Compton camera rapid three-dimensional imaging method and system for far-field global domain

Abstract

The invention discloses a Compton camera rapid three-dimensional imaging method and system for a far-field global domain, and relates to the technical field of nuclear radiation detection and application. According to the method, firstly, a Compton camera is used for obtaining respective solid angle distribution of a radioactive source under two spatial position visual angles; constructing two groups of three-dimensional space vectors based on angle distribution of solid angles by taking the central position of a detector of the camera as a starting point; and finally, obtaining three-dimensional position distribution of the radioactive source through intersection of the two groups of vectors. According to the method, the two groups of vectors are intersected, only the distribution and the probability of the intersection points are calculated, and the three-dimensional position distribution of the radioactive source can be obtained without traversing the whole imaging space, so that the computer memory and the calculation time are saved, and the three-dimensional imaging speed of the Compton camera can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of nuclear radiation detection and application technology, and in particular to a far-field full-domain Compton camera fast three-dimensional imaging method and system. Background Art

[0002] Compton imaging (Compton camera) is a gamma-ray imaging technology based on the Compton scattering effect. It can reconstruct the spatial distribution image of the radiation source without a mechanical collimator. Its imaging principle relies on the Compton scattering of photons and matter. The scattering angle is determined by the Compton scattering equation. By detecting the energy and scattering direction of scattered photons and recoil electrons, the direction of the radiation source can be determined. On a Compton cone with the reverse direction of the scattered photons as the axis and the Compton scattering angle as the semi-vertex angle, each scattering event will form a cone surface. The intersection of these cone surfaces is the theoretical spatial position of the radiation source.

[0003] The image reconstruction algorithm of the Compton camera mainly includes analytical reconstruction algorithm and iterative reconstruction algorithm. The analytical reconstruction algorithm directly back-projects the response recorded by the detector to all possible spatial positions, which is also called back-projection imaging. As the detection data accumulates, the actual position of the radiation source will gradually be strengthened and highlighted. However, since many background voxels are also assigned probabilities during the reconstruction process, the images generated by the analytical algorithm usually have poor resolution. The iterative reconstruction method usually solves the probability distribution of the radiation source in the imaging space based on the transfer relationship between the image space and the detector response. Each iteration corrects the estimate of the image, and multiple iterations are repeated until convergence. Compared with the analytical algorithm, the iterative method can handle complex image structures and background noise more accurately, and usually obtains higher quality images.

[0004] In near-field imaging (the distance between the radiation source and the detector is only a few centimeters), the three-dimensional information of the radiation source position can be directly obtained by superimposing each Compton cone, and its true position will be significantly enhanced due to the contribution of each cone. However, when the radiation source is far away from the detector, the difference in the distribution of the Compton cone vertices in the detector is difficult to reflect, resulting in the area in the direction of the radiation source being contributed by the Compton cone, and the distance information of the radiation source cannot be accurately obtained. Therefore, it is necessary to collect Compton scattering event data from multiple spatial positions so that the position of the radiation source is contributed by Compton cones from different angles, so as to correctly reconstruct the three-dimensional image of the radiation source.

[0005] Since traditional 3D Compton imaging requires dividing the imaging space into 3D grids to reconstruct the 3D distribution of the radiation source in the grids, the required imaging space range is significantly increased in order to obtain the position information of the radiation source far away from the detector. As the imaging space increases and the number of grids increases, the amount of calculation will increase sharply, making it difficult for the imaging speed to meet the real-time requirements. Summary of the invention

[0006] One of the purposes of the present invention is to provide a method for realizing fast three-dimensional imaging of a Compton camera in the entire far field, thereby improving the imaging speed of the Compton camera in actual application scenarios.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A Compton camera fast three-dimensional imaging method for the entire far field includes the following steps:

[0009] (1) Solid angle distribution reconstruction:

[0010] The solid angle of the radiation source is reconstructed by using the data obtained by the Compton camera at two different spatial positions, thereby obtaining the solid angle of the same radiation source at two spatial positions. Distributions and their corresponding probabilities;

[0011] (2) Vector construction:

[0012] Taking the detector center position of the two cameras at different spatial positions as the starting point, the respective solid angles of the radiation source at the two spatial positions Distribution as direction, construct two sets of three-dimensional space vectors;

[0013] (3) Vector intersection calculation:

[0014] Intersect two sets of three-dimensional space vectors, calculate the position of the intersection of the vectors, and calculate the probability of the intersection based on the probability of the vector directions;

[0015] (4) Three-dimensional distribution construction:

[0016] The three-dimensional position distribution of the radiation source is constructed based on the calculated intersection positions of all vectors and their probabilities.

[0017] Furthermore, before step (1), the method further includes the following steps:

[0018] A Compton camera is used to detect the radiation source at two different locations, collect and process data for a certain period of time, screen out Compton imaging events, and then reconstruct the solid angle distribution of the radiation source.

[0019] Furthermore, in step (1), the solid angle distribution of the radiation source is reconstructed according to the following steps:

[0020] First, the entire imaging space is quickly scanned using a large angular step size, and the focal area where the radiation source may exist is quickly determined by analytically reconstructing the detected Compton cone;

[0021] Then, these focal areas are finely divided with smaller angle steps, and the solid angle distribution of the radiation source is reconstructed in combination with an iterative algorithm, thereby quickly obtaining a high-precision solid angle distribution of the radiation source.

[0022] Further, the ratio between the larger angle step and the smaller angle step is 10: 1. For example, the larger angle step is 10°, and the smaller angle step is 1°.

[0023] Furthermore, in step (3), in the process of calculating the vector intersection point, for a pair of vectors that have different starting points and do not directly intersect, the point closest to them in space is taken as the intersection point, and this intersection point is calculated.

[0024] Furthermore, in step (3), the nearest point of a pair of vectors with different starting points and not directly intersecting in space is calculated by the following formula, and this point is used as the intersection point P of the vector pair: ij :

[0025]

[0026] Among them, P1 and P2 are the coordinate points of the Compton camera at two different positions, d i d j is the direction extracted from the solid angle distribution, P ij Taking P1 and P2 as the starting point, d i d j The intersection of two vectors constructed for the direction.

[0027] Furthermore, in step (4), the probability of all vector intersections is calculated by the following steps:

[0028] Extract d from the solid angle distribution i and d j The probability of each vector intersection P ij Corresponding to d i and d j The probability of each vector intersection P is obtained by multiplying the probability of each vector intersection P ij probability.

[0029] Furthermore, in step (1), a spherical coordinate system is used to divide the imaging space to reconstruct the solid angle distribution of the radiation source, and the origin of the coordinate system at each position is located at the center of the detector in the camera.

[0030] Another object of the present invention is to provide a Compton camera fast three-dimensional imaging system for the entire far field, which includes a storage unit and a computing unit, wherein the storage unit stores a Compton camera fast three-dimensional imaging program for the entire far field, and the Compton camera fast three-dimensional imaging program for the entire far field is run through the computing unit to execute the steps in the Compton camera fast three-dimensional imaging method for the entire far field described above.

[0031] Traditional 3D Compton imaging technology relies on constructing 3D grids in the imaging space and reconstructing the 3D distribution of the radiation source through these grids. When dealing with far-field radiation sources, this method often encounters the problem of long imaging time due to the need to process huge 3D grids. In contrast, the present invention proposes a new vector intersection method, which realizes 3D imaging through 2D imaging technology, effectively solving the problem of long imaging time caused by the huge 3D grid. This method avoids the processing of a large number of 3D grids, and reconstructs the stereo angle distribution of the data obtained by the Compton camera at two different positions respectively, and reconstructs the stereo angle distribution according to the stereo angle distribution under two viewing angles. By constructing the direction vectors and intersecting them in pairs, and combining them with the corresponding probability coefficients, the three-dimensional position distribution of the radiation source is directly constructed, thereby greatly improving the imaging efficiency and real-time performance.

[0032] The core idea of ​​the present invention is that the location of the radiation source can be found by only calculating the intersection of two sets of vectors, thereby avoiding the need to traverse the three-dimensional space grid of the entire imaging space in traditional three-dimensional Compton imaging and saving calculation time. Specifically, vectors are extracted from two detection positions and their corresponding solid angle distributions, and the intersection of the two sets of vectors is calculated. These intersections represent the locations where radiation sources may exist in three-dimensional space. By multiplying the probability of each vector pair in the solid angle distribution, the probability of the intersection of the vector pair is obtained, so that the three-dimensional position distribution of the radiation source can be constructed. This method significantly reduces the number of traversed grid cells, reduces the amount of calculation for searching the grid cells and verifying the Compton cone information, thereby greatly reducing the operation time and memory consumption, and improving the imaging speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the principle diagram of the vector intersection method in the embodiment;

[0034] Figure 2 Schematic diagram of imaging space division in the embodiment;

[0035] Figure 3 A schematic diagram of a process of a Compton camera fast three-dimensional imaging method for the entire far field in an embodiment;

[0036] Figure 4The images shown in the embodiment include two measured stereo angle distribution images and a final three-dimensional position distribution image; wherein (a) is a stereo angle distribution image of the Compton camera in the first position, (b) is a stereo angle distribution image of the Compton camera in the second position, and (c) is a three-dimensional position distribution image of the radiation source. DETAILED DESCRIPTION

[0037] In order to facilitate those skilled in the art to better understand the improvements of the present invention relative to the prior art, the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0038] The goal of the present invention is to provide a method that can achieve fast three-dimensional imaging of a Compton camera in the entire far field, so as to improve the imaging efficiency of the Compton camera in practical applications. In the face of the challenges faced by traditional three-dimensional Compton imaging technology in far-field radiation source measurement, especially the problem of long imaging time caused by processing large-scale three-dimensional grids, the present invention proposes a novel vector intersection method. This method realizes three-dimensional imaging through the vector intersection method, effectively solving the bottleneck problem in traditional methods.

[0039] The core idea of ​​the present invention is that the Compton camera extracts vectors from two detection positions and their corresponding solid angle distributions, and calculates their intersection to determine the location of the radiation source. This method avoids the complex process of searching and calculating the Compton cone information for each three-dimensional grid cell, thereby greatly saving computing time and memory consumption.

[0040] Specifically, the Compton camera provides information about the direction of the radiation source at two different locations. Due to the different starting points, vector pairs that can intersect can be constructed. The intersection point of these vector pairs is the location of the radiation source. Taking into account the measurement error, the actual vector pairs may not intersect exactly. Therefore, the point closest to the two vectors in space can be regarded as the intersection point, and this intersection point can be calculated using mathematical methods. Combined with the probability of the direction of each vector in the solid angle distribution, the final vector intersection distribution is the three-dimensional position distribution of the radiation source.

[0041] In order to optimize the allocation of computing resources and reduce the background computing consumption, the present invention adopts a method of doubly dividing the imaging space in the reconstruction of the stereoscopic angle distribution. First, the imaging space is divided with a larger angle step, and the analytical reconstruction algorithm is used to quickly scan the entire space to determine the "focal" area where the radiation source is located. Then, high-precision reconstruction is performed in these "focal" areas in combination with an iterative algorithm, which significantly improves the imaging speed and accuracy.

[0042] like Figure 1As shown, the present invention proposes a fast three-dimensional imaging method based on vector intersection, which effectively solves the contradiction between time efficiency and imaging space range in far-field three-dimensional imaging. The method uses data acquired by a Compton camera at two different positions to reconstruct the solid angle distribution. Then, vectors containing probability information are extracted from the solid angle distribution, and the three-dimensional positioning and imaging of the radiation source are realized by calculating the intersection of these vectors. Compared with traditional methods, this method reduces the spatial dimension in Compton imaging, improves the imaging speed, and can cover the imaging range of the entire far field.

[0043] The principle and structure of the three-dimensional fast Compton imaging method of the Compton camera facing the far-field full domain of the present invention will be described in detail below in conjunction with the embodiments. The general process of the method can be found in Figure 3 .

[0044] This example uses Geant4 to perform Monte Carlo simulation tests to verify the feasibility of the solution. The model used is a 44×44×10mm 3 The CZT detector is divided into 484 pixel arrays, each with a size of 2×2×10mm. 3 In the simulation, two CZT detectors were constructed, located at (-3,0,0)m and (3,0,0)m respectively, and a point source of gamma rays with an energy of 662keV was set at (0,0,4)m.

[0045] The implementation steps are outlined below:

[0046] First, the radiation source was detected at two preset positions (coordinates were (-3,0,0)m and (3,0,0)m). During the data processing, the detector was given an energy resolution of 1.5% and a depth position resolution of 2mm. Subsequently, Compton imaging events were screened from the raw data. Through this process, approximately 2500 Compton imaging events were obtained from each of the two measurement positions.

[0047] Next, two-dimensional imaging of the radiation source is performed. Figure 2 As shown in the figure, in the two-dimensional reconstruction process, the spherical coordinate system is used to divide the imaging space in order to reconstruct the three-dimensional angle distribution image of the radiation source. At the same time, the calculation amount of the background space is reduced by double-dividing the imaging space. The origin of the two-dimensional reconstruction coordinate system at each position is set at the center of the corresponding detector to ensure that the imaging range covers the entire 4π solid angle space. In the spherical coordinate system, θ represents the angle between a ray in a certain direction in space and the Z axis, and its value range is 0 to π; It represents the angle between the projection of the directional ray on the XY plane and the positive direction of the X-axis rotated counterclockwise. Its value range is 0 to 2π.

[0048] In order to optimize the allocation of computing resources and reduce the computing consumption at the background angle, the imaging space is first divided into larger angle steps (10°) and the entire space is quickly scanned. In this process, the detected Compton cone is analytically reconstructed to preliminarily determine several "focal" areas where the radiation source may exist.

[0049] Subsequently, these “focal” areas are finely divided with a smaller angular step size (1°), and the solid angle distribution of the radiation source is reconstructed using an iterative algorithm, thereby quickly obtaining a high-precision solid angle distribution of the radiation source.

[0050] This embodiment uses two-dimensional reconstruction instead of three-dimensional reconstruction and double-divides the imaging space, which effectively reduces the number of grids during reconstruction and greatly reduces the consumption of memory and computing time. This embodiment only performs high-precision calculations in the "focus" area, optimizes the allocation of computing resources, and effectively avoids the redundant burden caused by high-resolution calculations of the entire reconstruction space.

[0051] The following reference Figure 4 The experimental results illustrate the imaging process of the vector intersection method. The detector measures the radiation source at two positions, P1 and P2. Each measurement can provide the solid angle distribution information of the radiation source, which can generate the starting point P1, P2 and the direction d i ,d j By arranging and combining two sets of vectors, and using the following formula to calculate the point in space closest to the two vectors, this point is regarded as the intersection point P of the vectors ij :

[0052]

[0053] P ij The probability is d i and d j The probability product of all vector intersection points P ij The distribution and its corresponding probability are normalized to generate a three-dimensional distribution image. The positioning result in the test is (10.7, 7.7, 387.4) cm, which is close to the actual position of the radiation source.

[0054] Test results show that the vector intersection method only takes 35 seconds to generate a three-dimensional distribution image of a radiation source. In comparison, the traditional three-dimensional grid imaging method using Compton cone intersection takes 1485 seconds, a difference of more than 42 times in computing time. This is mainly because a total of 216,000 three-dimensional grids are divided in the Compton cone intersection method, and the system matrix occupies up to 8.64GB of memory in iterative reconstruction, which places a heavy burden on the computer. In the vector intersection method, only 3943 angles are divided for calculation, and the number of elements in the imaging space differs by about 55 times, which enables the vector intersection method to achieve a speed increase of more than 42 times in three-dimensional imaging. In addition, the imaging range corresponding to the three-dimensional space divided by the Compton cone intersection method in the experiment is 6×6×6m 3 , and the vector intersection method can theoretically perform three-dimensional imaging of radiation sources at any location.

[0055] In general, this embodiment provides a fast three-dimensional imaging method for Compton cameras in the entire far field. By simplifying the calculation process, only the solid angle distribution needs to be processed, and there is no need to calculate the distribution of the Compton cone in each three-dimensional grid, thereby significantly reducing the computational complexity. In addition, this method does not need to pre-set a fixed imaging space, and can directly generate the three-dimensional distribution of the radiation source through the calculation results, so that the stereo angle range of the imaging is larger. This method not only greatly shortens the time of far-field three-dimensional imaging, but also provides an imaging range of the entire far field, and has good application prospects.

[0056] In addition, the present invention may also be implemented in other ways, and any obvious replacement without departing from the concept of the present technical solution is within the protection scope of the present invention.

[0057] In order to make it easier for ordinary technicians in the field to understand the improvements of the present invention over the prior art, some drawings and descriptions of the present invention have been simplified, and for the sake of clarity, some other elements are omitted in this application document. Ordinary technicians in the field should realize that these omitted elements may also constitute the content of the present invention.

Claims

1. A Compton camera fast three-dimensional imaging method for the entire far field, characterized in that: The following steps are involved: (1) Solid angle distribution reconstruction: The solid angle of the radiation source is reconstructed by using the data obtained by the Compton camera at two different spatial positions, thereby obtaining the solid angle of the same radiation source at two spatial positions. Distributions and their corresponding probabilities; (2) Vector construction: Taking the detector center position of the two cameras at different spatial positions as the starting point, the respective solid angles of the radiation source at the two spatial positions Distribution as direction, construct two sets of three-dimensional space vectors; (3) Vector intersection calculation: Intersect two sets of three-dimensional space vectors, calculate the position of the intersection of the vectors, and calculate the probability of the intersection based on the probability of the vector directions; (4) Three-dimensional distribution construction: The three-dimensional position distribution of the radiation source is constructed based on the calculated intersection positions of all vectors and their probabilities.

2. The far-field full-domain Compton camera fast three-dimensional imaging method according to claim 1, characterized in that: In step (1), the solid angle distribution of the radiation source is reconstructed according to the following steps: First, the entire imaging space is quickly scanned using a large angular step size, and the detected Compton events are analytically reconstructed to quickly determine the focal area where the radiation source may exist; Then, these focal areas are finely divided with smaller angle steps, and the solid angle distribution of the radiation source is reconstructed in combination with an iterative algorithm, so that a high-precision solid angle distribution of the radiation source can be quickly obtained.

3. The far-field full-domain Compton camera fast three-dimensional imaging method according to claim 2, characterized in that: In step (3), in the process of calculating the vector intersection point, for a pair of vectors that have different starting points and do not directly intersect, the point closest to them in space is taken as the intersection point, and this intersection point is calculated.

4. The method for fast three-dimensional imaging of the far-field full-domain Compton camera according to claim 3 is characterized in that: The nearest point of a pair of vectors with different starting points and not directly intersecting in space is calculated using the following formula, and this point is used as the intersection point P of the vector pair ij : Among them, P1 and P2 are the coordinate points of the Compton camera at two different positions, d i ,d j is the direction extracted from the solid angle distribution, P ij Taking P1 and P2 as the starting point, d i ,d j The intersection of two vectors constructed for the direction.

5. The method for fast three-dimensional imaging of the far-field full-range Compton camera according to claim 4, characterized in that: In step (4), the probability of all vector intersections is calculated by the following steps: Extract d from the solid angle distribution i and d j The probability of each vector intersection P ij Corresponding to d i and d j The probability of each vector intersection P is obtained by multiplying the probability of each vector intersection P ij probability.

6. A Compton camera fast three-dimensional imaging system for the entire far field, comprising a storage unit and a computing unit, wherein the storage unit stores a Compton camera fast three-dimensional imaging program for the entire far field, and the Compton camera fast three-dimensional imaging program for the entire far field is run through the computing unit to execute the steps of the Compton camera fast three-dimensional imaging method for the entire far field as described in any one of claims 1 to 5.

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