CN103584877A

CN103584877A - Computer computerized tomography device and method

Info

Publication number: CN103584877A
Application number: CN201310546294.3A
Authority: CN
Inventors: 李亮; 陈志强; 张丽; 康克军; 李元景; 刘以农; 邢宇翔; 赵自然
Original assignee: Tsinghua University; Nuctech Co Ltd
Current assignee: Tsinghua University; Nuctech Co Ltd
Priority date: 2009-05-26
Filing date: 2009-05-26
Publication date: 2014-02-19
Anticipated expiration: 2029-05-26
Also published as: CN103584877B

Abstract

The invention discloses a method for performing computerized tomography on an interest area of an object to be detected. The method includes the steps that CT projection data of the interest area are obtained; CT projection data of an area B are obtained; a set of PI line segments is selected to cover the interest area, and a reconstructed image value on each PI line segment in the set of PI line segments is calculated; then, the reconstructed image values on all the PI line segments in the set of PI line segments are combined to obtain an image of the interest area. The invention further discloses a CT device adopting the method and a data processing unit in the CT device. Due to the fact that the interest area and the area B are only needed to be covered with X ray bundles, the two-dimensional or three-dimensional image of the interest area is obtained through accurate reconstruction, CT of the interest area of any position of a large-size object can be achieved with a small-size detector, and the radiation dose of X rays in the CT scanning process can be greatly reduced.

Description

A kind of computer chromatography imaging device and method

The application is to be that May 26, application number in 2009 are 200910085612.4 and the dividing an application of the denomination of invention application for a patent for invention that is " a kind of computer chromatography imaging device and method " the applying date.

Technical field

The present invention relates to a kind of computerized tomography (CT) equipment, especially a kind of equipment for CT imaging is carried out in (ROI) interested region, and the CT formation method using in these equipment.

Background technology

Since Hounsfield in 1972 has invented First CT machine, CT technology has been brought revolutionary impact to medical diagnosis and industrial nondestructive testing, and CT has become one of important detection means of the industries such as medical treatment, biology, Aero-Space, national defence.X ray Cone-Beam CT is widely used in fields such as clinical medicine, safety inspection, Non-Destructive Testings, and particularly, in medical clinic applications, spiral CT has become one of indispensable detection methods ^[1].

Although CT technology has obtained huge success in fields such as industry, safety check, medical treatment at present, due to complexity and the multiformity of engineering application conditions, further developing of CT technology had higher requirement.Especially in commercial Application, CT technology is in large scale, high accuracy imaging, and the aspects such as medical low dose imaging exist larger difficulty.This mainly due to: the CT scan visual field (FOV) is subject to the restriction at X-ray beam width, detector size and scanning visual angle, and this makes the data for projection of large object scanning may have blocking of detector direction and two aspects of scanning angle direction; And existing main flow CT algorithm is all the overall method for reconstructing for complete object, require X-ray beam must cover object tomography completely, to data for projection, there is the situation of blocking to be difficult to process.Therefore, while at present large object or irregularly shaped object being carried out to imaging, often be difficult to directly complete scanning, need to be by relying on the approximate conversion methods such as data rearrangement just can reconstruct final image after Multiple-Scan, this has caused negative impact to the speed of CT imaging and precision.

In addition, detector in CT equipment has become the most critical link of the hardware cost of restriction CT equipment, the price of detector directly and detector cells size and quantity be directly proportional, and the remaining high of detector price, this has greatly limited the cost space of CT product.

On the other hand, in medical CT imaging, in order to guarantee that X ray data for projection does not block, the X-ray beam width that CT scan is used at present must cover the width of human body tomography, and real often certain organ of human body just interested, this has increased the unnecessary radiation dose that human body is subject in CT scan process greatly, if do not change the thinking of current CT design, is difficult to reduce radiation dose.At present, medical exposure has become the artificial ionization source radiation of whole people's maximum, and the x-ray dose that reduces CT examination is the key subjects that are related to all public and offspring's health thereof.

In addition, along with the raising of living standards of the people, people are more and more higher to the requirement of medical diagnosis, particularly for some human body privileged sites, such as: the medical diagnosis at the positions such as female mammary gland, cochlea, tooth needs very high spatial resolution.For these situations, current main flow whole body spiral CT machine cannot meet the demand of normal medical diagnosis.Along with the develop rapidly of large-area flat-plate detector technology, Medical flat detector technology is quite ripe at present, as being applied to the X ray DR imaging of high spatial resolution.The current flat panel detector based on amorphous selenium, amorphous silicon technology, its effective detector area has surpassed 500mm * 500mm, and detector pixel size has also reached 0.1mm left and right, and the current detector unit sizes of the multi-layer spiral CT 0.5mm that only has an appointment utilizes flat panel detector can realize the CT image more much higher than existing spiral CT spatial resolution.But because flat panel detector data volume is huge, data transmission bauds also cannot meet the requirement of current cone-beam CT imaging, also there is no really to apply at present the CT equipment that flat panel detector carries out whole body imaging.If we are not for Whole Body, but utilize Small-scale Flat detector to realize high accuracy area-of-interest CT imaging to interested organ, so just can overcome the slow technical bottleneck of data transmission bauds, make it to become possibility.

For the above-mentioned shortcomings and limitations of CT system, we start to explore new CT image rebuilding method and CT imaging pattern.In fact, in a lot of engineerings application and do not require complete object is carried out to overall CT imaging, only need to obtain in the subject image, particularly medical clinical diagnosis of some area-of-interest (ROI), as long as can realize the imaging to suspicious lesions position ^[2].

Early 1980s, people's Local C T imaging problem of object that begun one's study, but limit by CT reconstruction theory at that time, therefore then seek a kind of approximate function relevant to object faultage image people cannot accurate reconstruction go out the CT image of object part.1985, Smith etc. proposed the partial reconstruction algorithm of a kind of lambda tomography, and this algorithm utilizes partial projection data reconstruction to go out one has the function of identical singularity with ROI density function ^[3].Subsequently, Katsevich has proposed the partial reconstruction algorithm of a kind of pseudolocal tomography, and this algorithm replaces original function by rebuilding a part for the Hilbert conversion of density function ^[4].But, because these functions all cannot replace real object faultage image, be difficult to meet the demand of practical engineering application, greatly reduced the meaning of Local C T imaging for practical engineering application.In very long subsequently following period of time, for the imaging research of the local ROI of object, sink into pause always, cannot be resolved.

Recent years, CT reconstruction theory gets a larger development.2002, first Katsevich proposed a kind of cone-beam helical CT exact reconstruction algorithm based on filtered back projection (Filtered Back Projection, FBP) form.This algorithm has solved long materials Problems of Reconstruction well, in the situation that Z-direction data for projection blocks, this algorithm still can accurately reconstruct the subject image that is scanned part, and because this algorithm is FBP form, in reconstruction speed, compare and have very large advantage with Class of Iterative algorithm for reconstructing, the development that Katsevich is CT algorithm provides a brand-new thinking ^[5-6].2004, Zou and Pan proposed the spiral CT exact reconstruction algorithm of a kind of backprojection-filtration (Back Projection Filtration, BPF) form, and the data for projection that the method only needs theoretical minimum just can accurate reconstruction goes out the faultage image of object ^[7-8].So far, the Issues of Basic Theory of Spiral CT Reconstruction has obtained solving preferably.Subsequently, BPF algorithm is promoted the use of in parallel beam, fan-beam, pyramidal CT image reconstruction.The BPF algorithm of Zou and Pan is the algorithm for reconstructing based on PI line, PI line is a line segment on any two points line on track while scan, BPF algorithm requires two end points of every PI line outside object support, its sharpest edges are still can accurate reconstruction go out the image on PI line when data for projection exists some to block, and this makes to become possibility for the CT reconstruction of ROI rather than complete object.2006, Defrise etc. have obtained further achievement on the basis of BPF algorithm, relax the restriction of PI line, proved when PI line only has an end points outside object support, by the data for projection by this PI line, still can accurate reconstruction go out PI line epigraph ^[9].2007, the people such as Wang further proved when PI line is during completely at interior of articles, if known this PI line image information of last minute just can by the data for projection accurate reconstruction of blocking the subject image on this PI line ^[10].But in actual CT engineering application, the reconstruction numerical information on interior of articles PI line is difficult to obtain in advance, therefore, the people's such as Wang method has certain limitation in actual applications.

Pertinent literature:

[1] Li Liang. CT projective transformation theory and cone-beam method for reconstructing research [doctorate paper]. Beijing: Department of Engineering Physics of Tsing-Hua University, 2007.

[2] Li Liang, Chen Zhiqiang ，Kang Ke army, Zhang Li, Xing Yuxiang. area-of-interest CT image rebuilding method and simulation experiment, CT theory and application research, 18:1-7,2009.

[3] A Faridani, E L Ritman, K T Smith. “Local tomography”, SIAM Appl Math, 52: 459-484, 1992.

[4] A Katsevich, A. G. Ramm. “Pseudolocal tomography”, SIAM Appl Math, 56: 167-191, 1996.

[5] Katsevich A. A general scheme for constructing inversion algorithms for cone beam CT. Int J Math Math Sci, 2003, 21:1305-1321.

[6] Katsevich A. An improved exact filtered backprojection algorithm for spiral computed tomography. Adv Appl Math, 2004, 32:681-697.

[7] Zou Y, Pan X. Exact image reconstruction on PI-lines from minimum data in helical cone-beam CT. Phys Med Biol, 2004, 49:941-959.

[8] Zou Y, Pan X. Image reconstruction on PI-lines by use of filtered backprojection in helical cone-beam CT. Phys Med Biol, 2004, 49:2717-2731.

[9] M Defrise, F Noo, R Clackdoyle, H Kudo. “Truncated Hilbert transform and image reconstruction from limited tomographic data”, Inverse Problems, 22: 1037-1053, 2006.

[10] Y B Ye, H Y Yu, Y Wei, G Wang. “A General Local Reconstruction Approach Based on a Truncated Hilbert Transform”, International Journal of Biomedical Imaging, Volume 2007, Article ID 63634。

Summary of the invention

Applicant of the present invention has found a brand-new CT accurate reconstruction data completeness condition:

For any point

Figure 2013105462943100002DEST_PATH_IMAGE001

if data for projection meets following condition, image function simultaneously

can be by accurate reconstruction:

1. there is vector

Figure 2013105462943100002DEST_PATH_IMAGE003

with two line segments

,

Figure 2013105462943100002DEST_PATH_IMAGE005

, wherein

be by put and be parallel to

at function

line segment in support,

;

2. line segment

have an end points at least outside function support, or line segment on

known;

3. for arbitrfary point

, arbitrarily angled by arbitrfary point in the small neighborhood that comprises this point under projection

equal collected obtaining, wherein

.

Above-mentioned condition can be explained by Fig. 1, when region of interest ROI is positioned at object support inside, FOV only covers ROI can not accurate reconstruction ROI image, need to increase the faultage image that extra projection information can reconstruct this ROI, in two kinds of situation: (a) (b) belongs to a class situation, increase an extra dark shaded areas, the data for projection by this shadow region also needs to collect, and the image of this dark shaded areas is known; (c) (d) belong to an other class situation, increase an extra shadow region B, this region some or all outside object support.As long as met one of two things above, can both realize the accurate CT imaging of region of interest ROI.Four kinds of situations in comparison diagram 1, we can find for two kinds of situations (c) below (d) owing to not needing the image information of known this extra shadow region, so both of these case is more convenient in engineering application, realizes; Particularly last a kind of situation (d) is because shadow region B is positioned at outside object support, thereby only need to measure the faultage image that X ray projection by ROI and region B can accurate reconstruction ROI, this just means that this CT scan mode is for regard to imaging of medical, and detected person can accept radiation dose still less.The x-ray dose that detected person only need to accept to scan the x-ray dose of its suspect tissue region and pass through the outer very little air section of its health, compare current whole body Spiral CT scan, can reduce to a great extent the radiation dose that detected person accepts.

The present invention based on above-mentioned CT accurate reconstruction data completeness condition, especially makes based on above-mentioned situation (d) just.

According to an aspect of the present invention, provide a kind of method of the area-of-interest of detected object being carried out to CT imaging, comprised step: the CT data for projection that obtains described area-of-interest; Obtain the CT data for projection in B region, the at least a portion in wherein said B region is positioned at outside the support of described detected object, and described B region is chosen as and makes it possible to the PI line segment of selecting one group to cover described area-of-interest, wherein the PI line segment of every described area-of-interest of process is all by B region; And the CT data for projection of rebuilding described area-of-interest according to the CT data for projection in the CT data for projection of described area-of-interest and described B region.

According to a further aspect in the invention, provide a kind of for the area-of-interest of detected object being carried out to the CT imaging device of CT imaging, having comprised: x ray generator, for generation of the X-ray beam for scanning, detector assembly, for surveying through the X equipment that is scanned region to produce data for projection, detected object bogey, passes in and out described CT imaging device for carrying described detected object, master controller, for controlling the operation of described CT imaging device, so that only covering described area-of-interest, the X ray that described x ray generator sends carries out CT scan to obtain the data for projection of described area-of-interest, and make X ray that described x ray generator sends only cover B region CT scan is carried out to obtain the data for projection in described B region in described B region, the at least a portion in described B region is positioned at outside the support of described detected object, and described B region is chosen as and makes it possible to the PI line segment of selecting one group to cover described area-of-interest, wherein the PI line segment of every described area-of-interest of process is all by B region, and data processing unit, for the data for projection of the area-of-interest based on obtained and the data for projection in B region, rebuild the image of described area-of-interest.

The X ray CT imaging device and the method that according to the present invention, propose, only need X-ray beam that X source sends to cover the two-dimensional/three-dimensional faultage image that area-of-interest can accurate reconstruction obtains this area-of-interest, so the detector that can use reduced size is realized the CT imaging of large sized object optional position area-of-interest, improved the speed of CT scan and image reconstruction, reduced the hardware cost of CT equipment, can greatly reduce the X-radiation dosage in CT scan process simultaneously.Therefore, the present invention has very high market application potential.

Accompanying drawing explanation

By reading below detailed description of the preferred embodiment, various other advantage and benefits will become cheer and bright for those of ordinary skills.Accompanying drawing is only for the object of preferred implementation is shown, and do not think limitation of the present invention.And in whole accompanying drawing, by identical reference marks, represent identical parts.In the accompanying drawings:

Fig. 1 has illustrated according to CT accurate reconstruction data completeness condition of the present invention;

Fig. 2 has described the flow chart of Computerized chromatographic (CT) formation method according to an embodiment of the invention;

The flow chart of the data for projection method for reconstructing that Fig. 3 has described according to an embodiment of the invention, carried out in the CT of Fig. 2 formation method;

Fig. 4 shows the structured flowchart of CT imaging device 400 according to an embodiment of the invention;

Fig. 5 shows the structured flowchart of the front collimator apparatus 420 in CT imaging device 400 according to an embodiment of the invention;

Fig. 6 shows the structured flowchart of the detector position control device 440 in CT imaging device 400 according to an embodiment of the invention; And

Fig. 7 shows the numerical simulation result that CT imaging device carries out CT imaging according to an embodiment of the invention.

Specific embodiment

Below in conjunction with accompanying drawing and concrete embodiment, the invention will be further described.

As above, about as described in the situation (d) of CT accurate reconstruction data completeness condition, only need to obtain the faultage image that gets final product accurate reconstruction ROI by the X ray projection in ROI and B region by scanning.

Fig. 2 has described Computerized chromatographic according to an embodiment of the invention (CT) formation method.In step S201, determine (ROI) the interested region in the detected object that will carry out CT imaging, and determine that according to determined ROI region at least a portion is positioned at the B region outside detected object support.B region is chosen as the PI line segment that makes it possible to select one group of covering ROI region, wherein guarantees that the every PI line through ROI region is all by B region (situation as shown in Figure 1 (d) shows).B region can be the area of space of an arbitrary size and shape, considers the size of actual detector unit and two factors of radiation dose that patient accepts, and usually, B region can be chosen as circle or the diameter of Spherical Volume region that diameter is 10 times of detector cells.Certainly, B region can be more than one.In addition, in order further to improve image reconstruction speed and precision, can further determine other reference zone.

After having determined ROI region and B region, in step S203, ROI region is adjusted within the scope of scan vision, so that scanning X-ray beam only covers this ROI, and CT scan is carried out to obtain the CT data for projection in ROI region in this ROI region.Then in step S205, B region is adjusted within the scope of scan vision, so that X-ray beam only covers this B region, and CT scan is carried out to obtain the CT data for projection in B region in this B region.Subsequently in step S207, the CT data for projection in the CT data for projection in the ROI region based on obtaining at step S203 and the B region that obtains at step S205, according to below described with reference to FIG. 3 method for reconstructing reconstruct the CT image in this ROI region.In CT formation method of the present invention, although need to carry out the CT image that twice CT scan can reconstruct ROI region, but in each scanning, X-ray beam only covers ROI and B region, so total X-radiation dosage that in twice sweep, detected object is subject to is far smaller than the radiation dose of conventional CT scans.

Fig. 3 has specifically described the method for reconstructing of carrying out in the step S207 shown in Fig. 2.In step S301, select one group of PI line segment that can cover ROI region, and guarantee that the every PI line through ROI region is all by B region.

The method enters step S303-S307 subsequently, wherein, for every PI line in PI sets of line segments selected in step S301, along this PI line, carries out image reconstruction.Then in step S309, the data reconstruction on all PI lines is combined and obtains final ROI image.This image reconstruction process based on PI line is the same in two and three dimensions is rebuild, take below two-dimension image rebuild as example illustrates image reconstruction process that carry out in step S303-S307, based on a PI line.

Two dimensional image along a PI line is defined as to function

, image reconstruction process is found the intersection function that meets all 5 constraints of formula (1) below exactly.

（1）

Wherein,

can directly be calculated by the CT data for projection measuring.In addition,

represent the one dimension PI line segment after normalization,

the B region B being positioned on this PI line segment outside detected object support, and

be the part that is arranged in the PI line segment in ROI region, this as shown in Figure 1 (d) shows.

being the subject image in the PI line segment part in B region, because it is outside the support of detected object, and being generally air, is 0 so its image reconstruction value generally can be set.

represent to rebuild the possible maximum in image, can be arranged to according to the feature of detected object the attenuation quotient value of the maximal density material in this object, for example, for medical CT imaging, detected object is people normally, its maximum of rebuilding image is generally osseous tissue, so can be by

being set to is the attenuation quotient value of the osseous tissue under corresponding X ray energy.

the one dimension Hilbert(Hilbert on PI line segment) transformed value, then back projection is to the result on PI line segment data for projection to be asked to difference, and this can calculate with formula below:

（2）

Herein,

that point on the one dimension PI line two-dimensional coordinate on faultage image space represents

, and

in some x corresponding one by one.Wherein,

represent data for projection,

the dimension coordinate on detector, the employing angle of projection,

.Here,

with there is identical implication, for no other reason than that be expressed as different variablees under different coordinates.

Constraints in above-mentioned formula (1) easily understand and realize, condition can utilize POCS(Projection onto Convex Set, convex set projection) iterative computation realizes, particularly, condition

can utilize following iterative computation to realize:

,

（3）

Wherein,

the intermediate reconstructed images that represents iteration,

represent iterative steps.Iteration initial pictures

can artificially arrange arbitrarily, usually get complete zero.

represent Hilbert inverse transformation, this transformation for mula is:

（4）

Wherein P.V. represents Cauchy principal value integral.

In formula (3)

be defined as:

（5）

Wherein,

by formula (2) above, calculate, in POCS iterative process, remain unchanged, do not need repetition back projection to calculate.

Constraints in formula (1)

computing formula be:

（6）。

According to the above-mentioned description to the concrete processing of solution formula (1), knownly below searching meets, in formula (1) in the intersection function of all 5 constraints, need to first carry out backprojection-filtration and (obtain

value), then carry out POCS iterative computation and obtain

value.And POCS iterative process is all to rebuild iterating between image area and two territories of Hilbert transformation space, there is not forward projection problem, therefore, the speed of image reconstruction is very fast.

Particularly, in step S303, select a PI line segment in PI sets of line segments.Then in step S305, calculate the one dimension Hilbert transformed value on selected PI line segment, this can calculate according to formula (2).Subsequently, in step S307, the one dimension Hilbert transformed value that step S305 is calculated carries out limited Hilbert inverse transformation, to obtain the reconstruction image value on PI line segment.In the processing of step S307, need to rebuild iterating between image area and Liang Ge territory, Hilbert transformation space territory, POCS iterative process obtains the reconstruction image meeting the demands that meets required precision.Processing in step S307 can be carried out according to above-mentioned formula (1) and (3)-(6).

It should be noted that, above-mentioned method for reconstructing is not limited to certain scan mode, it can be applicable to utilize the CT scan of parallel beam, fan-beam or cone-beam X-ray, simultaneously for different scan tracks, this method for reconstructing is applicable too, unique different be that back projection's formula (2) can only need to adjust accordingly according to concrete scan mode because the variation of concrete scan mode is slightly different on weight coefficient, at this, do not repeat.

In addition, also it is pointed out that Fig. 3 has only provided a kind of concrete mode that a kind of CT data for projection according to the CT data for projection in ROI region and B region is rebuild the CT image in ROI region.Also exist other according to principle of the present invention, the method for utilizing the CT data for projection in ROI region and the CT data for projection in B region to rebuild the CT image in ROI region, and all these methods are all within protection scope of the present invention.

Fig. 4 shows CT imaging device 400 according to an embodiment of the invention, and it utilizes CT formation method according to the present invention to carry out CT imaging.CT imaging device 400 comprises x ray generator 410, front collimator apparatus 420, detector assembly 430, detector position control device 440, rotating mechanism 450, detected object bogey 460, master controller 470, data processing unit 480 and the display device 490 for generation of the X-ray beam for scanning.

The X ray that x ray generator 410 sends is fladellum (corresponding to linear array detector) or cone beam (corresponding to area array detector) normally.Front collimator apparatus 420 is arranged on the position that the ray of x ray generator 410 goes out to restraint window, for limiting the width of X-ray beam, so that the width of X-ray beam is consistent with the detector width in detector assembly.As described according to described in CT formation method of the present invention above, the present invention needs respectively ROI region and B region to be scanned, therefore before needing, collimator apparatus 420 possesses the X ray of adjusting beam width, so that X-ray beam only covers the function in ROI region or B region.Fig. 5 shows the detailed structure of front collimator apparatus 420.As shown in Fig. 5 (a), this front collimator apparatus 420 blocks piece 421a-421d by four X ray and forms, and forms the effigurate X ray of tool and goes out to restraint window 423, and this shape can be circle, rectangle or other shapes.In the present embodiment, as shown in Fig. 5 (b), the rectangle of take describes as example.X ray blocks piece 421a-421d to be made by the material (it can be the highdensity materials such as lead, tungsten) of effective absorption of x-rays energy, and possesses certain thickness can stop seeing through of X ray.Each X ray blocks has the servomotor 425 of one group of independent operation and precision lead screw 427(after piece 421a-421d as shown in Fig. 5 (c)), servomotor 425 and precision lead screw 427 can, under the control of master controller 470, drive corresponding X ray to block piece 421a-421d and move to advance or retreat along precision lead screw 427 according to given parameter.Four groups of servomotors 425 and precision lead screw 427 just can make X ray go out to restraint window 423 according to set parameter running simultaneously and realize the change of corresponding window size and position for different ROI regions or B region, thereby reach the requirement that X-ray beam only covers ROI region or B region in scanning process.Certainly, X ray blocks not necessarily lucky four of pieces, and the polylith X ray that any X ray that can form definite shape goes out to restraint window blocks piece all within protection scope of the present invention.

Detector assembly 430 can be used linear array detector or area array detector, also can adopt flat panel detector, and corresponding auxiliary facilities.Detector assembly 430 survey see through be scanned region X ray to produce data for projection, and wired or wireless mode is transferred to data processing unit 480 by data for projection and is further processed with optical cable, netting twine etc.

Detector position control device 440 is for controlling the position of detector assembly 430, and comprises servomotor 441 and precision lead screw 443 etc.In the embodiment that it is area array detector that Fig. 6 has illustrated at detector assembly 430, the detailed structure of detector position control device 440.As shown in Figure 6, detector assembly 430 is fixed on precision lead screw 443 by the groove that is installed, and can by servomotor 441, under the control of master controller 470, be driven this detector assembly 430 to do rectilinear motion along leading screw 443.Owing to can selecting ROI region and B region, therefore need the scope of detector assembly 430 motions to want to cover ROI region and the B regional location that may select arbitrarily, therefore the position of detector assembly 430 under each X ray projection angle may change, to change as required at any time the position of detector assembly 430 under the control of master controller 270.

Rotating mechanism 450 comprises a gantry that can rotate around certain fixed center, and x ray generator 410, front collimator apparatus 420, detector assembly 430, detector position control device 440 etc. are all fixed on this gantry.In CT scan process, this gantry drives above-mentioned each device rotation under the control of master controller 470, and in rotation, x ray generator 410 is detected apparatus 430 through detected region (behind ROI region or B region) and detects to send X-ray beam under different angles, and the data processing unit 480 that data for projection is transferred to rear end is processed.Rotating mechanism 450 can carry out multipurpose rotary scanning, individual pen rotation sweep or reciprocal multipurpose rotary scanning; as long as these scan modes are enough to allow CT imaging device 400 obtain enough data for projection, rebuild image, all these scan modes are all within protection scope of the present invention.

Detected object bogey 460 carrying detected object turnover CT imaging devices 400, its structure and existing device are similar.Conventionally, detected object bogey 460 is positioned near the center of rotation of rotating mechanism 450, and a ROI region part for detected object normally.

Master controller 470 is controlled whole scanning process, and in an embodiment of the present invention, master controller 470 is controlled CT imaging device 400 in the mode of the CT formation method corresponding to described in Fig. 2.Master controller 470 is first according to determined ROI region, and before controlling, collimator apparatus 420 and detector position control device 440 are so that the X ray that x ray generator 410 sends only covers ROI region.Then master controller 470 is controlled CT imaging device 400 ROI region is carried out to CT scan to obtain the data for projection in ROI region and these data are sent to data processing unit 480.Subsequently, master controller 470 is first according to definite B region, and before controlling, collimator apparatus 420 and detector position control device 440 are so that the X ray that x ray generator 410 sends only covers B region.Finally, master controller 470 is controlled CT imaging device 400 ROI region is carried out to CT scan to obtain the data for projection in B region and these data are sent to data processing unit 480.

Data processing unit 480, after obtaining the data for projection in ROI region and B region, is rebuild the image in ROI region according to method for reconstructing as described in Figure 3.Particularly, data processing unit 480 comprises PI line division device 481, Hilbert transformation calculations device 483, Hilbert inverse transformation accountant 485 and data reconstruction combination unit 487.Wherein, PI line is divided device 481 according to the relative position in ROI region and B region, selects one group of PI line segment that can cover ROI region, and guarantees that the every PI line through ROI region is all by B region.Hilbert transformation calculations device 483 is that every PI line computation in one group of PI line is along the one dimension Hilbert transformed value of this PI line.485 pairs of Hilbert inverse transformation accountants utilize the one dimension Hilbert transformed value that Hilbert transformation calculations device 483 calculates to carry out limited Hilbert inverse transformation, to obtain the reconstruction image value on PI line segment, wherein in Hilbert inverse transformation accountant 485, need to rebuild iterating between image area and Liang Ge territory, Hilbert transformation space territory, POCS iterative process obtains the reconstruction image that meets required precision.Data reconstruction combination unit 487, for dividing according to PI line the PI line group that device 481 provides, combines reconstruction image every PI line in PI line group, that calculated by Hilbert inverse transformation accountant 485, and obtains final ROI image.The detail of the processing in data processing unit 480 was described in detail in the above, no longer repeated here.

In addition, data processing unit 480 is also carried out such as sclerosis, scatter correction, and metal artifacts is proofreaied and correct, and image is processed the view data of carrying out in the CT scan traditional with pattern recognition etc. and imaging device and processed.

Display device 490 shows rebuilds the ROI area image obtaining, display device 490 simultaneously can also show with CT scan process in control and the information of parameter correlation so that operator can obtain above-mentioned information intuitively.

Can be by respectively ROI region and B region being scanned fast and are accurately reconstructed the image in ROI region according to CT imaging device 400 of the present invention.Although need twice sweep, owing to only needing that ROI region and B region are scanned, so scanning and reconstruction speed have accelerated on the contrary.In addition has also significantly reduced in the region that, detected object is exposed under X ray.

Here it is to be noted, although in the above in the description for the embodiment of CT imaging device 400, the CT data for projection that first obtains ROI region has been described, then obtain the order of the CT data for projection in B region, but, this order is can be arbitrarily, and for example, then the CT data for projection that can first obtain B region obtains the CT data for projection in ROI region.Even, according to one embodiment of present invention, can obtain the CT data for projection in ROI region and B region simultaneously.All these obtain the mode of CT data for projection in ROI region and B region all within protection scope of the present invention.

Fig. 7 utilizes the numerical simulation result that carries out CT image scanning and reconstruction according to the application's CT imaging device.In experiment, we have used Shepp-logan head model, and this head model is limited in the circle that a diameter is 20cm, and ROI region is a square that the length of side is 6cm, is placed on head model center, and two other elongated rectangular region B1, B2 are placed on respectively

place.Definition by head model can know, the image values in these two elongated rectangular region B1, B2 is 0.While carrying out ROI region CT scan, parallel beam X ray only covers ROI and region B1, B2 in 180 degree scanning processes, as shown in Figure 7 (a).Fig. 7 (b) is the data for projection utilizing through ROI and region B1, B2, rebuilds the ROI image obtaining according to image rebuilding method of the present invention; And Fig. 7 (c) only utilizes the data for projection through ROI and region B1, according to image reconstruction algorithm of the present invention, rebuild the ROI image obtaining.According to (b) and reconstructed results (c), can find, utilize CT formation method of the present invention, can only cover in the scanning situation of ROI region and the little object exterior domain of another one at X ray, rebuild and obtain high-quality ROI image, can meet the demand of practical engineering application.And this CT imaging technique can be saved the size of detector to a great extent, reduce data for projection amount, improve CT image reconstruction speed, the most important thing is guaranteeing under the prerequisite of ROI region CT picture quality, significantly reduce object/patient's X-radiation dosage, this point is particularly important for medical CT imaging.

It should be noted above-described embodiment the present invention will be described rather than limit the invention, and those skilled in the art can design alternative embodiment in the situation that do not depart from the scope of claims.In the claims, any reference marks between bracket should be configured to limitations on claims.Word " comprises " not to be got rid of existence and is not listed as element or step in the claims.Being positioned at word " " before element or " one " does not get rid of and has a plurality of such elements.The present invention can be by means of including the hardware of some different elements and realizing by means of the computer of suitably programming.In having enumerated the unit claim of some devices, several in these devices can be to carry out imbody by same hardware branch.The use of word first, second and C grade does not represent any order.Can be title by these word explanations.

Claims

1. the area-of-interest of detected object is carried out to a method for CT imaging, comprises step:

Obtain the CT data for projection of described area-of-interest and the CT data for projection in B region simultaneously, the at least a portion in wherein said B region is positioned at outside the support of described detected object, and described B region is chosen as and makes it possible to the PI line segment of selecting one group to cover described area-of-interest, wherein the PI line segment of every described area-of-interest of process is all by B region; And

According to the CT data for projection in the CT data for projection of described area-of-interest and described B region, rebuild the CT data for projection of described area-of-interest.

2. CT formation method as claimed in claim 1, the CT data for projection that the wherein said CT data for projection according to the CT data for projection of described area-of-interest and described B region is rebuild described area-of-interest comprises step:

For every PI line segment in described PI sets of line segments:

The one dimension Hilbert transformed value of calculating on described PI line segment, and

Calculated one dimension Hilbert transformed value is carried out to limited Hilbert inverse transformation, to obtain the reconstruction image value on described PI line segment;

Combine the reconstruction image value on all PI line segments in described PI sets of line segments and obtain the image of described area-of-interest.

3. CT formation method as claimed in claim 2, wherein said limited Hilbert inverse transformation step comprises:

Between reconstruction image area and Liang Ge territory, Hilbert transformation space territory, carry out convex set projection iteration and obtain the described reconstruction image on PI line segment that meets required precision.

4. CT formation method as claimed in claim 1, the wherein said CT data for projection that obtains described area-of-interest and described in obtain B region CT data for projection comprise:

Utilize parallel beam, fan-beam or cone-beam X-ray to carry out CT scan to described area-of-interest and B region, to obtain the CT data for projection in described area-of-interest and B region.