CN119185814B - Radiotherapy homologous electron pair tomography imaging system and image reconstruction method - Google Patents
Radiotherapy homologous electron pair tomography imaging system and image reconstruction methodInfo
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Abstract
The radiotherapy homologous electron pair tomography imaging system and the image reconstruction method are provided with a linear accelerator head, two annular detectors which are located in the same axial plane and are symmetrically arranged, wherein the linear accelerator head is arranged at a notch of a double annular detector, and the annular detectors are formed by arranging a plurality of detection modules along a circular ring. The imaging system of the invention avoids the damage of the detector caused by the direct high-energy X-ray detector, and improves the clinical feasibility of the P2T imaging system. The image reconstruction method is based on a double-ring P2T imaging system, utilizes a Monte Carlo method to simulate the electron pair effect generated by the irradiation of high-energy X-ray pencil beams to human tissues, and acquires coincidence events formed by positron annihilation by a detection unit. And the attenuation, the random and the scattering correction are carried out on the coincidence event, and the P2T image is quickly reconstructed by using an intersecting line method, so that the reduction of imaging resolution is avoided.
Description
Technical Field
The invention relates to the technical field of radiotherapy images, in particular to a double-quarter annular radiotherapy homologous electron pair tomography imaging system and an image reconstruction method.
Background
On-line target area tracking and dose monitoring in tumor radiotherapy are critical to improving radiotherapy accuracy, reducing complications and improving patient quality of life. In order to dynamically monitor tumor position changes caused by physiological factors such as respiration, intestinal peristalsis and the like during radiotherapy, and to timely adjust the direction and dose distribution of a radiation beam so as to ensure accurate irradiation of tumor tissues and simultaneously minimize damage to surrounding normal tissues, current on-line tumor positioning methods include kilovolt-level X-ray imaging, megavolt-level X-ray electron portal imaging systems, megavolt Cone Beam Computed Tomography (CBCT) imaging, and other structural or functional imaging tracking technologies such as on-line ultrasound, magnetic Resonance (MR), positron Emission Tomography (PET) and the like. On the other hand, the on-line dose monitoring technology monitors the radiation dose distribution received by a patient through real-time imaging, compares the radiation dose distribution with a pre-established treatment plan, and timely discovers and corrects dose deviation, so that the patient is ensured to receive accurate radiation dose in the treatment process, the treatment effect is improved, and adverse reactions and complications during the treatment period are reduced. The existing on-line dose monitoring equipment comprises a megavoltage CBCT, an electronic portal imaging system, an ionization radiation induced acoustic imaging system, an X-ray induced Cerenkov luminescence imaging system and the like.
While the on-line target tracking and dose monitoring devices may be used independently, some devices have dual functions at the same time. For example, an X-ray electron portal imaging system, a megavoltage CBCT (computed tomography), an ionizing radiation induced acoustic imaging system and an X-ray induced Cerenkov luminescence imaging system can reduce the occupation of the space of a treatment room, save the equipment installation and calibration time and improve the stability of radiotherapy equipment. Compared with the megavoltage CBCT, the X-ray electronic portal imaging system, the ionizing radiation induced acoustic imaging system and the X-ray induced cerenkov luminescence imaging system have the advantages of homology of radiotherapy and image guidance, avoid exposing patients and medical staff to additional imaging radiation sources, prevent accumulated imaging dose caused by multi-time radiotherapy from exceeding the requirement of 5% of the planned dose of radiotherapy, and accord with the radiation protection safety concept better. However, due to limited penetration of the cerenkov light, X-ray induced cerenkov luminescence imaging may not provide clear imaging of deep tumors in the body, and the electron-field imaging system and ionizing radiation induced acoustic imaging have the limitation of low resolution of soft tissues.
In recent years, radiotherapy homologous electron Pair tomography (Pair-Production Tomography, P2T) imaging technology is used as an emerging radiotherapy imaging means, and by measuring electron Pair effect generated by irradiation of high-energy X-rays on human tissues, the high contrast distinction between tumors and normal tissues is hopefully realized on the premise of not increasing extra radiation exposure so as to realize on-line target positioning, and meanwhile, the spatial distribution of real-time radiation dose is dynamically monitored so as to realize target and dose double-guide radiotherapy. However, the P2T imaging system proposed at present has low clinical feasibility, and the design of the system references the full-circle detector structure and ideal detector performance of the PET imaging system, so that it is difficult to avoid the influence of the X-ray irradiation on the detector unit. Furthermore, the reconstruction techniques employed in current P2T imaging do not adequately account for physical factors that interfere with data acquisition (e.g., photon attenuation, scattering, and random events), resulting in reduced imaging resolution. Especially in radiotherapy, the real-time dynamic imaging requirement leads to lower amount of raw data which can be acquired in a short time frame, and under the condition of low counting rate, if physical factor correction is not carried out, the reconstructed image is easily interfered by noise, and the imaging quality is affected.
Therefore, it is necessary to provide a dual quarter-ring radiotherapy homologous electron pair tomographic imaging system and an image reconstruction method to overcome the deficiencies of the prior art.
Disclosure of Invention
In order to solve the above-mentioned P2T imaging technical problem, the present invention aims to provide a double-quarter annular P2T imaging system and an image reconstruction method taking physical factor correction into consideration, so as to overcome the influence of a high-energy X-ray source on a detector and improve the quality of P2T reconstructed images.
The object of the invention is achieved by the following technical measures.
There is provided a radiotherapy-homologous electron pair tomographic imaging system provided with:
A linear accelerator head;
The two annular detectors are positioned in the same axial plane and are symmetrically arranged;
The linear accelerator head is arranged at a notch of the double-ring detector and is used for preventing the X-rays from directly irradiating the detection unit, and the ring detector is formed by arranging detection modules along a ring.
Furthermore, in the radiotherapy homologous electron pair tomography imaging system, the two annular detectors have the same shape.
Preferably, the radiotherapy homogeneous electron pair tomographic imaging system has a ring detector with a ring structure of one quarter, three sixteenths or three eighths.
Preferably, in the radiotherapy homogeneous electron pair tomography imaging system, the detection module is composed of a plurality of scintillation crystals, and the scintillation crystals are fixed on the inner wall of the circular ring and are axially arranged.
Preferably, in the radiotherapy homogeneous electron pair tomographic imaging system, a plurality of scintillation crystals are arranged in a matrix.
Preferably, in the radiotherapy homogeneous electron pair tomography imaging system, the annular detector is formed by 12 detection modules along the circumferential direction, and each detection module is formed by arranging 3 groups of LSO (Lutetium Oxyorthosilicate) scintillation crystals with 13x13 size of 4x4mm 2 and thickness of 2 cm along the axial direction.
Preferably, in the radiotherapy homogeneous electron pair tomography imaging system, the radius of the annular detector is 82.4 cm.
The invention also provides a P2T image reconstruction method based on physical factor correction, which collects the tomographic imaging system through the radiotherapy homologous electrons and comprises the following steps,
(1) Simulating a linear accelerator head by adopting Monte Carlo simulation software to generate a high-energy X-pen-shaped beam;
(2) Simulating a double-ring detector formed by arranging scintillation crystals by adopting Monte Carlo simulation software;
(3) Constructing human tissue mold bodies with different densities by adopting Monte Carlo simulation software;
(4) Simulating a high-energy X-ray pencil beam irradiation die body by using Monte Carlo simulation software, simulating and tracking electron pair effect generated in the die body to emit positrons, annihilating the positrons and nearby electrons to generate a pair of 511 keV gamma photons with opposite movement directions, defining gamma photon events detected by two detection units simultaneously in extremely short time (usually less than 10 ns) as coincidence events, setting a coincidence event time window between a few nanoseconds and a few hundred nanoseconds as coincidence Response Lines (LORs) as Response paths between the two detection units, and recording the number of coincidence events;
(4) The physical factor correction is carried out on the acquired coincidence events, and the method comprises the following steps:
(4.1) calculating an attenuation correction factor by measuring the total length of the gamma photon path through the phantom tissue, and combining the tissue density, wherein the formula is:
......(1);
Where e is an exponential function, u is the attenuation coefficient of the penetrated tissue, and D is the total length of the attenuation path;
(4.2) by adding a delayed coincidence window when the coincidence event is recorded, regarding the coincidence event within the delayed coincidence window as an estimate of the random coincidence event;
(4.3) generating an attenuation map according to the human tissue density filled by the die body, initially reconstructing a P2T image according to the acquired coincidence event, and inputting the attenuation map and the P2T image as a Single Scattering Simulation (SSS) algorithm;
calculating single scattering distribution, and then scaling to the total scattering distribution to obtain scattering coincidence events;
(4.4) performing attenuation, random and scattering correction on the acquired coincidence events on each ROI according to the attenuation correction coefficient and the estimated random and scattering coincidence events, wherein the formula is as follows:
......(2);
Wherein pp is the number of coincidence events, r is the number of random coincidence events, s is the number of scattering coincidence events, ac is the attenuation correction coefficient, and wire is the number of coincidence events after correction;
(5) Reconstructing a P2T image characterizing the spatial distribution of electron pairs from the corrected coincidence events, comprising the steps of:
(5.1) carrying out sectional discretization on the X-pen-shaped beam according to the width of the detection unit;
(5.2) taking a LOR (coincidence response line), calculating the intersection point of the LOR and the X-shaped pencil beam, and superposing the coincidence event number corrected on the ROL in the section where the intersection point is located;
(5.3) repeating the operation (5.2) for all LORs;
(5.4) counting the total coincidence event number of each segment on the X-shaped beam as the P2T image intensity value of the segment.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the double-ring-shaped P2T imaging system, the medical linear accelerator and the scintillation crystal detector are integrated in the same axial plane, and the linear accelerator head is positioned at the notch of the detector ring, so that the damage to the detector caused by the high-energy X-ray direct incidence detector is avoided, and the clinical feasibility of the P2T imaging system is improved.
2. The invention also provides a P2T image reconstruction method combined with physical factor correction, which is based on a double-quarter annular P2T imaging system and utilizes a Monte Carlo method to simulate high-energy X-ray pencil beam to irradiate human tissues to generate an electron pair effect and a detection unit to collect coincidence events formed by positron annihilation. And carrying out attenuation, random and scattering correction on the coincidence event, and rapidly reconstructing a P2T image by using an intersection line method, thereby avoiding the reduction of imaging resolution of the P2T image caused by physical factors.
Drawings
The invention is further illustrated by the accompanying drawings, which are not to be construed as limiting the invention in any way.
FIG. 1 is a schematic diagram of the structure of a dual quarter-ring radiotherapy homogeneous electron pair tomographic imaging system of the present invention.
FIG. 2 is a schematic diagram of a dual quarter-circle P2T imaging reconstruction method.
Fig. 3 is a P2T reconstructed image of a simulated X-ray pencil illuminating tissue of different densities, wherein (a) is a reconstructed image without physical factor correction and (b) is a reconstructed image with physical factor correction.
In fig. 1 to 2, comprising:
A linear accelerator head 100,
Ring detector 200, detection module 210.
Detailed Description
The invention is further illustrated with reference to the following examples.
Example 1
A radiotherapy-homologous electron pair tomographic imaging system provided with:
A linear accelerator head;
The two annular detectors are positioned in the same axial plane and are symmetrically arranged;
The linear accelerator head is arranged at a notch of the double-ring detector and is used for preventing the X-rays from directly irradiating the detection unit, and the ring detector is formed by arranging detection modules along a ring.
The radiotherapy homologous electron pair tomography imaging system has two annular detectors in the same shape and the two annular detectors have the same radian, width and length and are assembled on the frame to form a symmetrical structure.
The annular detector is a quarter or three sixteenth or three eighth annular structure. The detection module is composed of a plurality of scintillation crystals, and the scintillation crystals are fixed on the inner wall of the circular ring and are axially arranged. The plurality of scintillation crystals are arranged in a matrix.
The embodiment also provides a P2T image reconstruction method based on physical factor correction, which collects the tomographic imaging system through the radiotherapy homologous electrons, comprising the following steps,
(1) The linac head was simulated using monte carlo simulation software to produce a high energy X-pencil beam.
(2) A dual annular detector consisting of an array of scintillation crystals was simulated using Monte Carlo simulation software.
(3) And constructing human tissue mold bodies with different densities by adopting Monte Carlo simulation software.
(4) The method comprises the steps of simulating a high-energy X-ray pen-shaped beam irradiation die body by using Monte Carlo simulation software, simulating electron pair effect generated in a tracking die body to emit positrons, annihilating the positrons and nearby electrons to generate a pair of 511 keV gamma photons with opposite movement directions, defining gamma photon events detected by two detection units simultaneously in extremely short time (usually less than 10 ns) as coincidence events, setting a Response path between the two detection units as a coincidence Response Line (LOR), setting a coincidence event time window to be between a few nanoseconds and a few hundred nanoseconds, and recording the number of the coincidence events. 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 the actual requirement.
(4) The physical factor correction is carried out on the acquired coincidence events, and the method comprises the following steps:
(4.1) calculating an attenuation correction factor by measuring the total length of the gamma photon path through the phantom tissue, and combining the tissue density, wherein the formula is:
......(1);
where e is an exponential function, u is the attenuation coefficient of the tissue traversed, and D is the total length of the attenuation path.
(4.2) By adding a delayed coincidence window when the coincidence event is recorded, treating the coincidence event within the delayed coincidence window as an estimate of the random coincidence event.
(4.3) Generating an attenuation map according to the human tissue density filled by the die body, initially reconstructing a P2T image according to the acquired coincidence event, and inputting the attenuation map and the P2T image as a Single Scattering Simulation (SSS) algorithm;
And calculating single scattering distribution, and then scaling to the total scattering distribution to obtain scattering coincidence events.
It should be noted that, the specific algorithm of single scattering estimation and scaling is a conventional algorithm, which is not an innovation point of the present invention and will not be described herein.
(4.4) Performing attenuation, random and scattering correction on the acquired coincidence events on each ROI according to the attenuation correction coefficient and the estimated random and scattering coincidence events, wherein the formula is as follows:
......(2);
wherein pp is the number of coincidence events, r is the number of random coincidence events, s is the number of scattered coincidence events, and ure is the number of corrected coincidence events.
(5) Reconstructing a P2T image characterizing the spatial distribution of electron pairs effect events from the corrected coincidence events, comprising the steps of:
(5.1) carrying out sectional discretization on the X-pen-shaped beam according to the width of the detection unit;
(5.2) taking a LOR (coincidence response line), calculating the intersection point of the LOR and the X-shaped pencil beam, and superposing the coincidence event number corrected on the ROL in the section where the intersection point is located;
(5.3) repeating the operation (5.2) for all LORs;
(5.4) counting the total coincidence event number of each segment on the X-shaped beam as the P2T image intensity value of the segment.
According to the double-ring-shaped P2T imaging system, the medical linear accelerator and the scintillation crystal detector are integrated in the same axial plane, and the linear accelerator head is positioned at the notch of the detector ring, so that the damage to the detector caused by the high-energy X-ray direct incidence detector is avoided, and the clinical feasibility of the P2T imaging system is improved.
The P2T image reconstruction method combined with physical factor correction is provided in this embodiment, and based on a dual-ring P2T imaging system, the method uses a monte carlo method to simulate the electron pair effect generated by the irradiation of a high-energy X-pencil beam to human tissues, and the detection unit collects coincidence events formed by positron annihilation. And carrying out attenuation, random and scattering correction on the coincidence event, and rapidly reconstructing a P2T image by using an intersection line method, thereby avoiding the reduction of imaging resolution of the P2T image caused by physical factors.
Example 2
The present embodiment will be described with respect to a specific configuration of a radiotherapy-homologous electron pair tomographic imaging system.
As shown in fig. 1 and 2, the present embodiment provides a dual quarter-ring P2T imaging system, which includes two planes with inner diameters of 82.4 cm and coincident central axes, which are axially equipped on a rapidly rotatable slip ring frame, and which are commonly referred to as axial planes in the industry of two planes arranged along an axis. Wherein the axial plane mounted near the gantry entrance is used for kilovolt CT imaging to provide positioning and therapeutic alignment of the patient. A second plane mounted axially along the entrance is used for P2T imaging guided radiation therapy, in which plane a linac head 100 is placed between the two curved quarter detectors for avoiding direct X-ray detection units. Each detector is arc-shaped and consists of 12 detection modules 210 along the circumferential direction, and each detection module 210 is formed by arranging 3 groups of LSO (Lutetium Oxyorthosilicate) scintillation crystals with 13x13 size of 4x4mm 2 and thickness of 2 cm along the axial direction. Each scintillation crystal constitutes a detection unit.
As shown in fig. 2, the P2T image reconstruction method taking into account physical factor correction provided in this embodiment includes the following steps:
(1) The linac head 100 is simulated using monte carlo simulation software to produce a high energy X-pencil beam and a double quarter-ring detector 200 of scintillation crystal arrangement.
(2) Human tissue phantom of different densities was constructed using Monte Carlo simulation software, which included six cubes of 5x5x5cm 3 filled sequentially with fat, lymph, liver, air, spine and ribs of densities 0.92 g/cm3、1.03 g/cm3、1.06 g/cm3、1.29x10-3g/cm3、1.42 g/cm3 and 1.92 g/cm 3, respectively. Six cubes are surrounded by a cuboid as background area and filled with water.
(3) And simulating the high-energy X-ray pen-shaped beam irradiation die body by adopting Monte Carlo simulation software, simulating and tracking electron pair effect generated in the die body to emit positrons, and annihilating the positrons and nearby electrons to generate 511 keV gamma photons with opposite movement directions. The gamma photon event detected by two detection units simultaneously in extremely short time is defined as a coincidence event, a response path between the two detection units is LOR, a coincidence event time window is set between a few nanoseconds and a few hundred nanoseconds, and the number of coincidence events is recorded.
(4) Physical factor correction is performed on the acquired coincidence events according to formulas (1) and (2), including attenuation correction, random event correction, and scattering event correction.
(5) Reconstructing a P2T image characterizing the spatial distribution of electron pairs from the corrected coincidence events, comprising the steps of:
(5.1) carrying out sectional discretization on the X-shaped pencil beam according to the width of the detection unit, wherein the length of each section is 2.05 mm. It should be noted that, the width of the detecting unit refers to the sum of the width of the scintillation crystal and the gap between the adjacent scintillation crystals, in this embodiment, LSO (Lutetium Oxyorthosilicate) scintillation crystals with the size of 4x4mm 2 are used, and the gap between two adjacent scintillation crystals is 0.1 mm, so the width of the detecting unit is 4.1 mm. The X-ray pencil beam was segmented discretized with each segment length of 2.05 mm.
And (5.2) taking a LOR, calculating the intersection point of the LOR and the X-shaped pencil beam, and superposing the corrected coincidence event number on the ROL in the section where the intersection point is located.
(5.3) Repeating the operation (5.2) for all LORs.
(5.4) Counting the total coincidence event number of each segment on the X-shaped beam as the P2T image intensity value of the segment.
Fig. 3 is a P2T image reconstructed without taking into account physical factor correction and with taking into account physical factor correction, respectively. With the increase of the tissue density of the die body, the intensity value of the reconstructed P2T image after the physical factor correction is increased. The existing reconstruction technology does not consider physical factor correction, and by comparing the results of fig. 3 (b) with those of fig. 3 (a), it can be seen that the contrast of different tissues in the reconstructed image after the physical factor correction is considered is increased, which is more beneficial to distinguishing different tissues. The method of the embodiment can improve the quality of the P2T reconstructed image.
As shown in Table 1, the local image intensity averages corresponding to the different tissues are calculated to be water 0.45, fat 0.39, lymph 0.47, liver 0.62, air 0, spine 1.26, rib 1.93, and the intensity average contrast of the different tissues relative to water is respectively fat-7.6%, lymph 2.2%, liver 16.2%, air-100%, spine 47.3%, rib 62.2%. If the physical factor correction is not considered, the contrast ratio of fat and lymph is calculated to be-2.0% and 1.3% respectively, so the physical factor correction is beneficial to improving the contrast ratio of the P2T image. Since lymph and liver densities were similar, P2T images of liver sites obtained before uncorrected in table 1 were more contrasted. After correction, the contrast results are more reasonable. Therefore, the corrected reconstruction result is favorable for distinguishing different tissues, and the quality of the P2T reconstructed image can be improved.
TABLE 1P 2T image intensity and tissue density relationship Table
The dual-ring-shaped P2T imaging system integrates the medical linear accelerator and the scintillation crystal detector in the same axial plane, and the linear accelerator head 100 is positioned at the notch of the detector ring, so that the damage to the detector caused by the high-energy X-ray direct incidence detector is avoided, and the clinical feasibility of the P2T imaging system is improved.
The P2T image reconstruction method combining physical factor correction of the present embodiment is based on a double-quarter-ring P2T imaging system, and utilizes a monte carlo method to simulate the electron pair effect generated by the irradiation of a high-energy X-pencil beam to human tissues, and the detection unit collects coincidence events formed by positron annihilation. And carrying out attenuation, random and scattering correction on the coincidence event, and rapidly reconstructing a P2T image by using an intersection line method, so that the reduction of imaging resolution of the P2T image caused by physical factors is avoided, and the quality of the P2T reconstructed image can be improved.
Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present invention and not for limiting the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention.
Claims (9)
1. A P2T image reconstruction method based on physical factor correction is characterized in that a tomography imaging system is acquired by radiotherapy homologous electrons, comprising the following steps,
(1) Simulating a linear accelerator head by adopting Monte Carlo simulation software to generate a high-energy X-pen-shaped beam;
(2) Simulating a double-ring detector formed by arranging scintillation crystals by adopting Monte Carlo simulation software;
(3) Constructing human tissue mold bodies with different densities by adopting Monte Carlo simulation software;
(4) Simulating a high-energy X-ray pencil beam irradiation die body by using Monte Carlo simulation software, simulating electron pair effect generated in a tracking die body to emit positrons, annihilating the positrons and nearby electrons to generate a pair of 511keV gamma photons with opposite motion directions, defining gamma photon events detected by two detection units simultaneously within a very short time of not more than 10ns as coincidence events, setting a coincidence event time window to be between a few nanoseconds and a few hundred nanoseconds as coincidence response lines, and recording the number of coincidence events;
(4) The physical factor correction is carried out on the acquired coincidence events, and the method comprises the following steps:
(4.1) calculating an attenuation correction factor by measuring the total length of the gamma photon path through the phantom tissue, and combining the tissue density, wherein the formula is:
ac=euD......(1);
Where ac is the attenuation correction coefficient, e is an exponential function, u is the attenuation coefficient of the tissue being traversed, and D is the total length of the attenuation path;
(4.2) by adding a delayed coincidence window when the coincidence event is recorded, regarding the coincidence event within the delayed coincidence window as an estimate of the random coincidence event;
(4.3) generating an attenuation map according to the human tissue density filled by the die body, initially reconstructing a P2T image according to the acquired coincidence event, and inputting the attenuation map and the P2T image as a single scattering simulation algorithm;
calculating single scattering distribution, and then scaling to the total scattering distribution to obtain scattering coincidence events;
(4.4) performing attenuation, random and scattering correction on the acquired coincidence events on each ROI according to the attenuation correction coefficient and the estimated random and scattering coincidence events, wherein the formula is as follows:
ture=(pp-r-s)·ac......(2);
wherein pp is the number of coincidence events, r is the number of random coincidence events, s is the number of scattering coincidence events, and ure is the number of corrected coincidence events;
(5) Reconstructing a P2T image representing the electron pair effect spatial distribution from the corrected coincidence events.
2. The method for reconstructing a P2T image based on physical factor correction as recited in claim 1, wherein reconstructing a P2T image characterizing a spatial distribution of electron pair effects from the corrected coincidence events comprises:
(5.1) carrying out sectional discretization on the X-pen-shaped beam according to the width of the detection unit;
(5.2) taking a coincidence response line, calculating the intersection point of the coincidence response line and the X-shaped pencil beam, and superposing the number of coincidence events corrected on the coincidence response line in the section where the intersection point is located;
(5.3) repeating the operation (5.2) for all the coincident lines of response;
(5.4) counting the total coincidence event number of each segment on the X-shaped beam as the P2T image intensity value of the segment.
3. The physical factor correction based P2T image reconstruction method as set forth in claim 1 or 2, wherein said radiotherapy-homologous electron pair tomographic imaging system is provided with:
A linear accelerator head;
The two annular detectors are positioned in the same axial plane and are symmetrically arranged;
the linear accelerator head is arranged at the notch of the two annular detectors, and the annular detectors are formed by arranging a plurality of detection modules along a circular ring.
4. The method for reconstructing a P2T image based on physical factor correction as recited in claim 3, wherein said two annular detectors are identical in shape.
5. The method for P2T image reconstruction based on physical factor correction as recited in claim 4, wherein said ring detector is a quarter, or three sixteenth, or three eighth ring structure.
6. The method for reconstructing a P2T image based on physical factor correction as recited in claim 5, wherein said detection module is composed of a plurality of scintillation crystals fixed to an inner wall of said ring and arranged in an axial direction.
7. The method for P2T image reconstruction based on physical factor correction as recited in claim 6, wherein the plurality of scintillator crystals are arranged in a matrix.
8. The method for reconstructing P2T images based on physical factor correction according to claim 7, wherein said annular detector is formed by 12 detection modules along the circumferential direction, each detection module is formed by arranging 3 groups of LSO scintillation crystals with 13X 13 size of 4X 4mm 2 and thickness of 2cm along the axial direction.
9. The method for reconstructing a P2T image based on physical factor correction as recited in claim 8, wherein said annular detector has a radius of 82.4cm.
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