A multi-modality iterative reconstruction method and apparatus

Abstract

The application provides a multi-mode iterative reconstruction method and device, and relates to the technical field of nuclear radiation detection. The method comprises the following steps: acquiring event information of interaction between gamma photons and three-dimensional position-sensitive semiconductor detection units in a panoramic gamma camera system; acquiring an information amount based on a prior energy, a Compton scattering event count in the event information and a photoelectric absorption event count in the event information, and calculating a weight according to the information amount; performing Compton sequence reconstruction based on the prior energy, constructing a multi-mode system transmission matrix according to the reconstructed Compton sequence; performing multi-mode iterative reconstruction based on the weight and the multi-mode system transmission matrix, outputting a stable high signal-to-noise ratio image and determining a spatial distribution of a radiation source. The application proposes a multi-mode iterative reconstruction method combining coded aperture, Compton and non-alignment technology, solves the problems of poor reconstruction resolution and unstable imaging signal-to-noise ratio in traditional multi-mode gamma imaging, and effectively improves imaging energy segment, imaging field of view and resolution.

Description

Technical Field

[0001] This invention relates to the field of nuclear radiation detection technology, and in particular to a multi-mode iterative reconstruction method and apparatus. Background Technology

[0002] Nuclear safety is a critical area for ensuring the safe use of nuclear energy, preventing the misuse of radioactive materials, and protecting the public and the environment from radiation hazards. Gamma-ray imaging technology can accurately locate radiation sources, enabling visualized monitoring of radiation, and has good response time and detection efficiency, effectively reducing the risk factor. It is currently widely used in nuclear safety monitoring.

[0003] In recent years, multimode imaging techniques based on coded aperture imaging and Compton imaging have gradually gained attention in the field due to their ability to increase the amount of photon information obtained, expand the imaging energy range, improve the image signal-to-noise ratio, reduce reconstruction uncertainty, and ensure detection efficiency. However, existing multimode image reconstruction algorithms have not yet studied the trade-offs of each mode term in the probability density function of the projection data. Therefore, the disadvantages of each mode can easily affect each other, and the advantages of each mode cannot be fully utilized. As a result, the overall resolution and signal-to-noise ratio of the final multimode reconstructed image are sometimes even worse than those of the single-mode reconstructed image. Summary of the Invention

[0004] To address the technical problems of poor reconstruction resolution and unstable signal-to-noise ratio in traditional multi-mode gamma imaging, this invention provides a multi-mode iterative reconstruction method and apparatus. The technical solution is as follows:

[0005] On the one hand, a multi-mode iterative reconstruction method is provided, which is implemented by a multi-mode iterative reconstruction device, and the method includes:

[0006] S1. Acquire event information about the interaction between gamma photons and the three-dimensional position-sensitive semiconductor detection unit within the panoramic gamma camera system.

[0007] S2. Obtain information based on prior energy, Compton scattering event counts in event information, and photoelectric absorption event counts in event information, and calculate weights based on information; reconstruct the Compton sequence based on prior energy, and construct a multimode system transmission matrix based on the reconstructed Compton sequence.

[0008] S3. Multimode iterative reconstruction is performed based on weights and the multimode system transfer matrix to output a stable high signal-to-noise ratio image and determine the spatial distribution of the radiation source.

[0009] Optionally, the event information in S1 includes: timestamp, energy, three-dimensional location coordinates, action sequence, and action type.

[0010] The types of interactions include Compton scattering events and photoelectric absorption events.

[0011] A timestamp is a time record triggered by signal pulses captured by the data acquisition system within a panoramic gamma camera system.

[0012] Energy is determined by the amplitude of the signal pulse.

[0013] The three-dimensional position coordinates are determined by using the position of the anode response pixel in the detector array to determine the two-dimensional lateral spatial coordinates of the photon interaction event, and by analyzing the ratio of the cathode and anode signal amplitudes to determine the interaction depth of the photon interaction event. The three-dimensional position coordinates are then determined based on the two-dimensional lateral spatial coordinates and the interaction depth.

[0014] The interaction sequence is determined by measuring the electron drift time and analyzing the timing information of the pulses corresponding to each interaction point.

[0015] The interaction type is determined by combining the number of interaction points and the energy deposition pattern at each point with location information.

[0016] Optionally, the weights in S2 are calculated as shown in equation (1) below:

[0017] (1)

[0018] In the formula, As weight, To optimize the degree factor, The a priori energy of the radioactive source, This represents the total count of Compton scattering events detected by the detector. This represents the total count of photoelectric absorption events detected by the detector.

[0019] Optionally, the Compton sequence reconstruction in S2 includes:

[0020] The interaction sequence in the full-energy double Compton coincidence event is determined by the magnitude of the deposition energy, and the Compton margin test is performed.

[0021] The Compton margin test calculation formula is shown in equation (2) below:

[0022] (2)

[0023] In the formula, For Compton edge energy, The a priori energy of the radioactive source, The rest mass of the electron. It is the speed of light.

[0024] Optionally, the multimode system transmission matrix in S2 includes: a non-collimation-mechanical collimation mode system transmission matrix and a Compton mode system transmission matrix.

[0025] The transmission matrix of the collimationless-mechanical collimation mode system is obtained by analytical calculation, as shown in equation (3) below:

[0026] (3)

[0027] In the formula, For the transmission matrix of the non-collimation-mechanical collimation mode system, For detector voxels, For image plane pixels, The attenuation coefficient of high-density alloys, For pixels captured by the mechanical collimator to detector voxel radiation path, The attenuation coefficient of the semiconductor detector is denoted as . For the pixels captured by the detector to detector voxel Surface radiation path, For the voxel captured by the detector, from the pixel to detector voxel The radiation path from the center.

[0028] The Compton mode system transfer matrix is ​​obtained by analytical calculation, as shown in equation (4) below:

[0029] (4)

[0030] In the formula, For the Compton mode system transmission matrix, For Compton to conform to the event action sequence, For the first The pixels captured by the detector in the action sequence The radiation path to the location of Compton scattering. for The Compton differential section, The Compton scattering angle is... For the first The radiation path from the Compton scattering location to the photoelectric absorption location, captured by the detector in each action sequence.

[0031] The calculation formula for the Compton differential section is shown in equation (5) below:

[0032] (5)

[0033] In the formula, , The a priori energy of the radioactive source, The rest mass of the electron. It is the speed of light.

[0034] Optionally, S3 performs multimode iterative reconstruction based on weights and the multimode system transfer matrix, as shown in equation (6) below:

[0035] (6)

[0036] In the formula, for The new estimate after the next iteration for The current estimate after the next iteration For image plane pixels, As weight, The total number of events in Compton is consistent. For the first Compton measurement counts in each action sequence For the Compton mode system transmission matrix, The total number of pixels in the image space. for In the normalization summation process of the nth iteration The current estimate of each image pixel. For image pixel index, This represents the total number of voxels in the detector. For detector voxels Photon measurement and counting at the location, For the transmission matrix of the non-collimation-mechanical collimation mode system, This is the sensitivity matrix.

[0037] Optionally, the panoramic gamma camera system includes: a three-dimensional position-sensitive semiconductor detection unit and an unshielded encoder module.

[0038] The three-dimensional position-sensitive semiconductor detection unit includes: a three-dimensional position-sensitive semiconductor, an application-specific integrated circuit chip, a field-programmable gate array, and a data acquisition system.

[0039] The unshielded encoder module includes: an encoder board and a side support layer.

[0040] On the other hand, a multi-modal iterative reconstruction apparatus is provided, which is applied to a multi-modal iterative reconstruction method. The apparatus includes:

[0041] The acquisition module is used to acquire event information about the interaction between gamma photons and the three-dimensional position-sensitive semiconductor detection unit within the panoramic gamma camera system.

[0042] The module is used to acquire information based on prior energy, Compton scattering event counts in event information, and photoelectric absorption event counts in event information, and to calculate weights based on the information; to reconstruct the Compton sequence based on prior energy, and to construct the multimode system transmission matrix based on the reconstructed Compton sequence.

[0043] The output module is used to perform multi-mode iterative reconstruction based on weights and the multi-mode system transfer matrix, outputting a stable high signal-to-noise ratio image and determining the spatial distribution of the radiation source.

[0044] Optionally, event information includes: timestamp, energy, three-dimensional location coordinates, action sequence, and action type.

[0045] The types of interactions include Compton scattering events and photoelectric absorption events.

[0046] A timestamp is a time record triggered by signal pulses captured by the data acquisition system within a panoramic gamma camera system.

[0047] Energy is determined by the amplitude of the signal pulse.

[0048] The three-dimensional position coordinates are determined by using the position of the anode response pixel in the detector array to determine the two-dimensional lateral spatial coordinates of the photon interaction event, and by analyzing the ratio of the cathode and anode signal amplitudes to determine the interaction depth of the photon interaction event. The three-dimensional position coordinates are then determined based on the two-dimensional lateral spatial coordinates and the interaction depth.

[0049] The interaction sequence is determined by measuring the electron drift time and analyzing the timing information of the pulses corresponding to each interaction point.

[0050] The interaction type is determined by combining the number of interaction points and the energy deposition pattern at each point with location information.

[0051] Optionally, the weights are calculated as shown in equation (1):

[0052] (1)

[0053] In the formula, As weight, To optimize the degree factor, The a priori energy of the radioactive source, This represents the total count of Compton scattering events detected by the detector. This represents the total count of photoelectric absorption events detected by the detector.

[0054] Optionally, Compton sequence reconstruction includes:

[0055] The interaction sequence in the full-energy double Compton coincidence event is determined by the magnitude of the deposition energy, and the Compton margin test is performed.

[0056] The Compton margin test calculation formula is shown in equation (2) below:

[0057] (2)

[0058] In the formula, For Compton edge energy, The a priori energy of the radioactive source, The rest mass of the electron. It is the speed of light.

[0059] Optionally, the multimode system transmission matrix includes: a non-collimation-mechanical collimation mode system transmission matrix and a Compton mode system transmission matrix.

[0060] The transmission matrix of the collimationless-mechanical collimation mode system is obtained by analytical calculation, as shown in equation (3) below:

[0061] (3)

[0062] In the formula, For the transmission matrix of the non-collimation-mechanical collimation mode system, For detector voxels, For image plane pixels, The attenuation coefficient of high-density alloys, For pixels captured by the mechanical collimator to detector voxel radiation path, The attenuation coefficient of the semiconductor detector is denoted as . For the pixels captured by the detector to detector voxel Surface radiation path, For the voxel captured by the detector, from the pixel to detector voxel The radiation path from the center.

[0063] The Compton mode system transfer matrix is ​​obtained by analytical calculation, as shown in equation (4) below:

[0064] (4)

[0065] In the formula, For the Compton mode system transmission matrix, For Compton to conform to the event action sequence, For the first The pixels captured by the detector in the action sequence The radiation path to the location of Compton scattering. for The Compton differential section, The Compton scattering angle is... For the first The radiation path from the Compton scattering location to the photoelectric absorption location, captured by the detector in each action sequence.

[0066] The calculation formula for the Compton differential section is shown in equation (5) below:

[0067] (5)

[0068] In the formula, , The a priori energy of the radioactive source, The rest mass of the electron. It is the speed of light.

[0069] Optionally, multimode iterative reconstruction can be performed based on weights and the multimode system transfer matrix, as shown in equation (6) below:

[0070] (6)

[0071] In the formula, for The new estimate after the next iteration for The current estimate after the next iteration For image plane pixels, As weight, The total number of events in Compton is consistent. For the first Compton measurement counts in each action sequence For the Compton mode system transmission matrix, The total number of pixels in the image space. for In the normalization summation process of the nth iteration The current estimate of each image pixel. For image pixel index, This represents the total number of voxels in the detector. For detector voxels Photon measurement and counting at the location, For the transmission matrix of the non-collimation-mechanical collimation mode system, This is the sensitivity matrix.

[0072] Optionally, the panoramic gamma camera system includes: a three-dimensional position-sensitive semiconductor detection unit and an unshielded encoder module.

[0073] The three-dimensional position-sensitive semiconductor detection unit includes: a three-dimensional position-sensitive semiconductor, an application-specific integrated circuit chip, a field-programmable gate array, and a data acquisition system.

[0074] The unshielded encoder module includes: an encoder board and a side support layer.

[0075] On the other hand, a multi-mode iterative reconstruction device is provided, the multi-mode iterative reconstruction device comprising: a processor; a memory storing computer-readable instructions, wherein when the computer-readable instructions are executed by the processor, any one of the methods described above for multi-mode iterative reconstruction is implemented.

[0076] On the other hand, a computer-readable storage medium is provided, wherein at least one instruction is stored therein, the at least one instruction being loaded and executed by a processor to implement any of the methods described above in the multi-mode iterative reconstruction method.

[0077] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following:

[0078] This invention addresses the problem that existing multi-mode image reconstruction algorithms have not yet studied the trade-offs of the mode terms in the probability density function of the projection data, resulting in the resolution of the final multi-mode reconstructed image being inferior to that of the single-mode reconstructed image in some cases. This invention provides a weighted multi-mode iterative reconstruction method. In this method, the Compton collimation method is combined with the collimation-free-mechanical collimation method, and the three-mode system matrix is ​​analytically calculated. Information such as the prior energy of the radioactive source, the ratio of Compton scattering event counts to photoelectric absorption event counts is introduced. Based on weighted iterative reconstruction, stable multi-mode imaging is achieved, with Compton imaging having a higher weighting for high-energy imaging results and the collimation-free-mechanical collimation method having a higher weighting for mid-to-low-energy imaging results. Therefore, this solves the problems of traditional iterative reconstruction algorithms, such as their inability to perform targeted high-resolution imaging based on the characteristics of the radioactive source, low efficiency and sensitivity, and unstable imaging results. It effectively improves the imaging energy range, imaging field of view, and resolution of multi-mode gamma cameras. Attached Figure Description

[0079] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0080] Figure 1 This is a flowchart of a multi-modal iterative reconstruction method provided in an embodiment of the present invention;

[0081] Figure 2This is a schematic diagram of the multi-mode panoramic gamma camera system and the field of view of each mode provided in the embodiments of the present invention;

[0082] Figure 3 This is a schematic diagram of a three-dimensional position-sensitive semiconductor detection unit provided in an embodiment of the present invention;

[0083] Figure 4 This is a block diagram of a multi-mode iterative reconstruction device provided in an embodiment of the present invention;

[0084] Figure 5 This is a schematic diagram of the structure of a multi-mode iterative reconstruction device provided in an embodiment of the present invention;

[0085] Reference numerals: 1. Full decoding field of view in coded aperture imaging mode; 2. Semi-decoded field of view in coded aperture imaging mode; 3. Field of view in non-collimated imaging mode; 4. Field of view in Compton imaging mode; 11. Encoding plate; 12. Side support layer; 13. Three-dimensional position-sensitive semiconductor detection unit; 14. Electronic system; 111. Semiconductor detection module; 112. Pixel-type anode; 113. Planar cathode; 114. Compton scattering event in the three-dimensional depth space corresponding to a planar pixel unit; 115. Photoelectric absorption event in the three-dimensional depth space corresponding to a planar pixel unit. Detailed Implementation

[0086] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0087] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0088] In the embodiments of this invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that, without emphasizing the distinction between them, they convey the same meaning. Similarly, the terms "of," "corresponding (relevant)," and "corresponding" may sometimes be used interchangeably. It should be noted that, without emphasizing the distinction between them, they convey the same meaning.

[0089] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0090] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0091] This invention provides a multi-modal iterative reconstruction method, which can be implemented by a multi-modal iterative reconstruction device, which can be a terminal or a server. Figure 1 The flowchart of the multi-modal iterative reconstruction method shown below includes the following steps:

[0092] S1. Acquire event information about the interaction between gamma photons and the three-dimensional position-sensitive semiconductor detection unit within the panoramic gamma camera system.

[0093] In one feasible implementation, event information of the interaction between gamma photons and the detection unit within the panoramic gamma camera system is obtained, including timestamps, energy, three-dimensional position coordinates, interaction sequence, and interaction type. The interaction types include Compton scattering events and photoelectric absorption events.

[0094] Specifically, the trigger time of the signal pulse captured by the high-speed data acquisition system is recorded as a timestamp;

[0095] The energy is determined by the amplitude of the signal pulse;

[0096] The two-dimensional lateral spatial coordinates of photon interaction events are determined by the position of the grid-like anode response pixels in the detector array;

[0097] The depth of photon interaction events is determined by analyzing the ratio of the amplitudes of the cathode and anode signals.

[0098] The interaction sequence is determined by analyzing the timing information of the pulses corresponding to each interaction point through measuring the electron drift time;

[0099] The interaction type is determined by combining the number of interaction points and the energy deposition pattern of each point with location information. The interaction type includes either a Compton scattering event or a photoelectric absorption event.

[0100] Information about the gamma photon interaction event is obtained based on the timestamp, energy, two-dimensional horizontal spatial coordinates, interaction depth, interaction sequence, and interaction type of the gamma photon interaction event.

[0101] S2. Obtain information based on prior energy, Compton scattering event counts in event information, and photoelectric absorption event counts in event information, and calculate weights based on information; reconstruct the Compton sequence based on prior energy, and construct a multimode system transmission matrix based on the reconstructed Compton sequence.

[0102] In one feasible implementation, information is obtained based on prior energy, Compton scattering events, and photoelectric absorption event counts to calculate weights, while Compton sequence reconstruction is performed to construct a multimode system transmission matrix.

[0103] Optionally, the weight calculation method based on information content is as follows:

[0104] (1)

[0105] In the formula, As weight, To optimize the degree factor, This is the a priori energy of the radioactive source, which is obtained based on existing nuclide identification techniques. This represents the total count of Compton scattering events detected by the detector. This represents the total count of photoelectric absorption events detected by the detector.

[0106] Optionally, the above The value can be calculated using any one of the following methods: random search, Bayesian optimization, evolutionary algorithm, gradient descent algorithm, or deep learning algorithm. Specifically, this embodiment uses a random search method; however, it is understood that this embodiment is not limited to any particular method. Selection of value calculation method.

[0107] Alternatively, the Compton sequence reconstruction method is as follows:

[0108] The interaction sequence in full-energy double Compton coincidence events is determined by the magnitude of the deposition energy, and a Compton edge test is performed. The Compton edge energy is used to filter out correct double Compton coincidence events; only coincidence events within the edge energy range are reconstructed. Therefore, edge calculation is essentially a conditional judgment for whether to further reconstruct the sequence.

[0109] The Compton edge calculation formula is as follows:

[0110] (2)

[0111] In the formula, For Compton edge energy, The a priori energy of the radioactive source, The rest mass of the electron. It is the speed of light.

[0112] Optionally, the multimode system transmission matrix in S2 includes: a non-collimated-mechanical collimation mode system transmission matrix and a Compton mode system transmission matrix. The coded aperture mode is a type of mechanical collimation mode.

[0113] The system matrix calculation methods include:

[0114] The transmission matrix of the collimationless-mechanical collimation mode system is obtained through analytical calculation. The analytical calculation formula for the transmission matrix of the collimationless-mechanical collimation mode system is as follows:

[0115] (3)

[0116] In the formula, For the transmission matrix of the non-collimation-mechanical collimation mode system, For detector voxels, For image plane pixels, The attenuation coefficient of high-density alloys, For pixels captured by the mechanical collimator to detector voxel radiation path, The attenuation coefficient of the semiconductor detector is denoted as . For the pixels captured by the detector to detector voxel Surface radiation path, For the voxel captured by the detector, from the pixel to detector voxel The radiation path from the center.

[0117] The Compton mode system transfer matrix is ​​obtained through analytical calculation. The analytical calculation formula for the Compton mode system transfer matrix is ​​as follows:

[0118] (4)

[0119] In the formula, For the Compton mode system transmission matrix, For Compton to conform to the event action sequence, For the first The pixels captured by the detector in the action sequence The radiation path to the location of Compton scattering. for The Compton differential section, The Compton scattering angle is... For the first The radiation path from the Compton scattering location to the photoelectric absorption location, captured by the detector in each action sequence.

[0120] The formula for calculating the Compton differential section is as follows:

[0121] (5)

[0122] In the formula, , The a priori energy of the radioactive source, The rest mass of the electron. It is the speed of light.

[0123] S3. Multimode iterative reconstruction is performed based on weights and the multimode system transfer matrix to output a stable high signal-to-noise ratio image and determine the spatial distribution of the radiation source.

[0124] In one feasible implementation, a multi-mode iterative reconstruction is performed based on weights using Compton, collimation-free, and coded aperture imaging modes to output a stable high signal-to-noise ratio image within a 4π range. High angular resolution images are obtained within the mechanically collimated field of view, thereby determining the spatial distribution of the radiation source.

[0125] Furthermore, the obtained list pattern data and information required for multimodal image reconstruction are used for iterative reconstruction using the list pattern maximum likelihood expectation maximization algorithm. This invention innovatively introduces information based on the characteristics of each pattern, deriving a weighted multimodal iterative image reconstruction formula:

[0126] (6)

[0127] In the formula, for The new estimate after the next iteration for The current estimate after the next iteration For image plane pixels, As weight, The total number of events in Compton is consistent. For the first Compton measurement counts in each action sequence For the Compton mode system transmission matrix, The total number of pixels in the image space. for In the normalization summation process of the nth iteration The current estimate of each image pixel. For image pixel index, This represents the total number of voxels in the detector. For detector voxels Photon measurement and counting at the location, For the transmission matrix of the non-collimation-mechanical collimation mode system, This is the sensitivity matrix.

[0128] Optionally, the panoramic gamma camera system includes: a three-dimensional position-sensitive semiconductor detection unit and an unshielded encoder module.

[0129] The three-dimensional position-sensitive semiconductor detection unit includes: a three-dimensional position-sensitive semiconductor, an application-specific integrated circuit chip, a field-programmable gate array, and a data acquisition system.

[0130] The unshielded encoder module includes: an encoder board and a side support layer.

[0131] The encoding method of the encoding board can be any one of random array, non-redundant array, uniform redundant array, and modified uniform redundant array.

[0132] The side support layer has a cuboid structure with a preset thickness and is made of a material that has a weak ability to block gamma rays.

[0133] One feasible implementation method is, for example Figure 2 As shown, the field of view of this multi-mode gamma camera system includes: fully decoded field of view 1 of coded aperture imaging mode, half decoded field of view 2 of coded aperture imaging mode, field of view 3 of non-collimated imaging mode, and field of view 4 of Compton imaging mode.

[0134] Among them, the fully decoded field of view 1 of the coded aperture imaging mode and the half-decoded field of view 2 of the coded aperture imaging mode constitute a high-resolution small imaging field of view;

[0135] The field of view in non-collimated imaging mode 3 is a large field of view with general resolution;

[0136] The Compton imaging mode field of view 4 is a panoramic field of view in 4π image space.

[0137] Furthermore, the fully decoded field of view 1 of the coded aperture imaging mode, the semi-decoded field of view 2 of the coded aperture imaging mode, the field of view 3 of the collimationless imaging mode, and the field of view 4 of the Compton imaging mode together constitute the 4π panoramic field of view of the multi-mode gamma camera system.

[0138] Furthermore, the multimode gamma camera system module includes: an encoder board 11, a side support layer 12, a three-dimensional position-sensitive semiconductor detection unit 13, and an electronics system 14.

[0139] Among them, the coding plate 11 is made of high-density alloy;

[0140] The side support layer 12 has a rectangular structure with a preset thickness and is made of a material with weak gamma ray blocking ability. Specifically, in this embodiment, the side support layer 12 is made of lightweight acrylic material with a thickness of 5 mm.

[0141] Electronic system 14 includes: Application Specific Integrated Circuit (ASIC), Field Programmable Gate Array (FPGA), and Data Acquisition (DAQ).

[0142] Optionally, the encoding method of the encoding board 11 can be any one of random arrays (NA), non-redundant arrays (NRA), uniformly redundant arrays (URA), and modified uniformly redundant arrays (MURA). Specifically, the encoding board 11 in this embodiment adopts a 2*2 nested cyclic 13th-order modified uniformly redundant array made of tungsten alloy. Of course, it is understood that this embodiment does not limit the volume, high-density alloy material, and encoding method of the encoding board 11.

[0143] Optionally, the semiconductor type of the aforementioned three-dimensional position-sensitive semiconductor detection unit 13 is any one of high-purity Germanium (HPGe), silicon (Si), cadmium telluride (CdTe), cadmium zinc telluride (CZT), mercuric iodide (HgI2), and gallium arsenide (GaAs). Specifically, in this embodiment, the three-dimensional position-sensitive semiconductor detection unit 13 uses cadmium zinc telluride as the semiconductor detection crystal. Of course, it is understood that this embodiment does not limit the semiconductor type of the three-dimensional position-sensitive semiconductor detection unit 13.

[0144] Optionally, the arrangement type of the above-mentioned three-dimensional position sensitive semiconductor detection unit 13 can be either a single probe or an array. Specifically, the three-dimensional position sensitive semiconductor detection unit 13 in this embodiment adopts a 2*2 array arrangement. Of course, it is understood that this embodiment does not limit the unit volume and arrangement type of the three-dimensional position sensitive semiconductor detection unit 13.

[0145] like Figure 3 As shown, the three-dimensional position-sensitive semiconductor detection unit comprises: a semiconductor detection module 111, a pixel-type anode 112, and a flat cathode 113.

[0146] Among them, the pixel-type anode 112 is used to collect electron-hole pairs that move toward the electrode under the action of an electric field, so as to determine the two-dimensional lateral coordinates of the interaction generated when gamma photons interact in the semiconductor detection module 111.

[0147] The flat cathode 113 is used to provide changes in the pulse signal to measure the time required for electrons to drift from the interaction point to the anode, thereby determining the depth of action.

[0148] Furthermore, the gamma photon interaction types that can be detected in the semiconductor detection module 111 include: Compton scattering event 114 in the three-dimensional interaction depth space corresponding to a planar pixel unit, and photoelectric absorption event 115 in the three-dimensional interaction depth space corresponding to a planar pixel unit.

[0149] Through the detailed explanation of the multi-mode iterative image reconstruction method above, we have achieved fast system matrix solving for the multi-mode panoramic gamma camera system and stable high signal-to-noise ratio iterative reconstruction of wide-energy gamma rays in the 4π imaging plane, and obtained high angular resolution images within the mechanical collimation field of view.

[0150] It should be noted that the sensitivity matrix acquisition method of the present invention can be any of the analytical calculation method, Monte Carlo simulation method, or experimental measurement method; the preliminary estimate in the multi-mode iterative reconstruction algorithm can be any of the random number, direct back projection, or filtered back projection result; the distance between the image space and the detector center position, the pixel size of the image space, the voxel size of the detector space, the energy window threshold used to screen full-energy Compton coincidence events, the number of effective Compton sequences, the iteration step size, the number of iterations, and the interpolation method for image visualization can be flexibly adjusted according to actual needs.

[0151] In addition to the advantages mentioned above, the multi-mode iterative image reconstruction method proposed in this invention is applicable to multiple fields such as nuclear safety and environmental monitoring, nuclear facility decommissioning, and nuclear medicine imaging because it can perform stable high signal-to-noise ratio imaging of far-field radiation sources across the entire panorama.

[0152] In this invention, addressing the problem that existing multi-mode image reconstruction algorithms have not yet studied the trade-offs of various mode terms in the probability density function of projection data, resulting in the resolution of the final multi-mode reconstructed image being inferior to that of the single-mode reconstructed image in some cases, this invention provides a weighted multi-mode iterative reconstruction method. This method combines the Compton collimation method with the collimation-free-mechanical collimation method, analytically calculates the three-mode system matrix, and introduces information such as the prior energy of the radioactive source, the ratio of Compton scattering event counts to photoelectric absorption event counts. Based on weighted iterative reconstruction, stable multi-mode imaging is achieved, with Compton imaging having a higher weighting for high-energy imaging results and the collimation-free-mechanical collimation method having a higher weighting for mid-to-low-energy imaging results. This solves the problems of traditional iterative reconstruction algorithms, such as their inability to perform targeted high-resolution imaging based on the characteristics of the radioactive source, low efficiency and sensitivity, and unstable imaging results, effectively improving the imaging energy range, imaging field of view, and resolution of multi-mode gamma cameras.

[0153] Figure 4 This is a block diagram of a multi-modal iterative reconstruction apparatus according to an exemplary embodiment, the apparatus being used in a multi-modal iterative reconstruction method. (Refer to...) Figure 4 The device includes an acquisition module 310, a construction module 320, and an output module 330. Wherein:

[0154] The acquisition module 310 is used to acquire event information about the interaction between gamma photons and the three-dimensional position-sensitive semiconductor detection unit within the panoramic gamma camera system.

[0155] The construction module 320 is used to obtain information based on prior energy, Compton scattering event counts in event information, and photoelectric absorption event counts in event information, and to calculate weights based on the information; to reconstruct the Compton sequence based on prior energy, and to construct a multimode system transmission matrix based on the reconstructed Compton sequence.

[0156] The output module 330 is used to perform multi-mode iterative reconstruction based on weights and the multi-mode system transfer matrix, outputting a stable high signal-to-noise ratio image and determining the spatial distribution of the radiation source.

[0157] In this invention, addressing the problem that existing multi-mode image reconstruction algorithms have not yet studied the trade-offs of various mode terms in the probability density function of projection data, resulting in the resolution of the final multi-mode reconstructed image being inferior to that of the single-mode reconstructed image in some cases, this invention provides a weighted multi-mode iterative reconstruction method. This method combines the Compton collimation method with the collimation-free-mechanical collimation method, analytically calculates the three-mode system matrix, and introduces information such as the prior energy of the radioactive source, the ratio of Compton scattering event counts to photoelectric absorption event counts. Based on weighted iterative reconstruction, stable multi-mode imaging is achieved, with Compton imaging having a higher weighting for high-energy imaging results and the collimation-free-mechanical collimation method having a higher weighting for mid-to-low-energy imaging results. This solves the problems of traditional iterative reconstruction algorithms, such as their inability to perform targeted high-resolution imaging based on the characteristics of the radioactive source, low efficiency and sensitivity, and unstable imaging results, effectively improving the imaging energy range, imaging field of view, and resolution of multi-mode gamma cameras.

[0158] Figure 5 This is a schematic diagram of the structure of a multi-mode iterative reconstruction device provided in an embodiment of the present invention, as shown below. Figure 5 As shown, the multi-mode iterative reconstruction device may include the above-mentioned Figure 4 The multi-mode iterative reconstruction apparatus shown. Optionally, the multi-mode iterative reconstruction apparatus 410 may include a first processor 2001.

[0159] Optionally, the multi-mode iterative reconstruction device 410 may also include a memory 2002 and a transceiver 2003.

[0160] The first processor 2001, memory 2002, and transceiver 2003 can be connected via a communication bus.

[0161] The following is combined Figure 5 A detailed description of each component of the multi-mode iterative reconstruction device 410 is provided below:

[0162] The first processor 2001 is the control center of the multi-mode iterative reconstruction device 410. It can be a single processor or a collective term for multiple processing elements. For example, the first processor 2001 can be one or more central processing units (CPUs), application-specific integrated circuits (ASICs), or one or more integrated circuits configured to implement embodiments of the present invention, such as one or more digital signal processors (DSPs), or one or more field-programmable gate arrays (FPGAs).

[0163] Optionally, the first processor 2001 can perform various functions of the multi-mode iterative reconstruction device 410 by running or executing software programs stored in the memory 2002 and calling data stored in the memory 2002.

[0164] In a specific implementation, as one example, the first processor 2001 may include one or more CPUs, for example... Figure 5 CPU0 and CPU1 are shown in the diagram.

[0165] In a specific implementation, as one example, the multi-modal iterative reconstruction device 410 may also include multiple processors, for example... Figure 5 The first processor 2001 and the second processor 2004 are shown in the diagram. Each of these processors can be a single-core processor or a multi-core processor. Here, a processor can refer to one or more devices, circuits, and / or processing cores used to process data (such as computer program instructions).

[0166] The memory 2002 is used to store the software program that executes the present invention, and is controlled by the first processor 2001 to execute it. The specific implementation method can be referred to the above method embodiment, and will not be repeated here.

[0167] Optionally, the memory 2002 may be a read-only memory (ROM) or other type of static storage device capable of storing static information and instructions, random access memory (RAM) or other type of dynamic storage device capable of storing information and instructions, or electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM) or other optical disc storage, optical disc storage (including compressed optical discs, laser discs, optical discs, digital universal optical discs, Blu-ray discs, etc.), magnetic disk storage media or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but not limited thereto. The memory 2002 may be integrated with the first processor 2001 or may exist independently, and may be connected to the interface circuit of the multi-mode iterative reconstruction device 410. Figure 5 (Not shown in the image) is coupled to the first processor 2001, and this embodiment of the invention does not specifically limit this.

[0168] The transceiver 2003 is used to communicate with network devices or with terminal devices.

[0169] Alternatively, transceiver 2003 may include a receiver and a transmitter. Figure 5 (Not shown separately). The receiver is used to implement the receiving function, and the transmitter is used to implement the transmitting function.

[0170] Optionally, the transceiver 2003 can be integrated with the first processor 2001, or it can exist independently, and its interface circuit of the device 410 can be reconstructed through multi-mode iterative reconstruction. Figure 5 (Not shown in the image) is coupled to the first processor 2001, and this embodiment of the invention does not specifically limit this.

[0171] It should be noted that, Figure 5 The structure of the multi-mode iterative reconstruction device 410 shown does not constitute a limitation on the router. Actual knowledge structure identification devices may include more or fewer components than shown, or combine certain components, or have different component arrangements.

[0172] Furthermore, the technical effects of the multi-mode iterative reconstruction device 410 can be referred to the technical effects of the multi-mode iterative reconstruction method described in the above method embodiments, and will not be repeated here.

[0173] It should be understood that the first processor 2001 in the embodiments of the present invention may be a central processing unit (CPU), or it may be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc.

[0174] It should also be understood that the memory in the embodiments of the present invention can be volatile memory or non-volatile memory, or may include both volatile and non-volatile memory. The non-volatile memory can be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. The volatile memory can be random access memory (RAM), which is used as an external cache. By way of example, but not limitation, many forms of random access memory (RAM) are available, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate synchronous DRAM (DDR SDRAM), enhanced synchronous DRAM (ESDRAM), synchronous linked DRAM (SLDRAM), and direct rambus RAM (DR RAM).

[0175] The above embodiments can be implemented, in whole or in part, by software, hardware (such as circuits), firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more sets of available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium. A semiconductor medium can be a solid-state drive.

[0176] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0177] In this invention, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of a single item or a plurality of items. For example, at least one of a, b, or c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be a single item or multiple items.

[0178] It should be understood that, in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0179] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0180] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the devices, apparatuses, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0181] In the several embodiments provided by this invention, it should be understood that the disclosed devices, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another device, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0182] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0183] In addition, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0184] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0185] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multi-modal iterative reconstruction method, characterized in that, The method includes: S1. Obtain event information about the interaction between gamma photons and the three-dimensional position-sensitive semiconductor detection unit within the panoramic gamma camera system; S2. Obtain information based on prior energy, Compton scattering event counts in event information, and photoelectric absorption event counts in event information; calculate weights based on the information; reconstruct the Compton sequence based on prior energy; and construct a multimode system transmission matrix based on the reconstructed Compton sequence; wherein, the multimode system transmission matrix includes: a non-collimated-mechanical collimated mode system transmission matrix and a Compton mode system transmission matrix; S3. Based on the weights and the multimode system transmission matrix, perform multimode iterative reconstruction to output a stable high signal-to-noise ratio image and determine the spatial distribution of the radiation source.

2. The multi-mode iterative reconstruction method according to claim 1, characterized in that, The event information in S1 includes: timestamp, energy, three-dimensional location coordinates, action sequence, and action type; The types of interaction include: Compton scattering events and photoelectric absorption events; The timestamp is triggered by the signal pulses captured by the data acquisition system within the panoramic gamma camera system. The energy is determined by the amplitude of the signal pulse; The three-dimensional position coordinates are determined by using the position of the anode response pixel of the detector array to determine the two-dimensional lateral spatial coordinates of the photon interaction event, and by analyzing the ratio of the cathode and anode signal amplitudes to determine the interaction depth of the photon interaction event. The three-dimensional position coordinates are then determined based on the two-dimensional lateral spatial coordinates and the interaction depth. The interaction sequence is determined by measuring the electron drift time and analyzing the timing information of the pulses corresponding to each interaction point; The interaction type is determined by combining the number of interaction points and the energy deposition pattern of each point with location information.

3. The multi-mode iterative reconstruction method according to claim 1, characterized in that, The calculation weights in S2 are shown in equation (1) below: （1） In the formula, As weight, To optimize the degree factor, The a priori energy of the radioactive source, This represents the total count of Compton scattering events detected by the detector. This represents the total count of photoelectric absorption events detected by the detector.

4. The multi-mode iterative reconstruction method according to claim 1, characterized in that, The Compton sequence reconstruction in S2 includes: The interaction sequence in the full-energy double Compton coincidence event is determined by the magnitude of the deposition energy, and the Compton margin test is performed. The Compton edge test calculation formula is shown in equation (2) below: （2） In the formula, For Compton edge energy, The a priori energy of the radioactive source, The rest mass of the electron. It is the speed of light.

5. The multi-mode iterative reconstruction method according to claim 1, characterized in that, The methods for obtaining the transmission matrix of the collimationless-mechanical collimation mode system and the Compton mode system in S2 include: The transmission matrix of the collimationless-mechanical collimation mode system is obtained by analytical calculation, as shown in equation (3) below: （3） In the formula, For the transmission matrix of the non-collimation-mechanical collimation mode system, For detector voxels, For image plane pixels, The attenuation coefficient of high-density alloys, For pixels captured by the mechanical collimator to detector voxel radiation path, The attenuation coefficient of the semiconductor detector is denoted as . For the pixels captured by the detector to detector voxel Surface radiation path, For the voxel captured by the detector, from the pixel to detector voxel The radiation path from the center; The Compton mode system transfer matrix is ​​obtained by analytical calculation, as shown in equation (4) below: （4） In the formula, For the Compton mode system transmission matrix, For Compton to conform to the event action sequence, For the first The pixels captured by the detector in the action sequence The radiation path to the location of Compton scattering. for The Compton differential section, The Compton scattering angle is... For the first The radiation path from the Compton scattering location to the photoelectric absorption location captured by the detector in each action sequence; The calculation formula for the Compton differential section is shown in equation (5) below: （5） In the formula, , The a priori energy of the radioactive source, The rest mass of the electron. It is the speed of light.

6. The multi-mode iterative reconstruction method according to claim 1, characterized in that, The multi-mode iterative reconstruction in S3, based on the weights and the multi-mode system transmission matrix, is shown in equation (6) below: （6） In the formula, for The new estimate after the next iteration for The current estimate after the next iteration For image plane pixels, As weight, The total number of events in Compton is consistent. For the first Compton measurement counts in each action sequence For the Compton mode system transmission matrix, The total number of pixels in the image space. for In the normalization summation process of the nth iteration The current estimate of each image pixel. For image pixel index, This represents the total number of voxels in the detector. For detector voxels Photon measurement and counting at the location, For the transmission matrix of the non-collimation-mechanical collimation mode system, This is the sensitivity matrix.

7. The multi-mode iterative reconstruction method according to claim 1, characterized in that, The panoramic gamma camera system includes: a three-dimensional position-sensitive semiconductor detection unit and an unshielded encoding board module; The three-dimensional position-sensitive semiconductor detection unit includes: a three-dimensional position-sensitive semiconductor, an application-specific integrated circuit chip, a field-programmable gate array, and a data acquisition system; The unshielded encoder module includes: an encoder board and a side support layer.

8. A multi-modal iterative reconstruction apparatus, wherein the multi-modal iterative reconstruction apparatus is used to implement the multi-modal iterative reconstruction method as described in any one of claims 1-7, characterized in that, The device includes: The acquisition module is used to acquire event information about the interaction between gamma photons and the three-dimensional position-sensitive semiconductor detection unit within the panoramic gamma camera system; The module is used to acquire information based on prior energy, Compton scattering event counts in event information, and photoelectric absorption event counts in event information; calculate weights based on the information; reconstruct the Compton sequence based on prior energy; and construct a multimode system transmission matrix based on the reconstructed Compton sequence. The output module is used to perform multi-mode iterative reconstruction based on the weights and the multi-mode system transfer matrix, output a stable high signal-to-noise ratio image, and determine the spatial distribution of the radiation source.

9. A multi-modal iterative reconstruction device, characterized in that, The multi-modal iterative reconstruction device includes: processor; A memory storing computer-readable instructions that, when executed by the processor, implement the method as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium contains program code that can be invoked by a processor to execute the method as described in any one of claims 1 to 7.

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