CN108030501B - geometric calibration device and method for static cone-beam CT imaging system - Google Patents
geometric calibration device and method for static cone-beam CT imaging system Download PDFInfo
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- CN108030501B CN108030501B CN201711121001.1A CN201711121001A CN108030501B CN 108030501 B CN108030501 B CN 108030501B CN 201711121001 A CN201711121001 A CN 201711121001A CN 108030501 B CN108030501 B CN 108030501B
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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
- A61B6/032—Transmission computed tomography [CT]
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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
- A61B6/40—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for generating radiation specially adapted for radiation diagnosis
- A61B6/4064—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for generating radiation specially adapted for radiation diagnosis specially adapted for producing a particular type of beam
- A61B6/4085—Cone-beams
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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
- A61B6/54—Control of apparatus or devices for radiation diagnosis
- A61B6/542—Control of apparatus or devices for radiation diagnosis involving control of exposure
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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
- A61B6/58—Testing, adjusting or calibrating apparatus or devices for radiation diagnosis
- A61B6/582—Calibration
Abstract
the invention belongs to the field of X-ray CT imaging, and provides a geometric calibration device of a static cone-beam CT imaging system, which comprises a plurality of cold cathode X-ray bulb tubes, wherein the cold cathode X-ray bulb tubes are arranged in a linear or arc manner to form a multi-beam X-ray source array, and each cold cathode X-ray bulb tube is used as an X-ray emission source; the support frame is reserved with an adjusting space on X, Y and Z axis, so that after a plurality of cold cathode X-ray tubes are installed on the support frame, the position of each cold cathode X-ray tube can be adjusted in X, Y or Z axis three directions respectively. By adjusting each cold cathode X-ray bulb tube in three directions of X, Y or Z axis, accurate calibration of the geometric position of each X-ray source is realized, and the calibration precision is extremely high. Meanwhile, the invention also provides a geometric calibration method of the static cone-beam CT imaging system, and the geometric calibration of the static cone-beam CT imaging system is realized by utilizing the device.
Description
Technical Field
The invention belongs to the field of X-ray CT imaging, and particularly relates to a geometric calibration device and method for a static cone-beam CT imaging system.
background
Because a Computed Tomography (CT) image reconstruction algorithm is based on ideal system geometric parameters, the CT system has very strict requirements on geometric parameters and installation accuracy of a radiation source, a scanned object and a detector. At present, the existing geometric calibration method of the cone beam CT system is divided into two types, namely, phantom calibration and algorithm calibration: the calibration method based on the phantom adopts a specially designed calibration phantom, obtains geometric error parameters of the system in the calibration process, and uses the parameters for hardware adjustment of the system or directly for later image reconstruction; the geometric calibration method based on the algorithm is to directly process projection data or projection images, calculate geometric error parameters of the CT system and use the geometric error parameters in the reconstruction algorithm. Most of the existing geometric calibration methods for cone beam CT systems aim at a single X-ray source, wherein the phantom calibration method needs to specially design and process a high-precision phantom to carry out geometric calibration on an imaging system, and because the precision of the processed phantom is limited, a certain error exists in a calibration result; the algorithm calibration method usually needs to design a complex algorithm, then the imaging geometric parameters are calibrated through a series of calculations, and the calibrated geometric parameters are limited.
At present, the existing static cone-beam CT system based on the integrally packaged multi-beam X-ray source array also adopts the geometric calibration mode of the single light source cone-beam CT system. However, in the static cone-beam CT system using the integrally packaged multi-beam X-ray source array, because the plurality of X-ray sources are integrally packaged in the same bulb tube, the geometric calibration method cannot calibrate the geometric position of each independent emission source in the multi-beam X-ray source array, and thus the application range is limited and the calibration accuracy is low.
Disclosure of Invention
the invention provides a geometric calibration device and method for a static cone-beam CT imaging system, and aims to solve the problems of limited application range and low calibration precision of the conventional geometric calibration mode of the static cone-beam CT imaging system.
in order to solve the technical problem, the invention provides a geometric calibration device of a static cone-beam CT imaging system, which is arranged on an optical platform and comprises a plurality of cold cathode X-ray ball tubes and a support frame:
each cold cathode X-ray bulb tube is used as an X-ray emission source, the support frame is used for mounting the cold cathode X-ray bulb tubes, and the plurality of cold cathode X-ray bulb tubes are arranged in a linear or arc mode to form a multi-beam X-ray source array; the support frame is reserved with an adjusting space on X, Y and Z axis, so that after the plurality of cold cathode X-ray tubes are installed on the support frame, the position of each cold cathode X-ray tube can be adjusted in X, Y or Z axis three directions respectively.
Furthermore, the device also comprises a detector, a two-axis displacement table, an object stage and a three-axis displacement table; the detector is carried on the two-axis displacement table to realize respective movement in the directions of the Y axis and the Z axis; the object stage is used for placing a scanning object and is carried on the three-axis displacement table, so that the scanning object can move along the three directions of the X axis, the Y axis and the Z axis respectively.
furthermore, the plurality of cold cathode X-ray bulbs are sequentially arranged on the support frame in a linear and equidistant manner to form a linear multi-beam X-ray source array; the number of the plurality of cold cathode X-ray bulbs is N, N is an odd number, and N > is 15; the (N +1)/2 th cold cathode X-ray tube is taken as the center, and the cold cathode X-ray tubes on the two sides of the cold cathode X-ray tube are symmetrically distributed relative to the center.
further, the angle range of the scanning object covered by the support frame is between 30 degrees and 45 degrees.
Further, the distance between the detector and the focal point of the bulb tube at the central position of the multi-beam X-ray source array is 60 cm-70 cm; the distance between the center of the scanned object and the detector is 5cm to 10 cm.
In order to solve the above technical problem, the present invention further provides a geometric calibration method for a static cone-beam CT imaging system, where the method uses the above geometric calibration apparatus for a static cone-beam CT imaging system, and the method includes:
Step 1: by utilizing the geometric calibration device of the static cone-beam CT imaging system, the three-axis displacement table carrying the block gauge body is controlled to move along the X-axis direction, the Y-axis direction and the Z-axis direction, the central X-ray source of the X-ray source array is controlled to be exposed, and the positions of the two-axis displacement table carrying the detector in the Y-axis direction and the Z-axis direction are adjusted according to the position of the block gauge body on a projected image acquired by the detector, so that the calibration of the imaging geometric central position is completed;
step 2: the geometric calibration device of the static cone-beam CT imaging system is utilized, the three-axis displacement table carrying the block gauge body is controlled to move along the X-axis direction, the Y-axis direction and the Z-axis direction, each bulb tube distributed on two sides of the central X-ray source is controlled to be respectively exposed, and the positions of the bulb tubes distributed on two sides of the central X-ray source along the X direction, the Y direction and the Z direction are adjusted according to the position of the block gauge body on a projected image acquired by the detector each time so as to finish the calibration of the distribution of the focuses of the X-ray sources.
Further, the method further comprises the step 3:
And step 3: by utilizing the geometric calibration device of the static cone-beam CT imaging system, a first distance parameter and a second distance parameter from the projection position of the spherical center of the small spherical mold body on the detector to the center of the detector are obtained by adjusting the positions of a three-axis displacement table carrying the small spherical mold body along the Y-axis direction and the Z-axis direction, and the imaging system geometric parameters SOD and SID are obtained by calculation according to the first distance parameter, the second distance parameter and a preset formula; wherein, SOD represents the distance from the central position of the multi-beam X-ray source to the scanned object, and SID represents the distance from the central position of the multi-beam X-ray source to the detector.
compared with the prior art, the invention has the beneficial effects that:
the invention provides a geometric calibration device of a static cone-beam CT imaging system, which comprises a plurality of cold cathode X-ray bulb tubes and a support frame. The cold cathode X-ray bulb tubes are arranged in a linear or arc shape to form a multi-beam X-ray source array, wherein each cold cathode X-ray bulb tube is used as an X-ray emission source; the support frame is used for installing the cold cathode X-ray bulb tubes, and adjusting spaces are reserved on X, Y and Z axes, so that after the plurality of cold cathode X-ray bulb tubes are installed on the support frame, the position of each cold cathode X-ray bulb tube can be adjusted in X, Y or Z axis three directions respectively. By adjusting each cold cathode X-ray bulb tube in three directions of X, Y or Z axis, accurate calibration of the geometric position of each X-ray source is realized, and the calibration precision is extremely high.
drawings
FIG. 1 is a schematic diagram of a geometric calibration apparatus of a static cone-beam CT imaging system according to a first embodiment of the present invention;
FIG. 2 is a schematic view of a support frame of a geometric calibration apparatus for a static cone-beam CT imaging system according to a first embodiment of the present invention;
FIG. 3 is a schematic diagram of a cold cathode X-ray tube of a geometric calibration apparatus for a static cone-beam CT imaging system according to a first embodiment of the present invention;
FIG. 4 is a flowchart of a geometric calibration method for a static cone-beam CT imaging system according to a second embodiment of the present invention;
FIG. 5 is a flowchart illustrating a geometric calibration method for a static cone-beam CT imaging system according to a third embodiment of the present invention in step S1;
FIG. 6 is a flowchart illustrating a geometric calibration method for a static cone-beam CT imaging system according to a third embodiment of the present invention in step S2;
FIG. 7 is a flowchart illustrating a geometric calibration method for a static cone-beam CT imaging system according to a third embodiment of the present invention in step S3;
FIG. 8 is a parameter diagram of a geometric calibration method for a static cone-beam CT imaging system according to a third embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As a first embodiment of the present invention, as shown in FIG. 1, the present invention provides a geometric calibration apparatus for a static cone-beam CT imaging system, which is disposed on an optical platform, and comprises a plurality of cold cathode X-ray tubes 20 and a support frame 10:
each of the cold cathode X-ray tubes 20 is used as an X-ray emission source (hereinafter referred to as an X-ray source), the support frame 10 (shown in fig. 2, which is a schematic view of the support frame 10) is used for mounting the cold cathode X-ray tube, and a plurality of the cold cathode X-ray tubes 20 are arranged in a linear or arc shape to form a multi-beam X-ray source array (shown in a linear shape in this embodiment). As shown in fig. 2, a plurality of cold cathode X-ray tubes 20 are mounted on a support frame 10, and the support frame 10 has a reserved adjustment space at X, Y and Z axis, so that after the plurality of cold cathode X-ray tubes 20 are mounted on the support frame 10, the position of each cold cathode X-ray tube can be adjusted in X, Y or Z axis direction. D in fig. 1 represents a standard cartesian rectangular coordinate system, and X, Y, Z are three axes of a spatial rectangular coordinate system.
In this embodiment, on the basis of designing the support frame 10 and the cold cathode X-ray tube 20, the apparatus further includes a detector 40 for detecting X-rays, a two-axis displacement stage 50, an object stage 30, and a three-axis displacement stage 60: the detector 40 is carried on a two-axis displacement stage 50 (not shown in FIG. 1) for movement in the Y-axis and Z-axis directions, respectively; the stage 30 is used for placing a scanning object and is mounted on a three-axis displacement table 60 (not shown in fig. 1) so as to enable the scanning object to move along three directions of an X axis, a Y axis and a Z axis. In this embodiment, the detector 40 is a digital flat panel detector (e.g., ASX-2430 amorphous selenium digital flat panel detector from analog).
A plurality of cold cathode X-ray bulbs 20 are sequentially arranged on the support frame 10 in a linear and equidistant manner to form a linear multi-beam X-ray source array; the number of the cold cathode X-ray bulbs is 20, N is an odd number, and N > is 15; the (N +1)/2 th cold cathode X-ray tube is taken as the center, and the cold cathode X-ray tubes on the two sides of the cold cathode X-ray tube are symmetrically distributed relative to the center. As shown in fig. 3, the very center 204 is the center of the cold cathode X-ray tube, the tubes 205 and 203 are symmetrical with respect to 204, the tubes 206 and 202 are symmetrical with respect to 204, and the tubes 207 and 201 are symmetrical with respect to 204.
in addition, in order to optimize the device for better operability and calibration process, the angle range of the scanning object covered by the support frame 10 should be controlled between 30 ° and 45 °; the distance between the detector 40 and the focal point of the bulb (204 in fig. 3) at the central position of the multi-beam X-ray source array should be 60cm to 70 cm; the distance between the center of the scanned object and the detector 40 should be 5cm to 10 cm.
in summary, the geometric calibration apparatus for a static cone-beam CT imaging system according to the first embodiment of the present invention realizes precise calibration of the geometric position of each X-ray source by adjusting each cold-cathode X-ray tube in three directions of X, Y or Z-axis, and has extremely high calibration accuracy.
as a second embodiment of the present invention, as shown in fig. 4, the present invention provides a method for geometry calibration of a static cone-beam CT imaging system, which needs to use the geometry calibration apparatus of the static cone-beam CT imaging system provided in the first embodiment, the method includes the following steps:
Step S1: by utilizing the geometric calibration device of the static cone-beam CT imaging system, the three-axis displacement table carrying the block gauge body is controlled to move along the X-axis direction, the Y-axis direction and the Z-axis direction, the X-ray source at the center of the X-ray source array is controlled to be exposed, and the positions of the two-axis displacement table carrying the detector in the Y-axis direction and the Z-axis direction are adjusted according to the position of the block gauge body on a projected image acquired by the detector, so that the calibration of the imaging geometric center position (namely the calibration of the center of the multi-beam X-ray source array and the center position of the imaging plane of the detector) is completed.
It should be noted that the geometric calibration apparatus for a static cone-beam CT imaging system according to the first embodiment of the present invention has been primarily assembled to linearly and equidistantly distribute the X-ray source bulbs of the multi-beam X-ray source array, but since there is a certain error in the machining precision and assembly process of the bulbs, the focal position needs to be accurately calibrated along the X-axis, Y-axis and Z-axis directions during the actual use, and therefore, the following step S2 needs to be performed.
Step S2: by utilizing the geometric calibration device of the static cone-beam CT imaging system, the three-axis displacement table carrying the block gauge bodies is controlled to move along the X-axis direction, the Y-axis direction and the Z-axis direction, and each bulb tube distributed on two sides of the central X-ray source is controlled to be respectively exposed, and the positions of the bulb tubes distributed on two sides of the central X-ray source along the X-axis direction, the Y-axis direction and the Z-axis direction are adjusted according to the position of the block gauge bodies acquired by the detector on a projected image every time, so that the calibration of the distribution of the focuses of all the X-ray sources is completed. After the calibration of the multi-beam X-ray source array is completed, the imaging geometry parameters may also be calculated, and the method provided by the present embodiment further includes step S3.
Step S3: by using the geometric calibration device of the static cone-beam CT imaging system, the distance parameter I and the distance parameter II from the projection position of the spherical center of the small spherical mold body on the detector to the center of the detector are obtained by adjusting the positions of a three-axis displacement table carrying the small spherical mold body along the Y-axis direction and the Z-axis direction, and the imaging system geometric parameters SOD and SID are obtained by calculation according to the distance parameter I and the distance parameter II and a preset formula. Wherein, SOD represents the distance from the central position of the multi-beam X-ray source to the scanned object, and SID represents the distance from the central position of the multi-beam X-ray source to the detector.
in summary, in the method provided by the second embodiment of the present invention, by using the geometric calibration apparatus for a static cone-beam CT imaging system, a position is reserved in the support frame for each individually installed bulb to be adjusted in X, Y, Z axial directions, so that the focal point distribution of the multi-beam X-ray source, the center of the multi-beam X-ray source array and the center of the detector imaging plane can be calibrated, and each independent emission source geometric position in the encapsulated X-ray source array can be calibrated, so that the calibration accuracy is high, and the calibration parameters can be obtained by simple calculation.
as a third embodiment of the present invention, as shown in fig. 4, this embodiment also provides a method for geometry calibration of a static cone-beam CT imaging system, which refines the steps based on the second embodiment, and the method needs to use the geometry calibration apparatus of a static cone-beam CT imaging system provided in the first embodiment, and the method includes the following steps:
step S1: by utilizing the geometric calibration device of the static cone-beam CT imaging system, the three-axis displacement table carrying the block gauge body is controlled to move along the X-axis direction, the Y-axis direction and the Z-axis direction, the X-ray source at the center of the X-ray source array is controlled to be exposed, and the positions of the two-axis displacement table carrying the detector in the Y-axis direction and the Z-axis direction are adjusted according to the position of the block gauge body on a projected image acquired by the detector, so that the calibration of the imaging geometric center position (namely the calibration of the center of the multi-beam X-ray source array and the center position of the imaging plane of the detector) is completed. As shown in fig. 5, step S1 includes the following steps S101 to S118:
step S101: the height of the focal point of the bulb tube at the central position of the multi-beam X-ray source array relative to the optical platform is determined through measurement, the two-axis displacement platform carrying the detector is controlled to move along the Z-axis direction, and the height of the central row of the detector relative to the height of the optical platform is adjusted to be approximately consistent with the focal point height/Z coordinate of the bulb tube at the central position of the multi-beam X-ray source array (namely, the central row of the detector and the central focal point of the multi-beam X-ray source array are adjusted to be approximately equal in the.
Step S102: and the Y coordinate of the focus of the bulb tube at the central position of the multi-beam X-ray source array is determined through measurement, the three-axis displacement table carrying the block gauge body and the two-axis displacement table carrying the detector are respectively controlled to move along the Y-axis direction, and the Y coordinate of the center of the objective table carrying the block gauge body and the Y coordinate of the center row of the detector are adjusted to be approximately consistent with the Y coordinate of the focus of the bulb tube at the central position of the multi-beam X-ray source array.
It should be noted that the object stage is used for placing the scanning object, and in this embodiment, when performing calibration, a standard block mold is placed on the object stage as the scanning object, so as to implement calibration by using the block mold. The invention can adopt block mold bodies of various standard models for calibration, does not need to specially design a calibration mold body, and is simpler compared with the traditional mold body calibration mode.
the above steps S101 and S102 are processes of first completing the rough adjustment, and the subsequent steps S103 to S118 are processes of fine adjustment. Wherein, the precise calibration of the multi-beam X-ray source array center and the detector center column is completed by the following steps S103 to S110.
step S103: and controlling a three-axis displacement table carrying the block gauge body to run along the X-axis direction, and adjusting the position of the block gauge body along the Y-axis direction by controlling the three-axis displacement table.
step S104: the X-ray source at the center of the X-ray source array (i.e., (N +1) th/2X-ray tube with cold cathode in the center according to the first embodiment) is turned on for exposure.
Step S105: and acquiring an exposure image through a detector, and judging (observing) whether the position of a projection column of the left edge/right edge (left edge or right edge) of the block mold body on the detector is kept unchanged according to the exposure image.
Step S106: if not, returning to execute the steps S103 to S105 until the position of the projection column of the left edge/right edge of the block mold body on the detector is kept unchanged.
Step S107: and controlling the two-axis displacement table carrying the detector to run along the Y-axis direction.
Step S108: and starting the X-ray source at the central position of the X-ray source array for exposure.
Step S109: and acquiring an exposure image through the detector, and judging whether the projection column of the left edge/right edge of the block gauge body on the detector is superposed with the central column of the detector according to the exposure image.
step S110: if not, returning to execute the steps S107 to S109 until the projection column of the left edge/right edge of the block mold body on the detector coincides with the central column position of the detector, so as to finish the calibration of the center of the multi-beam X-ray source array and the central column of the detector.
The precise alignment of the center of the multi-beam X-ray source array with the detector center row is accomplished by the following steps S103 to S110.
step S111: and controlling a three-axis displacement table carrying the block gauge body to run along the X-axis direction, and adjusting the position of the block gauge body along the Z-axis direction.
Step S112: and starting the X-ray source at the center of the X-ray source array for exposure.
Step S113: and acquiring an exposure image through a detector, and judging whether the position of a projection line of the upper surface of the block gauge body on the detector is kept unchanged according to the exposure image.
Step S114: if not, returning to execute the steps S111 to S113 until the position of the projection line of the upper surface of the block mold body on the detector is kept unchanged.
step S115: and controlling the two-axis displacement table carrying the detector to run along the Z-axis direction.
step S116: and starting the X-ray source at the central position of the X-ray source array for exposure.
Step S117: and acquiring an exposure image through the detector, and judging whether the projection line of the upper surface of the block gauge body on the detector is superposed with the central line of the detector according to the exposure image.
Step S118: if not, returning to execute the steps S115 to S117 until the projection line of the upper surface of the block mold body on the detector coincides with the central line position of the detector, so as to finish the calibration of the center of the multi-beam X-ray source array and the central line position of the detector.
The process of S101-S118 described above first completes the calibration of the imaging geometric center position.
step S2: by utilizing the geometric calibration device of the static cone-beam CT imaging system, the three-axis displacement table carrying the block gauge bodies is controlled to move along the X-axis direction, the Y-axis direction and the Z-axis direction, and each bulb tube distributed on two sides of the central X-ray source is controlled to be respectively exposed, and the positions of the bulb tubes distributed on two sides of the central X-ray source along the X-axis direction, the Y-axis direction and the Z-axis direction are adjusted according to the position of the block gauge bodies acquired by the detector on a projected image every time, so that the calibration of the distribution of the focuses of all the X-ray sources is completed. As shown in fig. 6, step S2 specifically includes the following steps S201 to S219:
first, in steps S201 to S204, the positions of the X-ray sources distributed on both sides of the central position in the Z-axis direction are adjusted with reference to the X-ray source focal position at the central position of the multi-beam X-ray source array.
step S201: and according to the final positions (for calibration) of the block mold body of the center of the multi-beam X-ray source array and the center line of the detector calibrated in the step S118, starting the X-ray source at the center position of the X-ray source array for exposure, so that the projection line of the upper surface of the block mold body on the detector coincides with the position of the center line of the detector.
Step S202: and starting one bulb tube distributed on two sides of the X-ray source at the central position for exposure, acquiring an exposure image of the block mold body under the current X-ray source through the detector, and judging whether the position of a projection line of the upper surface of the current block mold body on the detector is superposed with the position of the central line of the detector according to the exposure image.
step S203: and if the X-ray tube does not coincide with the cold cathode X-ray tube, finely adjusting the current cold cathode X-ray tube along the Z-axis direction, and repeating the step S202 until the position of the projection line of the upper surface of the block gauge body on the detector is determined to coincide with the position of the central line of the detector, so that the adjustment of the current X-ray source focus along the Z-axis direction is completed.
Step S204: according to the operations of steps S202 to S203, all X-ray source focuses on both sides of the X-ray source at the central position of the X-ray source array are sequentially adjusted along the Z-axis direction, so that the Z-coordinates of all X-ray source focuses are the same (i.e. the heights of all X-ray source focuses are the same).
The following steps S205 to S208 are performed to adjust the positions of the X-ray sources distributed on both sides of the central position along the X-axis direction, based on the focal position of the X-ray source at the central position of the multi-beam X-ray source array.
And S205, according to the final positions of the block mold body of the center line of the multi-beam X-ray source array and the center line of the detector calibrated in the step S118, starting the source of the center position of the X-ray source array for exposure, and recording the position of the projection line of the lower surface of the block mold body on the detector.
step S206: and starting one bulb tube distributed on two sides of the X-ray source at the central position for exposure, acquiring an exposure image of the block mold body under the current X-ray source through the detector, and judging whether the position of the projection line of the lower surface of the current block mold body on the detector is the same as the position of the projection line of the lower surface of the block mold body on the detector when the X-ray source at the central position is exposed recorded in the step S205 according to the exposure image.
step S207: and if not, fine-tuning the current cold cathode X-ray bulb along the X-axis direction, and repeating the step S206 until the position of the projection line of the lower surface of the current block gauge body on the detector is determined to be the same as the position of the projection line of the lower surface of the block gauge body on the detector when the X-ray source at the central position recorded in the step S205 is exposed, so as to complete the adjustment of the focus of the current X-ray source along the X-axis direction.
Step S208: according to the operations of steps S206 to S207, all X-ray source focuses on both sides of the X-ray source at the central position of the X-ray source array are sequentially adjusted along the X-axis direction, so that the X-coordinates of all X-ray source focuses are the same (i.e. the distances from the respective X-ray source focuses to the detector imaging plane are the same).
In the following steps S209 to S219, the bulbs distributed on both sides of the central X-ray source are adjusted to be equidistantly distributed along the linear array with the X-ray source focal position at the central position of the multi-beam X-ray source array as a reference.
step S209: and controlling the three-axis displacement table carrying the block gauge body and the two-axis displacement table carrying the detector to move along the positive direction of the Y axis respectively, wherein the moving distance is a preset theoretical distance between the focal positions of two adjacent X-ray sources. The preset theoretical distance refers to a reasonable distance predefined in practical application, for example, the preset theoretical distance between every two adjacent focal positions of the X-ray source is set to be 5 cm.
Step S210: and starting the ith X-ray source on the left side (along the positive direction of the Y axis, the same below) of the X-ray source at the central position for exposure, wherein the initial value of i is 1.
step S211: and acquiring an exposure image through a detector, and judging whether the projection column position of the left edge of the block gauge body on the detector is superposed with the central column position of the detector according to the exposure image.
step S212: and if the position of the projection column of the left edge of the block mold body on the detector is not coincident with the position of the central column of the detector, finely adjusting the current cold cathode X-ray bulb along the Y-axis direction, and returning to execute the steps S210 to S211 until the position of the projection column of the left edge of the block mold body on the detector is determined to be coincident with the position of the central column of the detector.
step S213: and if i is equal to i +1, sequentially completing the adjustment of all the X-ray sources on the left side of the X-ray source at the central position according to the operation methods of the steps S209 to S212, so that all the X-ray sources on the left side are equidistantly distributed along the Y-axis direction. In this step, when the ith X-ray source on the left side of the X-ray source in the central position is operated, the moving distance in step S209 is i times the theoretical distance of the adjacent focal points, and the X-ray exposed in step S210 is the current ith X-ray source on the left side.
step S214: and (after the calibration of the X-ray tubes distributed on the left side is finished), controlling the two-axis displacement table carrying the detector to return to a calibration position corresponding to the cold cathode X-ray tube at the central position (namely, the position when the calibration of the center of the multi-beam X-ray source array and the central row of the detector is finished).
Step S215: and controlling the three-axis displacement table carrying the block gauge body and the two-axis displacement table carrying the detector to move along the Y axis in opposite directions, wherein the moving distance is a preset theoretical distance between the focal positions of two adjacent X-ray sources.
Step S216: and starting the jth X-ray source on the right side of the X-ray source at the central position (along the opposite direction of the Y axis, the same below) for exposure, wherein the initial value of j is 1.
Step S217: and acquiring an exposure image through a detector, and judging whether the projection column position of the right edge of the block gauge body on the detector is superposed with the central column position of the detector according to the exposure image.
Step S218: and if the position of the projection column of the right edge of the block gauge body on the detector is not coincident with the position of the central column of the detector, finely adjusting the current cold cathode X-ray bulb along the Y-axis direction, and returning to execute the steps S215 to S216 until the position of the projection column of the right edge of the block gauge body on the detector is determined to be coincident with the position of the central column of the detector.
Step S219: and j is j +1, and according to the operation methods in the steps S215 to S218, sequentially completing the adjustment of all the X-ray sources on the right side of the X-ray source at the central position, so that all the X-ray sources on the right side are equidistantly distributed along the Y-axis direction. When the jth X-ray source on the right side is operated, the moving distance in step S216 is j times the theoretical distance of the adjacent focal point, and the X-ray exposed in step S219 is the current jth X-ray source on the right side.
it should be noted that, in the process of adjusting and calibrating the equidistant distribution of the bulbs on both sides of the central X-ray source along the linear array in steps S209 to S219, as described above, the bulbs on the left side of the central bulb may be calibrated one by one (S209 to S214), then the two-axis displacement table carrying the detector is controlled to return to the central position, and then the bulbs on the right side of the central bulb are calibrated one by one (S215 to S219); in the practical application process, the right side may be calibrated first, and then the left side may be calibrated, that is, S215 to S219 are executed first, then the two-axis displacement table with the detector mounted thereon is controlled to return to the central position, and then S209 to S214 are executed.
the accurate calibration of the focus of the multi-beam X-ray source in the direction of the X, Y, Z axis is completed through the above process, namely the distribution calibration of the focus position of the multi-beam X-ray source is realized. The invention carries out geometric calibration on the focus position of each independent emission source in the multi-beam X-ray source array, and has higher precision compared with the traditional mode that only the whole X-ray source array can be calibrated.
Step S3: by using the geometric calibration device of the static cone-beam CT imaging system, the distance parameter I and the distance parameter II from the projection position of the spherical center of the small spherical mold body on the detector to the center of the detector are obtained by adjusting the positions of a three-axis displacement table carrying the small spherical mold body along the Y-axis direction and the Z-axis direction, and the imaging system geometric parameters SOD and SID are obtained by calculation according to the distance parameter I and the distance parameter II and a preset formula. Wherein, SOD represents the distance from the central position of the multi-beam X-ray source to the scanned object, and SID represents the distance from the central position of the multi-beam X-ray source to the detector. As shown in fig. 8, the meaning of each parameter in step S3 is labeled. As shown in fig. 7, step 3 specifically includes the following steps S301 to S304:
Step S301: and placing the small spherical die body at the central position of the objective table, and controlling the three-axis displacement table carrying the small spherical die body to move along the Y-axis direction and the Z-axis direction until the projection of the spherical center of the small spherical die body on the detector in the central X-ray source exposure image acquired by the detector is superposed with the center of the imaging plane of the detector.
Step S302: starting any X-ray source in the left side and the right side of the X-ray source at the central position for exposure to obtain a distance parameter I from the projection position of the sphere center of the small sphere die body on the detector to the center of the detector1。
Step S303: controlling the three-axis displacement table carrying the small ball to move along the X axis by a distance a in the opposite direction, and starting the three-axis displacement tablestep S302, the same X-ray source is exposed to obtain a distance parameter II from the projection position of the sphere center of the small sphere phantom on the detector to the center of the detector2。
Step S304: solving the following equation system to obtain the distance SID from the center position of the X-ray source array to the detector and the distance SOD from the center position of the X-ray source array to the scanned object.
Wherein l1a first distance parameter, l, representing the projection position of the sphere center of the small sphere phantom on the detector to the center of the detector2and a second distance parameter representing the projection position of the sphere center of the small sphere phantom on the detector to the center of the detector, wherein S represents the distance from the focal point of the X-ray source at the center position to the focal point of the X-ray source selected in the step S302 for exposure.
Compared with an algorithm calibration mode, the method does not need to design an algorithm to obtain calibration parameters through a large amount of calculation, and can obtain the calibration parameters through simple calculation by directly acquiring the projection displacement of the die body through experiments.
In summary, the method provided in the third embodiment of the present invention utilizes the geometric calibration apparatus of the static cone-beam CT imaging system, and uses the standard block mold body and the small sphere mold body to calibrate the focal point distribution of the multi-beam X-ray source, the center of the multi-beam X-ray source array, and the central position of the detector imaging plane, and can calibrate the geometric position of each independent emission source in the encapsulated X-ray source array, so that the calibration accuracy is high, and the calibration parameters can be obtained by simple calculation.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (7)
1. A geometric calibration device for a static cone-beam CT imaging system, which is arranged on an optical platform, is characterized by comprising a plurality of cold cathode X-ray bulbs and a support frame:
each cold cathode X-ray bulb tube is used as an X-ray emission source, the support frame is used for mounting the cold cathode X-ray bulb tubes, and the plurality of cold cathode X-ray bulb tubes are arranged in a linear or arc mode to form a multi-beam X-ray source array;
an adjusting space is reserved on X, Y and a Z axis of the support frame, so that after the plurality of cold cathode X-ray bulbs are installed on the support frame, the position of each cold cathode X-ray bulb can be adjusted in three directions of X, Y or the Z axis respectively; wherein, the X-axis direction refers to the left-right direction, the Y-axis direction refers to the front-back direction, and the Z-axis direction refers to the up-down direction;
the device also comprises a detector, a two-axis displacement table, an object stage and a three-axis displacement table;
The detector is carried on the two-axis displacement table to realize respective movement in the directions of the Y axis and the Z axis;
the object stage is used for placing a scanning object and is carried on the three-axis displacement table so that the scanning object can respectively move along the three directions of the X axis, the Y axis and the Z axis;
the device is specifically configured to:
Step 101: determining the height of the focal point of the bulb tube at the central position of the multi-beam X-ray source array relative to the optical platform through measurement, controlling a two-axis displacement table carrying a detector to move along the Z-axis direction, and adjusting the height of the central row of the detector relative to the optical platform to be consistent with the height of the focal point of the bulb tube at the central position of the multi-beam X-ray source array;
step 102: the Y coordinate of the focus of the bulb tube at the central position of the multi-beam X-ray source array is determined through measurement, the three-axis displacement table carrying the block gauge body and the two-axis displacement table carrying the detector are respectively controlled to move along the Y-axis direction, and the Y coordinate of the center of the objective table carrying the block gauge body and the Y coordinate of the center row of the detector are adjusted to be consistent with the Y coordinate of the focus of the bulb tube at the central position of the multi-beam X-ray source array;
Step 103: controlling a three-axis displacement table carrying a block gauge body to run along the X-axis direction, and adjusting the position of the block gauge body along the Y-axis direction by controlling the three-axis displacement table;
Step 104: starting an X-ray source at the center of an X-ray source array for exposure;
step 105: acquiring an exposure image through a detector, and judging whether the position of a projection column of the left edge/right edge of the block gauge body on the detector is kept unchanged according to the exposure image;
Step 106: if not, returning to execute the steps 103 to 105 until the position of the projection column of the left edge/right edge of the block mold body on the detector is kept unchanged;
Step 107: controlling the two-axis displacement table carrying the detector to run along the Y-axis direction;
Step 108: starting an X-ray source at the central position of an X-ray source array for exposure;
Step 109: acquiring an exposure image through the detector, and judging whether the projection column of the left edge/right edge of the block gauge body on the detector is superposed with the central column of the detector according to the exposure image;
Step 110: if not, returning to execute the steps 107 to 109 until the projection column of the left edge/right edge of the block mold body on the detector coincides with the central column position of the detector, so as to finish the calibration of the center of the multi-beam X-ray source array and the central column position of the detector;
step 111: controlling a three-axis displacement table carrying a block gauge body to run along the X-axis direction, and adjusting the position of the block gauge body along the Z-axis direction;
step 112: starting an X-ray source at the center of an X-ray source array for exposure;
Step 113: acquiring an exposure image through a detector, and judging whether the position of a projection line of the upper surface of the block gauge body on the detector is kept unchanged according to the exposure image;
step 114: if not, returning to execute the steps 111 to 113 until the position of the projection line of the upper surface of the block mold body on the detector is kept unchanged;
Step 115: controlling the two-axis displacement table carrying the detector to run along the Z-axis direction;
step 116: starting an X-ray source at the central position of an X-ray source array for exposure;
Step 117: acquiring an exposure image through the detector, and judging whether a projection line of the upper surface of the block gauge body on the detector is superposed with the central line of the detector according to the exposure image;
Step 118: if not, returning to execute the steps 115 to 117 until the projection line of the upper surface of the block mold body on the detector coincides with the central line position of the detector, so as to finish the calibration of the center of the multi-beam X-ray source array and the central line position of the detector.
2. the apparatus of claim 1, wherein the plurality of cold cathode X-ray tubes are sequentially arranged in a straight line at equal distances on the support frame to form a linear multi-beam X-ray source array;
The number of the cold cathode X-ray bulbs is N, N is an odd number, and N is15；
The (N +1)/2 th cold cathode X-ray tube is taken as the center, and the cold cathode X-ray tubes on the two sides of the cold cathode X-ray tube are symmetrically distributed relative to the center.
3. The apparatus of claim 1, wherein the support frame covers a scan object angle in the range of 30 ° to 45 °.
4. the apparatus of claim 1, wherein a distance between the detector and a focal point of a bulb at a central position of the multi-beam X-ray source array is 60cm to 70 cm;
The distance between the center of the scanned object and the detector is 5cm to 10 cm.
5. a method for geometrical calibration of a static cone-beam CT imaging system, wherein the method employs the geometrical calibration apparatus of a static cone-beam CT imaging system as claimed in any one of claims 1 to 4, the method comprising:
step 1: by utilizing the geometric calibration device of the static cone-beam CT imaging system, the three-axis displacement table carrying the block gauge body is controlled to move along the X-axis direction, the Y-axis direction and the Z-axis direction, the central X-ray source of the X-ray source array is controlled to be exposed, and the positions of the two-axis displacement table carrying the detector in the Y-axis direction and the Z-axis direction are adjusted according to the position of the block gauge body on a projected image acquired by the detector, so that the calibration of the imaging geometric central position is completed;
step 2: by utilizing the geometric calibration device of the static cone-beam CT imaging system, the three-axis displacement table carrying the block gauge body is controlled to move along the X-axis direction, the Y-axis direction and the Z-axis direction, and each bulb tube distributed on two sides of the central X-ray source is controlled to be respectively exposed, and the positions of the bulb tubes distributed on two sides of the central X-ray source along the X direction, the Y direction and the Z direction are adjusted according to the position of the block gauge body on a projection image acquired by a detector each time so as to finish the calibration of the distribution of the focuses of each X-ray source; wherein, the X-axis direction refers to the left-right direction, the Y-axis direction refers to the front-back direction, and the Z-axis direction refers to the up-down direction;
the step 1 specifically comprises the following steps:
step A: determining the height of the focal point of the bulb tube at the central position of the multi-beam X-ray source array relative to the optical platform through measurement, controlling a two-axis displacement table carrying a detector to move along the Z-axis direction, and adjusting the height of the central row of the detector relative to the optical platform to be consistent with the height of the focal point of the bulb tube at the central position of the multi-beam X-ray source array;
and B: the Y coordinate of the focus of the bulb tube at the central position of the multi-beam X-ray source array is determined through measurement, the three-axis displacement table carrying the block gauge body and the two-axis displacement table carrying the detector are respectively controlled to move along the Y-axis direction, and the Y coordinate of the center of the objective table carrying the block gauge body and the Y coordinate of the center row of the detector are adjusted to be consistent with the Y coordinate of the focus of the bulb tube at the central position of the multi-beam X-ray source array;
Step C1: controlling a three-axis displacement table carrying a block gauge body to run along the X-axis direction, and adjusting the position of the block gauge body along the Y-axis direction by controlling the three-axis displacement table;
step C2: starting an X-ray source at the center of an X-ray source array for exposure;
Step C3: acquiring an exposure image through a detector, and judging whether the position of a projection column of the left edge/right edge of the block gauge body on the detector is kept unchanged according to the exposure image;
Step C4: if not, returning to execute the steps C1-C3 until the position of the projection column of the left edge/right edge of the block mold body on the detector is kept unchanged;
Step C5: controlling the two-axis displacement table carrying the detector to run along the Y-axis direction;
step C6: starting an X-ray source at the central position of an X-ray source array for exposure;
Step C7: acquiring an exposure image through the detector, and judging whether the projection column of the left edge/right edge of the block gauge body on the detector is superposed with the central column of the detector according to the exposure image;
step C8: if not, returning to execute the steps C5 to C7 until the projection column of the left edge/right edge of the block mold body on the detector coincides with the central column position of the detector so as to finish the calibration of the center of the multi-beam X-ray source array and the central column of the detector;
Step D1: controlling a three-axis displacement table carrying a block gauge body to run along the X-axis direction, and adjusting the position of the block gauge body along the Z-axis direction;
step D2: starting an X-ray source at the center of an X-ray source array for exposure;
step D3: acquiring an exposure image through a detector, and judging whether the position of a projection line of the upper surface of the block gauge body on the detector is kept unchanged according to the exposure image;
step D4: if not, returning to execute the steps D1 to D3 until the position of the projection line of the upper surface of the block mold body on the detector is kept unchanged;
Step D5: controlling the two-axis displacement table carrying the detector to run along the Z-axis direction;
Step D6: starting an X-ray source at the central position of an X-ray source array for exposure;
step D7: acquiring an exposure image through the detector, and judging whether a projection line of the upper surface of the block gauge body on the detector is superposed with the central line of the detector according to the exposure image;
Step D8: if not, returning to execute the steps D5 to D7 until the projection line of the upper surface of the block mold body on the detector coincides with the central line position of the detector, so as to finish the calibration of the center of the multi-beam X-ray source array and the central line position of the detector.
6. the method according to claim 5, wherein the step 2 comprises the steps of:
Step E1: according to the final positions of the block mold body of the center of the multi-beam X-ray source array and the center line of the detector calibrated in the step D8, starting the X-ray source at the center position of the X-ray source array for exposure, and enabling the projection line of the upper surface of the block mold body on the detector to coincide with the position of the center line of the detector;
Step E2: opening a bulb tube distributed on two sides of an X-ray source at the central position for exposure, acquiring an exposure image of the block mold body under the current X-ray source through the detector, and judging whether the position of a projection line of the upper surface of the current block mold body on the detector is superposed with the position of the central line of the detector or not according to the exposure image;
step E3: if the X-ray tube and the cold cathode X-ray tube are not coincident, fine tuning is carried out on the current cold cathode X-ray tube along the Z-axis direction, and the step E2 is repeated until the position of the projection line of the upper surface of the block gauge body on the detector is determined to be coincident with the position of the central line of the detector, so that the adjustment of the current X-ray source focus along the Z-axis direction is completed;
step E4: according to the operations of the steps E2 to E3, all X-ray source focuses on two sides of the X-ray source at the central position of the X-ray source array are adjusted along the Z-axis direction in sequence, so that the Z coordinates of all the X-ray source focuses are the same;
step F1: according to the final positions of the block gauge body of the center line of the multi-beam X-ray source array and the center line of the detector calibrated in the step D8, starting the X-ray source at the center position of the X-ray source array for exposure, and recording the positions of the projection lines of the lower surface of the block gauge body on the detector;
Step F2: starting a bulb tube distributed on two sides of the X-ray source at the central position for exposure, acquiring an exposure image of the block mold body under the current X-ray source through the detector, and judging whether the position of the projection line of the lower surface of the current block mold body on the detector is the same as the position of the projection line of the lower surface of the block mold body on the detector when the X-ray source at the central position is exposed, which is recorded in the step F1, according to the exposure image;
step F3: if not, fine tuning is carried out on the current cold cathode X-ray bulb along the X-axis direction, and the step F2 is repeated until the position of the projection line of the lower surface of the current block gauge body on the detector is determined to be the same as the position of the projection line of the lower surface of the block gauge body on the detector when the X-ray source at the central position recorded in the step F1 is exposed, so that the adjustment of the focus of the current X-ray source along the X-axis direction is completed;
Step F4: according to the operations of the steps F2 to F3, all X-ray source focuses on two sides of the X-ray source at the central position of the X-ray source array are adjusted along the X-axis direction in sequence, so that the X coordinates of all the X-ray source focuses are the same;
Step G1: controlling a three-axis displacement table carrying a block gauge body and a two-axis displacement table carrying a detector to move along the positive direction of a Y axis respectively, wherein the moving distance is a preset theoretical distance between the focal positions of two adjacent X-ray sources;
Step G2: starting the ith X-ray source on the left side of the X-ray source at the central position for exposure, wherein the initial value of i is 1;
Step G3: acquiring an exposure image through a detector, and judging whether the projection column position of the left edge of the block gauge body on the detector is superposed with the central column position of the detector according to the exposure image;
step G4: if the X-ray spherical tube is not coincident, fine adjustment is carried out on the current cold cathode X-ray spherical tube along the Y-axis direction, and the steps G2 to G3 are executed in a returning mode until the position of the projection column of the left edge of the block gauge body on the detector is determined to be coincident with the position of the central column of the detector;
step G5: making i = i +1, and according to the operation methods of steps G1 to G4, sequentially completing adjustment of all the X-ray sources on the left side of the X-ray source at the central position, so that all the X-ray sources on the left side are equidistantly distributed along the Y-axis direction;
step G6: controlling a two-axis displacement table carrying the detector to return to a calibration position corresponding to the cold cathode X-ray bulb tube at the central position;
step G7: controlling a three-axis displacement table carrying a block gauge body and a two-axis displacement table carrying a detector to move along the Y axis in opposite directions respectively, wherein the moving distance is a preset theoretical distance between the focal positions of two adjacent X-ray sources;
Step G8: starting the jth X-ray source on the right side of the X-ray source at the central position for exposure, wherein the initial value of j is 1;
Step G9: acquiring an exposure image through a detector, and judging whether the projection column position of the right edge of the block gauge body on the detector is superposed with the central column position of the detector according to the exposure image;
step G10: if the position of the right edge of the block gauge body on the detector is determined to be coincident with the position of the central column of the detector;
step G11: and enabling j = j +1, and according to the operation methods of the steps G7 to G10, sequentially completing the adjustment of all the X-ray sources on the right side of the X-ray source in the central position, so that all the X-ray sources on the right side are equidistantly distributed along the Y-axis direction.
7. The method of claim 5, wherein the method further comprises:
And step 3: by utilizing the geometric calibration device of the static cone-beam CT imaging system, a first distance parameter and a second distance parameter from the projection position of the spherical center of the small spherical mold body on the detector to the center of the detector are obtained by adjusting the positions of a three-axis displacement table carrying the small spherical mold body along the Y-axis direction and the Z-axis direction, and the imaging system geometric parameters SOD and SID are obtained by calculation according to the first distance parameter, the second distance parameter and a preset formula; wherein, SOD represents the distance from the central position of the multi-beam X-ray source to the scanned object, and SID represents the distance from the central position of the multi-beam X-ray source to the detector;
the step 3 specifically includes:
Step H1: the small spherical die body is placed in the center of the objective table, and the three-axis displacement table carrying the small spherical die body is controlled to move along the Y-axis direction and the Z-axis direction until the projection of the spherical center of the small spherical die body on the detector in the central X-ray source exposure image acquired by the detector is superposed with the center of the imaging plane of the detector;
Step H2: starting any X-ray source in the left side and the right side of the X-ray source at the central position for exposure to obtain a first distance parameter from the projection position of the sphere center of the small sphere die body on the detector to the center of the detector;
step H3: controlling the three-axis displacement table carrying the small ball to move in the opposite direction of the X axis, and starting the X-ray source which is the same as the X-ray source in the step H2 to expose to obtain a second distance parameter from the projection position of the spherical center of the small ball die body on the detector to the center of the detector; wherein, the opposite direction of the X axis refers to the left direction;
step H4: solving the following equation set to obtain the distance SID from the central position of the X-ray source array to the detector and the distance SOD from the central position of the X-ray source array to the scanned object;
；
wherein the content of the first and second substances,Indicating the centre of sphere of the small sphere phantom at said detectionthe distance parameter of the projection position on the device to the center of the detector is one,a second distance parameter representing the projection position of the sphere center of the small sphere phantom on the detector to the center of the detector,the distance between the X-ray source focal point at the center position and the X-ray source focal point selected for exposure in step H2.
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| CN109350097B (en) * | 2018-12-17 | 2021-11-05 | 深圳先进技术研究院 | X-ray source array, X-ray tomography system and method |
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