Reconstruction of instant gamma simultaneous occurrence data in PET scanning
Through the three-photon detection method, combined with the positron range and flight time model, the immediate gamma ray direction is identified and its associated events are counted, which solves the problems of low image resolution and sensitivity in PET imaging and achieves more efficient image reconstruction.
Patent Information
- Application Number
- CN202510302649.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-04-02
- Filing Date
- 2025-03-14
- Publication Date
- 2025-10-14
AI Technical Summary
In existing PET imaging technology, the positron range effect leads to low image resolution, and immediate gamma photons cannot be effectively identified and utilized, affecting sensitivity.
Through the three-photon detection method, two annihilation photons and one immediate gamma photon are used to determine the direction of the immediate gamma ray, and the immediate gamma correlation event is taken into account in the reconstruction. Combined with the positron range and flight time uncertainty model, forward and backward projection are performed to improve image resolution and sensitivity.
The sensitivity and image resolution of PET scans are improved, the influence of positron range is reduced, and more accurate determination of the location of radioisotopes is achieved.
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Figure CN120770830A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to the field of nuclear imaging systems, and more specifically, to a new method that accounts for prompt gamma associated events to increase sensitivity and reduce the positron range effect. BACKGROUND
[0002] One of the obstacles to obtaining high resolution positron emission tomography (PET) reconstructed images is the positron range. In PET imaging, many PET isotopes approximately co-emit a prompt gamma photon with a positron, the prompt gamma photon is currently treated as uniform background noise and is ignored. Prompt gamma correction during image reconstruction helps to obtain quantified images, but all events associated with prompt gamma are lost.
[0003] Until now, it has not been possible to distinguish between prompt gamma photons and annihilation gamma photons. Even if prompt gamma photons can be detected with energy qualification, in some cases, it is not possible to know the direction of the photon gamma ray that corresponds to these prompt gamma photons. This direction is necessary for forward and backward projection during reconstruction so that in the reconstruction prompt gamma ray associated events can be accounted for. Therefore, it has not been possible to perform prompt gamma reconstruction in a PET scanner.
[0004] If prompt gamma associated events can be accounted for in the reconstruction, PET scan sensitivity can be improved and image resolution can also be improved by reducing the effect of the positron range. Improved sensitivity is obtained by performing triple coincidence reconstruction simultaneously to obtain corresponding isotope images, or by separately reconstructing prompt gamma photons to obtain isotope images and then combining them with the isotope images we obtain from traditional reconstruction of annihilation gammas. Some recent efforts have been published that use a physical cluster collimator to identify the direction of prompt gamma rays, but this approach must overcome the disadvantages of using a physical collimator. Therefore, a better way is needed to identify prompt gamma photons along with the corresponding ray direction and account for them in the reconstruction to reduce the effect of the positron range and improve PET image resolution. SUMMARY
[0005] Some recent work has made it possible to approximately identify the direction of prompt gamma rays. With the combination of coincidence timing and energy qualification, prompt gamma photons can be identified directly with coincident annihilation photons. In general, prompt gamma photons are emitted before the positron annihilates, which allows the events to be related in time.
[0006] The energy window can also be adjusted to isolate prompt gamma photon interactions as in some cases prompt gammas have different energies. The inventors devised a method that forward and backward projects the prompt gammas by forming a ray between the detector crystal that detects the prompt gamma and the most likely annihilation location of the coincident photon. The reconstruction from the detected prompt gamma photons will require two successive kernels, one accounting for positron range and the other accounting for time of flight (TOF) blur. This is applied during forward and backward projection but can also be applied in the image domain. This will help improve sensitivity, data consistency, and can help improve resolution.
[0007] A new method is disclosed that utilizes prompt gamma photons in reconstructing PET scan images from PET scan list mode data acquired by scanning a subject body containing an amount of a radioisotope to reduce the effect of positron range and improve sensitivity. This method incorporates a new method of identifying prompt gamma photons by three-photon detection. The method of identifying prompt gamma photons involves using two annihilation photons and one prompt gamma photon to determine the direction of the corresponding prompt gamma ray. This allows prompt gamma correlated events to be accounted for in the reconstruction to improve PET scan sensitivity and image resolution. The method can be applied to PET, PET-CT, PET-MR, etc.
[0008] The present disclosure also provides an imaging system that utilizes the method disclosed herein. BRIEF DESCRIPTION OF DRAWINGS
[0009] The features of the embodiments described herein will be more fully understood in conjunction with the following detailed description and drawings, in which: Figure One Like numbers refer to like elements throughout.
[0010] Figure 1 is a schematic illustration of a PET detector ring with the lines of response (LOR) of the annihilation gamma photons from the most likely annihilation point, the radioisotope, the positron range of the radioisotope, and the time of flight uncertainty of the annihilation gamma photons.
[0011] Figure 2 is a schematic illustration of an imaging system incorporating components configured to perform the new method disclosed. DETAILED DESCRIPTION
[0012] The description of the example embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. The drawing is not necessarily to scale, and certain features can be shown exaggerated in scale or in a certain schematic form and some details can be omitted so as not to obscure the important aspects of the described embodiments. In the description, relative terms such as "horizontal," "vertical," "up," "down," "top," and "bottom" as well as derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.
[0013] A new method of identifying prompt gammas by three-photon detection is disclosed. The method involves using two annihilation photons and one prompt gamma photon to determine the direction of the corresponding prompt gamma ray. This information allows prompt gamma correlated events to be accounted for in the reconstruction, improving PET scan sensitivity and image resolution.
[0014] Figure 1 is a schematic illustration of a PET detector ring 100. Each segment in the ring 100 represents a detector crystal. The line of response (LOR) 25 of an annihilation gamma photon originating from the most likely annihilation point 20 is shown. The positron source is a radioisotope 200. The positron range PR of the radioisotope 200 is labeled. The time of flight uncertainty TOF-U of the annihilation gamma photon is also labeled.
[0015] The coincident prompt photon can be reconstructed by forming a LOR between the detector crystal 102 that detected the prompt gamma PG and the most likely annihilation point 20 of the LOR 25 of the annihilation photon. The positron range and TOF-U are modeled. A Gaussian distribution is typically taken to obtain the TOF kernel, but other distributions can potentially be used. The positron range kernel can be obtained by using Monte Carlo simulation, which is more accurate but tends to be slower, or by numerical methods, which are generally faster but less accurate.
[0016] For the methods disclosed herein, each dimension of the positron range kernel should be at least as large as the positron range in the medium. The medium can be soft tissue, bone, etc. in a patient, or a simulation material, depending on what is being scanned. Similarly, the TOF kernel value decreases as the distance from the annihilation point increases, and its size can be limited where the value becomes zero.
[0017] A kernel as used herein refers to a cube of data (i.e., an n*n*n dimensional array), which can be as large as the image size, but typically the value of a voxel is zero after a certain distance from the voxel to which the kernel is applied.
[0018] According to some embodiments of the present disclosure, a method of reconstructing a PET scan image from PET scan list mode data is disclosed. The PET scan list mode data is acquired by scanning a subject body (e.g., a patient) containing an amount of a radioisotope. The method includes: (A) accounting for prompt gammas emitted by the radioisotope in addition to coincident pairs of gamma photons (also known as annihilation gammas) to improve sensitivity; and (B) reconstructing the PET scan image from the list mode data, wherein the reconstruction accounts for prompt gamma events by modeling forward and backward projections along corresponding prompt gamma rays along with positron range and TOF uncertainty, thereby improving resolution of the PET scan image by reducing the effect of positron range.
[0019] List mode data means a storage file containing the position and energy of each detected photon.
[0020] In some embodiments, accounting for prompt gammas includes identifying two coincident annihilation gammas and associated prompt gammas to determine the direction of the corresponding prompt gamma ray. In some embodiments, the reconstruction of the prompt gamma events includes:
[0021] 1) identifying prompt gammas using time correlation with coincident annihilation gammas and / or using an energy window;
[0022] 2) using the TOF bin of the most likely annihilation point 20 in the list mode data of the coincident annihilation gammas as the point needed to determine the direction of the forward and backward projections along the prompt gamma ray during reconstruction;
[0023] 3) estimating the positron range kernel of the radioisotope used to generate the PET scan list mode data;
[0024] 4) estimating the TOF-U kernel using the TOF resolution of the PET scanner, wherein the size of the TOF-U kernel is determined by the TOF resolution of the PET scanner;
[0025] 5) estimating the random and scatter rates of the prompt gammas, resulting in a prompt gamma random rate and a prompt gamma scatter rate;
[0026] 6) creating a sensitivity image with the TOF-U and positron range kernels, normalization, and attenuation;
[0027] 7) initializing the prompt gamma image to a value of 1;
[0028] 8) iteratively performing the following steps a) through i) a specified number of times or until convergence, wherein the specified number of times is determined by the PET scanner system and desired image quality:
[0029] a) applying a positron range kernel to the prompt gamma photon image to obtain an updated image;
[0030] b) applying a TOF uncertainty kernel to the updated image to obtain a further updated image;
[0031] c) for each prompt gamma event in the list mode data, forward project along the further updated image to generate forward projected prompt gamma data;
[0032] d) add prompt gamma randoms and prompt gamma scatter rates for corresponding prompt gamma rays in the forward projected data;
[0033] e) back project the inverse of the forward projected data corresponding to all prompt gamma events to obtain a back projected image;
[0034] f) apply a positron range kernel to the back projected image data to obtain an updated back projected image;
[0035] g) apply a TOF-U kernel to the updated back projected image to obtain a further updated back projected image;
[0036] h) divide the further updated back projected image by a sensitivity image to obtain a prompt gamma update image and then multiply the prompt gamma update image by the current prompt gamma image to obtain an updated prompt gamma photon image; and
[0037] i) output the updated prompt gamma photon image after calibration for quantification. Typically, calibration is necessary for quantification of radio-activity. Thus, in step i), for Siemens Healthineers scanners, calibration is performed using a known radioactive source with activity typically between 0.3 to 3 mCi, but other known activities can be used for calibration. In some embodiments, other factors such as branching ratios can be included separately or with the calibration factor as needed.
[0038] With respect to the TOF bin of the most likely annihilation point 20 referenced in step 2) above, it should be noted that for the two photons forming the annihilation gamma (annihilation coincidence event), there is TOF bin number and energy level information in the list mode data file for the two detector crystals that coincided. Once the crystal numbers are identified, a LOR can be formed between the two detector crystals. Once the TOF bin number is identified, the corresponding location of the TOF bin center on that LOR can be determined. This location can be referred to as the most likely annihilation location. There are two crystals used for the annihilation photons, and a third crystal used for the prompt gamma. The most likely annihilation point is the TOF bin number reported for the LOR formed between the two detector crystals that correspond to the annihilation gamma. The LOR used for prompt gamma reconstruction is formed between the prompt gamma crystal and the most likely annihilation point.
[0039] The disclosed method takes list mode reconstruction. However, sinogram based reconstruction can also be performed. The disclosed method takes no point spread function modeling, but can also include point spread function modeling.
[0040] In step 1), prompt gamma rays can be identified by a combination of energy eligibility and time correlation. Prompt gamma photons are typically emitted within picoseconds of the positron emission, and are emitted at discrete energies. Energy bounds can be set to identify prompt gamma photons separately from annihilation gamma photons, and a detection time window can be set to ensure that prompt gamma photons coincide with the annihilation of a positron.
[0041] In step 3), the positron range kernel for the radioisotope under consideration can be estimated by calculating the 3D positron annihilation probability in each voxel. One example of an algorithm that can be used to calculate the 3D position annihilation probability is disclosed in Li et al., “Fast 3D kernel computation method for positron range correction in PET, Physics in Medicine and Biology, vol. 68(2), 2023”. The pseudo code description of the algorithm described by Li et al. is as follows:
[0042]
[0043] In step 4), the TOF resolution that is commonly used is Gaussian, but some other kernel can also be used. The taken distribution values according to the distance from the peak that are stored in the TOF-U kernel center are stored in the corresponding voxel location.
[0044] In step 5), since a pair of uncorrelated annihilation photons are detected within the same time window, the prompt gamma photons detected with them are considered random. The prompt gamma random probability and scatter probability of prompt gamma photons are estimated by the following methods. The methods used for annihilation photon scatter estimation, such as using Monte Carlo simulation, can be implemented for prompt photon scatter estimation, and a single scatter simulation can be adapted for prompt photon scatter estimation. Two popular methods for measuring the random probability of annihilation photons include using a delay window and using crystal singles to estimate a smoothed random probability. These methods, with some modifications, can be used to estimate the smoothed random probability of triple coincidences.
[0045] In step 6), the sensitivity image is a concept well known in the field of image reconstruction. The sensitivity image defines the probability of a detector detecting an event from a voxel. In this case, it will also include the effects of attenuation, normalization, positron range, and TOF uncertainty.
[0046] In step 7), the prompt gamma photon image can be initialized to any non-zero value, so the forward projection is not zero, but a value of 1 is typically used. The prompt gamma photon image can be initialized to any non-zero value, so the forward projection is not zero, but a value of 1 is typically used. A non-zero value in the forward projection is necessary for the update in the expectation likelihood-based algorithm for non-zero regions. A zero value will give a zero image at all updates. In iterative reconstruction, the image is started from and then at each iteration, the image is updated to the updated image. This image after all updates appears as the reconstructed prompt gamma image.
[0047] In step 8), determining the specified number of iterations to proceed through steps a) to i) involves looking at the image quality characteristics (such as resolution, contrast recovery, accuracy, and noise) for different numbers of iterations and subsets, and using the number that gives the desired image quality.
[0048] According to another aspect of the present disclosure, a method of reconstructing and identifying prompt gamma events by using triple photon detection from PET scan list mode data generated by a PET scanner is disclosed. The method can include steps 1) to 8) discussed above.
[0049] Reference Figure 2 The present disclosure also provides an imaging system 200 that utilizes the methods disclosed herein. Such an imaging system 200 can include:
[0050] a PET scanner 230 that scans and generates PET scan list mode data;
[0051] a memory unit 252 provided in the controller 250, on which instructions are stored;
[0052] A processor 253 provided in the controller 250 is configured to read instructions to perform a process of reconstructing a PET scan image from PET scan list mode data acquired by scanning a subject body containing an amount of a radioisotope, wherein the method comprises:
[0053] (A) accounting for prompt gammas emitted by the radioisotope in addition to simultaneous annihilation gamma pairs to improve sensitivity and more accurately determine the location of the radioisotope; and
[0054] (B) reconstructing the PET scan image from the list mode data, wherein the reconstruction accounts for prompt gamma associated events by modeling forward and backward projections along prompt gamma rays along with positron range and TOF uncertainty, thereby improving resolution of the PET scan image by reducing the effect of positron range.
[0055] In some embodiments of the imaging system, when the processor 253 performs the disclosed process, the process of accounting for prompt gammas includes identifying two simultaneous annihilation gammas and an associated prompt gamma to determine a direction of a corresponding prompt gamma ray.
[0056] Steps 1) through 8) discussed above provide for the reconstruction of prompt gamma events. In addition, steps 1) through 8) also aid in identifying associated prompt gammas to determine a direction of a prompt gamma ray.
[0057] The following is a list of non-limiting illustrative embodiments disclosed herein:
[0058] Illustrative Embodiment 1 : A method of reconstructing a positron emission tomography (PET) scan image from PET scan list mode data acquired by scanning a subject body containing an amount of a radioisotope, the method comprising:
[0059] accounting for prompt gammas emitted by the radioisotope in addition to simultaneous annihilation gamma pairs to improve sensitivity and more accurately determine the location of the radioisotope; and
[0060] reconstructing the PET scan image from the list mode data, wherein the reconstruction accounts for prompt gamma associated events by modeling forward and backward projections along prompt gamma rays, thereby improving resolution of the PET scan image by reducing the effect of positron range.
[0061] Illustrative Embodiment 2: The method of illustrative embodiment 1, wherein accounting for the prompt gamma rays comprises:
[0062] identifying two coincident annihilation gamma photons and an associated prompt gamma event to determine a direction of a corresponding prompt gamma ray.
[0063] Illustrative Embodiment 3: The method of illustrative embodiment 2, wherein identifying an associated prompt gamma event to determine a direction of a corresponding prompt gamma ray involves using a method that includes the following steps to reconstruct a prompt gamma ray:
[0064] 1) identifying the prompt gamma ray using a time correlation with coincident annihilation gamma photons and / or using an energy window;
[0065] 2) using a most probable annihilation point of a time-of-flight (TOF) bin of the coincident annihilation gamma photons in the list mode data as a point needed to determine directions of forward and back projections during reconstruction;
[0066] 3) estimating a positron range kernel for the radioisotope used to generate the PET scan list mode data;
[0067] 4) estimating a TOF uncertainty (TOF-U) kernel using a TOF resolution of a PET scanner, wherein a size of the TOF-U kernel is determined by the TOF resolution of the PET scanner;
[0068] 5) estimating a prompt gamma random probability and a prompt gamma scatter probability, resulting in a prompt gamma random probability and a prompt gamma scatter probability;
[0069] 6) creating a sensitivity image with positron range, normalization, and attenuation;
[0070] 7) initializing a prompt gamma photon image to a value of 1;
[0071] 8) iteratively performing the following steps a) through i) a specified number of times or until convergence, wherein the specified number of times is determined by a PET scanner system and a desired image quality:
[0072] a) applying the positron range kernel to the prompt gamma photon image to obtain an updated image;
[0073] b) applying the TOF uncertainty kernel to the updated image to obtain a further updated image;
[0074] c) for each prompt gamma photon event in the list mode data, performing a forward projection along the further updated image to generate forward projection data;
[0075] d) adding the prompt gamma random probability and the prompt gamma scatter probability for a corresponding prompt gamma ray in the forward projection data;
[0076] e) backprojecting the inverse of the forward projection data corresponding to all prompt gamma events to obtain a backprojection image;
[0077] f) applying the positron range kernel to the backprojection image data to obtain an updated backprojection image;
[0078] g) applying the TOF-U kernel to the updated backprojection image to obtain a further updated backprojection image;
[0079] h) dividing the further updated backprojection image by the sensitivity image to obtain a prompt gamma update image and then multiplying the prompt gamma update image with the current prompt gamma image to obtain an updated prompt gamma photon image; and
[0080] i) outputting the updated prompt gamma ray image for quantification after calibration.
[0081] Illustrative Embodiment 4: A method of reconstructing and identifying prompt gamma rays by three-photon detection of positron emission tomography (PET) scan list mode data generated by using a PET scanner, the method comprising:
[0082] 1) identifying the prompt gamma rays using time correlation with a coincident annihilation photon and / or using an energy window;
[0083] 2) using the most likely annihilation point of the time of flight (TOF) interval of the coincident annihilation gamma photons in the list mode data as a point needed to determine directions of forward projection and backprojection during reconstruction;
[0084] 3) estimating a positron range kernel of a radioisotope used to generate the PET scan list mode data;
[0085] 4) estimating a TOF uncertainty (TOF-U) kernel using a TOF resolution of the PET scanner, wherein a size of the TOF-U kernel is determined by the TOF resolution of the PET scanner;
[0086] 5) estimating a prompt gamma random rate and a prompt gamma scatter rate, resulting in a prompt gamma random rate and a prompt gamma scatter rate;
[0087] 6) creating a sensitivity image with positron range, normalization, and attenuation;
[0088] 7) initializing a prompt gamma photon image to a value of 1;
[0089] 8) iteratively performing the following steps a) through i) a specified number of times or until convergence, wherein the specified number of times is determined by the PET scanner system and desired image quality:
[0090] a) applying the positron range kernel to the prompt gamma photon image to obtain an updated image;
[0091] b) applying the TOF uncertainty kernel to the updated image to obtain a further updated image;
[0092] c) for each prompt gamma event in the list mode data, forward projecting along the further updated image to generate forward projection data;
[0093] d) adding the prompt gamma randoms rate and the prompt gamma scatter rate for corresponding prompt gamma rays in the forward projection data;
[0094] e) back projecting the inverse of the forward projection data corresponding to all prompt gamma events to obtain a back projection image;
[0095] f) applying the positron range kernel to the back projection image data to obtain an updated back projection image;
[0096] g) applying the TOF-U kernel to the updated back projection image to obtain a further updated back projection image;
[0097] h) dividing the further updated back projection image by the sensitivity image to obtain a prompt gamma update image and then multiplying the prompt gamma update image by the current prompt gamma image to obtain an updated prompt gamma photon image; and
[0098] i) outputting the updated prompt gamma photon image after calibration for quantification.
[0099] Illustrative Embodiment 5: An imaging system comprising:
[0100] a positron emission tomography (PET) scanner;
[0101] a memory having instructions stored thereon;
[0102] a processor configured to read the instructions to perform a process to reconstruct a PET scan image from PET scan list mode data acquired by scanning a body of a subject containing an amount of a radioisotope, wherein the method comprises:
[0103] accounting for prompt gamma photons emitted by the radioisotope in addition to simultaneous annihilation gamma photon pairs to improve sensitivity by correcting for positron range and more accurately determine the location of the radioisotope; and
[0104] reconstructing the PET scan image from the list mode data, wherein the reconstructing accounts for prompt gamma ray coincident events by forward and backward projection of the prompt gammas, thereby improving resolution of the PET scan image by reducing effects of positron range.
[0105] Illustrative Embodiment 6: The imaging system of illustrative embodiment 5, wherein accounting for the prompt gamma photons comprises:
[0106] identifying two simultaneous annihilation gamma photons and associated prompt gamma photons to determine a direction of a corresponding prompt gamma ray.
[0107] Illustrative Embodiment 7: The imaging system of illustrative embodiment 6, wherein identifying associated prompt gamma photons to determine a direction of a corresponding prompt gamma ray comprises:
[0108] 1) identifying the prompt gamma photons using time correlation with simultaneous annihilation gamma photons and / or using an energy window;
[0109] 2) using a most likely annihilation point of a time-of-flight (TOF) bin of the simultaneous annihilation gamma photons in the list mode data as a point needed to determine directions of forward and backward projections during reconstruction;
[0110] 3) estimating a positron range kernel for the radioisotope used to generate the PET scan list mode data;
[0111] 4) estimating a TOF uncertainty (TOF-U) kernel using a TOF resolution of a PET scanner, wherein a size of the TOF-U kernel is determined by the TOF resolution of the PET scanner;
[0112] 5) estimating a probability of random and a probability of scatter of prompt gamma photons, resulting in a prompt gamma random probability and a prompt gamma scatter probability;
[0113] 6) creating a sensitivity image with positron range, normalization, and attenuation;
[0114] 7) initializing a prompt gamma photon image to a value of 1;
[0115] 8) iteratively performing the following steps a) through i) a specified number of times or until convergence, wherein the specified number of times is determined by a PET scanner system and a desired image quality:
[0116] a) applying the positron range kernel to the prompt gamma photon image to obtain an updated image;
[0117] b) applying the TOF uncertainty kernel to the updated image to obtain a further updated image;
[0118] c) for each prompt gamma photon event in the list mode data, forward projecting along the further updated image to generate forward projected prompt gamma data;
[0119] d) adding the prompt gamma random probability and the prompt gamma scatter probability for corresponding prompt gamma rays in the forward projected data;
[0120] e) back projecting the inverse of the forward projected data corresponding to all prompt gamma events to obtain a back projected image;
[0121] f) applying the positron range kernel to the back projected image data to obtain an updated back projected image;
[0122] g) applying the TOF-U kernel to the updated back projected image to obtain a further updated back projected image;
[0123] h) dividing the further updated back projected image by the sensitivity image to obtain a prompt gamma updated image and then multiplying the prompt gamma updated image by the current prompt gamma image to obtain an updated prompt gamma photon image; and
[0124] i) outputting the updated prompt gamma photon image after calibration for quantification.
[0125] It will be understood that the foregoing description is directed to exemplary embodiments of the application and that various modifications can be made in the design and arrangement of parts without departing from the scope of the present application.
Claims
1. A method for reconstructing a positron emission tomography (PET) scan image from PET scan list mode data, the PET scan list mode data being acquired by scanning a subject's body containing a certain amount of radioactive isotope, the method comprising: taking into account prompt gamma photons emitted by the radioisotope in addition to the simultaneous annihilation gamma photon pairs to increase sensitivity and more accurately determine the position of the radioisotope; as well as The PET scan image is reconstructed from the list mode data, wherein the reconstruction accounts for prompt gamma photon correlation events by forward and backward projections along prompt gamma rays, thereby improving the resolution of the PET scan image by reducing the effects of positron range.
2. The method of claim 1 , wherein accounting for the prompt gamma rays comprises: Identify two simultaneous annihilation gamma photons and the associated prompt gamma event to determine the direction of the corresponding prompt gamma ray.
3. The method of claim 2, wherein identifying the associated prompt gamma event to determine the direction of the corresponding prompt gamma ray involves reconstructing the prompt gamma ray using a method comprising the steps of: 1) using temporal correlation with concurrent annihilation gamma photons and / or using energy windows to identify the prompt gamma ray; 2) using the most likely annihilation point of the time-of-flight (TOF) interval of the simultaneously occurring annihilated gamma photons in the list mode data as the point required to determine the direction of forward and backward projection during reconstruction; 3) estimating the positron range nucleus of the radioisotope used to generate the PET scan list mode data; 4) estimating a TOF uncertainty (TOF-U) kernel using the TOF resolution of the PET scanner, wherein the size of the TOF-U kernel is determined by the TOF resolution of the PET scanner; 5) estimating the random rate and scattering rate of the instantaneous gamma photons to obtain an instantaneous gamma random rate and an instantaneous gamma scattering rate; 6) Create sensitivity images using positron range, normalization, and attenuation; 7) Initializing the instantaneous gamma photon image to a value of 1; 8) Iterate the following steps a) to i) a specified number of times or until convergence, wherein the specified number of times is determined by the PET scanner system and the desired image quality: a) applying the positron range kernel to the instantaneous gamma photon image to obtain an updated image; b) applying the TOF uncertainty kernel to the updated image to obtain a further updated image; c) for each prompt gamma photon event in the list mode data, forward projecting along a further updated image to generate forward projection data; d) adding the prompt gamma random rate and the prompt gamma scatter rate for corresponding prompt gamma rays in the forward projection data; e) back-projecting the inverse of the forward-projected data corresponding to all prompt gamma events to obtain a back-projected image; f) applying the positron range kernel to the backprojected image data to obtain an updated backprojected image; g) applying the TOF-U kernel to the updated back-projected image to obtain a further updated back-projected image; h) dividing the further updated backprojected image by the sensitivity image to obtain an instantaneous gamma update image, and then multiplying the instantaneous gamma update image by the current instantaneous gamma image to obtain an updated instantaneous gamma photon image; as well as i) Output updated instantaneous gamma-ray images after calibration for quantification.
4. A method for reconstructing and identifying prompt gamma rays by three-photon detection of positron emission tomography (PET) scan list mode data generated by a PET scanner, the method comprising: 1) using temporal correlation with concurrent annihilation photons and / or using energy windows to identify the prompt gamma ray; 2) using the most likely annihilation point of the time-of-flight (TOF) interval of the simultaneously occurring annihilated gamma photons in the list mode data as the point required to determine the direction of forward and backward projection during reconstruction; 3) estimating the positron range nucleus of the radioisotope used to generate the PET scan list mode data; 4) estimating a TOF uncertainty (TOF-U) kernel using the TOF resolution of the PET scanner, wherein the size of the TOF-U kernel is determined by the TOF resolution of the PET scanner; 5) estimating the random rate and scattering rate of instantaneous gamma photons to obtain the instantaneous gamma random rate and the instantaneous gamma scattering rate; 6) Create sensitivity images using positron range, normalization, and attenuation; 7) Initializing the instantaneous gamma photon image to a value of 1; 8) Iterate the following steps a) to i) a specified number of times or until convergence, wherein the specified number of times is determined by the PET scanner system and the desired image quality: a) applying the positron range kernel to the instantaneous gamma photon image to obtain an updated image; b) applying the TOF uncertainty kernel to the updated image to obtain a further updated image; c) for each prompt gamma photon event in the list mode data, forward projecting along a further updated image to generate forward projection data; d) adding the prompt gamma random rate and the prompt gamma scatter rate for corresponding prompt gamma rays in the forward projection data; e) back-projecting the inverse of the forward-projected data corresponding to all prompt gamma events to obtain a back-projected image; f) applying the positron range kernel to the backprojected image data to obtain an updated backprojected image; g) applying the TOF-U kernel to the updated back-projected image to obtain a further updated back-projected image; h) dividing the further updated backprojected image by the sensitivity image to obtain an instantaneous gamma update image, and then multiplying the instantaneous gamma update image by the current instantaneous gamma image to obtain an updated instantaneous gamma photon image; as well as i) Output updated instantaneous gamma photon images after calibration for quantification.
5. An imaging system comprising: Positron emission tomography (PET) scanner; a memory having instructions stored therein; A processor configured to read the instructions to execute a process of reconstructing a PET scan image from PET scan list mode data acquired by scanning a body of a subject containing a quantity of radioactive isotope, wherein the method comprises: accounting for prompt gamma photons emitted by the radioisotope in addition to the simultaneous annihilation gamma photon pairs to increase sensitivity and more accurately determine the position of the radioisotope by correcting for the positron range; and The PET scan image is reconstructed from the list mode data, wherein the reconstruction accounts for prompt gamma ray-related events by forward and backward projection of the prompt gamma photons, thereby improving the resolution of the PET scan image by reducing the effect of positron range.
6. The imaging system of claim 5, wherein accounting for the prompt gamma photons comprises: The two simultaneous annihilation gamma photons and the associated prompt gamma photon are identified to determine the direction of the corresponding prompt gamma ray.
7. The imaging system of claim 6, wherein identifying the associated prompt gamma photons to determine the direction of the corresponding prompt gamma rays comprises: 1) using temporal correlation with concurrent annihilation gamma photons and / or using energy windows to identify the prompt gamma photons; 2) using the most likely annihilation point of the time-of-flight (TOF) interval of the simultaneously occurring annihilated gamma photons in the list mode data as the point required to determine the direction of forward and backward projection during reconstruction; 3) estimating the positron range nucleus of the radioisotope used to generate the PET scan list mode data; 4) estimating a TOF uncertainty (TOF-U) kernel using the TOF resolution of the PET scanner, wherein the size of the TOF-U kernel is determined by the TOF resolution of the PET scanner; 5) estimating the random rate and scattering rate of instantaneous gamma photons to obtain the instantaneous gamma random rate and the instantaneous gamma scattering rate; 6) Create sensitivity images using positron range, normalization, and attenuation; 7) Initializing the instantaneous gamma photon image to a value of 1; 8) Iterate the following steps a) to i) a specified number of times or until convergence, wherein the specified number of times is determined by the PET scanner system and the desired image quality: a) applying the positron range kernel to the instantaneous gamma photon image to obtain an updated image; b) applying the TOF uncertainty kernel to the updated image to obtain a further updated image; c) for each prompt gamma photon event in the list mode data, forward projecting along the further updated image to generate forward projected prompt gamma data; d) adding the prompt gamma random rate and the prompt gamma scatter rate for corresponding prompt gamma rays in the forward projection data; e) back-projecting the inverse of the forward-projected data corresponding to all prompt gamma events to obtain a back-projected image; f) applying the positron range kernel to the backprojected image data to obtain an updated backprojected image; g) applying the TOF-U kernel to the updated back-projected image to obtain a further updated back-projected image; h) dividing the further updated backprojected image by the sensitivity image to obtain an instantaneous gamma update image, and then multiplying the instantaneous gamma update image by the current instantaneous gamma image to obtain an updated instantaneous gamma photon image; and i) Output updated instantaneous gamma photon images after calibration for quantification.