CN107997780A - A kind of Cone-Beam CT instant scanning device and method for reconstructing - Google Patents
A kind of Cone-Beam CT instant scanning device and method for reconstructing Download PDFInfo
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- A61B6/02—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
- A61B6/03—Computerised tomographs
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- A—HUMAN NECESSITIES
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- 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
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- A61B6/42—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for detecting radiation specially adapted for radiation diagnosis
- A61B6/4208—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment with arrangements for detecting radiation specially adapted for radiation diagnosis characterised by using a particular type of detector
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- A—HUMAN NECESSITIES
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- A61B6/52—Devices using data or image processing specially adapted for radiation diagnosis
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Abstract
The present invention relates to a kind of Cone-Beam CT instant scanning device and method for reconstructing, comprise the following steps：S1：Objective table is placed in scanning means, scanned object is placed on objective table, starts scanning means；S2：Start all high speed flat panel detectors, the x-ray focus in scanning means are scanned object, and the x-ray focus are closed immediately after collecting the data for projection of object；S3：According to all x-ray focus of specified order traversal, data for projection of the current time object under scanning means is obtained；S4 repeat steps S2, S3, obtain data for projection of the subsequent time scanned object under scanning means, and close Cone-Beam CT instant scanning device；S5：The object at above-mentioned each moment is rebuild using based on the cone-beam CT reconstruction algorithm of L0 regularizations, the three-dimensional voxel of each moment scanned object is obtained and faultage image and shows.Apparatus of the present invention can be completed high without any mechanical movement, temporal resolution in scanning and scanning process to object as quick as thought.
Description
Technical Field
The invention belongs to the technical field of biomedical images and nondestructive testing, and relates to a cone beam CT instantaneous scanning device and a reconstruction method.
Background
The CT imaging technology is successfully applied to the fields of biomedical imaging and nondestructive testing and has been greatly developed. In order to meet the detection requirements of objects with different structures and sizes, scanning modes and reconstruction algorithms of different strategies are developed. Most scanning modes scan a static object, the object only rotates or moves in a translation mode in the scanning process, and the size, shape and internal structure of the object cannot change along with time; the reconstructed image with high spatial resolution can be obtained according to the scanning mode and the reconstruction algorithm of the static object, and the actual requirement can be met.
In the field of industrial nondestructive testing, there are many situations where the object to be tested is in dynamic change. For example: due to the action of external force, the defects in the material or the workpiece can be converted from a static state into an obvious motion state, and simultaneously, the elastic energy is released and transmitted in the form of stress waves. The acoustic emission nondestructive detection technology can provide the activity information of the defect when the object is stressed. Firstly, the acoustic emission detection must have the action of external force to make the material or workpiece sound; on the other hand, due to the action of external force, the internal structure of the material or the workpiece changes, such as crystal structure change, crack propagation, and the like, and sound is generated during the change of the internal structure of the material or the workpiece. Thus, acoustic emission inspection is a non-destructive inspection of the internal structure or defect of a material or workpiece during dynamic changes.
In the biomedical imaging field, common diseases such as craniocerebral trauma, encephalitis, intracranial tumors and the like have high lethality rate due to severe encephaledema and increased intracranial pressure in the course of the diseases. For patients with critical and rapid disease conditions, it is very necessary to monitor the dynamic change of the disease focus, judge the disease evolution in time and adjust the treatment scheme. Similarly, imaging studies in small animals play an important role in human understanding of disease, drug research, clinical evaluation, and the like. However, physiological movement of small animals is a critical issue faced by conventional imaging modalities. Because the traditional CT imaging technology needs a long time to obtain the projection data of the scanned object, the time resolution is low, the projection data are seriously inconsistent, and the traditional reconstruction algorithm is not strictly applicable any more and cannot meet the actual requirements. To solve the problem of low temporal resolution, high-speed CT scanning and imaging systems have been developed. R.a.robb and e.a.hoffman et al, in 1983, reported a fast scanning device in the institute of electrical and electronics engineers to scan organs such as heart and lung; the device installs a plurality of ray sources equidistance on a semicircle, and a plurality of detection device that install at the ray source facade are used for recording the projection data that each ray source corresponds, obtain the projection data of scanned object under a plurality of angles in the time of extremely short, and time resolution is high, because all ray sources are installed on same circumference, and scanning device structure is complicated, and is with high costs. S.j.schambach et al, in 2009, proposed a multi-focal radiation source and a digital flat panel detector for CT angiography of an anesthetized mouse, wherein during the acquisition of projection data, the mouse continuously rotates at a constant speed for 180 degrees within 40 seconds to obtain 1200 pieces of projection data, and an FBP (Filtered diagnosis) algorithm is used to reconstruct an image, and the method has a long scanning time and a low time resolution. Baodong Liu et al propose an overspeed micro-focus CT system for two-dimensional CT imaging of dynamic small animals in 2011 in medical and biophysical magazines, wherein the system comprises a plurality of ray source and detector pairs, and in order to obtain more projection data, each ray source and detector pair only need to rotate by a small angle; respectively reconstructing by adopting TVM-SD (Total Variation Minimization with the stereotest delete) and TDM-STF (Total Difference Minimization with Soft-Threshold filtration) algorithms to obtain two-dimensional sectional images of the region of interest; as the number of pairs of radiation sources and detectors increases, the angle of rotation required for each pair of radiation source and detector decreases, the scanning speed is faster, and the time resolution is higher.
Disclosure of Invention
In view of this, the present invention provides a cone-beam CT instantaneous scanning device and a reconstruction method, which can rapidly complete scanning of an object, and have no mechanical motion and high time resolution in the scanning process.
In order to achieve the purpose, the invention provides the following technical scheme:
a cone beam CT instantaneous scanning device is in a square shape and comprises 12X-ray sources based on carbon nano tubes, wherein the X-ray sources are respectively arranged on 12 edges of the scanning device;
each X-ray source integrates a plurality of X-ray focuses, and all the X-ray focuses are aligned to the center of the scanning device;
the scanning device also comprises a plurality of high-speed flat panel detectors which are respectively arranged on six surfaces of the scanning device, each X-ray source and four corresponding detectors form a subsystem of the scanning device, and the field radius gamma determined by each subsystem is adjusted according to the size of the scanned object.
Furthermore, one of the high-speed flat panel detectors is detachable, so that an object can be conveniently placed in the scanning device.
Furthermore, twelve X-ray sources in the scanning device are divided into three groups, each group comprises four X-ray sources, the three groups of X-ray sources are respectively positioned on three planes which are vertical to each other, and the common point of the three planes is the center O of a cube where the scanning device is positioned.
A cone beam CT instantaneous scanning reconstruction method comprises the following steps:
s1: placing an object stage in a scanning device, locating the object stage in the central area of a cube, placing a scanned object on the object stage, and starting the scanning device;
s2: starting all the high-speed flat panel detectors, scanning an object by an X-ray focus in a scanning device, and immediately closing the X-ray focus after acquiring projection data of the object;
s3: traversing all X-ray focuses according to a specified sequence to obtain projection data of the object under the scanning device at the current moment;
s4: repeating the steps S2 and S3 to obtain the projection data of the scanned object under the scanning device at the next moment, and closing the cone beam CT instantaneous scanning device;
s5: and reconstructing the object at each moment by adopting a cone-beam CT reconstruction algorithm based on L0 regularization, and obtaining and displaying three-dimensional voxels and tomographic images of the scanned object at each moment.
Further, in step S5, reconstructing the object at each time by using a cone-beam CT reconstruction algorithm based on L0 regularization specifically includes:
s51: grouping the projection data corresponding to the same group of X-ray sources into one group to obtain three groups of projection data, and recording the three groups of projection data as g xoy ,g xoz ,g yoz Respectively representing X-ray focal points in an XOY plane, an XOZ plane and a YOZ plane and projection data groups obtained by corresponding detectors;
s52: image reconstruction by using cone-beam CT iterative reconstruction algorithm based on L0 regularization
Wherein, f is an image to be reconstructed,g is projection data under a cone beam CT instantaneous scanning device, A is an M multiplied by N matrix, N is the number of voxels in a reconstructed image f, M is the number of rays passing through a scanned object in each direction, | | · | 2 Represents the L2 norm of the vector, | | · | | non-woven phosphor 0 L0 norm representing the vector, W represents the wavelet transform, λ and γ are parameters of the reconstruction model,
introducing an auxiliary variable α such that α = Wf converts (1) to:
wherein τ is a non-zero parameter, v is a Lagrangian multiplier,
decoupling the L2 and L0 portions of the objective function in (2),
v n+1 ＝v n -(α n+1 -Wf n+1 ) (5)
where t is a parameter in the objective function, f n+1 For iterative reconstruction of the reconstructed image of step n +1, α n+1 Reconstructing an image f for the step (n + 1) of the iterative reconstruction n+1 The wavelet coefficients of (a) are calculated,
the step (3) is simplified and arranged into,
wherein the content of the first and second substances,
further, step S52 specifically includes:
s521: initializing parameters in an iterative reconstruction algorithm based on L0 regularization: given iterative reconstruction algorithm parameter ε 1 ，λ＞0，t＞0，γ＝1，f 1 ＝0，v 1 ＝α 1 ＝Wf 1 ，ε＝1，ω＝1，n＝1，ε 1 Is the relative error limit of the difference of the two adjacent iteration images relative to the current image, epsilon is the relative error of the difference of the two adjacent iteration images relative to the current image, omega is a relaxation factor, N is the current iteration number, N is the current iteration number ite The maximum iteration times of the iterative reconstruction algorithm are set;
s522: reconstructing by adopting SART to obtain an approximate image:
wherein the content of the first and second substances,reconstructing the reconstructed image f of step n for iteration n The (j) th component of (a),is f n Reconstructed image after one SARTThe jth component of (a);
s523: applying PCM algorithm to the approximate image obtained in step S522Updating to obtain approximate solution f of formula (6) n+1 ，
Wherein f is n+1 Is an approximate solution to equation (6),
s524: calculating formula (4) by adopting an IHT algorithm to obtain a solution of formula (4),
wherein the content of the first and second substances,hard threshold operator H η (x) Is defined as:eta is a threshold value, and the value is positive;
s525: obtaining a reconstructed image f of the iterative reconstruction step n +1 according to the steps S521-S524 n+1 Sum wavelet coefficient alpha n+1 Calculating an updated Lagrange multiplier v n+1 ，
v n+1 ＝v n -(α n+1 -Wf n+1 )
Updating parameters epsilon and gamma of iterative reconstruction algorithm n+1 And n, wherein:
if ε > ε 1 And N is less than N ite If true, return to step S522, otherwise output f n+1 。
Further, the PCM algorithm process is as follows:
s5231: order toInitializing a PCM algorithm parameter beta 0 ＝1,ν∈(0,1),f 0 ∈Ω,k＝0；
S5232: computing
When r is k When nu is established, executing:
when r is k When nu is not satisfied, executing:
if r k < 0.4, then beta k ＝1.5β k ；
Wherein, P Ω [·]Representing the projection operator, beta, onto the subspace omega k ,r k V is a parameter in the PCM algorithm, K is the iteration number of the PCM algorithm, and the PCM iteration is terminated when the maximum iteration number K of the PCM algorithm is reached;
s5233: let beta k+1 ＝β k K = k +1; if K < K, S5232 is performed, otherwise the iteration terminates.
The invention has the beneficial effects that: the cone beam CT instantaneous scanning device adopts the X-ray source based on the carbon nano tube and the high-speed flat panel detector, has simple structure, can integrate a plurality of X-ray focuses in the X-ray source based on the carbon nano tube, can very quickly complete the scanning of an object, has no mechanical motion in the scanning process, and has high time resolution.
Drawings
In order to make the object, technical scheme and beneficial effect of the invention more clear, the invention provides the following drawings for explanation:
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a schematic view of a radiation source distribution of the scanning device of the present invention;
FIG. 3 is a schematic view of a scanning device subsystem according to the present invention;
FIG. 4 is a schematic diagram of a virtual detector corresponding to the device subsystem of the present invention.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
The working process of the cone beam CT instantaneous scanning device is shown in figure 1; the shape of the cone beam CT instantaneous scanning device is a cube; the cone-beam CT instantaneous scanning device includes twelve carbon nanotube-based X-ray sources, as shown in fig. 2, which are respectively denoted as n1, n2, n3, n4, n5, n6, n7, n8, n9, n10, n11, n12, the X-ray sources are respectively installed on twelve sides of a cube, and a plurality of X-ray focuses can be integrated in each X-ray source, which takes the simplest case as an example: there is only one X-ray focal spot within each X-ray source. All the X-ray focuses are always aligned with the center O of the scanning device; the cone-beam CT instantaneous scanning device includes six high-speed flat panel detectors, which are respectively denoted as pl1, pl2, pl3, pl4, pl5, pl6 as shown in fig. 2, and the six flat panel detectors constitute six faces of the cone-beam CT instantaneous scanning device. The flat panel detector pl1 is designed to be detachable, so that an object can be conveniently placed in the cone-beam CT instantaneous scanning device. The cone-shaped X-ray emitted from each X-ray focus can reach four detectors, as shown in fig. 3, and the X-ray focus n7 and the corresponding four detectors pl1, pl3, pl5, pl6 form a subsystem of the cone-beam CT instantaneous scanning device; the radius gamma of the field of view determined by each subsystem is adjusted according to the size of the scanned object; the cone beam CT instantaneous scanning device is started to scan the rapidly-changing object, the reconstruction algorithm based on L0 regularization is adopted to reconstruct the object, and the working process comprises the following steps:
step 1) placing an object stage in a cone beam CT instantaneous scanning device, locating the object stage in the central area of a cube, placing a scanned object on the object stage, and starting the cone beam CT instantaneous scanning device;
step 2) starting all high-speed detectors, exciting an X-ray focus in a cone-beam CT instantaneous scanning device to scan an object, and immediately closing the X-ray focus after acquiring projection data of the object;
step 3) traversing all X-ray focuses according to a certain sequence according to the mode in the step 2) to obtain the projection data of the object under the cone beam CT instantaneous scanning device at the current moment; twelve ray sources in the cone beam CT instantaneous scanning device are divided into three groups, the three groups of ray sources are respectively positioned on three planes which are vertical to each other, and as shown in figure 2, the three groups of ray sources are respectively marked as an XOY plane, an XOZ plane and a YOZ plane, wherein X-ray focuses n5, n6, n7 and n8 are positioned on the XOY plane, X-ray focuses n1, n3, n9 and n11 are positioned on the XOZ plane, X-ray focuses n2, n4, n10 and n12 are positioned on the YOZ plane, and the common point of the three planes is the center O of a cube where the cone beam CT instantaneous scanning device is positioned; taking an XOY plane as an example, the subsystems where four X-ray focuses n5, n6, n7 and n8 in the XOY plane are located obtain projection data of an object in four directions; as shown in fig. 4, according to the geometry of a cube, irregular projection data obtained by a subsystem in which each ray source is located in the XOY plane is converted onto a corresponding virtual flat panel detector pl; the L0 regularization based cone-beam CT reconstruction algorithm utilizes projection data on a virtual flat panel detector.
Step 4) repeating the step 2) and the step 3) to obtain the projection data of the scanned object under the cone beam CT instantaneous scanning device at the next moment until the cone beam CT instantaneous scanning device is closed;
step 5), adopting a cone beam CT reconstruction algorithm based on L0 regularization to reconstruct the object at each moment, and obtaining and displaying three-dimensional voxels and tomographic images of the scanned object at each moment; the image reconstruction at each moment has the same process, and the method comprises the following steps:
step 5-1) grouping the projection data corresponding to the same group of X-ray sources into one group to obtain three groups of projection data, and recording the three groups of projection data as g xoy ,g xoz ,g yoz Respectively representing projection data obtained by subsystems where X-ray focuses in an XOY plane, an XOZ plane and a YOZ plane are located;
step 5-2) image reconstruction is carried out by adopting a cone beam CT iterative reconstruction algorithm based on L0 regularization, and an image reconstruction model is as follows:
wherein the content of the first and second substances,f is an image to be reconstructed, N voxels are arranged in the image to be reconstructed f, and the three-dimensional volume data are arranged into vectors point by point, so that a reconstructed image f = (f) 1 ,f 2 ,…,f N ) T (ii) a g is projection data of cone beam CT instantaneous scanner, M rays pass through the scanned object at each angle, and the projection data are arranged point by point to form vector so that g = (g) 1 ，g 2 ,…,g M ) T (ii) a The projection data g are represented in three groups: g xoy ，g xoz ，g yo z, three groups of classifications corresponding to ray sources; omega is N-dimensional vector space R N A convex set of (1); a is a projection matrix of the cone beam CT instantaneous scanning device, A is an M multiplied by N matrix, and A is set i The ith row, a, of the projection matrix A i,j Is the element of ith row and j column of the matrix A; assuming that the width of the X-ray is zero, a i,j Representing the length of the intersection of the ith ray with the jth voxel of the image; i | · | purple wind 2 Represents the L2 norm of the vector, | | · | | non-woven phosphor 0 Representing the norm of the vector L0, W representing the wavelet transform, and λ and γ are parameters of the reconstruction model. Introducing an auxiliary variable a such that a = Wf, and penalizing the equation translates problem (1) into,
decoupling the L2 and L0 parts of the target function in the step (2) by adopting a splitting technology to obtain three subproblems, and alternately executing the following steps to obtain a reconstructed image:
sub-problem 1:
sub-problem 2:
sub-problem 3: v. of n+1 ＝v n -(α n+1 -Wf n+1 ) (5)
Where t is a parameter in the objective function, f n+1 For iterative reconstruction of the reconstructed image of step n +1, α n+1 Reconstructing an image f for the step (n + 1) of the iterative reconstruction n+1 V is a Lagrange multiplier, v is n And reconstructing the Lagrangian multiplier of the nth step for iteration.
Note the bookTheta (f) at point f in the N-dimensional vector subspace omega n The linear approximation function of (a) is:where tau is a non-zero parameter,<·，·>, represents the inner product of the vectors,
θ' (f) is the derivative of θ (f), approximating subproblem 1 as:
further formulation finishing, sub-problem 1 is approximately:
wherein, the first and the second end of the pipe are connected with each other,the image reconstruction is carried out by adopting a cone-beam CT iterative reconstruction algorithm based on L0 regularization, and the method comprises the following steps:
step 5-2-1) initializing parameters in the cone beam CT iterative reconstruction algorithm based on L0 regularization, and giving the parameters of the iterative reconstruction algorithm: epsilon 1 ，λ＞0，t＞0，γ＝1，f 1 ＝0，ε＝1，ω＝1，v 1 ＝α 1 ＝Wf 1 ,n＝1，ε 1 Is the relative error limit of the difference of the two adjacent iteration images relative to the current image, epsilon is the relative error of the difference of the two adjacent iteration images relative to the current image, omega is a relaxation factor, N is the current iteration number, N is the current iteration number ite The maximum iteration times of the iterative reconstruction algorithm are set;
step 5-2-2) obtaining an approximate image by adopting SART:
wherein the content of the first and second substances,reconstructing the reconstructed image f of step n for iteration n The (j) th component of (a),is f n Reconstructed image after one-time SART updatingThe jth component of (a);
step (ii) of5-2-3) adopting PCM algorithm to approximate the image obtained in the step 5-2-2)Updating to obtain approximate solution f of subproblem 1 n+1 ；
Order toThe implementation process of the PCM algorithm is as follows:
1. initializing a PCM algorithm parameter beta 0 ＝1,ν∈(0,1),f 0 ∈Ω,k＝0；
2、
When r is k When nu is established, executing:
when r is k When nu is not satisfied, executing:
if r k < 0.4, then beta k ＝1.5β k ；
3. Let beta k+1 ＝β k K = k +1; if K < K, S5232 is performed, otherwise the iteration terminates.
Wherein, P Ω [·]The projection operator, β, onto the subspace Ω k ,r k V is a parameter in the PCM algorithm; k is the current iteration number of the PCM algorithm; and terminating the PCM iteration when the maximum iteration number K of the PCM algorithm is reached.
And 5-2-4) solving the subproblem 2 by adopting an IHT algorithm, wherein the minimum solution of the subproblem 2 is obtained by:
wherein the content of the first and second substances,hard threshold operator H η (x) Is defined as:η is a threshold and takes a positive value.
Step 5-2-5) the step 5-2-1), the step 5-2-2), the step 5-2-3) and the step 5-2-4) are used for solving the sub-problem 1 and the sub-problem 2 to obtain a reconstructed image f of the step n +1 of iterative reconstruction n+1 Sum wavelet coefficient alpha n+1 Finally solving the subproblem 3 and updating the Lagrange multiplier v n+1 ：
v n+1 ＝v n -(α n+1 -Wf n+1 ).
Updating iterative reconstruction algorithm parameters epsilon and gamma n+1 And n, wherein:
when ε > ε 1 And N is less than N ite When the result is right, the step 5-2-2) is returned, otherwise, f is output n+1 。
The cone-beam CT iterative reconstruction algorithm based on L0 regularization is summarized as follows:
1. performing step 5-2-1);
2. when ε > ε 1 And N is less than N ite When true, the following steps are repeated:
when epsilon＞ε 1 And N < N ite When the two are not completely satisfied, executing step 3;
3. outputting the current reconstructed image f n+1 。
The invention relates to a cone beam CT instantaneous scanning device and a reconstruction method, wherein the cone beam CT instantaneous scanning device adopts an X-ray source and a high-speed flat panel detector based on carbon nano tubes, has a simple structure, can integrate a plurality of X-ray focuses in the X-ray source based on the carbon nano tubes, can extremely quickly complete the scanning of an object, does not have any mechanical motion in the scanning process, and has high time resolution.
Finally, it is noted that the above-mentioned preferred embodiments illustrate rather than limit the invention, and that, although the invention has been described in detail with reference to the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims.
Claims (7)
1. A cone beam CT instantaneous scanning device is characterized in that: the scanning device is in a square shape and comprises 12X-ray sources based on carbon nano tubes, wherein the X-ray sources are respectively arranged on 12 edges of the scanning device;
each X-ray source integrates a plurality of X-ray focuses, and all the X-ray focuses are aligned to the center of the scanning device;
the scanning device also comprises a plurality of high-speed flat panel detectors which are respectively arranged on six surfaces of the scanning device, each X-ray source and four corresponding detectors form a subsystem of the scanning device, and the radius gamma of a view field determined by each subsystem is adjusted according to the size of an object to be scanned.
2. The cone beam CT transient scanning apparatus of claim 1, wherein: one of the high-speed flat panel detectors is detachable, so that an object can be conveniently placed in the scanning device.
3. The cone beam CT transient scanning apparatus of claim 1, wherein: twelve X-ray sources in the scanning device are divided into three groups, each group comprises four X-ray sources, the three groups of X-ray sources are respectively positioned on three planes which are vertical to each other, and the common point of the three planes is the center O of a cube where the scanning device is positioned.
4. A cone beam CT instantaneous scanning reconstruction method is characterized in that: the method comprises the following steps:
s1: placing an object stage in a scanning device, locating the object stage in the central area of a cube, placing a scanned object on the object stage, and starting the scanning device;
s2: starting all the high-speed flat panel detectors, scanning an object by an X-ray focus in a scanning device, and immediately closing the X-ray focus after acquiring projection data of the object;
s3: traversing all X-ray focuses according to a specified sequence to obtain projection data of the object under the scanning device at the current moment;
s4: repeating the steps S2 and S3 to obtain the projection data of the scanned object under the scanning device at the next moment, and closing the cone beam CT instantaneous scanning device;
s5: and reconstructing the object at each moment by adopting a cone-beam CT reconstruction algorithm based on L0 regularization, and obtaining and displaying three-dimensional voxels and tomographic images of the scanned object at each moment.
5. The cone beam CT temporary scanning reconstruction method as claimed in claim 4, characterized in that: in step S5, reconstructing the object at each time by using a cone-beam CT reconstruction algorithm based on L0 regularization specifically includes:
s51: grouping the projection data corresponding to the same group of X-ray sources into one group to obtain three groups of projection data, which are marked as g xoy ,g xoz ,g yoz Respectively representing X-ray focal points in an XOY plane, an XOZ plane and a YOZ plane and projection data groups obtained by corresponding detectors;
s52: image reconstruction by using cone-beam CT iterative reconstruction algorithm based on L0 regularization
Wherein, f is an image to be reconstructed,g is projection data under a cone beam CT instantaneous scanning device, A is an M multiplied by N matrix, N is the number of voxels in a reconstructed image f, M is the number of rays penetrating through a scanned object in each direction, | | · | 2 Represents the L2 norm of the vector, | | · | | non-woven phosphor 0 L0 norm representing the vector, W representing the wavelet transform, λ and γ being parameters of the reconstruction model,
introducing an auxiliary variable α such that α = Wf converts (1) to:
wherein τ is a non-zero parameter, v is a Lagrangian multiplier,
decoupling the L2 and L0 portions of the objective function in (2),
v n+1 ＝v n -(α n+1 -Wf n+1 ) (5)
where t is a parameter in the objective function, f n+1 For iterative reconstruction of the reconstructed image of step n +1, α n+1 Reconstructing an image f for the step n +1 of the iterative reconstruction n+1 The wavelet coefficients of (a) are calculated,
the step (3) is simplified and arranged into,
wherein the content of the first and second substances,
6. the cone beam CT temporary scanning reconstruction method as claimed in claim 5, characterized in that: step S52 specifically includes:
s521: initializing parameters in an iterative reconstruction algorithm based on L0 regularization: given iterative reconstruction algorithm parameter ε 1 ，λ＞0，t＞0，γ＝1，f 1 ＝0，v 1 ＝α 1 ＝Wf 1 ，ε＝1，ω＝1，n＝1，ε 1 Is the relative error limit of the difference of the two adjacent iteration images relative to the current image, epsilon is the relative error of the difference of the two adjacent iteration images relative to the current image, omega is a relaxation factor, N is the current iteration times, N is the relative error of the current image ite The maximum iteration number of the iterative reconstruction algorithm is set;
s522: reconstructing by adopting SART to obtain an approximate image:
wherein the content of the first and second substances,reconstructing the reconstructed image f of step n for iteration n The (j) th component of (a),is f n Reconstructed image after one SARTThe jth component of (a);
s523: applying PCM algorithm to the approximate image obtained in step S522Updating to obtain approximate solution f of formula (6) n +1 ，
Wherein f is n+1 Is an approximate solution to the equation (6),
s524: calculating formula (4) by adopting an IHT algorithm to obtain a solution of formula (4),
wherein, the first and the second end of the pipe are connected with each other,hard threshold operator H η (x) Is defined as:eta is a threshold value, and the value is positive;
s525: obtaining a reconstructed image f of the iterative reconstruction step n +1 according to the steps S521-S524 n+1 Sum wavelet coefficient alpha n+1 Calculating an updated Lagrange multiplier v n+1 ，
v n+1 ＝v n -(α n+1 -Wf n+1 )
Updating parameters epsilon and gamma of iterative reconstruction algorithm n+1 And n, wherein:
if ε > ε 1 And N is less than N ite If true, return to step S522, otherwise output f n+1 。
7. The cone beam CT temporary scanning reconstruction method as claimed in claim 6, characterized in that: the PCM algorithm process is as follows:
s5231: order toInitializing a PCM algorithm parameter beta 0 ＝1,ν∈(0,1),f 0 ∈Ω,k＝0；
S5232: calculating out
When r is k When nu is established, executing:
when r is k When nu is not satisfied, executing:
if r k Less than 0.4, then beta k ＝1.5β k ；
Wherein, P Ω [·]Representing the projection operator, beta, onto the subspace omega k ,r k V is a parameter in the PCM algorithm, K is the iteration number of the PCM algorithm, and the PCM iteration is terminated when the maximum iteration number K of the PCM algorithm is reached;
s5233: let beta k+1 ＝β k K = k +1; if K < K, S5232 is performed, otherwise the iteration terminates.
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