An annular coded gamma imaging method and system

Abstract

The application discloses a kind of annular coding gamma imaging method and system.The method is:1) a circular code board is placed between a gamma detector and several radioactive sources;The circular code board is made of multiple concentric circles, and the coding mode of each concentric circle on the circular code board is set according to the principle of coding mode unrelated;2) rotate the circular code board during imaging, modulate the gamma ray flux of the gamma ray emitted by the radioactive source to reach the gamma detector;The gamma detector converts the gamma ray received during the rotation of the circular code board into count rate and sends it to the data processing unit;After the circular code board rotates a cycle, the data processing unit obtains a projection matrix D with the change of rotation angle;3) the data processing unit decodes and reconstructs to obtain the position distribution image O of the radioactive source according to the projection matrix D.The imaging flexibility of the application is greatly increased, and the cost and failure rate are also greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of nuclear radiation detection and imaging applications, and in particular relates to a ring-coded gamma imaging method and system. Background Technology

[0002] Nuclear radiation imaging technology can provide images of the distribution of radioactivity in a scene from a distance, offering advantages such as intuitive measurement results and accurate positioning. It has broad application prospects in fields such as nuclear radiation monitoring, nuclear emergency response, nuclear medicine, and astronomy.

[0003] To accurately locate a radiation source, a mechanical collimator made of heavy metal can be used to modulate the gamma rays within the field of view. The location and distribution of the radiation source in space can then be reconstructed by decoding the observation results. This radiation imaging system that uses a collimator to modulate gamma rays can be broadly classified into two categories: space-based modulation and time-based modulation.

[0004] Modulation of gamma rays in space can be categorized into pinhole imaging, parallel-hole imaging, coded-aperture imaging, and so on, depending on the collimator used. Figure 1 The MURA design scheme of the coded aperture collimator is shown. Spatial modulation of gamma rays usually requires cooperation with a position-sensitive detector to obtain a projection matrix. Image decoding and reconstruction are then performed based on this projection matrix.

[0005] Time-based modulation methods can eliminate the need for position-sensitive detectors. By scanning and rotating a mechanical collimator, the flux (count rate) of gamma rays can be obtained as a function of time on the detector. Then, the location information of the radiation source can be obtained through appropriate reconstruction algorithms. Cylindrical Time-Encoded Imaging System (c-TEI), Rotating Modulator (RM), and Hemispherical Rotational Modulation (HRM) are all examples of time modulation of gamma rays. Figure 2 The demonstration shows the Hexagonally Uniformly Redundant Array (HURA) scheme used in rotation modulation.

[0006] The problem to be solved is: to locate the gamma-ray source using a single-pixel detector and a circular coded collimator.

[0007] Traditional X-ray imaging, such as coded aperture imaging, requires complex electronic devices such as position-sensitive detectors. If coded schemes such as URA or MURA are used, careful consideration must be given to the number of codes on the code plate and the pixel size of the code plate (which needs to match the pixel size of the position-sensitive detector). Once the overall structure is determined, the field of view of the imaging system is determined and there is no possibility of change. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention aims to provide a ring-coded gamma imaging method and system. This invention constructs a novel circular code plate, and modulates the gamma ray flux through continuous rotation of the code plate. This enables two-dimensional localization of the radiation source without the need for a position-sensitive detector, while simultaneously making the entire gamma imaging system simpler and more flexible. In this scheme, the number of rings can actually be varied, meaning the field of view of the imaging system is variable. Combined with a single-pixel detector, the flexibility of the imaging system is greatly increased, while cost and failure rate are significantly reduced.

[0009] In this invention, the encoding method (hole opening method) of each ring in the circular code plate must be different; the number of rings in the circular code plate can be increased or decreased according to actual needs.

[0010] The imaging method of this invention can image not only gamma rays but also neutrons, and the principle is the same.

[0011] The technical solution of this invention is as follows:

[0012] A ring-coded gamma imaging method, comprising the following steps:

[0013] 1) Place a circular code plate between a gamma detector and several radiation sources; the circular code plate is composed of multiple concentric rings, and the encoding mode of each concentric ring on the circular code plate is set according to the principle that the encoding modes are unrelated.

[0014] 2) During the imaging process, the circular code plate is rotated to modulate the gamma ray flux of the gamma rays emitted by the radiation source to the gamma detector; the gamma detector converts the gamma rays received during the rotation of the circular code plate into a count rate and sends it to the data processing unit; after the circular code plate rotates for one cycle, the data processing unit obtains a projection matrix D in which the count rate changes with the rotation angle.

[0015] 3) The data processing unit decodes and reconstructs the location distribution image O of the radiation source based on the projection matrix D.

[0016] Furthermore, the method for decoding and reconstructing the position distribution image O of the radiation source based on the projection matrix D is as follows: obtain the curve of the count rate changing with the rotation angle based on the projection matrix D; then obtain the position information and angle of the ray passing through each concentric ring on the circular code plate based on the curve; then determine the position of the radiation source in the imaging space based on the geometric relationship between the detector and the pixels on each ring, and reconstruct the position distribution image O of the radiation source.

[0017] Furthermore, by solving The location distribution image O of the radiation source is obtained; wherein, a binary encoding matrix is ​​generated according to the opening state of each position on the circular code plate; the element a in the binary encoding matrix i，j The value represents the opening method of the j-th ring at degree i on the circular code plate, with 0 representing a closed hole and 1 representing an open hole; the column number of the binary encoding matrix represents the number of rings, d i The normalized count rate measured by the gamma detector at each rotation angle corresponds to the i-th element in the projection matrix D, i = 0 to 359, j = 0 to n+1; the column matrix [X0, X1, X2, ..., X... n X n+1 ] T The object to be solved represents the contribution of each ring in the circular code plate to the count of the gamma detector at each angle; the projection matrix D is convolved with the binary encoding matrix to obtain a relative intensity-angle map; the position of each radiation source is determined according to the ring and angle where the peak value is located in the relative intensity-angle map, and the position distribution image O of each radiation source is reconstructed.

[0018] Furthermore, the encoding numbers in each ring exclude those that are not divisible by 360, and then the encoding number of each ring is expanded into an array of 360 numbers to obtain the encoding method of the corresponding ring.

[0019] Furthermore, with the center of the circular code plate and the geometric center of the gamma detector as the axis, the circular code plate rotates continuously around the axis to modulate the gamma ray flux reaching the gamma detector.

[0020] Furthermore, the gamma detector is a single-pixel gamma detector or a position-sensitive detector array with position resolution capability.

[0021] A ring-coded gamma imaging system, characterized in that it includes a circular code plate, a gamma detector and a data processing unit; the circular code plate is placed between the gamma detector and several radiation sources, and the circular code plate is composed of multiple concentric rings, with the encoding modes of each concentric ring on the circular code plate set according to the principle that the encoding modes are independent of each other.

[0022] The circular code plate is used to modulate the gamma ray flux of the gamma rays emitted by the radiation source to the gamma detector;

[0023] The gamma detector is used to convert the gamma rays received during the rotation of the circular encoder plate into a count rate and send it to the data processing unit.

[0024] The data processing unit is used to obtain a projection matrix D that varies with the rotation angle based on the count rate obtained by rotating the circular encoder plate for one cycle; and then decode and reconstruct the position distribution image O of the radiation source based on the projection matrix D.

[0025] The advantages of this invention are as follows:

[0026] Compared to the reliance on high-channel counting and position-sensitive detectors in spatial modulation systems, the detectors used in this system are non-position-sensitive detectors. This reduces the cost and complexity of the imaging system, while also reducing system uncertainty and improving the overall stability of the imaging system.

[0027] Meanwhile, because this system also has the advantage of time coding, that is, angular resolution and energy resolution can be optimized separately, and axial resolution and circumferential resolution in angular resolution can also be optimized separately, the flexibility of the imaging system in dealing with different scenarios is enhanced. Attached Figure Description

[0028] Figure 1 This is a diagram of a coded aperture collimator.

[0029] Figure 2 This is a hexagonal uniform redundant array diagram.

[0030] Figure 3 This is a schematic diagram of the overall system of the present invention.

[0031] Figure 4 This is a schematic diagram showing how gamma photons reach the detector via a code plate under far-field conditions.

[0032] Figure 5 This is a normalized detector count rate-angle image under ideal conditions.

[0033] Figure 6 This is a diagram of the codeboard encoding of the present invention.

[0034] Figure 7 This is a count rate-angle diagram for the ray passing through the outermost ring under ideal conditions.

[0035] Figure 8 The relative intensity-angle diagram is obtained after convolving the ideal signal with each ring.

[0036] Figure 9The polar coordinate heatmap of the hot spot is (r, θ) = (8, 180°). Detailed Implementation

[0037] The present invention will now be described in further detail with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0038] As a methodological innovation in the design of nuclear radiation imaging systems, the purpose of this invention is to propose a novel code plate (collimator) design scheme, providing new technical means for nuclear radiation detection and imaging, and realizing radiation hotspot imaging under a single-pixel detector.

[0039] The overall system structure diagram of the present invention is shown below. Figure 3 As shown:

[0040] In this system, the code plate is designed as a circle, composed of different rings, each with a unique pattern (encoding scheme). This is the core of the design. To ensure consistent spatial resolution within the field of view, the area occupied by each pixel on the code plate should be approximately the same. The circular code plate is placed directly in front of the single-pixel gamma detector. Around the center of the circular code plate and the geometric center of the detector, the code plate continuously rotates around this axis during imaging to modulate the gamma ray flux reaching the detector.

[0041] The detector can be a single-pixel gamma detector without position resolution, or an array of position-sensitive detectors with position resolution. The code plate rotates continuously around its center, driven by a motor. The gamma detector behind the code plate converts the gamma rays received during the rotation into a count rate, which is then sent to the data processing unit. After one rotation cycle, the data processing unit obtains a projection matrix D showing the count rate changing over time. After one rotation cycle, the complete projection of the encoded pattern is obtained, and then the reconstructed image O is obtained through decoding and reconstruction. The uniqueness of the gamma ray projection at a certain azimuth angle within the detection field of view determines the feasibility of back-projection reconstruction.

[0042] Basic Imaging Principle: Since the application scope of this invention is in the field of nuclear radiation imaging, it satisfies the conditions of the far-field approximation. Under far-field conditions, gamma photons can be regarded as parallel incident on the code plate, such as... Figure 4 As shown, gamma photons from different directions (represented by dashed lines) reach the detector through different rings on the code plate. Since each ring on the code plate has a different coded pattern, different count (rate)-time (angle) change curves are obtained on the single-pixel detector during one rotation of the code plate, as shown in the diagram. Figure 5As shown, a count rate of 0 indicates that the gamma rays are blocked by the code plate, while a count rate of 1 indicates that the gamma rays pass through the code plate unobstructed and reach the detector. After determining the initial position of the code plate, the code plate rotates one revolution to obtain the count rate curve. By analyzing this curve, the incident rings and angles of the rays can be obtained simultaneously. Based on the geometric relationship between the detector and the pixels on each ring, the position of the radiation source in the imaging space can be determined.

[0043] In mathematics, the process of locating a radiation source using a circular code plate sampling imaging system can be described as solving the following matrix equations.

[0044]

[0045] The element a of the binary encoding matrix i，j Given that represents the opening method of the j-th ring at degree i on the circular code plate (0 represents a closed hole, 1 represents an open hole; each ring starts from 0° in polar coordinates, a) 60，3 This represents the opening status at the 60-degree angle position on the 3rd ring of the code plate (1 indicates an open hole, 0 indicates a closed hole). The number of columns in the sparse matrix represents the number of rings (the number of code plate rings, from 0 to n+1, a total of n+2 rings). d i The normalized count rate (measured value) at each rotation angle measured by the detector corresponds to the i-th element in the projection matrix D, and the column matrix [X0, X1, X2, ..., X... n X n+1 ] T This is what we are looking for; here it represents the contribution of each ring in the code plate to the detector count at each angle. Assume X0 = 1, X1 ~ X n+1 If all values ​​are 0, it means that the distant rays only reached the detector through the innermost ring. Therefore, after calculating the matrix equation, only the first column remains, representing the innermost ring of the code plate. In other words, the count rate curve obtained by the detector matches the pattern of the innermost ring. By matching the signal recorded by the detector with each ring, we can determine which ring the ray passed through before reaching the detector. Then, using the recorded angle information of the incident ray relative to the initial position of the code plate, we can obtain the direction of the radiation source. This is the imaging principle of this invention. Since d... i Since these are measured values, this matrix equation must have a physical solution.

[0046] For encoding patterns, to simultaneously distinguish gamma rays from multiple directions, different modes (different rings) must be used to encode the gamma ray flux from each direction. Therefore, the encoding modes of each ring should ideally be independent of each other, so that the presence of one mode does not hinder the detection of another. More precisely, the mode set is ideally a complete set of mutually orthogonal functions. This allows for optimal separation of the recorded modes even in the presence of statistical noise naturally generated during the nuclear decay to detection process. Specifically, a mutually orthogonal mode set provides image information with the highest signal-to-noise ratio.

[0047] In selecting the number of codes (i.e., the number of pixels), to reduce the difficulty of code plate processing and simplify the calculation of reconstructed images, code numbers not divisible by 360 can be excluded. The initial design, from the inside out, has 6, 12, 18, 24, 30, 36, 40, and 45 pixels; a total of 8 rings and 211 pixels. Furthermore, a code plate pattern can be selected for illustration by generating random numbers using a computer. It should be noted that the number of rings on the circular code plate and the number of codes on each ring are not unique and can be adjusted according to actual use. The application of computer random number generation is as follows... Figure 6 The circular code plate is shown. Ideally, after the code plate is rotated 360° for complete sampling, the count rate-angle image of the far-field gamma rays reaching the detector only through the outermost ring encoding is shown below. Figure 7 As shown in the figure.

[0048] By convolving this ideal signal with the coding patterns of each ring (formula attached), we can obtain the following: Figure 8 The relative intensity-angle plot shown (the result of gamma transformation after extreme value normalization) allows us to determine the relative position of the radiation source with respect to the imaging system by using the ring containing the peak (ring 8) and the angle (180°). The sources detected in this invention may exist simultaneously in multiple locations; therefore, is it possible to...? Figure 8 This only applies to the case where there is only one source. Figure 9 It is Figure 8 The information is displayed on a heatmap in polar coordinates.

[0049] Figure 6 The coded collimator pattern shown below (from the inside out) is represented as follows, where 0 represents a closed aperture and 1 represents an open aperture.

[0050] Ring_1 = [1.0.1.1.0.0.]

[0051] Ring_2=[1.0.0.0.1.1.1.0.1.0.1.0.]

[0052] Ring_3=[1.0.0.1.0.1.0.0.1.0.0.1.1.1.1.0.1.1.]

[0053] Ring_4=[0.1.0.1.1.1.1.0.1.1.0.1.0.0.1.0.0.1.0.0.1.0.1.0.]

[0054] Ring_5=[0.1.0.1.0.0.0.1.0.1.0.1.0.1.0.0.1.1.1.0.1.0.1.1.1.1.0.0.1.1.]

[0055] Ring_6=[1.1.1.0.0.1.0.1.0.0.1.1.0.0.0.1.1.1.1.1.1.0.0.1.0.1.0.1.0.0.1.0.1.1.0.0.]

[0056] Ring_7=[1.0.0.0.1.0.0.0.1.1.1.1.0.1.1.0.1.1.0.0.0.1.0.1.1.0.1.1.1.0.1.0.1.1.1.1.0.0.1.0.]

[0057] Ring_8=[1.0.1.0.1.0.1.1.1.1.0.0.1.1.0.1.0.1.1.1.1.1.1.1.0.0.0.1.0.0.0.0.1.0.0.1.1.0.0.1.1.0.0.0.0.]

[0058] Before performing the convolution calculation, the array needs to be expanded into an array of 360 numbers. For example, the 6 numbers in Ring_1 divide the 360-number array into 6 parts, each with 60 numbers. The first part has 60 numbers all 1, the second part has 60 numbers all 0, the third part has 60 numbers all 1, the fourth part has 60 numbers all 1, the fifth part has 60 numbers all 0, and the sixth part has 60 numbers all 0. The innermost ring of 360 numbers is thus formed as: [1. ... 1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1. 1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 .0 ... Figure 6 The codeboard shown contains an array of 8 numbers, each containing 360 numbers.

[0059] Figure 7The signal shown is the count rate-angle signal when the ray passes through the outermost ring under ideal conditions. It is essentially the same as the array of 360 numbers after the outermost ring is expanded using Ring_8, but in order to display the maximum value of the reconstructed image... Figure 8 In the middle, the extended array of Ring_8 was shifted by 180 positions, specifically: [1.1.1.1.1.1.1.1.1.1.1.1.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1. .1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 1.1.1.1.1.1.1.1.0.0.0.0.0.0.0.0.0.1.1.1.1.1.1.1.1.0.0.0.0.0.0.0.0.0.1.1.1.1.1.1.1.1.1.0.0.0.0.0.0.0.0.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.0.0.0.0.0.0.0.0.0.0.0.1 .1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.0.0.0.0.0.0.0.0.0.1.1.1.1.1.1.1.1.1.0.0.0.0.0.0.0.0.0.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.1.], convolving this array with the extended arrays of each ring respectively, yields the... Figure 8 The signal strength-angle diagram shown.

[0060] Convolution calculation formula

[0061]

[0062] Where O is the reconstructed image, 0≤k<360, D is the projection matrix, which is the detector's count during the code plate rotation process, and A is the ideal signal matrix, representing the code plate opening method of each ring in the circular code plate.

[0063] The gamma transform is used simply to improve the signal-to-noise ratio and make hotspots clearer. The formula is as follows:

[0064] s = cr γ

[0065] Where s is the hotspot image, r is the image after normalization of the reconstructed image after direct convolution, c is the grayscale scaling factor, which is set to 1; γ is the gamma factor, which controls the scaling degree of the entire transformation, and can be set to 2.

[0066] Although specific embodiments of the invention have been disclosed for illustrative purposes to aid in understanding and implementing the invention, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the content disclosed in the preferred embodiments, and the scope of protection claimed by the invention is defined by the claims.

Claims

1. A ring-coded gamma imaging method, comprising the following steps: 1) Place a circular code plate between a gamma detector and several radiation sources; the circular code plate is composed of multiple concentric rings, and the encoding mode of each concentric ring on the circular code plate is set according to the principle that the encoding modes are unrelated. 2) During the imaging process, the circular code plate is rotated to modulate the gamma ray flux of the gamma rays emitted by the radiation source to the gamma detector; the gamma detector converts the gamma rays received during the rotation of the circular code plate into a count rate and sends it to the data processing unit; after the circular code plate rotates for one cycle, the data processing unit obtains a projection matrix D in which the count rate changes with the rotation angle. 3) The data processing unit decodes and reconstructs the location distribution image O of the radiation source based on the projection matrix D.

2. The method according to claim 1, characterized in that, The method for decoding and reconstructing the position distribution image O of the radiation source based on the projection matrix D is as follows: obtain the curve of the count rate changing with the rotation angle based on the projection matrix D; then obtain the position information and angle of the ray passing through each concentric ring on the circular code plate based on the curve; and then determine the position of the radiation source in the imaging space based on the geometric relationship between the detector and the pixels on each ring, and reconstruct the position distribution image O of the radiation source.

3. The method according to claim 1 or 2, characterized in that, By solving The location distribution image O of the radiation source is obtained; wherein, a binary encoding matrix is ​​generated according to the opening state of each position on the circular code plate; the element a in the binary encoding matrix i，j The value represents the opening method of the j-th ring at degree i on the circular code plate, with 0 representing a closed hole and 1 representing an open hole; the column number of the binary encoding matrix represents the number of rings, d i The normalized count rate measured by the gamma detector at each rotation angle corresponds to the i-th element in the projection matrix D, i = 0 to 359, j = 0 to n+1; the column matrix [X0, X1, X2, ..., X... n X n+1 ] T The object to be solved represents the contribution of each ring in the circular code plate to the count of the gamma detector at each angle; the projection matrix D is convolved with the binary encoding matrix to obtain a relative intensity-angle map; the position of each radiation source is determined according to the ring and angle where the peak value is located in the relative intensity-angle map, and the position distribution image O of each radiation source is reconstructed.

4. The method according to claim 1, characterized in that, The encoding numbers in each ring exclude those that are not divisible by 360, and then the encoding number of each ring is expanded into an array of 360 numbers to obtain the encoding method of the corresponding ring.

5. The method according to claim 1, characterized in that, With the center of the circular code plate and the geometric center of the gamma detector as the axis, the circular code plate rotates continuously around the axis to modulate the gamma ray flux reaching the gamma detector.

6. The method according to claim 1, characterized in that, The gamma detector is a single-pixel gamma detector or a position-sensitive detector array with position resolution capability.

7. A ring-coded gamma imaging system, characterized in that, It includes a circular code plate, a gamma detector and a data processing unit; the circular code plate is placed between the gamma detector and several radiation sources, and the circular code plate is composed of multiple concentric rings, and the encoding mode of each concentric ring on the circular code plate is set according to the principle that the encoding modes are independent of each other. The circular code plate is used to modulate the gamma ray flux of the gamma rays emitted by the radiation source to the gamma detector; The gamma detector is used to convert the gamma rays received during the rotation of the circular code plate into a counting rate and send it to the data processing unit. The data processing unit is used to obtain a projection matrix D that varies with the rotation angle based on the count rate obtained by rotating the circular code plate for one cycle; and then decode and reconstruct the position distribution image O of the radiation source based on the projection matrix D.

8. The system according to claim 7, characterized in that, By solving The location distribution image O of the radiation source is obtained; wherein, a binary encoding matrix is ​​generated according to the opening state of each position on the circular code plate; the element a in the binary encoding matrix i，j The value represents the opening method of the j-th ring at degree i on the circular code plate, with 0 representing a closed hole and 1 representing an open hole; the column number of the binary encoding matrix represents the number of rings, d i The normalized count rate measured by the gamma detector at each rotation angle corresponds to the i-th element in the projection matrix D, i = 0 to 359, j = 0 to n+1; the column matrix [X0, X1, X2, ..., X... n X n+1 ] T The object to be solved represents the contribution of each ring in the circular code plate to the count of the gamma detector at each angle; the projection matrix D is convolved with the binary encoding matrix to obtain a relative intensity-angle map; the position of each radiation source is determined according to the ring and angle where the peak value is located in the relative intensity-angle map, and the position distribution image O of each radiation source is reconstructed.

9. The system according to claim 7, characterized in that, The encoding numbers in each ring exclude those that are not divisible by 360, and then the encoding number of each ring is expanded into an array of 360 numbers to obtain the encoding method of the corresponding ring.

10. The system according to claim 7, characterized in that, With the center of the circular code plate and the geometric center of the gamma detector as the axis, the circular code plate rotates continuously around the axis to modulate the gamma ray flux reaching the gamma detector; the gamma detector is a single-pixel gamma detector.

Images