CN-122004910-A - Crystal detector modeling method, equipment and medium for SPECT

CN122004910ACN 122004910 ACN122004910 ACN 122004910ACN-122004910-A

Abstract

The application relates to the technical field of nuclear medicine imaging, and particularly provides a modeling method, equipment and medium of a crystal detector for SPECT, wherein the method comprises the steps of acquiring an ideal system transmission matrix, pinhole position arrangement, nuclide type and energy window of the crystal detector used by a current SPECT system; extracting a corresponding conversion matrix from a pre-constructed mapping relation table about pinhole position arrangement, nuclide type, energy window and conversion matrix according to the pinhole position arrangement, nuclide type and energy window to serve as an actual conversion matrix, wherein the actual conversion matrix represents the count of each actual detection pixel in a crystal detector used by a current SPECT system when photons are incident to ideal detection pixels in a second ideal detector, and the actual system transmission matrix is calculated according to the ideal system transmission matrix and the actual conversion matrix.

Inventors

LI KUN
XU CHENGCONG
DENG XIAO
HUANG GANG

Assignees

瑞石心禾(河北)医疗科技有限公司

Dates

Publication Date: 20260512
Application Date: 20251231

Claims (10)

1. A method for modeling a crystal detector for SPECT, for constructing an actual system transmission matrix of crystal detectors, the method comprising the steps of: S1, acquiring an ideal system transmission matrix, pinhole position arrangement, nuclide type and energy window of a crystal detector used by a current SPECT system, wherein the ideal system transmission matrix represents the count of each ideal detection pixel in a second ideal detector constructed based on the crystal detector used by the current SPECT system after the voxel decays, and the second ideal detector is a detector with the action depth of 0 and the efficiency of 100% of the crystal detector used by the current SPECT system; s2, extracting a corresponding conversion matrix from a pre-constructed mapping relation table about pinhole position arrangement, nuclide type, energy window and conversion matrix according to the pinhole position arrangement, nuclide type and energy window to serve as an actual conversion matrix, wherein the actual conversion matrix represents the count of each actual detection pixel in a crystal detector used by a current SPECT system when photons are incident to the ideal detection pixels in the second ideal detector; s3, calculating an actual system transmission matrix according to the ideal system transmission matrix and the actual conversion matrix.
2. The method of modeling a crystal detector for SPECT of claim 1 wherein the crystal detector includes a plurality of actual detection pixels, and the pre-construction process of the mapping table for pinhole location arrangement, species type, energy window, and conversion matrix includes: a1, constructing a first ideal detector aiming at crystal detectors with different pinhole position arrangement, nuclide types and energy window combinations, and dividing the first ideal detector into a plurality of ideal detection pixels based on the positions and the sizes of the crystal detectors, wherein the first ideal detector is a detector with the action depth of 0 and the efficiency of 100 percent and positioned on the surface of the current crystal detector; A2, aiming at the crystal detector with different pinhole position arrangements, nuclide types and energy window combinations, acquiring actual count vectors corresponding to all the ideal detection pixels by using a Monte Carlo simulation method, and integrating all the actual count vectors into a conversion matrix to obtain a mapping relation of the pinhole position arrangements, nuclide types, energy windows and the conversion matrix, wherein the actual count vectors are used for representing counts generated by all the actual detection pixels in a preset energy window when photons are incident to the ideal detection unit; a3, integrating all the mapping relations about pinhole position arrangement, nuclide type, energy window and conversion matrix into a mapping relation table about pinhole position arrangement, nuclide type, energy window and conversion matrix.
3. The method of modeling a crystal detector for SPECT of claim 2 wherein the process of obtaining actual count vectors for each of the ideal detection pixels using a monte carlo simulation method includes: B1, setting a mask above the first ideal detector for each ideal detection pixel, setting a pinhole opening which is opposite to the ideal detection pixel and has the same size as the ideal detection pixel on the mask, and setting a point source at the center of the pinhole opening; B2, simulating the process that photons generated by the corresponding point sources of the ideal detection pixels are incident to the ideal detection pixels through the openings corresponding to the ideal detection pixels by using a Monte Carlo program for each ideal detection pixel, and acquiring the total number of primary ray events, the solid angle of the surface of the ideal detection pixels relative to the positions of the point sources and the count of each actual detection pixel; b3, for each of said ideal detection pixels, calculating an actual count vector from the corresponding solid angle, said total number of primary ray events and said count.
4. A method of modeling a crystal detector for SPECT as claimed in claim 3 wherein the solid angle of the ideal detection pixel is calculated as: ; Where Ω denotes the solid angle of the ideal detection pixel, To substitute x + 、y + and d into The specific values to be obtained later are, To substitute x - 、y - and d into The specific values to be obtained later are, To substitute x - 、y + and d into The specific values to be obtained later are, To substitute x + 、y - and d into The specific values to be obtained later are, Representing the positive pyramidal solid angles with base lengths alpha and beta and heights gamma respectively, X and y represent the position coordinates of the projection of the center of the ideal detector on the ideal detector plane relative to the point source, a and b represent the length and width of the ideal detector, respectively, and d represents the distance from the point source to the ideal detector plane; The calculation formula of the positive pyramid solid angle is shown as follows: ; the calculation formula of the elements in the actual conversion matrix is shown as follows: ; Wherein d ij represents a specific value of an actual count vector corresponding to the ith ideal detection pixel in the actual conversion matrix at the jth actual detection unit, pi represents a circumference ratio, m j represents a count of the jth actual detection pixel, and N i represents a total number of primary ray events when the ith ideal detection pixel is simulated.
5. A method of modeling a crystal detector for SPECT as claimed in claim 3 wherein step B2 includes: B2, simulating the process that photons generated by a point source at the center of an opening of a pinhole enter the ideal detection pixel through an opening corresponding to the ideal detection pixel aiming at each ideal detection pixel, and acquiring the total number of primary ray events, the solid angle of the ideal detection pixel, the count of actual detection pixels positioned right below the ideal detection pixel and the count of actual detection pixels in a preset circle taking the ideal detection pixel as the center, wherein the preset circle is that the ratio of the count of the actual detection pixels in an r+1 circle taking the ideal detection pixel as the center to the count of the actual detection pixels positioned right below the ideal detection pixel is smaller than r of a preset ratio threshold value.
6. A method of modeling a crystal detector for SPECT as claimed in claim 3 wherein the emission spectrum of the point source is the emission spectrum of the type of nuclear species to which the point source corresponds.
7. The method of modeling a crystal detector for SPECT of claim 1 wherein step S1 includes: s11, acquiring pinhole position arrangement, nuclide type and energy window of a crystal detector used by a current SPECT system; S12, constructing a second ideal detector based on a crystal detector used by the current SPECT system, and then calculating an ideal system transmission matrix corresponding to the second ideal detector based on attenuation correction, decay correction or collimator response, wherein the second ideal detector is a detector with the action depth of 0 and the efficiency of 100% on the surface of the crystal detector used by the current SPECT system.
8. The method of modeling a crystal detector for SPECT of claim 1 wherein the calculation formula of the actual system transmission matrix is shown as: ; Wherein, the The actual system transmission matrix elements representing the voxels k through the j-th actual detection unit, An ideal system transmission matrix representing voxels k through the ith real detection unit, The specific value of the actual count vector corresponding to the ith ideal detection pixel in the actual conversion matrix in the jth actual detection unit is shown.
9. An electronic device comprising a processor and a memory storing computer readable instructions that, when executed by the processor, perform the steps in the method of any of claims 1-8.
10. A computer readable storage medium, on which a computer program is stored, characterized in that the computer program, when being executed by a processor, performs the steps of the method according to any of claims 1-8.

Description

Crystal detector modeling method, equipment and medium for SPECT Technical Field The application relates to the technical field of nuclear medicine imaging, in particular to a method, equipment and medium for modeling a crystal detector for SPECT (single photon emission computed tomography). Background The pixelated crystal detector based on the silicon-based photomultiplier is widely applied in the field of nuclear medicine imaging, and has the advantages of low cost and high precision. Such detectors are typically of modular design, with a plurality of detector modules constituting a complete system. The internal structure of a single detector module is complex, reflection layers are filled between pixel crystal bars and at the edges of the module, and a mechanical installation reserved gap exists between the modules. These structural characteristics make it difficult to model accurately by conventional analytical methods, on the one hand, the reflective layer and void regions do not produce photon counts, and on the other hand, their X-ray absorption characteristics differ significantly from that of scintillation crystals. The use of pinhole collimators further exacerbates modeling difficulties in single photon emission computed tomography systems. Compared with the traditional parallel hole collimator, the pinhole collimator causes incident photons to present a larger angle variation range on the surface of the detector, and the incidence angle difference between the central area and the edge area is obvious. Such non-uniform incidence characteristics make conventional detector response function calculation methods based on effective depth of action no longer applicable. The modeling accuracy of the system transmission matrix directly influences the fault reconstruction quality, and the accuracy of the detector response modeling is particularly important as a key link in the fault reconstruction quality. For a combined system of a multi-module pixelized detector and a pinhole collimator, how to establish a system transmission matrix capable of accurately reflecting the actual physical process becomes a technical bottleneck for restricting the improvement of imaging quality. In view of the above problems, no effective technical solution is currently available. Disclosure of Invention The application aims to provide a crystal detector modeling method, equipment and medium for SPECT, which can effectively improve the quality of SPECT imaging and the accuracy of diagnosis. In a first aspect, the present application provides a method for modeling a crystal detector for SPECT, for constructing an actual system transmission matrix of the crystal detector, the method comprising the steps of: S1, acquiring an ideal system transmission matrix, pinhole position arrangement, nuclide type and energy window of a crystal detector used by a current SPECT system, wherein the ideal system transmission matrix represents the count of each ideal detection pixel in a second ideal detector constructed based on the crystal detector used by the current SPECT system after the voxel decays, and the second ideal detector is a detector with the action depth of 0 and the efficiency of 100% of the crystal detector used by the current SPECT system; S2, extracting a corresponding conversion matrix from a pre-constructed mapping relation table about pinhole position arrangement, nuclide type, energy window and conversion matrix according to the pinhole position arrangement, nuclide type and energy window to serve as an actual conversion matrix, wherein the actual conversion matrix characterizes the count of each actual detection pixel in a crystal detector used by a current SPECT system when photons are incident to the ideal detection pixels in a second ideal detector; s3, calculating an actual system transmission matrix according to the ideal system transmission matrix and the actual conversion matrix. According to the crystal detector modeling method for SPECT, the ideal system transmission matrix and the actual conversion matrix are introduced to decompose the complex modeling problem into two relatively independent sub-problems, the acquisition of the ideal system transmission matrix can ignore the complex response of the detector, the initial modeling process is simplified, the actual conversion matrix is obtained by inquiring a pre-constructed mapping relation table of pinhole position arrangement, nuclide type, energy window and conversion matrix according to the pinhole position arrangement, nuclide type and energy window, and the complexity of the internal structure of the detector and the non-uniform incidence characteristic caused by a pinhole collimator are efficiently processed, so that the comprehensive consideration of various influencing factors can be realized by the step-by-step integration mode to generate a comprehensive and accurate system transmission matrix, and the SPECT imaging quality and the diagnosis accuracy