CN111508049A - Image reconstruction method, system, device and storage medium for finite angle CT scanning - Google Patents
Image reconstruction method, system, device and storage medium for finite angle CT scanning Download PDFInfo
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Abstract
The invention relates to an image reconstruction method, a system, a device and a storage medium for finite angle CT scanning, which establish a projection matrix according to a projection data set P and select L0And establishing an objective equation of the optimization problem by the norm regular term, and iteratively optimizing and reconstructing an optimal image. The method is suitable for finite angle CT detection of the carbon fiber composite core wire, can effectively recover the details of the carbon fiber composite core wire under a smaller scanning angle, and reduces finite angle artifacts, thereby improving the applicability of the finite angle CT detection of the carbon fiber composite core wire.
Description
Technical Field
The present application belongs to the field of image reconstruction technology, and in particular, to an image reconstruction method and system for limited angle CT scanning and a CT scanning device.
Background
(Aluminum conductor Composite Core, ACCC for short) is a new type of conductor for overhead transmission lines. The earliest new type of wire developed by countries such as the united states and japan was mainly used for space equipment and space stations. The core wire of the cable is a single core rod which is made by carbon fiber as a central layer and glass fiber in a wrapping mode, the outer layer and the adjacent outer layer of the aluminum strand are trapezoidal sections, the cable is a novel cable with excellent performance, the carbon fiber cable is divided into a carbon fiber rod core aluminum stranded wire and a heat-resistant carbon fiber rod core aluminum alloy stranded wire, the carbon fiber cable is made by carbon fiber as the central layer, the glass fiber in the wrapping mode is made into the single core rod, and the single core rod is externally made into a T-shaped. From the structure of the carbon fiber composite core wire, the surface damage of the wire is easy to observe, and the shielding carbon fiber core rod of the peripheral aluminum stranded wire cannot be observed, and in addition, the aluminum stranded wire core rod is also twisted together by separated individuals, so that the failure of the conventional detection method is caused.
Industrial CT (Computed Tomography) detection is independent of the geometric structure of a substance, can clearly see the structural hierarchy in a fracture of the detected substance, and can directly obtain the spatial position, shape and size information of a target feature from a CT image. Therefore, the industrial CT can obtain the damage condition of the aluminum stranded wire of the carbon fiber composite core wire and the defect distribution of the carbon fiber core rod, and is the optimal detection method at present. Because the in-service carbon fiber composite core wire is installed in a high-voltage network, the wire can not rotate during CT detection, and therefore, the industrial CT complete scanning condition can not be met, namely the relative rotation angle is larger than 180 degrees + the fan angle.
Due to the self-winding structure of the carbon fiber composite core wire and the limitation that the in-service wire cannot rotate, the defects of the internal composite core cannot be seen clearly by conventional digital radiography, and therefore, a CT scanning imaging method of the carbon fiber composite core wire needs to be researched. In view of this, it is necessary to directly place the detection device on the line for in-service detection, to implement the limited-angle CT scan, and further to determine the quality of the wire.
The cost of a CT detection apparatus depends on the complexity of the apparatus, while the image quality depends on the image reconstruction method. Aiming at the problem of finite angle CT scanning of the carbon fiber composite core wire, the traditional analytic reconstruction algorithm such as a Filtered back-projection (FBP) algorithm is difficult to solve the problem of reconstructing a projection image with a finite angle, and the finite angle artifact is inevitably introduced, so that the actual imaging detection requirement is difficult to meet.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the image reconstruction method and the CT detection device for the limited angle CT scanning aim to solve the problem that limited angle artifacts are inevitably introduced to reconstruction of limited angle projection images by a traditional image reconstruction algorithm in the prior art.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the invention provides an image reconstruction method of limited angle CT scanning in a first aspect, which comprises the following steps:
s1, acquiring projection data of the target object and establishing a projection data set;
s2, obtaining an image to be reconstructed according to the projection data set;
s3, introducing L according to the projection data set and the image to be reconstructed0Norm regularization term, set up L0Normalizing the target optimization equation by using a norm;
s4, carrying out iterative operation on the target optimization equation through an SART reconstruction algorithm to obtain a reconstructed image;
s10 calculating L gradient of reconstructed image0Norm, L for the reconstructed image gradient0Performing minimization operation on the norm to obtain an optimized and updated reconstructed image;
s11, judging whether the reconstructed image meets the iterative convergence condition, if so, outputting the optimized and updated reconstructed image to complete the image reconstruction; otherwise, adjusting the regularization parameters, and entering S4 to perform the next iteration reconstruction until the convergence condition is satisfied.
A second aspect of the present invention provides an image reconstruction system for limited angle CT scanning, comprising:
the data acquisition module is used for acquiring projection data of a target object and establishing a projection data set;
the initialization module is used for obtaining an image to be reconstructed according to the projection data set;
an optimization objective establishing module for establishing an optimization objective based on the projection data set and the image to be reconstructedLike, introduce L0Norm regularization term, set up L0Normalizing the target optimization equation by using a norm;
the reconstructed image module is used for carrying out iterative operation on the target optimization equation through an SART reconstruction algorithm to obtain a reconstructed image;
a reconstructed image optimization module for L performing on the reconstructed image gradients0Performing minimization operation on the norm to obtain an optimized and updated reconstructed image;
the convergence judging module is used for judging whether the reconstructed image meets an iterative convergence condition, and if so, outputting an optimized and updated reconstructed image to complete image reconstruction; otherwise, adjusting the regularization parameters, and performing the next iteration reconstruction until the convergence condition is met.
A third aspect of the invention provides a storage medium having stored thereon a computer program which, when executed by a processor, is operative to perform the image reconstruction method of claim 1.
The invention provides a finite angle CT scanning device, which comprises a driving device, a ray source component, a detector component and an arc-shaped bracket, wherein the ray source component and the detector component are arranged on the inner side of the arc-shaped bracket and are arranged oppositely;
the driving device is used for driving the ray source assembly and the detector assembly to perform scanning motion around a target object along a preset arc motion track, the angle range of the scanning motion is within 180 degrees, and finite-angle CT scanning is performed through the X-ray source, so that DR images of the target object can be collected at multiple angles.
The method has the advantages of utilizing the image gradient L0Norm regularization eliminates finite angle artifacts, effectively restores image details, and reconstructs the image clearly with high quality.
Drawings
The technical solution of the present application is further explained below with reference to the drawings and the embodiments.
FIG. 1 is a flowchart of an image reconstruction method according to an embodiment of the present application;
FIG. 2 is a schematic structural diagram of a detection apparatus according to an embodiment of the present application;
FIG. 3 is a diagram of the results of the SART reconstruction algorithm in different finite angle ranges;
FIG. 4 is a graph of the results of a TV regularization method reconstruction over a range of different finite angles;
fig. 5 is a diagram showing the reconstruction result of the image reconstruction method of the present invention in different limited angle ranges.
The reference numbers in the figures are: the device comprises a first moving platform 1, a horizontal rotating shaft 2, a vertical rotating shaft 3, a first fixed block 4, a second moving platform 5, a second fixed block 6, an X-ray source 7, a flat panel detector 8, a target object 9, a first supporting plate 10, a second supporting plate 11 and an arc-shaped support 12.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The technical solutions of the present application will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
Example 1
The present embodiment provides an image reconstruction method for limited angle CT scanning, as shown in fig. 1, including:
s1, acquiring projection data of the target object and establishing a projection data set;
s2, obtaining an image to be reconstructed according to the projection data set;
s3, introducing L according to the projection data set and the image to be reconstructed0Norm regularization term, set up L0Normalizing the target optimization equation by using a norm;
s4, carrying out iterative operation on the target optimization equation through an SART reconstruction algorithm to obtain a reconstructed image;
s10, conducting L on the reconstructed image gradient0Performing minimization operation on the norm to obtain an optimized and updated reconstructed image;
s11, judging whether the reconstructed image meets the iterative convergence condition, if so, outputting the optimized and updated reconstructed image to complete the image reconstruction; otherwise, adjusting the regularization parameters, and entering S4 to perform the next iteration reconstruction until the convergence condition is satisfied.
The target object of the present embodiment may be, for example, an in-service carbon fiber composite core wire, and during CT scanning detection, since the in-service wire itself cannot rotate, the condition of industrial CT complete scanning (relative rotation angle is greater than 180 ° + fan angle) cannot be satisfied, and a finite angle (relative rotation angle is less than 180 °) CT scanning mode must be adopted for detection.
This embodiment utilizes image gradients L0Norm regularization eliminates finite angle artifacts, effectively restores image details, and reconstructs the image clearly with high quality.
Optionally, the projection data of the target object is acquired, and the specific implementation manner of establishing the projection data set may be:
and (3) carrying out multi-angle limited angle scanning on the target object by using a cone-beam X ray emitted by the ray source to obtain projection data. The projection data is the logarithm of the ratio of the intensities of the input X-rays to the output X-rays, numerically equal to the line integral of the attenuation coefficient of the object of interest along the ray direction.
In the embodiment, an equiangular scanning mode with better data uniformity is adopted to obtain the projection values of each X ray at different angles, so as to form a projection data set. For example, a scan graduation of 300 is set, i.e., the source and detector are projected every 0.3 ° over the calculated travel segment, which requires a total of 300 images to be acquired.
Optionally, the implementation manner of obtaining the image to be reconstructed according to the projection data set is as follows:
in this embodiment, the projection data is initially reconstructed by using an FBP algorithm to obtain an image to be reconstructed, where the image to be reconstructed is a digital image data matrix representation mode, that is, pixel data of a grayscale image.
Optionally, the present embodiment introduces L in dependence on the projection data set and the image to be reconstructed0Norm regularization term, set up L0The norm regularization target optimization equation is specifically realized as follows:
the target optimization equation established in this embodiment is:
wherein X' is the reconstructed image after optimization, A is a system projection matrix, P is a projection data set, X is the image to be reconstructed,
l being image gradients0Norm regularization term, λ0Is a regularization parameter.
The projection matrix A of the system is obtained under the mode that the projection rays are fan-shaped and equally spaced.
Optionally, the iterative operation is performed on the target optimization equation through an SART reconstruction algorithm, and the specific implementation of the reconstructed image is as follows:
the iterative operation of the objective optimization equation is calculated in two parts:
for the
Partial solution adopts a traditional SART iterative algorithm, and the expression is as follows:
wherein, Xj (k+1)Representing a reconstructed image updated by the (k + 1) th iteration, wherein k represents the iteration number;
Xj (k)a reconstructed image representing a kth iterative update;
i represents the number of rays, i is more than or equal to 1 and less than or equal to M, j represents the pixel number when the projection data is estimated, and j is more than or equal to 1 and less than or equal to N;
pian estimate representing an ith ray projection;
aijrepresenting the weight of the estimated ith ray to the jth pixel;
n represents a pixel number at the time of measurement and calculation of actual projection data;
ainis a rightA weight factor representing a contribution of the nth pixel to the projection value of the ith ray;
lambda is relaxation factor, 0 < lambda < 2;
Iθis a set of projection indices at the projection angle theta.
wherein, # { } is a count operator,
indicates that the condition is satisfied
The number of reconstruction points q of (2),
the gradient components in the x-direction and y-direction at the reconstruction point q, respectively.
Optionally, L is performed on the reconstructed image gradients0The specific implementation of the minimized norm operation to obtain the optimized and updated reconstructed image is as follows:
the embodiment pair
And part of the solution is carried out by adopting an approximate processing mode, namely:
introducing auxiliary variables corresponding to gradient components in the x direction and the y direction at a reconstruction point q to the equation to be solved, and then decomposing the auxiliary variables into two subproblems for solving, wherein the method specifically comprises the following steps:
sub-problem 1: calculating X, and the corresponding solving function is as follows:
sub-problem 2: (h, v) is calculated, and the corresponding solving function is as follows:
the solution result of sub-problem 1 is:
the solution result of sub-problem 2 is:
wherein β is the gradient control parameter, λ is the relaxation factor, t represents the solution L0Number of cycles of norm, XqFor optimizing the updated reconstructed image at reconstruction point q, IqTo reconstruct the input image at point q, F (-) represents the fast fourier transform,
gradient components in the x direction and the y direction at a reconstruction point q are respectively shown, h and v respectively represent auxiliary variables corresponding to the gradient components in the x direction and the y direction of a reconstructed image, hqAnd vqAre respectively as
The corresponding auxiliary variable, represents the complex conjugate.
Further optionally, judging whether the reconstructed image meets an iterative convergence condition, if so, outputting an optimized and updated reconstructed image, and finishing image reconstruction; otherwise, adjusting the regularization parameters, and entering S3 to perform the next iteration reconstruction until the convergence condition is satisfied.
In order to verify the effectiveness and stability of the reconstruction method, the limited angle CT scanning ranges of 0,100 degrees, 0,110 degrees, 0,120 degrees, 0,130 degrees, 0,140 degrees and 0,150 degrees are respectively selected. The number of iterations is set to 100, the number of detector units is 1024, the unit size is 0.2mm, the distance from the X-ray source to the center of rotation is 356.9mm, and the distance from the X-ray source to the detector is 800 mm.
Using SART, TV regularization and gradient L, respectively0The norm regularization method performs image reconstruction on the projection data, and the reconstructed image and a partial enlarged image thereof are respectively shown in fig. 3, fig. 4, and fig. 5. As can be seen, the reconstructed image of the SART method is blurred and there are severe limited angle artifacts; compared with an SART algorithm, the TV regularization method improves the finite angle artifact, but cannot completely recover the object details; the method eliminates the finite angle artifact, effectively recovers the image details, and has clear image and high image quality.
Example 2:
the present embodiment provides an image reconstruction system for limited angle CT scanning, including:
the data acquisition module is used for acquiring projection data of the CT scanning image and establishing a projection data set;
the initialization module is used for obtaining initialization parameters and an image to be reconstructed according to the projection data set;
an optimization objective establishing module for introducing L a projection data set and an image to be reconstructed0Norm regularization term, set up L0Normalizing the target optimization equation by using a norm;
the reconstructed image module is used for carrying out iterative operation on the target optimization equation through an SART reconstruction algorithm to obtain a reconstructed image;
a reconstructed image optimization module L for calculating a gradient of the reconstructed image0Norm, L for the reconstructed image gradient0Performing minimization operation on the norm to obtain an optimized and updated reconstructed image;
the convergence judging module is used for judging whether the reconstructed image meets an iterative convergence condition, and if so, outputting an optimized and updated reconstructed image to complete image reconstruction; otherwise, adjusting the regularization parameters, and performing the next iteration reconstruction until the convergence condition is met.
The specific implementation method of image reconstruction in this embodiment is the same as that in embodiment 1.
Example 3:
the embodiment provides a finite angle CT scanning device, which comprises a driving device, a ray source component, a detector component and an arc-shaped support, wherein the ray source component and the detector component are arranged on the inner side of the arc-shaped support and are arranged oppositely, and the arc-shaped support is used for ensuring the arc-shaped movement track of the ray source component and the detector component;
the driving device is used for driving the ray source assembly and the detector assembly to perform scanning motion around a target object along a preset arc motion track, the angle range of the scanning motion is within 180 degrees, and finite-angle CT scanning is performed through the X-ray source, so that DR (Digital Radiography) images of the target object are collected at multiple angles.
Optionally, as shown in fig. 2, the radiation source assembly of the present embodiment includes a cone-beam X-ray source 7, and the detector assembly includes a flat panel detector 8.
The cone-beam X-ray source 7 and the flat panel detector 8 are arranged oppositely, the target object 9 is positioned between the X-ray source 7 and the flat panel detector 8, the CT scanning device of the embodiment is started according to the received CT control signal, and the cone-beam X-ray source 7 and the flat panel detector 8 synchronously move around the target object 9 along an arc-shaped movement track to realize finite angle CT scanning.
The cone-beam X-ray source 7 emits cone-beam X-rays, which penetrate through the target object 9 and then enter the flat panel detector 8, the flat panel detector 8 receives the radiation, generates an electrical signal proportional to the radiation intensity, and obtains projection data related to the target object for image reconstruction as described in embodiment 1.
In the CT scanning process, the cone-beam X-ray source 7 and the flat panel detector 8 realize synchronous movement under the control of the driving device, the movement angle range is limited within 180 degrees, and DR images of the target object 9 are collected at a plurality of angles. The target object 9 shown in fig. 2 is a carbon fiber composite core wire.
The initial image obtained by CT scan inspection of a cone-beam X-ray source is a two-dimensional projection that is transformed into a three-dimensional data set by image reconstruction. In this embodiment, the reconstruction algorithm using the cone-beam X-ray source CT can significantly reduce the artifact of the two-dimensional reconstructed three-dimensional image, and the reconstruction processing of data can be completed within a time of <20s by using the cone-beam X-ray source CT through a common computer. In addition, the spatial resolution of the cone-beam X-ray source CT is higher and far exceeds that of other types of CT, and researches show that the spatial resolution range of the cone-beam X-ray source CT is 0.076-0.4 mm.
Optionally, the radiation source assembly further includes a first supporting plate 10, the detector assembly further includes a second supporting plate 11, the first supporting plate 10 is used for fixing the cone-beam X-ray source 7, the second supporting plate 11 is used for fixing the flat panel detector 8, and the first supporting plate 10 and the second supporting plate 11 are both installed inside the arc-shaped support. By arranging the first supporting plate 10 and the second supporting plate 11, the cone-beam source 7 and the flat panel detector 8 can be better fixed, and the cone-beam source 7 and the flat panel detector 8 can be more conveniently installed on the arc-shaped bracket.
Optionally, a feasible implementation manner of the scanning motion of the radiation source assembly and the detector assembly around the target object along the predetermined arc-shaped motion track is that, as shown in fig. 2, the radiation source assembly and the detector assembly include a fixed frame, the driving device is installed on the fixed frame, a through hole in clearance fit with the arc-shaped support 12 is formed in the fixed frame, the driving device is configured to drive the arc-shaped support 12 to rotate in the vertical direction along the through hole, and the arc-shaped support 12 drives the cone-beam X-ray source 7 and the flat panel detector 8 to scan around the target object along the predetermined arc-shaped motion track while rotating.
As shown in fig. 2, the driving device in this embodiment includes a first motor, and the first motor is configured to drive the arc-shaped support to rotate in the vertical direction, so as to drive the cone-beam X-ray source 7 and the flat panel detector 8 to scan around the arc-shaped trajectory of the target object.
As a further embodiment, the driving device further comprises a second motor, a third motor and a fourth motor, wherein the second motor is used for controlling the horizontal rotation of the arc-shaped bracket; the third motor and the fourth motor respectively control the left, right and front and back movement of the arc-shaped support in the horizontal direction.
By arranging the second motor, the third motor and the fourth motor, scanning detection of different directions of the target object 9 can be realized.
As a possible implementation manner, as shown in fig. 2, the fixing frame of the present embodiment includes a first moving platform 1, a second moving platform 5, a first fixing block 4, and a second fixing block 6.
The second motor and the third motor are respectively used for driving the first moving platform 1 and the second moving platform 5, slide rails in the front-back direction are arranged on the second moving platform 5, slide grooves matched with the slide rails in the front-back direction of the second moving platform 5 are formed in the lower surface of the first moving platform 1, and the lower surface of the second moving platform 5 is fixedly installed in a matched mode with the first fixing block 4.
The upper surface of first moving platform 1 is provided with the slide rail of left right direction, just the below of second fixed block 6 seted up with the slide rail matched with spout of left right direction, just vertical pivot 3 through fourth motor drive is installed to the top of second fixed block 6, be provided with on the first fixed block 4 through first motor drive's horizontal rotating shaft 2.
Under the drive of the third motor, the second moving platform 5 can move back and forth relative to the first moving platform 1, so that the arc-shaped support 12 is driven to move back and forth. Under the drive of the second motor, the first moving platform 1 can move left and right relative to the sliding block, so that the arc-shaped support 12 is driven to move left and right.
Example 4
The present embodiment provides a limited angle CT scanning apparatus, and the present embodiment is different from embodiment 3 in that: an implementation mode of driving a ray source assembly and a detector assembly to perform scanning motion around a target object along a preset arc motion track specifically comprises the following steps:
the inboard arc track of installing with arc support assorted of arc support, ray source subassembly and detector subassembly are installed on the arc track, just ray source subassembly and detector subassembly can follow arc track relative motion.
The arc-shaped track of the embodiment includes a first arc-shaped track and a second arc-shaped track, and the first supporting plate 10 is installed on the first arc-shaped track and can move along the first arc-shaped track; the second supporting plate 11 is installed on the second arc-shaped track and can move along the second arc-shaped track. In this embodiment, the cone-beam X-ray source 7 runs along a first arc track through the first supporting plate 10, the running track is an arc line, the flat panel detector 8 runs along a second arc track through the second supporting plate 11, and the running track is an arc line.
The driving device of this embodiment further includes two driving motors for driving the first supporting plate 10 and the second supporting plate 11 to move along the first arc-shaped track and the second arc-shaped track, so as to realize the synchronous relative movement of the cone-beam X-ray source 7 and the flat panel detector 8 in the arc-shaped tracks.
Example 5
The present embodiments provide a computer-readable storage medium having stored thereon a computer program which, when being executed by a processor, is operative to carry out a method of image reconstruction for limited angle CT scanning.
Please refer to embodiment 1 for an image reconstruction method of limited angle CT scan in this embodiment.
In light of the foregoing description of the preferred embodiments according to the present application, it is to be understood that various changes and modifications may be made without departing from the spirit and scope of the invention. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of the claims.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Claims (10)
1. An image reconstruction method for limited angle CT scanning, comprising:
s1, acquiring projection data of the target object and establishing a projection data set;
s2, obtaining an image to be reconstructed according to the projection data set;
s3, introducing L according to the projection data set and the image to be reconstructed0Norm regularization term, set up L0Normalizing the target optimization equation by using a norm;
s4, carrying out iterative operation on the target optimization equation through an SART reconstruction algorithm to obtain a reconstructed image;
s5, conducting L on the reconstructed image gradient0Performing minimization operation on the norm to obtain an optimized and updated reconstructed image;
s6, judging whether the reconstructed image meets the iterative convergence condition, if so, outputting the optimized and updated reconstructed image, and finishing the image reconstruction; otherwise, adjusting the regularization parameters, and entering S4 to perform the next iteration reconstruction until the convergence condition is satisfied.
2. The image reconstruction method for limited angle CT scan of claim 1, wherein said L0The norm regularization target optimization equation is as follows:
wherein, A is a system projection matrix, P is a projection data set, X is an image to be reconstructed, X' is an optimized output reconstructed image, and lambda0In order to regularize the parameters of the process,
is L of the image X gradient0Norm regularization term.
3. Image reconstruction method for limited angle CT scanning according to claim 2, characterized in that for
In part, using SART reconstructionThe method performs iterative operations.
4. Image reconstruction method for limited angle CT scan according to claim 2, characterized in that L is performed on the reconstructed image gradients0The norm minimization operation method comprises the following steps:
to pair
Partial minimization is solved by adopting an approximate processing mode, namely:
wherein β is gradient control parameter, λ is relaxation factor, and X isqFor optimizing the updated reconstructed image at reconstruction point q, IqTo reconstruct the input image at point q,
gradient components in the x direction and the y direction at a reconstruction point q respectively, h and v represent auxiliary variables corresponding to the gradient components of the reconstructed image in the x direction and the y direction respectively, hqAnd vqAre respectively as
The corresponding auxiliary variable, represents the complex conjugate.
5. An image reconstruction system for a limited angle CT scan, comprising:
the data acquisition module is used for establishing a projection data set according to the projection data of the target object;
the initialization module is used for obtaining an image to be reconstructed according to the projection data set;
optimization target establishing moduleFor introducing L from the projection data set and the image to be reconstructed0Norm regularization term, set up L0Normalizing the target optimization equation by using a norm;
the reconstructed image module is used for carrying out iterative operation on the target optimization equation through an SART reconstruction algorithm to obtain a reconstructed image;
a reconstructed image optimization module for L performing on the reconstructed image gradients0Performing minimization operation on the norm to obtain an optimized and updated reconstructed image;
the convergence judging module is used for judging whether the reconstructed image meets an iterative convergence condition, if so, outputting an optimized and updated reconstructed image and finishing image reconstruction; otherwise, adjusting the regularization parameters, and performing the next iteration reconstruction until the convergence condition is met.
6. A storage medium having stored thereon a computer program for implementing the image reconstruction method according to any one of claims 1 to 4 when being executed by a processor.
7. The device for finite angle CT scanning is characterized by comprising a ray source component, a detector component and an arc-shaped bracket, wherein the ray source component and the detector component are arranged on the inner side of the arc-shaped bracket and are arranged oppositely, and the arc-shaped bracket is used for ensuring the arc-shaped movement track of the ray source component and the detector component;
the X-ray CT scanning device is characterized by further comprising a driving device, wherein the driving device is used for driving the ray source assembly and the detector assembly to perform scanning motion around a target object along a preset arc-shaped motion track, the angle range of the scanning motion is within 180 degrees, limited-angle CT scanning is performed through the X-ray source, and DR images of the target object are collected at multiple angles.
8. The limited angle CT scanning apparatus of claim 7, further comprising a fixing frame, wherein the driving device is mounted on the fixing frame, and the fixing frame is provided with a through hole in clearance fit with the arc-shaped support, and the driving device is configured to drive the arc-shaped support to rotate in a vertical direction along the through hole.
9. The apparatus of claim 7, wherein the arc-shaped support has an arc-shaped track mounted inside thereof, the radiation source assembly and the detector assembly are mounted on the arc-shaped track, and the radiation source assembly and the detector assembly are relatively movable along the arc-shaped track.
10. Apparatus for a limited angle CT scan according to claim 8 or 9, wherein the radiation source assembly comprises a cone beam X-ray source and the detector assembly comprises a flat panel detector.
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