　一般に、Ｘ線ＣＴ装置では、寝台に載せられた被検体に対して、Ｘ線源を体軸周りに周回させながらファンビーム又はコーンビーム状にＸ線を照射し、複数の検出素子を円弧状に配置した検出器で被検体を透過したＸ線を受光することにより撮影が行われる。通常、周回方向における１回の撮影を１ビューと称し、周回方向１周あたり約１０００回の撮影を行っている。 In general, in an X-ray CT apparatus, a subject placed on a bed is irradiated with X-rays in a fan beam or cone beam shape while rotating an X-ray source around a body axis, and a plurality of detection elements are formed in an arc shape. Imaging is performed by receiving X-rays that have passed through the subject with a detector disposed in the area. Normally, one shooting in the rotation direction is referred to as one view, and about 1000 shootings are performed per one rotation in the rotation direction.
　このようにＸ線源を回転させながら撮影を行うスキャン（撮影）方式として、主に以下の方式が知られている。 The following methods are mainly known as scanning (imaging) methods for performing imaging while rotating the X-ray source in this way.
　すなわち、ノーマルスキャン、アキシャルスキャン、又はコンベンショナルスキャンと称され、寝台が固定されＸ線源が被検体の周りを円軌道状に周回する撮影方式（図７Ａ）、ステップスキャン又はステップアンドシュートスキャンと称され、撮影後に寝台が体軸方向に移動してアキシャルスキャンを繰り返す撮影方式、螺旋スキャン、ヘリカルスキャン又はスパイラルスキャンと称され、寝台が体軸方向に一定速度で移動してＸ線源が被検体の周りを螺旋軌道状に周回する撮影方式（図７Ｂ）、シャトルスキャンと称され、寝台が体軸方向に往復運動してＸ線源が被検体の周りを螺旋軌道状に周回する撮影方式（図７Ｃ）、及び、バリアブルピッチスキャンと称され、寝台が可変速度で移動しＸ線源が被検体の周りを螺旋軌道状に周回する撮影方式、などが主なスキャン方式として知られている。 That is, it is called a normal scan, an axial scan, or a conventional scan, and is called an imaging method in which the bed is fixed and the X-ray source circulates around the subject in a circular orbit (FIG. 7A), step scan or step and shoot scan. An imaging method in which the bed moves in the body axis direction after imaging and repeats an axial scan, which is called spiral scan, helical scan, or spiral scan. The bed moves at a constant speed in the body axis direction and the X-ray source becomes the subject. An imaging method (FIG. 7B) that circulates around the subject in a spiral orbit, called a shuttle scan, an imaging method in which the bed reciprocates in the body axis direction and the X-ray source circulates around the subject in a spiral orbit ( FIG. 7C) and called variable pitch scan, the bed moves at a variable speed, and the X-ray source orbits around the subject in a spiral orbit. Imaging method, and the like are known as the main scanning method that.
　また、Ｘ線源を回転させずに行う撮影方式として、スキャノグラムと称され、Ｘ線源が固定された状態で寝台が移動する撮影方式（図７Ｄ）も知られている。 Also, as an imaging method performed without rotating the X-ray source, an imaging method called a scanogram, in which the bed moves with the X-ray source fixed (FIG. 7D) is also known.
　ところで、Ｘ線ＣＴ装置において、上述のようにＸ線源を回転させながら撮影を行う場合は、Ｘ線源から扇形のファンビーム状又は円錐形のコーンビーム状のＸ線が照射されるため、Ｘ線が照射される回数（期間）は被検体の部位に応じて異なる。つまり、例えば、被検体の体軸中心近傍と被検体の体表面とではＸ線が照射される回数（期間）が、異なる。 By the way, in the X-ray CT apparatus, when imaging is performed while rotating the X-ray source as described above, fan-shaped fan beam-shaped or conical cone-beam-shaped X-rays are emitted from the X-ray source. The number (period) of irradiation with X-rays varies depending on the region of the subject. That is, for example, the number of times (period) of X-ray irradiation differs between the vicinity of the body axis center of the subject and the body surface of the subject.
　より具体的には、被検体のある位置ではＸ線に曝露されている時間が長くなり、他の位置ではＸ線に曝露されている時間が短くなる。このとき、Ｘ線曝露されている時間が長い位置ほど被曝線量は高くなる。 More specifically, the time that the subject is exposed to X-rays becomes longer, and the time that the subject is exposed to X-rays becomes shorter at other positions. At this time, the exposure dose becomes higher as the position exposed to X-rays is longer.
　例えば、マルチスライスＣＴで撮影を行った場合、図８Ａ、図８Ｂ、図９Ａ及び図９Ｂに示すように、Ｘ線が照射される期間は被検体の部位（画像位置）毎に異なるので、Ｘ線源の回転中心から離れた位置と比較して回転中心位置ではＸ線が照射される期間（画素位置が撮影されている周回角度幅）が長くなる。つまり、再構成に使用可能な投影データが、回転中心では多くの角度幅に亘って収集されるものの、回転中心から離れた位置では少ない角度幅から収集されるに留まる。このことから、図８Ａ、図８Ｂ、図９Ａ及び図９Ｂに示すように、再構成に使用可能な投影データの角度幅（逆投影位相幅）は、画素位置や寝台移動速度に関連し、Ｘ線源の軌道に応じて被検体の各位置における撮影の冗長性が異なり、一般的な螺旋スキャンでは位置に応じて１．５倍から２倍の線量ムラを生じ得る。
画像ノイズに関しても同様であり、図１０、図１１に示す、螺旋スキャンにおける画像ノイズ比マップのようなムラを生ずる。 For example, when imaging with multi-slice CT, as shown in FIGS. 8A, 8B, 9A, and 9B, the period during which X-rays are irradiated differs for each region (image position) of the subject. Compared with the position away from the rotation center of the radiation source, the period during which X-rays are irradiated (the rotation angle width at which the pixel position is imaged) is longer at the rotation center position. That is, projection data that can be used for reconstruction is collected over many angular widths at the rotation center, but is collected from a small angular width at positions away from the rotation center. Therefore, as shown in FIGS. 8A, 8B, 9A, and 9B, the angular width (back projection phase width) of projection data that can be used for reconstruction is related to the pixel position and the bed movement speed, and X The imaging redundancy at each position of the subject differs depending on the trajectory of the radiation source, and in general spiral scanning, dose unevenness of 1.5 to 2 times can occur depending on the position.
The same applies to the image noise, and unevenness such as the image noise ratio map in the spiral scan shown in FIGS. 10 and 11 occurs.
　このように、同一の被検体の位置であってもＸ線源の軌道によってＸ線照射量に１．５～２倍のムラが生じ得ることから、例えば、特定の一方向からの照射線量を２分の１にしても、Ｘ線源の軌道によっては２倍の線量になる場合がある。つまり、Ｘ線源の軌道を考慮しない場合には、必ずしもＸ線被曝量を低減することはできない。 Thus, even at the same subject position, the X-ray irradiation amount can vary 1.5 to 2 times depending on the trajectory of the X-ray source. Even if it is half, depending on the trajectory of the X-ray source, the dose may be doubled. That is, if the trajectory of the X-ray source is not taken into account, the X-ray exposure dose cannot always be reduced.
　また、Ｘ線源の軌道は、以下に説明するように、Ｘ線源の撮影開始角度（位置）によっても変化し得る。 Also, the trajectory of the X-ray source can change depending on the imaging start angle (position) of the X-ray source, as will be described below.
　図１２Ａは、撮影開始角度０度から、図１２Ｂは撮影開始角度１８０度から、夫々２５０度撮影された場合を示し、図１２Ａ及び図１２Ｂ中、ａ，ｂ，ｃは被検体の位置を示している。 FIG. 12A shows the case where the image is taken from 250 degrees from the image taking start angle 0 degree and FIG. 12B is from the image taking start angle 180 degree. In FIGS. 12A and 12B, a, b, and c show the positions of the subjects. ing.
　図１２Ａでは、点ａ，ｂ，ｃともにＸ線源からファンビーム状のＸ線が照射されて、２５０度分に亘って撮影されることを示している。各画素から見ると（パラレルビームで考えると）、点ｂでは１８０度分、点ｃでは２７０度以上に亘って撮影されたと見做される。 FIG. 12A shows that the points a, b, and c are both irradiated with fan beam-shaped X-rays from the X-ray source and photographed for 250 degrees. When viewed from each pixel (considering with a parallel beam), it is considered that the image is taken over 180 degrees at the point b and 270 degrees or more at the point c.
　一方、図１２Ｂは、図１２Ａと同様に点ａ，ｂ，ｃともにＸ線源からファンビーム状のＸ線が照射され、２５０度分に亘って撮影されることを示している。図１２Ｂでは、各画素から見ると（パラレルビームで考えると）点ｃでは１８０度分、点ｂでは２７０度以上に亘って撮影されたと見做される。 On the other hand, FIG. 12B shows that points a, b, and c are irradiated with fan beam-shaped X-rays from the X-ray source and imaged over 250 degrees as in FIG. 12A. In FIG. 12B, when viewed from each pixel (considering a parallel beam), it is considered that the image is taken over 180 degrees at the point c and over 270 degrees at the point b.
　このように撮影時間（ファンビームでの撮影角度範囲）が同じであっても、パラレルビームで見た場合の角度範囲が各画素で異なり、撮影開始角度に応じてこれらの関係が変化することから、Ｘ線源の軌道は撮影開始角度に応じて変化することがわかる。つまり、撮影開始角度に応じて、被検体のＸ線被曝量や、アキシャル面内でのノイズ分布や時間分解能の分布が変化することがわかる。 In this way, even if the shooting time (shooting angle range with a fan beam) is the same, the angle range when viewed with a parallel beam is different for each pixel, and these relationships change according to the shooting start angle. It can be seen that the trajectory of the X-ray source changes according to the imaging start angle. That is, it can be seen that the X-ray exposure dose of the subject, the noise distribution in the axial plane, and the temporal resolution distribution change according to the imaging start angle.
　図１３Ａ及び図１３Ｂは、撮影開始角度と線源軌道の関係を示している。図１３Ａに示すように、アキシャルスキャンやステップスキャンにおいて、３６０度撮影する場合にはデータが収集される位置は撮影開始角度に依存しない。しかし、撮影範囲が３６０度未満の場合には、撮影開始角度に応じて撮影される角度範囲、つまり、データ収集される位置が変化する。 13A and 13B show the relationship between the imaging start angle and the source trajectory. As shown in FIG. 13A, in the axial scan or the step scan, when shooting 360 degrees, the position where data is collected does not depend on the shooting start angle. However, when the shooting range is less than 360 degrees, the angle range for shooting, that is, the position where data is collected, changes according to the shooting start angle.
　螺旋スキャンの場合には、図１３Ｂに示すように、撮影開始角度が変わるとＸ線源の軌道が変化しデータ収集位置が変化する。 In the case of spiral scanning, as shown in FIG. 13B, when the imaging start angle changes, the trajectory of the X-ray source changes and the data collection position changes.
　なお、プリコリメータを適用してスライス方向端部で体軸方向のビーム幅を狭くする場合には、被検体の同一範囲を撮影する際に、Ｘ線源の体軸方向位置を異ならせることができる。したがって、ステップスキャンの場合には撮影開始角度に加えて撮影するＸ線源の体軸方向位置によっても撮影される角度範囲は変化しうる。 When the pre-collimator is applied to narrow the beam width in the body axis direction at the end in the slice direction, the body axis direction position of the X-ray source may be varied when imaging the same range of the subject. it can. Therefore, in the case of step scan, the angle range to be imaged can be changed by the body axis direction position of the X-ray source to be imaged in addition to the imaging start angle.
　以上説明したように、被検体のＸ線被曝量は、Ｘ線源の軌道に依存するものであり、Ｘ線源の軌道は、スキャン方式、撮影開始角度等によって変動する。このため、Ｘ線感受性の高い部位についてＸ線被曝線量を低減するには、スキャン方式に応じて、撮影開始角度を含めたＸ線源軌道等の撮影条件を設定する必要がある。 As described above, the X-ray exposure dose of the subject depends on the trajectory of the X-ray source, and the trajectory of the X-ray source varies depending on the scanning method, the imaging start angle, and the like. For this reason, in order to reduce the X-ray exposure dose for a part having high X-ray sensitivity, it is necessary to set imaging conditions such as an X-ray source trajectory including an imaging start angle in accordance with the scanning method.
　本発明は、このような背景の下、Ｘ線感受性の高い部位等の被検体の特定の部位について、無用なＸ線被曝線量をより効果的に低減することを目的としている。 The present invention aims to more effectively reduce the unnecessary X-ray exposure dose for a specific part of a subject such as a part having high X-ray sensitivity under such a background.
　以下、本発明の一実施形態について、図面を参照して説明する。
＜第１の実施形態＞
　本実施形態に係るＸ線ＣＴ装置１は、例えば、マルチスライスＣＴ装置に適用することができ、スキャン方式として、例えば、ローテート－ローテート方式（第３世代）を採用することができる。 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
<First Embodiment>
The X-ray CT apparatus 1 according to the present embodiment can be applied to, for example, a multi-slice CT apparatus, and for example, a rotation-rotation system (third generation) can be adopted as a scanning system.
　Ｘ線ＣＴ装置１は、図１及び図２に示すように、スキャナ１０と、操作ユニット２０と、寝台３０とを備えている。Ｘ線ＣＴ装置では、スキャナ１０が操作ユニット２０による指示に従って、寝台３０に戴置される被検体のスキャン処理を行う。 As shown in FIGS. 1 and 2, the X-ray CT apparatus 1 includes a scanner 10, an operation unit 20, and a bed 30. In the X-ray CT apparatus, the scanner 10 performs a scan process on the subject placed on the bed 30 in accordance with an instruction from the operation unit 20.
　スキャナ１０は、Ｘ線源としてのＸ線発生装置５、高電圧発生装置６、Ｘ線制御装置７、コリメータ８、コリメータ制御装置９、検出器１１、中央制御装置１２、スキャナ制御装置１３、寝台制御装置１４、寝台移動計測装置１５、駆動装置１６、プリアンプ１７、及びＡ／Ｄコンバータ１８を備えている。 The scanner 10 includes an X-ray generator 5 as an X-ray source, a high voltage generator 6, an X-ray controller 7, a collimator 8, a collimator controller 9, a detector 11, a central controller 12, a scanner controller 13, and a bed. A control device 14, a couch movement measuring device 15, a driving device 16, a preamplifier 17, and an A / D converter 18 are provided.
　Ｘ線発生装置５は、後述する駆動装置１６によって寝台に載置された被検体の周囲を周回しながら、高電圧発生装置６に印加された高電圧によってＸ線を生じさせ、これを被検体へ照射する。高電圧発生装置６は、Ｘ線制御装置７からの制御信号に従って、Ｘ線発生装置５へ高電圧を供給する。 The X-ray generator 5 generates X-rays by the high voltage applied to the high-voltage generator 6 while circling around the subject placed on the bed by the driving device 16 to be described later. Irradiate. The high voltage generator 6 supplies a high voltage to the X-ray generator 5 in accordance with a control signal from the X-ray controller 7.
　コリメータ８は、コリメータ制御装置９によって制御され、コリメータ制御装置９からの制御信号に従って、Ｘ線発生装置によって照射されるＸ線の照射領域を制御する。 The collimator 8 is controlled by the collimator control device 9 and controls an X-ray irradiation region irradiated by the X-ray generator according to a control signal from the collimator control device 9.
　検出器１１は、Ｘ線発生装置５に対向して配置され、Ｘ線発生装置５から照射され被検体を透過したＸ線を検出し、検出結果を電流値としてプリアンプ１７へ出力する。なお、検出器１１としては、単一列検出器又は多列検出器のいずれを適用することもできる。多列検出器は、単列検出器が周回軸方向に複数配列され、全体として、単一検出器よりも広い範囲を一度に撮影することができるという利点がある。 The detector 11 is disposed facing the X-ray generator 5, detects X-rays irradiated from the X-ray generator 5 and transmitted through the subject, and outputs the detection result to the preamplifier 17 as a current value. As the detector 11, either a single-row detector or a multi-row detector can be applied. The multi-row detector has an advantage that a plurality of single-row detectors are arranged in the direction of the rotation axis, and as a whole, a wider range than that of the single detector can be photographed.
　プリアンプ１７は、検出器１１から受信した検出結果を増幅させ、Ａ／Ｄコンバータ１８に出力する。Ａ／Ｄコンバータ１８では、プリアンプ１７で増幅されたアナログの電流値をデジタルデータに変換し、さらにＬＯＧ変換し、キャリブレーションを行って投影データとして後述する演算装置２２に出力する。 The preamplifier 17 amplifies the detection result received from the detector 11 and outputs it to the A / D converter 18. In the A / D converter 18, the analog current value amplified by the preamplifier 17 is converted into digital data, further LOG-converted, calibrated, and output as projection data to an arithmetic unit 22 described later.
　なお、Ｘ線発生装置５、コリメータ８、検出器１１及びプリアンプ１７等は円盤（図示せず）に配置され、駆動装置１６によって円盤を駆動させることによりＸ線発生装置５が被検体の周囲を周回するようになっている。 Note that the X-ray generator 5, the collimator 8, the detector 11, the preamplifier 17, and the like are arranged on a disk (not shown), and the X-ray generator 5 is driven around the subject by driving the disk by the driving device 16. It is designed to go around.
　スキャナ制御装置１３は、後述する中央制御装置１２からの制御信号に従って、Ｘ線源としてのＸ線発生装置５を搭載した円盤を周回駆動させる駆動装置１６及びコリメータ制御装置９を制御する。 The scanner control device 13 controls the drive device 16 and the collimator control device 9 for driving the disk on which the X-ray generation device 5 as the X-ray source is mounted in accordance with a control signal from the central control device 12 described later.
　寝台制御装置１４は、中央制御装置１２からの制御信号に従って、寝台３０の移動速度等を制御する。寝台３０は、寝台移動計測装置１５によって、その移動速度や距離が計測される。 The couch controller 14 controls the moving speed and the like of the couch 30 according to the control signal from the central controller 12. The bed 30 is measured for movement speed and distance by the bed movement measuring device 15.
　中央制御装置１２は、操作ユニット２０から入力される指示に基づいて、上述したＸ線制御装置７、スキャナ制御装置１３、及び寝台制御装置１４を制御する。 The central control device 12 controls the above-described X-ray control device 7, scanner control device 13, and bed control device 14 based on an instruction input from the operation unit 20.
　操作ユニット２０は、ユーザによる操作、再構成画像の生成、画像の表示等を行うものであり、入出力装置２１と演算装置２２とを備えている。 The operation unit 20 performs operations by the user, generation of reconstructed images, display of images, and the like, and includes an input / output device 21 and an arithmetic device 22.
　入出力装置２１は、演算装置２２によって生成された再構成画像及び後述する撮影特徴量マップ等を表示装置２９に表示させる表示制御装置２３、撮影条件や再構成条件の入力を行う入力装置２４、入力された条件や表示する画像を記憶する記憶装置２５を含む。 The input / output device 21 includes a display control device 23 for displaying on the display device 29 a reconstructed image generated by the arithmetic device 22 and a photographing feature amount map, which will be described later, an input device 24 for inputting photographing conditions and reconstruction conditions, It includes a storage device 25 that stores input conditions and images to be displayed.
　なお、表示制御装置２３には、表示制御装置２３からの指示に従って各種画像を表示する表示装置２９が接続されている。表示装置２９としては、液晶ディスプレイ等のディスプレイ装置を適用することができ、入力装置２４としては、マウス、キーボード、タッチパネル等を１又は複数適用することができる。また、記憶装置２５としては、ハードディスクや各種の記憶媒体等のドライブ装置を適用することができる。 Note that a display device 29 that displays various images in accordance with instructions from the display control device 23 is connected to the display control device 23. As the display device 29, a display device such as a liquid crystal display can be applied, and as the input device 24, one or more of a mouse, a keyboard, a touch panel, and the like can be applied. Further, as the storage device 25, a drive device such as a hard disk or various storage media can be applied.
　ユーザによって入力装置２４から入力される撮影条件としては、例えば、寝台移動速度、管電流、管電圧、スライス位置などが挙げられる。この他、アキシャルスキャンや螺旋スキャン等の撮影方式、撮影開始角度、体軸方向の撮影範囲、ビームピッチや管電流、管電圧などがあり、Ｘ線曝射制御（ＡＥＣ）などの設定も行われる。 Examples of photographing conditions input from the input device 24 by the user include a bed moving speed, tube current, tube voltage, and slice position. In addition, there are imaging methods such as axial scan and spiral scan, imaging start angle, imaging range in the body axis direction, beam pitch, tube current, tube voltage, etc., and settings such as X-ray exposure control (AEC) are also performed. .
　また、ユーザによって入力装置２４から入力される再構成条件としては、例えば、再構成法、画像スライス厚、逆投影位相幅、ビュー重みスロープ幅、関心領域、再構成画像マトリクスサイズ、再構成フィルタ関数、基準点の位置などが挙げられる。 The reconstruction conditions input from the input device 24 by the user include, for example, a reconstruction method, an image slice thickness, a backprojection phase width, a view weight slope width, a region of interest, a reconstructed image matrix size, and a reconstruction filter function. And the position of the reference point.
　なお、撮影条件や再構成条件の入力に際して、部位毎に撮影条件や再構成条件を推奨設定した撮影プロトコルを使用することもできる。 It should be noted that when inputting imaging conditions and reconstruction conditions, an imaging protocol in which imaging conditions and reconstruction conditions are recommended for each part can be used.
　演算装置２２は、スキャナにより収集された投影データに基づいて再構成画像を生成する再構成演算装置２６と、再構成画像に対して必要な画像処理を行う画像処理装置２７と、再構成画像の撮影特徴量をマッピングした撮影特徴量マップ生成装置２８を含む。なお、演算装置２２に含まれる各装置の機能は、演算装置２２が有する図示しないＣＰＵが予めＲＯＭ等のメモリに格納されたプログラムを読み込んで実行することによりソフトウエアとして実現することができる。また、演算装置２２に含まれる各装置が実行する動作の一部又は全部を、ＡＳＩＣ（application specific integrated circuit）やＦＰＧＡ（field-programmable gate array）により実現することもできる。 The computing device 22 includes a reconstruction computing device 26 that generates a reconstructed image based on projection data collected by the scanner, an image processing device 27 that performs necessary image processing on the reconstructed image, and a reconstructed image. A shooting feature value map generation device 28 that maps the shooting feature values is included. The function of each device included in the arithmetic device 22 can be realized as software by a CPU (not shown) included in the arithmetic device 22 reading and executing a program stored in a memory such as a ROM in advance. Also, some or all of the operations executed by each device included in the arithmetic device 22 can be realized by ASIC (application specific integrated circuit) or FPGA (field-programmable gate array).
　再構成演算装置２６は、取得した投影データを種々の方法で再構成することができる。
再構成演算装置２６は、例えば、所謂ファンビーム再構成や、所謂パラレルビーム再構成等公知の方法によって再構成することができ、この際、再構成に用いる逆投影位相範囲は再構成画素毎に異なっていてもよく、同一範囲でもよい。 The reconstruction calculation device 26 can reconstruct the acquired projection data by various methods.
The reconstruction calculation device 26 can be reconstructed by a known method such as so-called fan beam reconstruction or so-called parallel beam reconstruction. At this time, the backprojection phase range used for reconstruction is determined for each reconstruction pixel. They may be different or in the same range.
　画像処理装置２７は、再構成演算装置２６により再構成された再構成画像に対して、表示装置２９に表示するために最適な形態となるように、必要な画像処理を行う。 The image processing device 27 performs necessary image processing on the reconstructed image reconstructed by the reconstruction computing device 26 so that the reconstructed image is in an optimum form for display on the display device 29.
　撮影特徴量マップ生成装置２８は、入力装置２４に入力された撮影条件に従って投影データを取得する場合に、再構成演算装置２６において生成される再構成画像の特徴を示す情報としての特徴量をマッピングした撮影特徴量マップを生成する。撮影特徴量マップの詳細については後述する。 The shooting feature amount map generation device 28 maps feature amounts as information indicating the features of the reconstructed image generated by the reconstruction calculation device 26 when acquiring projection data according to the shooting conditions input to the input device 24. A photographed feature map is generated. Details of the shooting feature map will be described later.
　このように構成されたＸ線ＣＴ装置における撮影処理及び再構成処理は、以下のように行われる。 The imaging process and the reconstruction process in the X-ray CT apparatus configured as described above are performed as follows.
　ユーザにより入力装置２４に撮影開始の指示が入力されると、撮影開始信号が生成されて操作ユニット２０から中央制御装置１２に入力される。中央制御装置１２は、入力された撮影開始信号を受けて、Ｘ線制御装置７、スキャナ制御装置１３、及び寝台制御装置１４に対して撮影に必要な制御信号を送り撮影を開始する。 When an instruction to start shooting is input to the input device 24 by the user, a shooting start signal is generated and input from the operation unit 20 to the central controller 12. The central control device 12 receives the input imaging start signal, and sends a control signal necessary for imaging to the X-ray control device 7, the scanner control device 13, and the bed control device 14, and starts imaging.
　撮影が開始されると、Ｘ線制御装置７によって高電圧発生装置６に制御信号が送信され、Ｘ線発生装置５に高電圧が印加され、Ｘ線発生装置５からＸ線が被検体に照射される。
同時に、スキャナ制御装置１３から駆動装置１６に制御信号が送信され、円盤を周回させることによりＸ線発生装置５、検出器１１、プリアンプ１７等を被検体４の周りに周回させる。 When imaging is started, a control signal is transmitted from the X-ray controller 7 to the high voltage generator 6, a high voltage is applied to the X-ray generator 5, and the subject is irradiated with X-rays from the X-ray generator 5. Is done.
At the same time, a control signal is transmitted from the scanner control device 13 to the drive device 16, and the X-ray generator 5, the detector 11, the preamplifier 17, etc. circulate around the subject 4 by rotating the disk.
　併せて、寝台制御装置１６からの制御信号に従って、被検体が載置された寝台３０が、静止（ノーマルスキャン時）、又は被検体の体軸方向に平行移動（螺旋スキャン時）を行う。Ｘ線発生装置によって照射されたＸ線は、コリメータ６により照射領域が制限され、被検体内の各組織において吸収（減衰）され、被検体を透過して、検出器１１によって検出される。 At the same time, according to the control signal from the bed control device 16, the bed 30 on which the subject is placed moves still (normal scan) or translates in the body axis direction of the subject (spiral scan). X-rays irradiated by the X-ray generator are limited in irradiation area by the collimator 6, absorbed (attenuated) in each tissue in the subject, transmitted through the subject, and detected by the detector 11.
　検出器１１によって検出されたＸ線は、電流に変換され、プリアンプ１９によって増幅され、Ａ／Ｄコンバータ２０によってデジタルデータに変換され、ＬＯＧ変換され、キャリブレーションが行われて投影データとして演算装置２２に入力される。 The X-rays detected by the detector 11 are converted into current, amplified by a preamplifier 19, converted to digital data by an A / D converter 20, LOG converted, calibrated, and subjected to calibration as an arithmetic unit 22 as projection data. Is input.
　再構成演算装置２６では、演算装置３２に入力された投影データに基づいて再構成処理を行い、再構成画像を生成する。生成された再構成画像は、記憶装置２５に保存され、表示装置２９によってＣＴ画像として表示される。あるいは、画像処理装置２７によって画像処理がなされた後、表示装置２９によってＣＴ画像として表示される。 The reconstruction calculation device 26 performs a reconstruction process based on the projection data input to the calculation device 32 to generate a reconstructed image. The generated reconstructed image is stored in the storage device 25 and displayed as a CT image by the display device 29. Alternatively, after image processing is performed by the image processing device 27, the image is displayed as a CT image by the display device 29.
　ところで、上述した撮影に際して、撮影特徴量マップ生成装置２８では、再構成画像の特徴を示す情報としての特徴量をマッピングした撮影特徴量マップを生成する。生成された再構成画像は、記憶装置２５に保存され、図３及び図４に示すように表示装置２９に表示される。 By the way, at the time of shooting described above, the shooting feature amount map generation device 28 generates a shooting feature amount map in which feature amounts as information indicating features of the reconstructed image are mapped. The generated reconstructed image is stored in the storage device 25 and displayed on the display device 29 as shown in FIGS.
　ここで、撮影特徴量マップについて詳細に説明する。撮影特徴量マップ生成装置２８は、上述のように、入力装置２４に入力された撮影条件に従って投影データを取得する場合に、再構成演算装置２６において生成される再構成画像の特徴を示す情報としての特徴量をマッピングした撮影特徴量マップを生成する。 Here, the shooting feature map will be described in detail. As described above, the shooting feature amount map generation device 28 is information indicating the characteristics of the reconstructed image generated by the reconstruction calculation device 26 when acquiring projection data according to the shooting conditions input to the input device 24. A shooting feature amount map in which the feature amount is mapped is generated.
　すなわち、本実施形態においては、ユーザにより入力された撮影条件に従って被検体を本撮影したと仮定した場合に、投影データを取得する際のＸ線被曝量や、取得した投影データから生成される再構成画像の画質等を示す情報を特徴量と定義する。 That is, in the present embodiment, when it is assumed that the subject is actually imaged in accordance with the imaging conditions input by the user, the X-ray exposure amount when acquiring the projection data and the re-generation generated from the acquired projection data. Information indicating the image quality of the constituent image is defined as a feature amount.
　そして、撮影特徴量マップ生成装置２８は、この特徴量をマッピング、すなわち、画像上に表現したマップを撮影特徴量マップとして生成する。撮影特徴量マップとしては、例えば、照射線量比のマップ、画像ノイズ比のマップ、時間分解能比のマップ、空間分解能比のマップ等を生成することができる。 The shooting feature value map generation device 28 maps this feature value, that is, generates a map expressed on the image as a shooting feature value map. As the imaging feature amount map, for example, an irradiation dose ratio map, an image noise ratio map, a time resolution ratio map, a spatial resolution ratio map, and the like can be generated.
　従って、ユーザに特徴量の程度を提示するために、撮影特徴量マップ生成装置２８は、撮影特徴量マップを生成し、表示装置２９に表示させる。特に、撮影特徴量マップ生成装置２８は、位置決め画像を取得し、位置決め画像と対応させて撮影特徴量マップを生成し、位置決め画像と共に表示装置２９に表示することが好ましい。これにより、ユーザが設定した撮影条件に従って撮影処理及び再構成処理を行った場合に、得られる画像や被検体のＸ線被曝量をユーザに提示することができる。 Therefore, in order to present the degree of the feature amount to the user, the shooting feature amount map generation device 28 generates a shooting feature amount map and displays it on the display device 29. In particular, it is preferable that the shooting feature amount map generation device 28 acquires a positioning image, generates a shooting feature amount map corresponding to the positioning image, and displays it on the display device 29 together with the positioning image. Thereby, when the imaging process and the reconstruction process are performed according to the imaging conditions set by the user, the obtained image and the X-ray exposure dose of the subject can be presented to the user.
　図３及び図４に表示装置２９の表示画面の一例を示す。図３に示す表示画面では、位置決め画像と共に、二つの撮影特徴量マップ、再構成画像及び撮影条件を設定する領域が表示されている。また、図４に示す表示画面では、位置決め画像と共に、断面方向の異なる二つの撮影特徴量マップ、撮影条件を設定する領域、及び撮影条件の一つである撮影開始角度と撮影特徴量（照射線量、画像ノイズ、時間分解能）との関係を表したグラフ（曲線）が夫々表示されている。 3 and 4 show an example of the display screen of the display device 29. FIG. In the display screen shown in FIG. 3, an area for setting two shooting feature amount maps, a reconstructed image, and shooting conditions are displayed together with the positioning image. In the display screen shown in FIG. 4, together with the positioning image, two imaging feature quantity maps having different cross-sectional directions, an area for setting imaging conditions, and an imaging start angle and imaging feature quantity (irradiation dose) which are one of the imaging conditions. , Graphs (curves) representing the relationship with image noise, time resolution) are displayed.
　ユーザは、撮影特徴量マップにより、Ｘ線被曝量やノイズの程度を把握することができる。特に、表示装置２９に、撮影特徴量マップを位置決め画像と共に表示させることで、ユーザはＸ線被曝量の多くなる箇所やノイズが多くなる箇所が、被検体のいずれの部位において生じ得るかを把握することができる。 The user can grasp the X-ray exposure dose and the degree of noise from the imaging feature map. In particular, by causing the display device 29 to display the imaging feature amount map together with the positioning image, the user grasps in which part of the subject an area where the X-ray exposure amount or noise increases may occur. can do.
　以下、撮影特徴量マップ生成装置２８により生成される撮影特徴量マップの例について説明する。撮影特徴量マップとして、例えば、照射線量比のマップや画像ノイズ比のマップ、時間分解能比のマップ、空間分解能比のマップ、体軸分解能比のマップ等を用いることができ、それぞれ次のように作成することができる。 Hereinafter, an example of the shooting feature amount map generated by the shooting feature amount map generation device 28 will be described. As an imaging feature map, for example, an irradiation dose ratio map, an image noise ratio map, a temporal resolution ratio map, a spatial resolution ratio map, a body axis resolution ratio map, and the like can be used. Can be created.
　（照射線量比のマップ）
　照射線量比マップは、例えば、１ビューあたりの管電流・時間積（ｍＡｓ）を投影値として逆投影処理することにより取得することができる。この場合、ファンビーム逆投影を用いて以下の数式（１）及び（２）のように表すことができる。 (Irradiation dose ratio map)
The irradiation dose ratio map can be acquired, for example, by performing a back projection process using a tube current / time product (mAs) per view as a projection value. In this case, it can be expressed as the following formulas (1) and (2) using fan beam back projection.
Figure JPOXMLDOC01-appb-I000001
Figure JPOXMLDOC01-appb-I000001
　ここで、数式（１）及び（２）中、ＤＳＲＭは照射線量比マップ、βはファンビーム投影におけるビューのインデックス、αはファンビーム投影における検出器チャネルのインデックス、νはファンビーム投影における検出器列のインデックス、Ｎｖｉｅｗはビュー数、ｍＡはビュー方向への管電流変調関数［ｍＡ］、Ｔｓｃａｎはスキャン速度［ｓ］、β１はファンビームでの逆投影開始ビュー、β２はファンビームでの逆投影終了ビュー、ｘ，ｙ，ｚは画素のインデックスである。 Here, in Equations (1) and (2), DSRM is a dose ratio map, β is a view index in fan beam projection, α is a detector channel index in fan beam projection, and ν is a detector in fan beam projection. Column index, N view is the number of views, mA is the tube current modulation function [mA] in the view direction, T scan is the scan speed [s], β 1 is the back projection start view with the fan beam, β 2 is the fan beam The backprojection end view at x, y, z is the pixel index.
　（画像ノイズ比のマップ）
　画像ノイズ（ＳＤ）比マップは、例えば、ファンビーム逆投影を用いて以下の数式（３）及び（４）ように表すことができる。 (Image noise ratio map)
The image noise (SD) ratio map can be expressed as the following formulas (3) and (4) using, for example, fan beam back projection.
Figure JPOXMLDOC01-appb-I000002
Figure JPOXMLDOC01-appb-I000002
　上記数式（３）及び（４）では、被検体を考慮せず、ビュー重み、撮影管電流、スキャン速度、ビュー数の影響を考慮している。しかしながら、位置決め画像から推定した被検体の減弱を考慮して、例えば、以下の数式（５）及び（６）に示すように画像ノイズ比マップを生成してもよい。 In the above formulas (3) and (4), the influence of view weight, tube current, scan speed, and number of views is considered without considering the subject. However, in consideration of the attenuation of the subject estimated from the positioning image, for example, an image noise ratio map may be generated as shown in the following formulas (5) and (6).
Figure JPOXMLDOC01-appb-I000003
Figure JPOXMLDOC01-appb-I000003
　位置決め画像においてボリューム画像が得られている場合には、ボリューム画像から実測し画像ノイズ比マップを作成してもよい。 When a volume image is obtained in the positioning image, an image noise ratio map may be created by actually measuring the volume image.
　上記数式（３）～（６）において、ＳＤＲＭは画像ノイズ比マップ、βはファンビーム投影におけるビューのインデックス、αはファンビーム投影における検出器チャネルのインデックス、νはファンビーム投影における検出器列のインデックス、Ｎｖｉｅｗはビュー数、Ｗｆはビュー重み関数、ｍＡはビュー方向への管電流変調関数［ｍＡ］、Ｔｓｃａｎはスキャン速度［ｓ］、Ｇは投影値を作成する際に対数変換後の値に付加されたゲインの逆数、Ｐｅは位置決め画像や位置決め画像用撮影データから推定される被検体の投影データ、ＰａはＡｉｒキャル撮影により得られるＢｏｗｔｉｅフィルタやＸ線フィルタの投影データ、β１はファンビームでの逆投影開始ビュー、β２はファンビームでの逆投影終了ビュー、ｘ，ｙ，ｚは画素のインデックスである。 In the above formulas (3) to (6), SDRM is an image noise ratio map, β is a view index in fan beam projection, α is a detector channel index in fan beam projection, and ν is a detector row in fan beam projection. Index, N view is the number of views, W f is a view weight function, mA is a tube current modulation function [mA] in the view direction, T scan is a scan speed [s], and G is logarithmically converted when creating a projection value. Reciprocal of the gain added to the value, Pe is the projection data of the subject estimated from the positioning image and the imaging data for positioning image, Pa is the projection data of the Bowtie filter and the X-ray filter obtained by Air cal imaging, β 1 backprojection startup view of a fan beam, beta 2 backprojection ends view of a fan-beam, x, y, z are the pixel It is an index.
　なお、位置決め画像を撮影する際に螺旋スキャンが行われた場合には、Ｐｅとして、位置決め撮影データや得られた位置決め画像（ボリュームデータ）の順投影データを使用することができる。また、スキャノグラム撮影が行われた場合には、Ｐｅとして、スキャノグラムの投影値分布から得られる被検体モデルを基に推定した投影値を用いてもよい。この被検体モデルはＡＥＣなどでスキャノグラムから被検体形状を推定する方法を用いて取得することができる。 If a spiral scan is performed when a positioning image is captured, positioning imaging data and forward projection data of the obtained positioning image (volume data) can be used as Pe. When scanogram imaging is performed, a projection value estimated based on the object model obtained from the projection value distribution of the scanogram may be used as Pe. This object model can be acquired by using a method of estimating the object shape from the scanogram by AEC or the like.
　（時間分解能比のマップ）
　時間分解能比マップ（総時間幅のマップ）は、例えば、以下の数式（７）に示すように、１ビューあたりの撮影時間ΔＴｓｃａｎを投影値として重み付き逆投影処理することにより取得することができる。 (Map of time resolution ratio)
The time resolution ratio map (total time width map) can be obtained, for example, by weighted backprojection processing using the imaging time ΔT scan per view as a projection value, as shown in the following formula (7). it can.
Figure JPOXMLDOC01-appb-I000004
Figure JPOXMLDOC01-appb-I000004
　また、実効時間幅のマップとする場合には、以下の数式（８）に示すように、１ビューあたりの撮影時間ΔＴｓｃａｎを投影値として重み付き逆投影を行うことにより取得することができる。 Further, when the effective time width map is used, it can be obtained by performing weighted backprojection using the imaging time ΔT scan per view as a projection value, as shown in the following formula (8).
Figure JPOXMLDOC01-appb-I000005
Figure JPOXMLDOC01-appb-I000005
なお、ＴＲＲＭは時間分解能比マップ、βはファンビーム投影におけるビューのインデックス、Ｎｖｉｅｗはビュー数、Ｗｆはビュー重み関数、Ｔｓｃａｎはスキャン速度［ｓ］、β１はファンビームでの逆投影開始ビュー、β２はファンビームでの逆投影終了ビュー、ｘ，ｙ，ｚは画素のインデックスである。 TRRM is a temporal resolution ratio map, β is a view index in fan beam projection, N view is the number of views, W f is a view weight function, T scan is a scan speed [s], and β 1 is back projection with a fan beam. The start view, β 2 is the back projection end view with the fan beam, and x, y, and z are pixel indices.
　（空間分解能比のマップ）
　空間分解能比マップは、例えば、Ｘ線源としてのＸ線発生装置から画素までの距離に応じたチャネル方向のビーム幅の値を重み付き逆投影処理することにより取得することができる。この場合、ファンビーム逆投影を用いて以下の数式（９）及び（１０）のように表すことができる。 (Spatial resolution ratio map)
The spatial resolution ratio map can be obtained, for example, by performing a weighted back projection process on the value of the beam width in the channel direction according to the distance from the X-ray generator as an X-ray source to the pixel. In this case, it can be expressed as the following formulas (9) and (10) using fan beam back projection.
Figure JPOXMLDOC01-appb-I000006
Figure JPOXMLDOC01-appb-I000006
　上記数式（９）及び（１０）において、ＳＲＲＭは空間分解能比マップ、βはファンビーム投影におけるビューのインデックス、αはファンビーム投影における検出器チャネルのインデックス、νはファンビーム投影における検出器列のインデックス、Ｎｖｉｅｗはビュー数［ｖｉｅｗ］、Ｗｆはビュー重み関数、Ｄｓｉｄは線源－検出器素子間距離［ｍｍ］、Ｌは線源－画素間距離［ｍｍ］、Δｄｃｓはチャネル方向検出器素子サイズ［ｍｍ］、β１はファンビームでの逆投影開始ビュー、β２はファンビームでの逆投影終了ビュー、ｘ，ｙ，ｚは画素のインデックスである。 In the above equations (9) and (10), SRRM is a spatial resolution ratio map, β is a view index in fan beam projection, α is a detector channel index in fan beam projection, and ν is a detector row in fan beam projection. Index, N view is the number of views [view], W f is the view weight function, D sid is the source-detector element distance [mm], L is the source-pixel distance [mm], and Δdcs is the channel direction detection. The element size [mm], β 1 is a back projection start view with a fan beam, β 2 is a back projection end view with a fan beam, and x, y, and z are pixel indexes.
　（体軸分解能比のマップ）
　体軸分解能比マップは、例えば、Ｘ線源としてのＸ線発生装置から画素までの距離に応じた体軸方向のビーム幅の値を重み付き逆投影処理することにより取得することができる。この場合、ファンビーム逆投影を用いて以下のように表すことができる。 (Body axis resolution ratio map)
The body axis resolution ratio map can be obtained, for example, by performing weighted back projection processing on the value of the beam width in the body axis direction according to the distance from the X-ray generator as an X-ray source to the pixel. In this case, it can be expressed as follows using fan beam back projection.
Figure JPOXMLDOC01-appb-I000007
Figure JPOXMLDOC01-appb-I000007
　上記数式（１１）及び（１２）において、ＺＲＲＭは体軸分解能比マップ、βはファンビーム投影におけるビューのインデックス、αはファンビーム投影における検出器チャネルのインデックス、νはファンビーム投影における検出器列のインデックス、Ｎｖｉｅｗはビュー数［ｖｉｅｗ］、Ｗｆはビュー重み関数、Ｄｓｉｄは線源－検出器素子間距離［ｍｍ］、Ｌは線源－画素間距離［ｍｍ］、Δｄｒｓは列方向検出器素子サイズ［ｍｍ］、β１はファンビームでの逆投影開始ビュー、β２はファンビームでの逆投影終了ビュー、ｘ，ｙ，ｚは画素のインデックスである。 In the above equations (11) and (12), ZRRM is a body axis resolution ratio map, β is a view index in fan beam projection, α is a detector channel index in fan beam projection, and ν is a detector array in fan beam projection. , N view is the view number [view], W f is the view weight function, D sid is the source-detector element distance [mm], L is the source-pixel distance [mm], and Δdrs is the column direction. Detector element size [mm], β 1 is a back projection start view with a fan beam, β 2 is a back projection end view with a fan beam, and x, y, and z are pixel indexes.
　撮影特徴量マップとして、照射線量比のマップ、画像ノイズ比のマップ、時間分解能比のマップ、空間分解能比のマップ、及び体軸分解能比のマップ生成手法の一例について説明したが、上述した内容に限定されず、撮影特徴量マップには画像の特徴を示す他の特徴量に基づく特徴量マップを適用することができることはもちろん、上述した特徴量マップの生成方法についても、他の公知の方法を用いることができる。 As an imaging feature map, an example of a method for generating an irradiation dose ratio map, an image noise ratio map, a temporal resolution ratio map, a spatial resolution ratio map, and a body axis resolution ratio map has been described. The feature amount map based on other feature amounts indicating the features of the image can be applied to the shooting feature amount map, and other known methods can be used for the above-described feature amount map generation method. Can be used.
　上述した撮影特徴量マップは３次元画像として生成しており、位置決め画像が螺旋スキャンで生成されたボリュームデータである場合には、位置決め画像の表示に合わせて表示するのが好ましい。その際に、同一断面を並べて表示したり、撮影特徴量マップを色づけして位置決め画像に重ねて表示たり、カーソルで選択した位置に対する値を撮影特徴量マップから参照して表示したり、位置決め画像上で円形や矩形等の所定領域の平均値や最大値や最小値を計算して表示したりすることができる。また、撮影特徴量マップは位置決め画像と同様の面以外に、アキシャル面など複数面を表示してもよい。 The above-described shooting feature amount map is generated as a three-dimensional image, and when the positioning image is volume data generated by a spiral scan, it is preferably displayed in accordance with the display of the positioning image. At that time, the same cross section is displayed side by side, the shooting feature map is colored and displayed superimposed on the positioning image, the value for the position selected by the cursor is displayed by referring to the shooting feature map, the positioning image The average value, maximum value, and minimum value of a predetermined area such as a circle or rectangle can be calculated and displayed. In addition to the surface similar to the positioning image, the imaging feature map may display a plurality of surfaces such as an axial surface.
　また、位置決め画像がスキャノグラムである場合には、撮影特徴量マップである３次元画像をスキャノグラム撮影と同方向から順投影し、撮影特徴量マップのスキャノグラムを作成して表示してもよい。この際、順投影に代えて、最大値投影や最小値投影等を用いてもよい。さらに撮影特徴量マップである３次元画像の回転中心を通る断面や被検体中心となる断面を表示してもよい。この際の被検体中心断面は位置決め画像から推定することができる。 In addition, when the positioning image is a scanogram, a three-dimensional image that is a shooting feature map may be projected in the same direction as the scanogram shooting to create and display a scanogram of the shooting feature map. At this time, instead of forward projection, maximum value projection, minimum value projection, or the like may be used. Furthermore, a cross section that passes through the rotation center of the three-dimensional image that is the imaging feature amount map or a cross section that becomes the center of the subject may be displayed. The subject center cross section at this time can be estimated from the positioning image.
　続いて、上述したＸ線ＣＴ装置において、位置決め画像を取得し、撮影条件の設定を行い、再構成画像を生成する処理について図５のフローチャートに従って説明する。 Subsequently, processing for acquiring a positioning image, setting imaging conditions, and generating a reconstructed image in the above-described X-ray CT apparatus will be described with reference to the flowchart of FIG.
　はじめに、撮影特徴量マップ生成装置２８を含む演算装置２２は、ユーザにより設定された位置決め画像の撮影条件を、入力装置２４を介して受信し、（ステップＳ１１）、設定された撮影条件に従って位置決め画像を撮影するための指示をスキャナ１０に送信する（ステップ１２）。なお、位置決め画像の撮影条件の設定及び位置決め画像撮影は公知の方法で行うことができ、例えば、スキャノグラム撮影や低線量螺旋スキャンなどを適用することができる。 First, the arithmetic unit 22 including the imaging feature value map generation device 28 receives the imaging condition of the positioning image set by the user via the input device 24 (step S11), and the positioning image according to the imaging condition set. Is sent to the scanner 10 (step 12). In addition, the setting of the imaging condition of the positioning image and the imaging of the positioning image can be performed by a known method. For example, scanogram imaging or low-dose spiral scanning can be applied.
　続いて、図３の表示画面の一例に示す、表示装置２９に表示された撮影条件設定領域５０において、位置決め画像に基づいて、本撮影における撮影条件及び再構成条件がユーザにより設定される。演算装置２２は、設定された各種条件を入力装置２４を介して受け付ける（ステップＳ１３）。画像再構成法が複数選択できる場合においては再構成条件として画像再構成法を設定することができる。撮影条件としては、アキシャルスキャンや螺旋スキャンといった撮影方式、撮影開始角度、体軸方向の撮影範囲、ビームピッチや管電流、管電圧の他、Ｘ線曝射制御（ＡＥＣ）等の設定も行われる。また、演算すべき撮影特徴量の種類も撮影条件設定領域５０において選択される。 Subsequently, in the imaging condition setting area 50 displayed on the display device 29 shown in the example of the display screen of FIG. 3, the imaging conditions and reconstruction conditions in the actual imaging are set by the user based on the positioning image. The arithmetic unit 22 receives the set various conditions via the input device 24 (step S13). When a plurality of image reconstruction methods can be selected, the image reconstruction method can be set as a reconstruction condition. As imaging conditions, an imaging method such as an axial scan and a spiral scan, an imaging start angle, an imaging range in the body axis direction, a beam pitch, a tube current, a tube voltage, and X-ray exposure control (AEC) are also set. . In addition, the type of shooting feature value to be calculated is also selected in the shooting condition setting area 50.
　次のステップＳ１４において、撮影特徴量マップ生成装置２８は、先のステップＳ１３においてユーザにより設定され、入力された撮影条件から撮影特徴量マップを生成する。
このとき、撮影特徴量マップ生成装置２８は、先のステップで選択された特徴量の種類に応じて、上述した数式（１）～（１２）の何れかに従って特徴量を算出し撮影特徴量マップを生成し、生成した撮影特徴量マップを表示制御装置２３に送信する。表示制御装置２３では、位置決め画像と共に撮影特徴量マップを表示装置２９に表示させる。 In the next step S14, the shooting feature value map generating device 28 generates a shooting feature value map from the shooting conditions set and input by the user in the previous step S13.
At this time, the shooting feature value map generation device 28 calculates the feature value according to any one of the above-described formulas (1) to (12) according to the type of the feature value selected in the previous step, and the shooting feature value map. And the generated shooting feature amount map is transmitted to the display control device 23. The display control device 23 causes the display device 29 to display a shooting feature amount map together with the positioning image.
　続いて、表示装置２９に表示された撮影特徴量マップを確認し、ユーザによる撮影条件変更の要否の入力を、入力装置２４を介して受け付ける（ステップＳ１５）。つまり、撮影特徴量マップを確認したユーザが撮影条件を変更しない場合には、演算装置２２は入力装置２４から撮影条件を変更しない旨の信号を受信し、次のステップＳ１６に進み、設定された撮影条件にて本撮影を行うようにスキャナ１０に指示を送信する。 Subsequently, the shooting feature amount map displayed on the display device 29 is confirmed, and an input of whether or not the user needs to change the shooting conditions is accepted via the input device 24 (step S15). In other words, if the user who has confirmed the shooting feature map does not change the shooting conditions, the arithmetic unit 22 receives a signal indicating that the shooting conditions are not changed from the input device 24, proceeds to the next step S16, and is set. An instruction is transmitted to the scanner 10 to perform the main photographing under the photographing conditions.
　一方、ユーザが撮影条件の変更をする場合には、演算装置２２は入力装置２４から撮影条件を変更する旨の信号を受信し、ステップＳ１３に戻り、再設定された撮影条件の入力を受け付ける。そして、撮影特徴量マップ生成装置２８では、再設定された撮影条件に従って、再度、撮影特徴量マップを作成する（ステップＳ１４）。 On the other hand, when the user changes the shooting condition, the arithmetic unit 22 receives a signal to change the shooting condition from the input device 24, returns to step S13, and accepts the input of the reset shooting condition. Then, the shooting feature value map generation device 28 creates a shooting feature value map again according to the reset shooting conditions (step S14).
　ここで、例えば、被検体に対するＸ線被曝量を重視する場合には、ユーザにより撮影条件設定領域５０において照射線量比が選択され、撮影特徴量マップ生成装置２８は、撮影特徴量マップとして照射線量比マップを生成して表示装置２９に表示させ。これにより、ユーザは、被検体の各部位におけるＸ線照射量を把握することができる。そして、ユーザは、脾臓や水晶体や甲状腺等のＸ線感受性の高い部位へのＸ線照射が低減されるように撮影条件として撮影開始角度を調整する。 Here, for example, when the X-ray exposure dose on the subject is emphasized, the irradiation dose ratio is selected in the imaging condition setting region 50 by the user, and the imaging feature value map generation device 28 uses the irradiation dose as the imaging feature value map. A ratio map is generated and displayed on the display device 29. Thereby, the user can grasp | ascertain the X-ray irradiation amount in each site | part of a subject. Then, the user adjusts the imaging start angle as an imaging condition so that X-ray irradiation to highly sensitive X-ray parts such as the spleen, the lens, and the thyroid gland is reduced.
　撮影開始角度は、図３に示すように表示装置２９の表示画面上に表示されたスライドバーにより調整可能とすることができ、また、ユーザによる手動入力で直接指定することも可能である。なお、バリアブルピッチスキャンの場合には脾臓や水晶体や甲状腺等のＸ線感受性の高い部位において寝台移動速度を速くする等に調整してもよく、ステップスキャンの場合にはＸ線被曝量の多くなる撮影のつなぎ目がＸ線感受性の高い部分からずれるようにＸ線発生装置５の体軸方向位置を調整することもできる。 The photographing start angle can be adjusted by a slide bar displayed on the display screen of the display device 29 as shown in FIG. 3, or can be directly designated by a user's manual input. In the case of a variable pitch scan, it may be adjusted to increase the bed moving speed in a highly sensitive X-ray sensitive region such as the spleen, the lens or the thyroid gland. In the case of a step scan, the X-ray exposure amount increases. The position in the body axis direction of the X-ray generator 5 can also be adjusted so that the joint of imaging shifts from a portion having high X-ray sensitivity.
　ステップＳ１７では、ステップＳ１６で行われた本撮影によって収集された投影データを画像再構成することで断層像を生成し、表示装置２９に表示する。このとき、断層像のみを表示することもできる他、ユーザにより選択された撮影特徴量マップを断層像と並べて表示したり、撮影特徴量マップを色づけして断層像に重ねて表示したり、カーソルで選択した位置に対する値を撮影特徴量マップから参照し表示したり、位置決め画像上で円形や矩形で囲まれた領域の平均値や最大値や最小値を計算し表示したりすることもできる。 In step S17, a tomographic image is generated by reconstructing the projection data collected by the main imaging performed in step S16, and displayed on the display device 29. At this time, in addition to displaying only the tomographic image, the imaging feature amount map selected by the user is displayed side by side with the tomographic image, the imaging feature amount map is colored and displayed over the tomographic image, or the cursor It is also possible to display the value for the position selected by referring to the shooting feature map, or to calculate and display the average value, maximum value, or minimum value of the area surrounded by a circle or rectangle on the positioning image.
　上記実施形態によれば、スキャナにより、Ｘ線源としてのＸ線発生装置を被検体の周囲に周回させて、Ｘ線発生装置から照射され、被検体を透過したＸ線量をＸ線検出器により検出した投影データを取得し、この投影データを再構成演算装置により再構成して再構成画像を取得する。 According to the above embodiment, the X-ray generator as an X-ray source is circulated around the subject by the scanner, and the X-ray dose irradiated from the X-ray generator and transmitted through the subject is detected by the X-ray detector. The detected projection data is acquired, and the projection data is reconstructed by a reconstruction calculation device to obtain a reconstructed image.
　この場合において、投影データの取得に先立って、被検体に応じて投影データを取得するための撮影条件を設定する。そして、設定された撮影条件に従ってスキャナにより投影データを取得した場合に、得られる再構成画像における特徴を示す情報としての特徴量をマッピングした撮影特徴量マップを生成し、これを表示装置に表示する。 In this case, prior to the acquisition of projection data, imaging conditions for acquiring projection data are set according to the subject. Then, when projection data is acquired by the scanner according to the set shooting conditions, a shooting feature amount map is generated by mapping feature amounts as information indicating features in the obtained reconstructed image, and this is displayed on the display device. .
　このようにすることで、Ｘ線ＣＴ装置では、生成される再構成画像の特徴量をユーザに提示することができ、ユーザは表示された撮影特徴量マップを確認することにより、再構成画像における画像の特徴量を把握することができる。従って、ユーザは、必要に応じて撮影条件を再度設定することができ、例えば、脾臓、水晶体及び甲状腺等のＸ線感受性の高い部位へのＸ線照射を低減させたい場合には、スキャナの撮影開始角度等を調整することができる。これにより、Ｘ線源の軌道が変更させられ、Ｘ線感受性の高い部位に対するＸ線照射期間を低減させることで、Ｘ線被曝量を低減させることができる。 By doing in this way, in the X-ray CT apparatus, the feature amount of the generated reconstructed image can be presented to the user, and the user confirms the displayed imaging feature amount map to thereby display the reconstructed image in the reconstructed image. The feature amount of the image can be grasped. Therefore, the user can set the imaging conditions again as necessary. For example, when it is desired to reduce the X-ray irradiation to the X-ray sensitive parts such as the spleen, the lens and the thyroid gland, The starting angle and the like can be adjusted. Thereby, the trajectory of the X-ray source is changed, and the X-ray exposure amount can be reduced by reducing the X-ray irradiation period for the site having high X-ray sensitivity.
　つまり、特に、撮影特徴量マップとして、撮影開始角度に応じた照射線量比マップを表示させることで、ユーザは、被検体のＸ線感受性の高い部位等の注目部位に対してＸ線照射線量が適切であるか否かを判断することができる。照射線量比マップを参照して、Ｘ線感受性の高い部位へのＸ線照射線量が多い場合には、撮影開始角度を変更してＸ線発生装置の軌道を変更させることにより、Ｘ線感受性の高い部位に対するＸ線被曝量を低減させることができる。 That is, in particular, by displaying an irradiation dose ratio map corresponding to the imaging start angle as an imaging feature amount map, the user can obtain an X-ray irradiation dose for a site of interest such as a site with high X-ray sensitivity of the subject. It can be determined whether it is appropriate. Referring to the irradiation dose ratio map, when the X-ray irradiation dose to a part having high X-ray sensitivity is large, the X-ray sensitivity is changed by changing the trajectory of the X-ray generator by changing the imaging start angle. The X-ray exposure dose for high sites can be reduced.
　同様に、生成及び表示させる撮影特徴量マップとして、時間分解能比マップ、画像ノイズ比マップ等の何れか適宜選択することで、注目部位について良好な画像ノイズ、時間分解能、空間分解能を有するような、注目領域にて所望の撮影特徴量を有する再構成画像、すなわち断層像を生成し得る撮影条件を設定することができる。 Similarly, as an imaging feature amount map to be generated and displayed, by appropriately selecting any one of a time resolution ratio map, an image noise ratio map, etc., the image of interest has good image noise, time resolution, spatial resolution, An imaging condition that can generate a reconstructed image having a desired imaging feature amount, that is, a tomographic image, in the region of interest can be set.
　一例として、アーティファクトを低減させた再構成画像を取得したい場合には、以下のように考えることができる。 For example, when it is desired to obtain a reconstructed image with reduced artifacts, the following can be considered.
　図７Ａはノーマルスキャン時のＸ線発生装置の軌道、図７Ｂは螺旋スキャン時のＸ線発生装置の軌道を示している。図７Ａのようにノーマルスキャン（円軌道）で撮影された場合には、フィルタ補正２次元逆投影を行うことでＸ線源位置の画像を正確に再現することができる。 FIG. 7A shows the trajectory of the X-ray generator during normal scanning, and FIG. 7B shows the trajectory of the X-ray generator during helical scanning. When the image is captured by normal scanning (circular orbit) as shown in FIG. 7A, the image at the X-ray source position can be accurately reproduced by performing filter-corrected two-dimensional backprojection.
　しかし、図７Ｂのように螺旋スキャン（螺旋軌道）で撮影された場合には、被写体が動いた場合と同様に、撮影端部位相におけるデータの不連続性により、フィルタ補正２次元逆投影のみでは該位置でストリーク状のアーティファクトを生ずる。 However, when the image is captured by a spiral scan (spiral trajectory) as shown in FIG. 7B, as in the case where the subject moves, the discontinuity of the data at the imaging end phase causes only the filter-corrected two-dimensional backprojection. A streak-like artifact is produced at this position.
　そこで、図７Ｂのように螺旋軌道で得られたデータに対し、データ補間を用いることで図７Ａのような円軌道データに補正し、その後にフィルタ補正２次元逆投影を行う。このように補間を用いることで不連続性を低減した画像を得ることができる。そして、この場合のアーティファクトの程度は、Ｘ線源軌跡における不連続の程度によって決定され、つまり、被写体の移動速度によってアーティファクト程度は変動する。 Therefore, the data obtained by the spiral orbit as shown in FIG. 7B is corrected to the circular orbit data as shown in FIG. 7A by using data interpolation, and then the filter correction two-dimensional backprojection is performed. In this way, an image with reduced discontinuity can be obtained by using interpolation. In this case, the degree of artifact is determined by the degree of discontinuity in the X-ray source locus, that is, the degree of artifact varies depending on the moving speed of the subject.
　このため、このようなＸ線発生装置の軌道に起因するアーティファクトを低減させることが好ましい。この場合にも本実施形態によれば、撮影条件設定の後、所望の撮影特徴量マップを表示することにより設定した撮影条件により投影データを取得して再構成画像を生成すると、アーティファクトの程度がどのようになるかを提示することができる。従って、ユーザは必要に応じて撮影条件を再設定することができ、取得される再構成画像の品質を向上させることができる。 For this reason, it is preferable to reduce artifacts resulting from the trajectory of such an X-ray generator. Also in this case, according to the present embodiment, after the shooting conditions are set, when the projection data is acquired according to the shooting conditions set by displaying the desired shooting feature amount map and the reconstructed image is generated, the degree of the artifact is increased. You can present what will happen. Therefore, the user can reset the photographing conditions as necessary, and can improve the quality of the acquired reconstructed image.
　＜第２の実施形態＞
　以下、本発明の第２の実施形態について説明する。本実施形態において、Ｘ線ＣＴ装置は、位置決め画像を取得した後に、位置決め画像において関心領域、すなわちＲＯＩ（Ｒｅｇｉｏｎ　ｏｆ　Ｉｎｔｅｒｅｓｔ）設定を行い、設定されたＲＯＩ内における特徴量を最適化する。 <Second Embodiment>
Hereinafter, a second embodiment of the present invention will be described. In this embodiment, after acquiring a positioning image, the X-ray CT apparatus sets a region of interest, that is, a ROI (Region of Interest) in the positioning image, and optimizes a feature amount in the set ROI.
　ここで、最適化とは、ＲＯＩ全体での撮影特徴量について、例えば、平均値、最大値、最小値等を指標値として定め、その撮影特徴量に係る指標値が最良となるように撮影条件を決定することをいう。 Here, the optimization refers to, for example, an average value, a maximum value, a minimum value, etc. as an index value for the imaging feature amount in the entire ROI, and the imaging conditions so that the index value related to the imaging feature amount is the best. It means to decide.
　具体的には、例えば、撮影特徴量が照射線量比である場合、ＲＯＩ内での照射線量比に係る指標値（照射線量比の平均値、最大値、積分値等）が低くなるように撮影条件を決定することで最適化することができる。 Specifically, for example, when the imaging feature amount is an irradiation dose ratio, the imaging is performed such that an index value (average value, maximum value, integral value, etc. of the irradiation dose ratio) related to the irradiation dose ratio in the ROI is low. It can be optimized by determining the conditions.
　また、例えば、撮影特徴量が時間分解能である場合、ＲＯＩ内での時間分解能に係る指標値（時間分解能の平均値、最小値、積分値等）が高くなるように撮影条件を決定することで最適化することができる。 Also, for example, when the imaging feature value is time resolution, the imaging condition is determined so that the index value (average value, minimum value, integral value, etc.) of the time resolution in the ROI becomes high. Can be optimized.
　さらに、例えば、撮影特徴量が空間分解能比である場合、ＲＯＩ内での空間分解能比に係る指標値（空間分解能比の平均値、最小値、積分値等）が高くなるように撮影条件を決定することで最適化することができる。 Furthermore, for example, when the imaging feature quantity is a spatial resolution ratio, the imaging conditions are determined so that an index value (average value, minimum value, integrated value, etc.) of the spatial resolution ratio in the ROI is high. It can be optimized by doing.
　このため、撮影特徴量マップ生成装置２８が、設定された撮影条件とＲＯＩとに基づいて撮影特徴量マップを生成する他、併せて、ＲＯＩ位置に対応する撮影特徴量の値を撮影開始角度毎に算出し、撮影開始角度－特徴量曲線を生成する。そして、撮影特徴量生成装置２８は、この撮影開始角度－特徴量曲線から、最適な撮影条件として、適切な撮影開始角度を自動設定する。 Therefore, the shooting feature value map generation device 28 generates a shooting feature value map based on the set shooting conditions and the ROI, and at the same time, sets the value of the shooting feature value corresponding to the ROI position for each shooting start angle. And a shooting start angle-feature amount curve is generated. Then, the shooting feature value generation device 28 automatically sets an appropriate shooting start angle as an optimum shooting condition from the shooting start angle-feature value curve.
　つまり、本実施形態において、撮影特徴量生成装置２８は、撮影開始角度－特徴量曲線から、ＲＯＩ範囲に相当する撮影開始角度－特徴量曲線の平均値や積分値が最良となるように撮影開始角度を決定する。 In other words, in the present embodiment, the imaging feature value generation device 28 starts imaging so that the average value or integral value of the imaging start angle-feature amount curve corresponding to the ROI range is optimized from the imaging start angle-feature value curve. Determine the angle.
　本実施形態におけるＸ線ＣＴ装置のその他の構成は、上述した第１の実施形態におけるＸ線ＣＴ装置と同一であるため、その繰り返しの説明は省略する。 Since the other configuration of the X-ray CT apparatus in the present embodiment is the same as that of the X-ray CT apparatus in the first embodiment described above, repeated description thereof is omitted.
　また、上述した第１の実施形態と同様に、位置決め画像の取得方法や、撮影条件の設定、画像の再構成法については種々の方法から適宜選択することができる。 Also, as in the first embodiment described above, the positioning image acquisition method, imaging condition setting, and image reconstruction method can be appropriately selected from various methods.
　本実施形態に係るＸ線ＣＴ装置における、位置決め画像の取得から再構成画像の生成までの処理について図６のフローチャートに従って説明する。 The processing from acquisition of the positioning image to generation of the reconstructed image in the X-ray CT apparatus according to the present embodiment will be described with reference to the flowchart of FIG.
　はじめに、撮影特徴量マップ生成装置２８を含む演算装置２２では、ユーザにより設定された位置決め画像の撮影条件を、入力装置２４を介して受信し（ステップＳ２１）、設定された撮影条件に従って位置決め画像を撮影するための指示をスキャナ１０に送信する（ステップＳ２２）。 First, the arithmetic device 22 including the imaging feature value map generation device 28 receives the imaging condition of the positioning image set by the user via the input device 24 (step S21), and the positioning image is obtained according to the imaging condition set. An instruction for photographing is transmitted to the scanner 10 (step S22).
　次に、図４に示すように、演算装置２２は、ユーザにより入力装置２４において設定され入力された位置決め画像における注目部位をＲＯＩ５１として設定する。（ステップＳ２３）。 Next, as shown in FIG. 4, the arithmetic unit 22 sets a region of interest in the positioning image set and input by the user in the input device 24 as the ROI 51. (Step S23).
　続いて、図４に示すような表示装置２９に表示される表示画面上の撮影条件設定領域５０において、位置決め画像に基づいて本撮影における撮影条件及び再構成条件がユーザにより設定され、演算装置２２は、設定された各種条件を、入力装置２４を介して受け付ける（ステップＳ２４）。 Subsequently, in the shooting condition setting area 50 on the display screen displayed on the display device 29 as shown in FIG. 4, shooting conditions and reconstruction conditions in the main shooting are set by the user based on the positioning image, and the arithmetic device 22 Accepts various set conditions via the input device 24 (step S24).
　次のステップＳ２５では、撮影特徴量マップ生成装置２８が、設定された撮影条件とＲＯＩとに基づいて、撮影特徴量マップを生成し、生成した撮影特徴量マップを表示装置２９に送信する。また、併せて、撮影特徴量マップ生成装置２８において、ＲＯＩ位置に対応する撮影特徴量の値を撮影開始角度毎に算出し、撮影開始角度と特徴量との関係を示すグラフである撮影開始角度－特徴量曲線を生成する。撮影特徴量マップ生成装置２８は、生成した撮影開始角度－特徴量曲線を表示制御装置２３に送信し、図４に示すように、表示装置２９に撮影開始角度－特徴量曲線を表示させる。ここでは、撮影特徴量として、照射線量、画像ノイズ及び時間分解能の３つについて、夫々撮影開始開角度との関係を示すグラフを生成している。 In the next step S25, the shooting feature value map generation device 28 generates a shooting feature value map based on the set shooting conditions and ROI, and transmits the generated shooting feature value map to the display device 29. At the same time, the shooting feature value map generation device 28 calculates the value of the shooting feature value corresponding to the ROI position for each shooting start angle, and is a graph showing the relationship between the shooting start angle and the feature value. -Generate a feature curve. The shooting feature amount map generation device 28 transmits the generated shooting start angle-feature amount curve to the display control device 23, and causes the display device 29 to display the shooting start angle-feature amount curve as shown in FIG. Here, as the imaging feature amount, a graph showing the relationship between the irradiation start, the image noise, and the time resolution with the imaging start opening angle is generated.
　続いて、撮影特徴量マップ生成装置２８は、これら３つの撮影開始角度－特徴量曲線に対して、夫々優先度を考慮し、優先すべき特徴量についての値が最も目標値に近い、すなわち最良となる撮影開始角度を候補として算出し、表示装置２９に表示させる。演算装置２２では、候補が１つの場合には、当該候補である撮影開始角度を自動的に決定する（ステップＳ２６）。 Subsequently, the shooting feature value map generation device 28 considers the priority for each of these three shooting start angle-feature value curves, and the value of the feature value to be prioritized is closest to the target value, that is, the best. Is calculated as a candidate and displayed on the display device 29. In the arithmetic device 22, when there is one candidate, the photographing start angle which is the candidate is automatically determined (step S26).
　撮影開始角度－特徴量曲線を用いて優先度を考慮しながら撮影開始角度を決定する場合、より具体的には、３つの撮影開始角度－特徴量曲線から、優先度が最も高い撮影特徴量がＲＯＩ内で最良となるように、撮影開始角度を決定する。このとき、ＲＯＩ内での撮影特徴量が最良となる撮影開始角度が複数存在した場合は、優先度が２番目に高い撮影特徴量がＲＯＩ内で最良となる撮影開始角度を候補として決定する。また、２番目に優先度が高い撮影特徴量を用いても候補となる撮影開始角度が複数存在する場合には、３番目に優先度が高い撮影特徴量がＲＯＩ内で最良となる撮影開始角度を候補として決定する。 When the shooting start angle is determined while taking the priority into account using the shooting start angle-feature amount curve, more specifically, from the three shooting start angle-feature amount curves, the shooting feature amount with the highest priority is determined. The imaging start angle is determined so as to be the best within the ROI. At this time, when there are a plurality of shooting start angles with the best shooting feature value in the ROI, the shooting start angle with the second highest shooting feature value in the ROI is determined as a candidate. If there are a plurality of candidate shooting start angles even when the second highest priority shooting feature amount is used, the third highest priority shooting feature amount is the best shooting start angle in the ROI. Are determined as candidates.
　図４に示すように、優先係数を用いる場合には、まず、撮影特徴量を、１となる場合に最良（最大値）となり、０となる場合に最も不良（最小値）となるように予め規格化しておき、各撮影特徴量にそれぞれの優先係数を乗じた値の総和が最も高くなるように撮影開始角度を決定する。なお、規格化において、最大値が１、最小値が０となるように撮影特徴量を修正した後、撮影特徴量の値が小さいことが望ましい場合には、１から撮影特徴量を引いた値を撮影特徴量の候補として用いることができる。 As shown in FIG. 4, in the case of using the priority coefficient, first, the shooting feature amount is first set to be the best (maximum value) when it is 1 and is most defective (minimum value) when it is 0. The shooting start angle is determined so that the sum of values obtained by multiplying each shooting feature value by the respective priority coefficient is the highest. In normalization, when the shooting feature value is desired to be small after correcting the shooting feature value so that the maximum value is 1 and the minimum value is 0, a value obtained by subtracting the shooting feature value from 1 Can be used as candidates for the imaging feature amount.
　次のステップＳ２７では、撮影特徴量マップ生成装置２８は、先に入力された撮影条件及びステップＳ２６で自動的に決定された撮影開始角度に基づいて撮影特徴量マップが生成され、位置決め画像とともに表示装置２９に表示させる。 In the next step S27, the shooting feature value map generation device 28 generates a shooting feature value map based on the previously input shooting conditions and the shooting start angle automatically determined in step S26, and displays it together with the positioning image. It is displayed on the device 29.
　続いて、ユーザにより表示装置に表示された撮影特徴量マップが確認され、ユーザによる撮影条件変更の要否の入力を、入力装置２４を介して受け付ける（ステップＳ２８）。
本ステップＳ２８において、ユーザにより撮影条件変更が必要と判断され、演算装置２２が入力装置２４から撮影条件を変更する旨の信号を受信した場合には、ステップＳ２４に戻りユーザにより撮影条件が再設定され、再設定された撮影条件の入力を受け付ける。そして、撮影特徴量マップ生成装置２８では、再設定された撮影条件に従って、再度、撮影開始角度－特徴量曲線を算出し（ステップＳ２５）、再び最良となる撮影開始角度を決定し（ステップＳ２６）、撮影特徴量マップを作成する（ステップＳ２７）。 Subsequently, the shooting feature amount map displayed on the display device is confirmed by the user, and an input indicating whether the user needs to change the shooting conditions is accepted via the input device 24 (step S28).
In step S28, when it is determined that the user needs to change the shooting condition, and the arithmetic unit 22 receives a signal to change the shooting condition from the input device 24, the process returns to step S24 to reset the shooting condition by the user. Then, the input of the reset imaging conditions is accepted. Then, the shooting feature amount map generation device 28 calculates again the shooting start angle-feature amount curve according to the reset shooting conditions (step S25), and again determines the best shooting start angle (step S26). Then, a shooting feature amount map is created (step S27).
　ステップＳ２８において、ユーザにより撮影条件変更が不要と判断された場合には、演算装置２２は入力装置２４から撮影条件を変更しない旨の信号を受信し、次のステップＳ２９に進み、設定された撮影条件にて本撮影を行うようにスキャナ１０に指示を送信する。そして、得られた投影データを画像再構成することで再構成画像としての断層像を生成し表示装置２９に表示する（ステップＳ３０）。 If it is determined in step S28 that the user does not need to change the shooting condition, the arithmetic unit 22 receives a signal indicating that the shooting condition is not changed from the input device 24, and proceeds to the next step S29 to set the set shooting condition. An instruction is transmitted to the scanner 10 so as to perform actual photographing under conditions. Then, by reconstructing the obtained projection data, a tomographic image as a reconstructed image is generated and displayed on the display device 29 (step S30).
　なお、ヘリカルスキャンの場合の撮影特徴量は体軸方向にビームピッチの周期で変動するため、ＲＯＩの体軸方向サイズが大きい場合にはＲＯＩ内全体が所望の撮影特徴量とならない場合がある。そのため、ＲＯＩ体軸方向サイズが大きい場合には、バリアブルピッチスキャンを用いてＲＯＩ領域で自動的にビームピッチが大きくなるように修正することが望ましく、このような情報をユーザに提示してもよく、撮影条件の修正候補をユーザに提案してもよい。 In addition, since the imaging feature amount in the case of the helical scan fluctuates with the period of the beam pitch in the body axis direction, if the ROI body axis direction size is large, the entire ROI may not be a desired imaging feature amount. Therefore, when the ROI body axis size is large, it is desirable to automatically correct the beam pitch in the ROI region using variable pitch scanning, and such information may be presented to the user. Alternatively, a correction candidate for the shooting condition may be proposed to the user.
　また、上述の例では、撮影開始角度－特徴量曲線から、特徴量が最良となる撮影開始角度が演算装置によって自動的に決定することについて記載したが、これに限られず、撮影開始角度の設定は、撮影開始角度－特徴量曲線を確認したユーザにより、手動で行われるようにすることもできる。 In the above-described example, it has been described that the shooting start angle with the best feature amount is automatically determined by the calculation device from the shooting start angle-feature amount curve. However, the present invention is not limited to this. Can be performed manually by a user who has confirmed the shooting start angle-feature amount curve.
　＜第３の実施形態＞
　以下、本発明の第３の実施形態について説明する。本実施形態において、Ｘ線ＣＴ装置は、複数の特徴量を考慮して撮影開始角度を決定する。そこで、図４に示すように、複数の特徴量に対して、考慮すべき優先度を示す優先係数を夫々設定すると共に、各特徴量に対して夫々撮影開始角度－特徴量曲線を作成する。そして、撮影特徴量と優先係数の積から計算される値が最も良好となるように撮影開始角度を決定する。 <Third Embodiment>
Hereinafter, a third embodiment of the present invention will be described. In the present embodiment, the X-ray CT apparatus determines the imaging start angle in consideration of a plurality of feature amounts. Therefore, as shown in FIG. 4, priority coefficients indicating priorities to be considered are set for a plurality of feature amounts, and a shooting start angle-feature amount curve is created for each feature amount. Then, the shooting start angle is determined so that the value calculated from the product of the shooting feature value and the priority coefficient is the best.
　この他、優先係数を基に複数種類の撮影開始角度－特徴量曲線を合成することで得られた、優先係数を考慮した１つの撮影開始角度－特徴量曲線を生成することとしてもよい。
表示された複数種類の撮影開始角度－特徴量曲線を基にユーザが手動で撮影開始角度を決定することもできる。 In addition, one shooting start angle-feature amount curve obtained by combining a plurality of types of shooting start angle-feature amount curves based on the priority coefficient may be generated in consideration of the priority coefficient.
The user can manually determine the shooting start angle based on the plurality of displayed shooting start angle-feature amount curves.
　ここで、撮影開始角度－特徴量曲線の合成は以下のように行われる。例えば、複数の撮影特徴量を設定し、夫々に対して優先係数が定められている場合において、まず、各撮影特徴量を、１となる場合に最良となり、０となる場合に最も不良となるように予め規格化しておく。その後、撮影開始角度に対する各撮影特徴量に優先係数を乗じた値の総和の関数を作成することにより、複数の撮影開始角度－特徴量曲線から合成した１つの撮影開始角度－特徴量曲線を作成することができる。 Here, the synthesis of the shooting start angle-feature amount curve is performed as follows. For example, in the case where a plurality of shooting feature amounts are set and priority coefficients are set for the respective shooting feature amounts, first, each shooting feature amount is best when it is 1, and is lowest when it is 0. Thus, it is standardized in advance. After that, by creating a function of the sum of values obtained by multiplying each shooting feature value by the priority coefficient with respect to the shooting start angle, one shooting start angle-feature amount curve synthesized from a plurality of shooting start angle-feature amount curves is created. can do.
　このようにすることで、優先係数（優先度）を考慮した撮影特徴量が撮影開始角度に対してどのような関数形状を示すのかを容易に確認できるようになる。 In this way, it becomes possible to easily confirm what function shape the shooting feature value considering the priority coefficient (priority) shows with respect to the shooting start angle.
　なお、規格化において、最大値が１、最小値が０となるように撮影特徴量を修正した後、撮影特徴量の値が小さいことが望ましい場合には、１から撮影特徴量を引いた値を撮影特徴量の候補として用いることができる。 In normalization, when the shooting feature value is desired to be small after correcting the shooting feature value so that the maximum value is 1 and the minimum value is 0, a value obtained by subtracting the shooting feature value from 1 Can be used as candidates for the imaging feature amount.
　＜第４の実施形態＞
　以下、本発明の第４の実施形態について説明する。本実施形態において、Ｘ線ＣＴ装置は、複数のＲＯＩでの特徴量を考慮して撮影開始角度を決定する。 <Fourth Embodiment>
The fourth embodiment of the present invention will be described below. In the present embodiment, the X-ray CT apparatus determines an imaging start angle in consideration of feature quantities in a plurality of ROIs.
　すなわち、本実施形態に係るＸ線ＣＴ装置では、位置決め画像においてＲＯＩを複数設定し、各ＲＯＩ位置での撮影開始角度－特徴量曲線を生成し、表示する。このとき、各ＲＯＩで設定した優先係数を基に撮影開始角度に対する特徴量と優先係数の積の合計が最も良好となるように撮影開始角度の候補を決定する。なお、各ＲＯＩで設定した優先係数を基に、各ＲＯＩ位置での撮影開始角度－特徴量曲線を合成し、得られた１つの撮影開始角度－特徴量曲線を用いてもよい。 That is, in the X-ray CT apparatus according to the present embodiment, a plurality of ROIs are set in the positioning image, and an imaging start angle-feature amount curve at each ROI position is generated and displayed. At this time, the candidate for the shooting start angle is determined so that the sum of the product of the feature amount with respect to the shooting start angle and the priority coefficient is the best based on the priority coefficient set in each ROI. Note that, based on the priority coefficient set in each ROI, a shooting start angle-feature amount curve at each ROI position may be synthesized, and one obtained shooting start angle-feature amount curve may be used.
　＜第５の実施形態＞
　以下、本発明の第５の実施形態について説明する。本実施形態に係るＸ線ＣＴ装置は、所謂２管球ＣＴ装置であり、この２管球ＣＴ装置において特徴量を考慮して撮影開始角度を決定する。 <Fifth Embodiment>
The fifth embodiment of the present invention will be described below. The X-ray CT apparatus according to this embodiment is a so-called two-tube CT apparatus, and the imaging start angle is determined in consideration of the feature amount in the two-tube CT apparatus.
　通常、２管球ＣＴ装置では、Ｘ線管と検出器の対（撮影系）が回転方向に異なる角度（２つの角度差をθとする）で２セット配置されている（撮影系Ａ、撮影系Ｂ）。２管球ＣＴでは、各撮影系Ａ，Ｂは同一速度で回転し、螺旋撮影の際のビームピッチは各撮影系で同一となる。一方、各撮影系Ａ，Ｂで異なるＸ線フィルタを使用することができ、各Ｘ線管から出力されるＸ線を異ならせることができる。最終的に、２つの撮影系で得られたデータを組み合わせて１枚の断層像が生成される。 Usually, in a two-tube CT apparatus, two sets of X-ray tube and detector pairs (imaging system) are arranged at different angles in the rotation direction (the difference between the two angles is θ) (imaging system A, imaging system). System B). In the two-tube CT, the imaging systems A and B rotate at the same speed, and the beam pitch at the time of spiral imaging is the same in each imaging system. On the other hand, different X-ray filters can be used for the imaging systems A and B, and the X-rays output from the X-ray tubes can be made different. Finally, a single tomographic image is generated by combining data obtained by the two imaging systems.
　このような２管球ＣＴ装置の場合、各撮影系Ａ，ＢでＸ線フィルタや撮影線量が異なり、螺旋スキャン時のＸ線発生装置の軌道も異なることから、各撮影系それぞれについて互いに異なる撮影特徴量マップ、撮影開始角度－特徴量曲線が得られる。 In the case of such a two-tube CT apparatus, the X-ray filter and the imaging dose are different between the imaging systems A and B, and the trajectory of the X-ray generator at the time of spiral scanning is also different. A feature amount map and a shooting start angle-feature amount curve are obtained.
　この場合の撮影特徴量マップの表示方法としては、２つの撮影特徴量マップを別々に表示することもでき、また、視認性の向上の観点から、２つの撮影特徴量マップを加算した合成マップを用いることが望ましい。同様に、撮影開始角度－特徴量曲線も合成マップから得られる、もしくは２つの撮影開始角度－特徴量曲線を加算して得られる、合成曲線を用いる。そして、撮影開始角度の候補を自動決定する際には、この合成曲線を用いることができる。 In this case, as a display method of the shooting feature value map, two shooting feature value maps can be displayed separately, and from the viewpoint of improving visibility, a composite map obtained by adding the two shooting feature value maps is used. It is desirable to use it. Similarly, a shooting start angle-feature amount curve is also obtained from a composite map, or a combined curve obtained by adding two shooting start angle-feature amount curves is used. Then, this composite curve can be used when automatically determining the photographing start angle candidates.
　１・・・Ｘ線ＣＴ装置、５・・・Ｘ線発生装置、６・・・高電圧発生装置、７・・・Ｘ線制御装置、８・・・コリメータ、９・・・コリメータ制御装置、１０・・・スキャナ、１１・・・検出器、１２・・・中央制御装置、１３・・・スキャナ制御装置、１４・・・寝台制御装置、１５・・・寝台移動計測装置、１６・・・駆動装置、１７・・・プリアンプ、１８・・・Ａ／Ｄコンバータ、２０・・・操作ユニット、２１・・・入出力装置、２２・・・演算装置、２３・・・表示制御装置、２４・・・入力装置、２５・・・記憶装置、２６・・・再構成演算装置、２７・・・画像処理装置、２８・・・撮影特徴量マップ生成装置、２９・・・表示装置、３０・・・寝台 DESCRIPTION OF SYMBOLS 1 ... X-ray CT apparatus, 5 ... X-ray generator, 6 ... High voltage generator, 7 ... X-ray controller, 8 ... Collimator, 9 ... Collimator controller, DESCRIPTION OF SYMBOLS 10 ... Scanner, 11 ... Detector, 12 ... Central control device, 13 ... Scanner control device, 14 ... Bed control device, 15 ... Bed movement measuring device, 16 ... Drive device, 17 ... preamplifier, 18 ... A / D converter, 20 ... operation unit, 21 ... input / output device, 22 ... calculation device, 23 ... display control device, 24. ..Input device 25 ... Storage device 26 ... Reconstruction operation device 27 ... Image processing device 28 ... Photographing feature map generation device 29 ... Display device 30 ... ·bed

Claims (11)

  1. 　寝台上の被検体の周囲を周回するＸ線源と、該Ｘ線源から照射され、前記被検体を透過したＸ線の線量を検出するＸ線検出器を含み、投影データを取得するスキャナと、
    　前記投影データに基づいて再構成画像を取得する再構成演算部と、
    　前記投影データを取得する際の撮影条件を設定する撮影条件設定部と、
    　前記撮影条件に従って投影データを取得する場合に生成される再構成画像の特徴を示す情報としての特徴量をマッピングした撮影特徴量マップを生成する撮影特徴量マップ生成部と、
    　前記撮影特徴量マップを表示部に表示させる表示制御部と、
    　を備えたＸ線ＣＴ装置。     An X-ray source that circulates around the subject on the bed, an X-ray detector that detects the dose of X-rays irradiated from the X-ray source and transmitted through the subject, and a scanner that acquires projection data; ,
    A reconstruction calculator that obtains a reconstructed image based on the projection data;
    A shooting condition setting unit for setting shooting conditions when acquiring the projection data;
    A shooting feature value map generating unit that generates a shooting feature value map in which a feature value is mapped as information indicating characteristics of a reconstructed image generated when projection data is acquired according to the shooting conditions;
    A display control unit for displaying the shooting feature amount map on a display unit;
    X-ray CT apparatus provided with
  2. 　前記スキャナ及び前記再構成演算部により前記被検体の位置決め画像を取得し、
    　前記表示制御部が、前記撮影特徴量マップと前記位置決め画像とを共に表示させる請求項１記載のＸ線ＣＴ装置。     A positioning image of the subject is acquired by the scanner and the reconstruction calculation unit,
    The X-ray CT apparatus according to claim 1, wherein the display control unit displays both the imaging feature amount map and the positioning image.
  3. 　前記撮影特徴量マップ生成部が、前記特徴量と前記撮影条件との関係を示すグラフを生成し、
    　前記表示制御部が、前記表示部に前記グラフを表示させる請求項１記載のＸ線ＣＴ装置。     The shooting feature amount map generation unit generates a graph showing a relationship between the feature amount and the shooting condition;
    The X-ray CT apparatus according to claim 1, wherein the display control unit displays the graph on the display unit.
  4. 　前記撮影特徴量マップ生成部が、複数種の前記特徴量に対して夫々優先度を示す優先係数を乗じ、前記複数種の特徴量と各優先係数との積算値の総和に基づいて撮影条件候補を少なくとも１以上算出し、
    　前記表示制御部が、前記表示部に前記撮影条件候補を表示する請求項１記載のＸ線ＣＴ装置。     The shooting feature amount map generation unit multiplies a plurality of types of feature amounts by a priority coefficient indicating a priority, and based on the sum of integrated values of the plurality of types of feature amounts and each priority coefficient, shooting condition candidates Calculate at least one or more
    The X-ray CT apparatus according to claim 1, wherein the display control unit displays the imaging condition candidates on the display unit.
  5. 　前記撮影条件候補から、ユーザによる選択を受け付ける入力部を備える請求項４記載のＸ線ＣＴ装置。 The X-ray CT apparatus according to claim 4, further comprising an input unit that receives a selection by a user from the imaging condition candidates.
  6. 　前記撮影条件が、少なくとも前記Ｘ線源の前記被検体に対する撮影開始角度を含む請求項１記載のＸ線ＣＴ装置。 The X-ray CT apparatus according to claim 1, wherein the imaging condition includes at least an imaging start angle of the X-ray source with respect to the subject.
  7. 　前記撮影開始角度を含む前記撮影条件をユーザが設定する入力部を備える請求項６記載のＸ線ＣＴ装置。 The X-ray CT apparatus according to claim 6, further comprising an input unit for a user to set the imaging condition including the imaging start angle.
  8. 　前記撮影特徴量マップ生成部が、被検体の位置に応じて異なる、Ｘ線照射量を示すＸ線照射量比マップ、画像ノイズ比マップ、時間分解能比マップ、空間分解能比マップの少なくとも何れか１つを前記撮影特徴量マップとして生成する請求項１記載のＸ線ＣＴ装置。 The imaging feature amount map generating unit is at least one of an X-ray irradiation amount ratio map indicating an X-ray irradiation amount, an image noise ratio map, a time resolution ratio map, and a spatial resolution ratio map, which differ depending on the position of the subject. The X-ray CT apparatus according to claim 1, wherein one is generated as the imaging feature amount map.
  9. 　前記位置決め画像において、関心領域を設定する領域設定部を備え、
    　前記撮影特徴量マップ生成部が前記関心領域における前記特徴量を算出し、該特徴量と前記Ｘ線源の前記被検体に対する撮影開始角度との関係を示す情報を生成し、
    　前記表示制御部が、前記特徴量と前記Ｘ線源の前記被検体に対する撮影開始角度との関係を示す情報を前記表示部に表示させる請求項２記載のＸ線ＣＴ装置。     In the positioning image, comprising a region setting unit for setting a region of interest,
    The imaging feature map generation unit calculates the feature in the region of interest, and generates information indicating a relationship between the feature and the imaging start angle of the X-ray source with respect to the subject;
    The X-ray CT apparatus according to claim 2, wherein the display control unit displays information indicating a relationship between the feature amount and an imaging start angle of the X-ray source with respect to the subject on the display unit.
  10. 　寝台上の被検体の周囲から照射され、前記被検体を透過したＸ線の線量を検出して投影データを取得するステップと、
    　前記投影データに基づいて再構成画像を取得するステップと、
    　前記投影データを取得する際の撮影条件を設定するステップと、
    　前記撮影条件に従って投影データを取得する場合に生成される再構成画像の特徴を示す情報としての特徴量をマッピングした撮影特徴量マップを生成するステップと、
    　前記撮影特徴量マップを表示させるステップと、
    　を備えた撮影条件設定方法。     Detecting a dose of X-rays irradiated from around the subject on the bed and transmitted through the subject to obtain projection data;
    Obtaining a reconstructed image based on the projection data;
    Setting shooting conditions when acquiring the projection data;
    Generating a shooting feature amount map in which a feature amount is mapped as information indicating a feature of a reconstructed image generated when acquiring projection data according to the shooting conditions;
    Displaying the shooting feature map;
    Shooting condition setting method with
  11. 　Ｘ線ＣＴ装置において撮影を行う際の撮影条件を受け付けるステップと、
    　前記撮影条件に従って撮影を行った場合に生成される再構成画像の特徴を示す情報としての特徴量をマッピングした撮影特徴量マップを生成するステップと、
    　前記撮影特徴量マップを表示させるステップと、
    　をコンピュータに実行させる撮影条件設定プログラム。     Receiving imaging conditions when imaging is performed in the X-ray CT apparatus;
    Generating a shooting feature amount map in which a feature amount is mapped as information indicating features of a reconstructed image generated when shooting is performed according to the shooting conditions;
    Displaying the shooting feature map;
    Shooting condition setting program that causes a computer to execute
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