Radiotherapy homologous electron pair tomography imaging system and image reconstruction method

Abstract

The invention relates to a radiotherapy homologous electron pair tomography imaging system and an image reconstruction method. The radiotherapy homologous electron pair tomography imaging system is provided with a linear accelerator head; the two annular detectors are located in the same axial plane and are symmetrically arranged; the linear accelerator head is arranged at the notch of the double-ring-shaped detector; the annular detector is formed by arranging a plurality of detection modules along a circular ring. According to the imaging system, the detector is prevented from being damaged due to the fact that high-energy X-rays directly irradiate the detector, and the clinical feasibility of the P2T imaging system is improved. According to the image reconstruction method, on the basis of the double-ring P2T imaging system, the Monte Carlo method is utilized, the electron pair effect generated by irradiating the human tissue through the high-energy X pencil beam is simulated, and the coincidence event formed by positron annihilation is collected through the detection unit. Attenuation, random and scattering correction is carried out on coincidence events, and a P2T image is quickly reconstructed by using an intersection line method, so that the reduction of imaging resolution is avoided.

Description

Technical Field

[0001] The present invention relates to the field of radiotherapy imaging technology, and in particular to a double quarter-ring radiotherapy homologous electron pair tomography imaging system and an image reconstruction method. Background Art

[0002] Online target tracking and dose monitoring in tumor radiotherapy are crucial to improving the accuracy of radiotherapy, reducing the occurrence of complications, and improving the quality of life of patients. In order to dynamically monitor the changes in tumor position caused by physiological factors such as breathing and intestinal peristalsis during radiotherapy, and to adjust the direction and dose distribution of the radiation beam in time to ensure accurate irradiation of tumor tissue while minimizing damage to surrounding normal tissues, the commonly used online tumor positioning methods currently include kilovoltage X-ray imaging, megavoltage X-ray electronic portal imaging system, megavoltage cone beam computed tomography (CBCT) imaging, and other structural or functional imaging tracking technologies, such as online ultrasound, magnetic resonance (MR) and positron emission tomography (PET). On the other hand, online dose monitoring technology monitors the radiation dose distribution received by the patient through real-time imaging, compares it with the pre-established treatment plan, and promptly detects and corrects dose deviations, thereby ensuring that the patient receives an accurate radiation dose during treatment, improving the treatment effect and reducing adverse reactions and complications during treatment. Existing online dose monitoring equipment includes megavoltage CBCT, electronic portal imaging system, ionizing radiation induced acoustic imaging system, and X-ray induced Cherenkov luminescence imaging system.

[0003] Although online target tracking and dose monitoring equipment can be used independently, some equipment also has dual functions. For example, X-ray electronic portal imaging system, megavoltage CBCT, ionizing radiation induced acoustic imaging system and X-ray induced Cherenkov luminescence imaging system can not only reduce the space occupied by the treatment room, save equipment installation and calibration time, but also improve the stability of radiotherapy equipment. Among them, the advantages of X-ray electronic portal imaging system, ionizing radiation induced acoustic imaging system and X-ray induced Cherenkov luminescence imaging system over megavoltage CBCT are that their radiotherapy and image guidance are homologous, which avoids patients and medical staff from being exposed to additional imaging radiation sources, and prevents the cumulative imaging dose caused by multi-fractionated radiotherapy from exceeding the requirement of 5% of the planned radiotherapy dose, which is more in line with the concept of radiation protection safety. However, due to the limited penetration of Cherenkov light, X-ray induced Cherenkov luminescence imaging may not be able to provide clear imaging of tumors deep in the body, and electronic portal imaging system and ionizing radiation induced acoustic imaging have the limitation of low soft tissue resolution.

[0004] In recent years, radiotherapy homologous electron pair tomography (P2T) imaging technology has become an emerging radiotherapy imaging method. By measuring the electron pair effect produced by high-energy X-ray irradiation of human tissue, it is expected to achieve high contrast distinction between tumors and normal tissues to achieve online target positioning without increasing additional radiation exposure. At the same time, it dynamically monitors the spatial distribution of real-time radiation dose to achieve dual-guided radiotherapy of target and dose. However, the clinical feasibility of the currently proposed P2T imaging system is low. Its design draws on the full-ring detector structure and ideal detector performance of the PET imaging system, and it is difficult to avoid the influence of X-ray irradiation on the detector unit. In addition, the reconstruction technology used in current P2T imaging does not fully consider the interference of physical factors on data acquisition (such as photon attenuation, scattering and random events), resulting in a decrease in imaging resolution. Especially in radiotherapy, the demand for real-time dynamic imaging leads to a low amount of raw data that can be collected in a short time frame. In this low count rate, if physical factors are not corrected, the reconstructed image is easily interfered by noise, which affects the imaging quality.

[0005] Therefore, in view of the shortcomings of the existing technology, it is necessary to provide a double quarter-ring radiotherapy homologous electron pair tomography imaging system and an image reconstruction method to overcome the shortcomings of the existing technology. Summary of the invention

[0006] In order to solve the above-mentioned P2T imaging technology problems, the purpose of the present invention is to provide a double quarter-ring P2T imaging system and an image reconstruction method that takes physical factors into consideration to correct the image, so as to overcome the influence of high-energy X-ray sources on detectors and improve the quality of P2T reconstructed images.

[0007] The purpose of the present invention is achieved through the following technical measures.

[0008] Provided is a radiotherapy homologous electron pair tomography imaging system, comprising: A straight line accelerator head; Two annular detectors, the two annular detectors are located in the same axial plane and are symmetrically arranged; The linear accelerator head is placed at the gap of the double-ring detector to prevent X-rays from directly irradiating the detection unit; the ring detector is composed of detection modules arranged along a ring.

[0009] Furthermore, in the radiotherapy homologous electron pair tomography imaging system, the two annular detectors have the same shape.

[0010] Preferably, in the radiotherapy homologous electron pair tomography imaging system, the annular detector is a one-quarter, three-sixteenth, or three-eighths annular structure.

[0011] Preferably, in the above-mentioned radiotherapy homologous electron pair tomography imaging system, the detection module is composed of a plurality of scintillation crystals, and the plurality of scintillation crystals are fixed to the inner wall of the ring and arranged along the axial direction.

[0012] Preferably, in the radiotherapy homologous electron pair tomography imaging system, a plurality of scintillation crystals are arranged in a matrix.

[0013] Preferably, in the radiotherapy homologous electron pair tomography imaging system, the annular detector is composed of 12 detection modules along the circumferential direction, and each detection module is composed of 3 groups of 13x13 and 4x4mm in size along the axial direction. 2 , composed of 2 cm thick LSO (Lutetium Oxyorthosilicate) scintillation crystals.

[0014] Preferably, in the radiotherapy homologous electron pair tomography imaging system, the radius of the annular detector is 82.4 cm.

[0015] The present invention also provides a P2T image reconstruction method based on physical factor correction, which is collected by the above-mentioned radiotherapy homologous electron pair tomography imaging system, and includes the following steps: (1) Monte Carlo simulation software is used to simulate the generation of high-energy X-ray pencil beams by linear accelerator heads; (2) Monte Carlo simulation software was used to simulate a double-ring detector composed of scintillation crystals. (3) Using Monte Carlo simulation software to construct human tissue phantoms of different densities; (4) Monte Carlo simulation software was used to simulate the high-energy X-ray pencil beam irradiation phantom. The electron pair effect generated in the phantom was simulated and tracked to emit positrons. The positrons annihilated with nearby electrons to generate a pair of 511 keV gamma photons moving in opposite directions. The gamma photon event detected simultaneously by two detection units within an extremely short time (usually less than 10 ns) was defined as a coincidence event. The response path between the two detection units was defined as the coincidence response line (LOR). The coincidence event time window was set between a few nanoseconds and several hundred nanoseconds, and the number of coincidence events was recorded. (4) Performing physical factor correction on the collected coincident events, including the following steps: (4.1) The total path length of the gamma photon pair passing through the phantom tissue is measured, and then the attenuation correction coefficient is calculated based on the tissue density. The formula is: ……(1); Where e is an exponential function, u is the attenuation coefficient of the tissue passed through, and D is the total length of the attenuation path; (4.2) By adding a delayed coincidence window when recording coincidence events, the coincidence events within the delayed coincidence window are used as estimates of random coincidence events; (4.3) Generate an attenuation map based on the density of human tissue filled in the phantom, preliminarily reconstruct a P2T image based on the collected coincident events, and use the attenuation map and P2T image as inputs to the Single Scatter Simulation (SSS) algorithm; Calculate the single scattering distribution, and then scale it to the total scattering distribution to obtain the scattering coincidence events; (4.4) According to the attenuation correction coefficient and the estimated random and scattered coincidence events, attenuation, random and scattered corrections are performed on the coincidence events on each collected ROI. The formula is: ……(2); Where pp is the number of coincidence events, r is the number of random coincidence events, s is the number of scattered coincidence events, ac is the attenuation correction coefficient, and ture is the number of corrected coincidence events; (5) Reconstructing a P2T image representing the spatial distribution of the electron pair effect from the corrected coincidence events, which includes the following steps: (5.1) According to the width of the detection unit, the X-pencil beam is discretized piecewise; (5.2) Take a LOR (line of coincidence response), calculate its intersection with the X-pencil beam, and superimpose the corrected number of coincidence events on the ROL in the segment where the intersection is located; (5.3) Repeat operation (5.2) for all LORs; (5.4) The total number of coincident events in each segment of the X-pencil beam is counted as the P2T image intensity value of that segment.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides a dual-ring P2T imaging system, which integrates a medical linear accelerator and a scintillation crystal detector in the same axial plane, and the linear accelerator head is located at the notch of the detector ring, thereby avoiding damage to the detector caused by direct high-energy X-rays and improving the clinical feasibility of the P2T imaging system.

[0017] 2. The present invention also proposes a P2T image reconstruction method combined with physical factor correction. The method is based on a double quarter-ring P2T imaging system and uses the Monte Carlo method to simulate the electron pair effect produced by high-energy X-ray pencil beam irradiating human tissue and the detection unit collecting coincidence events formed by positron annihilation. The coincidence events are corrected for attenuation, randomness, and scattering, and the P2T image is quickly reconstructed using the intersection line method, avoiding the reduction of imaging resolution of the P2T image due to physical factors. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention is further described with reference to the accompanying drawings, but the contents in the accompanying drawings do not constitute any limitation to the present invention.

[0019] Figure 1 It is a structural schematic diagram of the double quarter ring radiotherapy homologous electron pair tomography imaging system of the present invention.

[0020] Figure 2 It is a schematic diagram of the double quarter-ring P2T imaging reconstruction method.

[0021] Figure 3 These are P2T reconstructed images simulating X-ray pencil beam irradiation of tissues of different densities, where (a) is the reconstructed image without considering physical factor correction, and (b) is the reconstructed image with physical factor correction.

[0022] exist Figure 1 to Figure 2 Including: Linear accelerator head 100, Ring detector 200 and detection module 210 . DETAILED DESCRIPTION

[0023] The present invention will be further described with reference to the following examples.

[0024] Example 1 A radiotherapy homologous electron pair tomography imaging system, comprising: A straight line accelerator head; Two annular detectors, the two annular detectors are located in the same axial plane and are symmetrically arranged; The linear accelerator head is placed at the gap of the double-ring detector to prevent X-rays from directly irradiating the detection unit; the ring detector is composed of detection modules arranged along a ring.

[0025] The radiotherapy homologous electron pair tomography imaging system has two annular detectors of the same shape, same curvature, same width and same length, which are assembled on a frame to form a symmetrical structure.

[0026] The ring detector is a one-quarter, three-sixteenth, or three-eighth ring structure. The detection module is composed of a plurality of scintillation crystals, which are fixed to the inner wall of the ring and arranged along the axial direction. The plurality of scintillation crystals are arranged in a matrix.

[0027] This embodiment also provides a P2T image reconstruction method based on physical factor correction, which is collected by the above-mentioned radiotherapy homologous electron pair tomography imaging system, and includes the following steps: (1) Monte Carlo simulation software is used to simulate the generation of high-energy X-ray pencil beams by linear accelerator heads.

[0028] (2) Monte Carlo simulation software is used to simulate a double-ring detector composed of scintillation crystals.

[0029] (3) Monte Carlo simulation software was used to construct human tissue phantoms with different densities.

[0030] (4) Monte Carlo simulation software is used to simulate the high-energy X-ray pencil beam irradiation phantom, simulating the electron pair effect generated in the tracking phantom to emit positrons. The positrons annihilate with nearby electrons to generate a pair of 511 keV gamma photons moving in opposite directions. The gamma photon event detected by two detection units simultaneously within an extremely short time (usually less than 10 ns) is defined as a coincidence event. The response path between the two detection units is the coincidence response line (LOR). The coincidence event time window is set between a few nanoseconds and hundreds of nanoseconds, and the number of coincidence events is recorded. It should be noted that the extremely short time is usually less than 10 ns, and the specific time value can be flexibly set according to actual needs.

[0031] (4) Performing physical factor correction on the collected coincident events, including the following steps: (4.1) The total path length of the gamma photon pair passing through the phantom tissue is measured, and then the attenuation correction coefficient is calculated based on the tissue density. The formula is: ……(1); Where e is an exponential function, u is the attenuation coefficient of the tissue passed through, and D is the total length of the attenuation path.

[0032] (4.2) By adding a delayed coincidence window when recording coincidence events, the coincidence events within the delayed coincidence window are used as estimates of random coincidence events.

[0033] (4.3) Generate an attenuation map based on the density of human tissue filled in the phantom, preliminarily reconstruct a P2T image based on the collected coincident events, and use the attenuation map and P2T image as inputs to the Single Scatter Simulation (SSS) algorithm; Calculate the single scattering distribution and scale it to the total scattering distribution to obtain the scattering coincidence events.

[0034] It should be noted that the specific algorithm of single scattering estimation and scaling is a conventional algorithm, which is not the innovation of the present invention and will not be described in detail here.

[0035] (4.4) According to the attenuation correction coefficient and the estimated random and scattered coincidence events, attenuation, random and scattered corrections are performed on the coincidence events on each collected ROI. The formula is: ……(2); Among them, among them, pp To match the number of events, r is the number of random coincidence events, s is the number of scattering coincidence events, ture is the number of corrected matching events.

[0036] (5) Reconstructing a P2T image representing the spatial distribution of electron pair effect events from the corrected coincident events, which includes the following steps: (5.1) According to the width of the detection unit, the X-pencil beam is discretized into pieces; (5.2) Take a LOR (line of coincidence response), calculate its intersection with the X-pencil beam, and superimpose the corrected number of coincidence events on the ROL in the segment where the intersection is located; (5.3) Repeat operation (5.2) for all LORs; (5.4) The total number of coincident events in each segment of the X-pencil beam is counted as the P2T image intensity value of that segment.

[0037] The dual-ring P2T imaging system provided in this embodiment integrates a medical linear accelerator and a scintillation crystal detector in the same axial plane, and the linear accelerator head is located at the notch of the detector ring, thereby avoiding damage to the detector caused by direct high-energy X-rays, and improving the clinical feasibility of the P2T imaging system.

[0038] This embodiment proposes a P2T image reconstruction method combined with physical factor correction. The method is based on a dual-ring P2T imaging system and uses the Monte Carlo method to simulate the electron pair effect generated by high-energy X-ray pencil beam irradiating human tissue and the detection unit collecting coincidence events formed by positron annihilation. Attenuation, randomness, and scattering corrections are performed on the coincidence events, and the intersection line method is used to quickly reconstruct the P2T image, thereby avoiding the reduction of imaging resolution of the P2T image due to physical factors.

[0039] Example 2 This embodiment is described by taking a radiotherapy homologous electron pair tomography imaging system with a specific structure as an example.

[0040] like Figure 1 , Figure 2As shown, this embodiment provides a double quarter-ring P2T imaging system, which includes two planes with an inner diameter of 82.4 cm and a coincident central axis equipped axially on a rapidly rotating slip ring frame. The two planes arranged and installed along the axis are generally referred to as axial planes in the industry. Among them, the axial plane installed near the entrance of the frame is used for kilovoltage CT imaging, which can be used to position and align the patient for treatment. The second plane installed axially along the entrance is used for P2T imaging-guided radiotherapy. In this plane, a linear accelerator head 100 is placed between two arc-shaped quarter detectors to avoid direct X-rays to the detection unit. Each detector is arc-shaped and consists of 12 detection modules 210 in the circumferential direction, and each detection module 210 is composed of 3 groups of 13x13 and 4x4mm in size along the axial direction. 2 The detector is composed of 2 cm thick LSO (Lutetium Oxyorthosilicate) scintillation crystals. Each scintillation crystal constitutes a detection unit.

[0041] like Figure 2 As shown, the P2T image reconstruction method considering physical factor correction provided by this embodiment includes the following steps: (1) Monte Carlo simulation software is used to simulate the linear accelerator head 100 generating a high-energy X-ray pencil beam and the double quarter-ring detector 200 composed of a scintillation crystal arrangement.

[0042] (2) Monte Carlo simulation software was used to construct human tissue phantoms of different densities, including six phantoms with a size of 5x5x5cm. 3 The packing density of the cubes is 0.92 g / cm 3 , 1.03 g / cm 3 , 1.06 g / cm 3 , 1.29x10 -3 g / cm 3 , 1.42 g / cm 3 and 1.92 g / cm 3 The six cubes are surrounded by a rectangular block, which serves as the background area and is filled with water.

[0043] (3) Monte Carlo simulation software was used to simulate the high-energy X-ray pencil beam irradiation phantom, simulating the electron pair effect generated in the tracking phantom to emit positrons, which annihilated with nearby electrons to generate a pair of 511 keV gamma photons moving in opposite directions. The gamma photon event detected by two detection units simultaneously in a very short time was defined as a coincidence event, the response path between the two detection units was defined as LOR, the coincidence event time window was set between a few nanoseconds and several hundred nanoseconds, and the number of coincidence events was recorded.

[0044] (4) The collected coincident events are corrected for physical factors according to formulas (1) and (2), including attenuation correction, random event correction and scattering event correction.

[0045] (5) Reconstructing a P2T image representing the spatial distribution of the electron pair effect from the corrected coincidence events, which includes the following steps: (5.1) According to the width of the detection unit, the X-pencil beam is discretized into segments, and the length of each segment is 2.05 mm. It should be noted that the width of the detection unit refers to the sum of the width of the scintillation crystal and the gap between adjacent scintillation crystals. In this embodiment, the size of 4x4mm is used. 2 The gap between two adjacent LSO (Lutetium Oxyorthosilicate) scintillation crystals is 0.1 mm, so the width of the detection unit is 4.1 mm. The X-pencil beam is discretized into segments, and the length of each segment is 2.05 mm.

[0046] (5.2) Take a LOR, calculate its intersection with the X-beam, and superimpose the corrected number of coincident events on the ROL within the segment where the intersection is located.

[0047] (5.3) Repeat step (5.2) for all LORs.

[0048] (5.4) The total number of coincident events in each segment of the X-pencil beam is counted as the P2T image intensity value of that segment.

[0049] Figure 3 The P2T images reconstructed without and with physical factor correction are shown. As the density of the phantom tissue increases, the intensity value of the reconstructed P2T image after physical factor correction increases. The existing reconstruction technology does not consider physical factor correction. Figure 3 (b) with Figure 3 Comparing the results of (a), it can be seen that in the reconstructed image after the physical factor correction, the contrast of different tissues is increased, which is more conducive to distinguishing different tissues. The method of this embodiment can improve the quality of P2T reconstructed images.

[0050] As shown in Table 1, the calculated local image intensity means corresponding to different tissues are 0.45 for water, 0.39 for fat, 0.47 for lymph, 0.62 for liver, 0 for air, 1.26 for spine, and 1.93 for ribs, and the intensity mean contrasts of different tissues relative to water are -7.6% for fat, 2.2% for lymph, 16.2% for liver, -100% for air, 47.3% for spine, and 62.2% for ribs. If physical factor correction is not considered, the calculated contrasts of fat and lymph are -2.0% and 1.3% respectively, so physical factor correction is beneficial to improve the P2T image contrast. Due to the similar density of lymph and liver, the P2T image contrast of the liver obtained before correction in Table 1 is too large. After correction, the contrast result is more reasonable. It can be seen that the reconstruction result after correction is conducive to distinguishing different tissues and can improve the quality of P2T reconstructed images.

[0051] Table 1 Relationship between P2T image intensity and tissue density

[0052] The present embodiment provides a dual-ring P2T imaging system, which integrates a medical linear accelerator and a scintillation crystal detector in the same axial plane, and the linear accelerator head 100 is located at the notch of the detector ring, thereby avoiding damage to the detector caused by direct high-energy X-rays, and improving the clinical feasibility of the P2T imaging system.

[0053] The P2T image reconstruction method combined with physical factor correction in this embodiment is based on a double quarter-ring P2T imaging system and uses the Monte Carlo method to simulate the electron pair effect produced by high-energy X-ray pencil beam irradiating human tissue and the detection unit collecting coincidence events formed by positron annihilation. Attenuation, randomness, and scattering corrections are performed on the coincidence events, and the P2T image is quickly reconstructed using the intersection line method, thereby avoiding the reduction of imaging resolution of the P2T image due to physical factors and improving the quality of the P2T reconstructed image.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A radiotherapy homologous electron pair tomography imaging system, characterized in that: The settings are: A straight line accelerator head; Two annular detectors, the two annular detectors are located in the same axial plane and are symmetrically arranged; The linear accelerator head is placed at the gap of the double-ring detector; the ring detector is composed of a plurality of detection modules arranged along a ring.

2. The radiotherapy homologous electron pair tomography imaging system according to claim 1, characterized in that: The two ring detectors have the same shape.

3. The radiotherapy homologous electron pair tomography imaging system according to claim 2, characterized in that: The annular detector is a one-quarter, three-sixteenth, or three-eighths annular structure.

4. The radiotherapy homologous electron pair tomography imaging system according to any one of claims 1 to 3, characterized in that: The detection module is composed of a plurality of scintillation crystals, which are fixed to the inner wall of the ring and arranged along the axial direction.

5. The radiotherapy homologous electron pair tomography imaging system according to claim 4, characterized in that: Multiple scintillation crystals are arranged in a matrix.

6. The radiotherapy homologous electron pair tomography imaging system according to claim 5, characterized in that: The annular detector is composed of 12 detection modules along the circumferential direction, and each detection module is composed of 3 groups of 13x13 and 4x4mm in size along the axial direction. 2 , LSO scintillation crystals with a thickness of 2 cm are arranged.

7. The radiotherapy homologous electron pair tomography imaging system according to claim 6, characterized in that: The radius of the ring detector is 82.4 cm.

8. A P2T image reconstruction method based on physical factor correction, which is acquired by the radiotherapy homologous electron pair tomography imaging system according to any one of claims 1 to 7, characterized in that: The following steps are included: (1) Monte Carlo simulation software is used to simulate the generation of high-energy X-ray pencil beams by linear accelerator heads; (2) Monte Carlo simulation software was used to simulate a double-ring detector composed of scintillation crystals. (3) Using Monte Carlo simulation software to construct human tissue phantoms of different densities; (4) Monte Carlo simulation software was used to simulate the high-energy X-ray pencil beam irradiation of the phantom. The electron pair effect generated in the phantom was simulated and tracked to emit positrons. The positrons annihilated with nearby electrons to generate a pair of 511 keV gamma photons moving in opposite directions. The gamma photon event detected simultaneously by two detection units within an extremely short time of no more than 10 ns was defined as a coincidence event. The response path between the two detection units was defined as a coincidence response line. The coincidence event time window was set between a few nanoseconds and several hundred nanoseconds, and the number of coincidence events was recorded. (4) Performing physical factor correction on the collected coincident events, including the following steps: (4.1) The total path length of the gamma photon pair passing through the phantom tissue is measured, and then the attenuation correction coefficient is calculated based on the tissue density. The formula is: ……（1）； in, ac is the attenuation correction factor, e is an exponential function, u is the attenuation coefficient of the tissue passed through, D is the total length of the attenuation path; (4.2) By adding a delayed coincidence window when recording coincidence events, the coincidence events within the delayed coincidence window are used as estimates of random coincidence events; (4.3) Generate an attenuation map based on the density of human tissue filled in the phantom, preliminarily reconstruct a P2T image based on the collected coincident events, and use the attenuation map and P2T image as inputs to the single scattering simulation algorithm; Calculate the single scattering distribution, and then scale it to the total scattering distribution to obtain the scattering coincidence events; (4.4) According to the attenuation correction coefficient and the estimated random and scattered coincidence events, attenuation, random and scattered corrections are performed on the coincidence events on each collected ROI. The formula is: ……（2）； in, pp To match the number of events, r is the number of random coincidence events, s is the number of scattering coincidence events, ture is the number of corrected events; (5) Reconstruct the P2T image representing the spatial distribution of the electron pair effect from the corrected coincidence events.

9. The P2T image reconstruction method based on physical factor correction according to claim 8, characterized in that: Reconstructing a P2T image representing the spatial distribution of the electron pair effect from the corrected coincidence events specifically includes the following steps: (5.1) According to the width of the detection unit, the X-pencil beam is discretized piecewise; (5.2) Take a coincident response line, calculate the intersection of the coincident response line and the X-beam, and superimpose the corrected coincident event number on the coincident response line in the segment where the intersection is located; (5.3) Repeat operation (5.2) for all the response lines that meet the requirements; (5.4) The total number of coincident events in each segment of the X-pencil beam is counted as the P2T image intensity value of that segment.

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