Image reconstruction method and system, detection device, electronic device and storage medium

Abstract

The present application relates to the field of data processing. Disclosed are an image reconstruction method and system, a detection device, an electronic device and a storage medium. The image reconstruction method comprises: on the basis of prior information, acquiring the TOF resolutions of some lines of response; on the basis of the TOF resolutions of the some lines of response and a prearranged model, obtaining the temporal resolutions of all of scintillation crystals; on the basis of the temporal resolutions of all of the scintillation crystals and the prearranged model, obtaining the TOF resolutions of remaining lines of response; and, on the basis of all of the TOF resolutions and a first preset algorithm, reconstructing an image. The solution of the present application implements differentiated processing of the TOF resolutions of different lines of response, and especially associates the TOF resolutions of the lines of response with the temporal resolutions of corresponding scintillation crystals, so as to accurately estimate the TOF resolutions of the lines of response, thus effectively improving image reconstruction quality.

Description

Image reconstruction method, system, detection device, electronic device and storage medium

[0001] This application claims priority to Chinese patent application No. 202311859527.5 filed on December 30, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of image reconstruction, and specifically to image reconstruction methods, systems, detection equipment, electronic equipment, and storage media. Background Art

[0003] Positron Emission Tomography (PET) technology is one of the most advanced molecular imaging technologies in the world. It has many functions such as early cancer detection, efficacy evaluation, and pharmacokinetic observation. It can non-invasively, quantitatively and dynamically evaluate the metabolic levels, biochemical reactions and functional activities of various functional organs in the body by imaging compounds labeled with radionuclides in the body. It has high sensitivity and accuracy and plays an irreplaceable role in clinical medicine and drug research and development.

[0004] In the early days of PET, image reconstruction primarily relied on the number of coincident events along the lines connecting each detector pair. However, the photon time-of-flight (TOF) resolution of early detectors was insufficient, providing little gain in image reconstruction. However, with the advancement of PET detector technology in recent years, the TOF resolution of PET detectors has reached 200ps-600ps. This TOF information significantly improves the quality of TOF image reconstruction compared to non-TOF image reconstruction. TOF resolution has become a key metric for evaluating PET system performance, and TOF image reconstruction has become widely used.

[0005] The existing method divides the number of coincident events on a line of response (LOR) into different time bins. Each time bin corresponds to a line segment in space. TOF image reconstruction requires the contribution H of the gamma photon emitted by the jth voxel to the kth time bin on the i-th LOR. ijk Modeling. ijk =H ij K ijk , where K ijkIt is usually referred to as the TOF kernel. The value of the TOF kernel on the kth time bin is usually modeled with a Gaussian distribution. The half-height width of the Gaussian distribution is the TOF resolution of the PET system. It is usually assumed that all LORs have the same TOF resolution. Under this assumption, the TOF kernel of any LOR has the same Gaussian distribution standard deviation σ (that is, the half-height width of the Gaussian distribution divided by 2.355). However, in actual systems, there are certain differences in the TOF resolution of each LOR. This difference distorts the TOF information modeling, resulting in the inability to achieve the optimal performance of TOF image reconstruction.

[0006] The description of the background technology is only for facilitating understanding of the relevant technology in this field and is not regarded as an admission of the prior art. Summary of the Invention

[0007] Therefore, the present application intends to provide an image reconstruction method, system, detection device, electronic device and storage medium, which can solve at least one problem existing in the prior art.

[0008] In a first aspect, an image reconstruction method is provided, comprising: obtaining the TOF resolution of some response lines based on prior information; obtaining the temporal resolution of all scintillation crystals based on the TOF resolution of the some response lines and a preset model; obtaining the TOF resolution of the remaining response lines based on the temporal resolution of all scintillation crystals and the preset model; and reconstructing an image based on all TOF resolutions and a first preset algorithm.

[0009] In an embodiment of the present application, obtaining the time resolution of all scintillation crystals according to the TOF resolution of the partial response line and the preset model includes: inputting the TOF resolution of the partial response line as an input value into the preset model to obtain the time resolution of all scintillation crystals;

[0010] Obtaining the TOF resolutions of the remaining response lines based on the time resolutions of all scintillation crystals and the preset model includes: listing the time resolutions corresponding to two scintillation crystals located on the same response line into a group, and inputting all groups of time resolutions as input values ​​into the preset model to obtain the TOF resolutions of the remaining response lines.

[0011] In the embodiment of the present application, the preset model is:

[0012] Among them, σ i represents the temporal resolution of scintillation crystal i, σ j represents the temporal resolution of scintillation crystal j, σ ij It represents the TOF resolution of the response line formed by scintillation crystals i and j.

[0013] In the embodiment of the present application, the preset model is:

[0014] Among them, σ i represents the temporal resolution of scintillation crystal i, σ j represents the temporal resolution of scintillation crystal j, δ r represents the variable related to the incident angle of the photon, σ ij It represents the TOF resolution of the response line formed by scintillation crystals i and j.

[0015] In an embodiment of the present application, the prior information is obtained according to the following steps: an image detection test is performed under experimental conditions to obtain the number of matching events on all response lines and the time difference of each matching event; a response line whose number of matching events is a first preset threshold is selected as a target response line; and the TOF resolution of all the target response lines is obtained as the prior information based on a second preset algorithm and the time difference of each matching event.

[0016] In the embodiment of the present application, the second preset algorithm is:

[0017] Where n is the total number of coincidence events on a target response line, Δt i is the time difference of the i-th matching event, is the mean of the time difference on the target response line, σ is the standard deviation of the time difference on the target response line, and the TOF resolution of the target response line is 2.355σ.

[0018] In an embodiment of the present application, the first preset threshold is greater than or equal to 5.

[0019] In an embodiment of the present application, the test conditions include: selecting a source that only emits positrons as the target source; and / or the shape of the target source includes a shell source, a line source, or a point source.

[0020] In an embodiment of the present application, when the target radiation source is the shell source, before selecting the response line whose number of matching events exceeds a first preset threshold as the target response line, the step of obtaining the prior information further includes: excluding the response line whose distance from the central axis of the shell source reaches a second preset threshold.

[0021] In the embodiment of the present application, the second preset threshold is 80% of the maximum distance corresponding to the detector's field of view.

[0022] In an embodiment of the present application, when the target radiation source is the shell source, after selecting the response line whose number of matching events exceeds a first preset threshold as the target response line, the step of obtaining the prior information further includes: using a preset method to perform flight time compensation for all matching events.

[0023] In an embodiment of the present application, the preset method is: obtaining the two intersection points of the response line and the shell source and the flight time difference of the coincident event generated by the annihilation of the two intersection points; drawing a time difference spectrum according to the time difference of the coincident event to obtain two peaks, and the two peaks respectively correspond to the two intersection points of the response line and the shell source; using the k-mean algorithm to classify the coincident event into one of the two peaks; and compensating the flight time difference of the coincident event according to the intersection point to which the coincident event belongs and the calculated flight time difference.

[0024] In an embodiment of the present application, the test condition further includes: the size of the target radiation source is smaller than a preset requirement.

[0025] In an embodiment of the present application, the preset requirements include: the thickness of the shell source is less than or equal to 1 cm; or, the diameter of the line source is less than or equal to 1 cm; or, the diameter of the point source is less than or equal to 0.5 cm.

[0026] In an embodiment of the present application, the test condition further includes: the position of the target radiation source satisfies the requirement to ensure that the connection line between any single detection unit and at least two detection units at different positions passes through the target radiation source.

[0027] In an embodiment of the present application, the height of the shell source is parallel to the axis of the PET; or, among the intersections of the cross section of the detection ring and the line source, at least three points are not collinear; or, at least four of the point sources are not coplanar.

[0028] In the embodiment of the present application, the target radiation source includes 18 F. 22 Na or 68 Ge.

[0029] In the embodiment of the present application, the first preset algorithm is:

[0030] in, is the j-th pixel value of the n-th iteration, N i and A i are the normalization factor and attenuation factor of the ith response line, r ik and s ik are the random and scattered coincident events on the kth time bin of the i-th response line, S is the set of response line numbers and time bin numbers of all list-mode events, and H ijis the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction'.

[0031] In the embodiment of the present application, the first preset algorithm is:

[0032] in, is the jth pixel value of the lth subset in the nth iteration, N i and A i are the normalization factor and attenuation factor of the ith response line, r ik and s ik are the random and scattered coincidence events on the kth time bin of the i-th response line, S l is the set of response line number i and time bin number k of all list-mode events in the lth subset, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0033] In the embodiment of the present application, the first preset algorithm is:

[0034] in, is the j-th pixel value of the n-th iteration, N i and A i are the normalization factor and attenuation factor of the ith response line, r ik and s ik are the random and scattered coincidence events on the kth time bin of the i-th response line, respectively, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0035] In the embodiment of the present application, the first preset algorithm is:

[0036] in, is the jth pixel value of the lth subset in the nth iteration, N i and A i are the normalization factor and attenuation factor of the ith response line, r ik and s ik are the random and scattered coincidence events on the kth time bin of the i-th response line, S l is the set of response lines numbered i in the lth subset.

[0037] In the embodiment of the present application, H ijk =H ij Kijk

[0038] Where T0 is the start time of the kth time bin, T1 is the end time of the kth time bin, t is the integration variable, and σ represents the TOF resolution of the response line.

[0039] In a second aspect, an image reconstruction system is provided, comprising: an acquisition unit for acquiring the TOF resolution of some response lines based on prior information; a calculation unit for obtaining the temporal resolution of all scintillation crystals based on the TOF resolution of the some response lines and a preset model, and obtaining the TOF resolution of the remaining response lines based on the temporal resolution of all scintillation crystals and the preset model; and a reconstruction unit for reconstructing an image based on all TOF resolutions and a first preset algorithm.

[0040] In an embodiment of the present application, the calculation unit is used to input the TOF resolutions of the partial response lines as input values ​​into the preset model to obtain the time resolutions of all scintillation crystals, and to group the time resolutions corresponding to two scintillation crystals located on the same response line into a group, and input all groups of time resolutions as input values ​​into the preset model to obtain the TOF resolutions of the remaining response lines.

[0041] In a third aspect, a detection device is provided, comprising the image reconstruction system described in the second aspect.

[0042] In a fourth aspect, an electronic device is provided, characterized in that it includes: a processor and a memory storing a computer program, and the processor is configured to implement the method described in the embodiment of the present application when running the computer program.

[0043] In a fifth aspect, a storage medium is provided, wherein the storage medium stores a computer program, and the computer program is configured to implement the method described in the embodiments of the present application when executed.

[0044] Compared with the prior art, the solution of the embodiment of the present application performs differentiated processing on the TOF resolution of different response lines, especially correlating the TOF resolution of the response line with the time resolution of the corresponding scintillation crystal, accurately estimating the TOF resolution of the response line, and effectively improving the quality of image reconstruction.

[0045] Some of the optional features and other effects of the embodiments of the present application are described below, and some can be understood by reading this document. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The present application will be further described in the form of exemplary embodiments, which will be described in detail with reference to the accompanying drawings. These embodiments are not limiting, and in these embodiments, the same reference numerals represent the same structure, wherein:

[0047] FIG1 shows a flow chart of an image reconstruction method according to an embodiment of the present application;

[0048] FIG2 shows a flow chart of an image reconstruction method according to an embodiment of the present application;

[0049] FIG3 shows a cross-sectional schematic diagram of a shell source and a detector according to an embodiment of the present application;

[0050] FIG4 shows a cross-sectional schematic diagram of a line source / point source and a detector according to an embodiment of the present application;

[0051] FIG5 shows an original time difference distribution diagram on a response line of a shell source according to an embodiment of the present application;

[0052] FIG6 shows a distribution diagram of a response line in a shell source after flight time difference compensation according to an embodiment of the present application;

[0053] FIG7 shows a simulated time-of-flight diagram of a shell source detection test according to an embodiment of the present application;

[0054] FIG8 shows a structural block diagram of an image reconstruction system according to an embodiment of the present application;

[0055] FIG9 shows a schematic diagram of an electronic device according to an embodiment of the present application. DETAILED DESCRIPTION

[0056] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0057] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may also be an element centered. When an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be an element centered at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only. The described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided so as to provide a full understanding of the embodiments of the present application. However, those skilled in the art will appreciate that the technical solutions of the present application can be practiced without one or more of these specific details, or other modes, components, materials, devices or operations, etc. may be adopted. In these cases, well-known structures, methods, devices, implementations, materials or operations will not be shown or described in detail.

[0058] The flowcharts shown in the accompanying drawings are for illustrative purposes only and do not necessarily include all contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps may be decomposed, while others may be combined or partially combined. Therefore, the actual execution order may vary depending on the actual situation.

[0059] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices. The term "and / or" or "and / or" includes any and all combinations of one or more relevant listed items.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0061] The image reconstruction method, system, detection device, electronic device and storage medium provided in this application particularly relate to positron emission tomography (PET) technology.

[0062] As previously mentioned, existing technologies known to the inventors for TOF image reconstruction typically assume that all lines of response (LORs) have the same TOF resolution. However, in actual systems, the TOF resolution of each LOR varies. This variation distorts the TOF information modeling, making it impossible to achieve optimal TOF image reconstruction performance.

[0063] In this regard, the present application provides an image reconstruction method. As shown in FIG1 , the image reconstruction method provided by the present application generally includes the following steps:

[0064] S110: Obtaining the TOF resolution of some response lines according to the prior information.

[0065] The number or ratio requirement for the partial response lines is such that the temporal resolution of all scintillator crystals can be derived from the TOF resolution of the partial response lines. In practice, compared to existing TOF image reconstruction, where the TOF resolution of all response lines is identical through extreme cases, the TOF resolution of all response lines ultimately obtained through the TOF resolution of partial response lines in this application is typically not identical, which is closer to the actual state.

[0066] It should be noted that, generally speaking, a detection device includes several detectors. For example, all detectors are combined to form at least one detection ring. When there are multiple detection rings, all detection rings are concentrically stacked. Each detector comprises an array of several detection units, each of which includes scintillation crystals and other components. When the line connecting any two scintillation crystals passes through the field of view of the detection ring, it may form a response line. In other words, a response line is connected to a scintillation crystal at each end. In this application, the scintillation crystals connected at both ends of the response line must cover all scintillation crystals. In other words, each scintillation crystal corresponds to at least one response line.

[0067] The purpose of setting the number or proportion of partial response lines in this application is to ensure that the response line acquisition amount and the TOF resolution calculation amount are balanced on the basis of sufficient basic data (TOF resolution of partial response lines) to smoothly obtain the TOF resolution of all response lines. It is understandable that when the number of partial response lines is large, the calculation amount of TOF resolution of the remaining response lines can be reduced, and conversely, the calculation amount of TOF resolution of the remaining response lines can be increased. However, when the number of partial response lines is large, the data amount of prior information is also required to be large enough, so the number or proportion of partial response lines should be appropriate.

[0068] S120: Obtaining the time resolution of all scintillation crystals according to the TOF resolution of the partial response lines and a preset model.

[0069] Exemplarily, step S120 may further include: inputting the TOF resolutions of the partial response lines as input values ​​into the preset model to obtain the time resolutions of all scintillation crystals.

[0070] In the above step S110 , the TOF resolution of some response lines has been obtained according to the prior information, and since the number of these partial response lines is appropriate, the time resolution of all scintillation crystals can be obtained through the TOF resolution of these partial response lines.

[0071] For example, the preset model is:

[0072] Among them, σ i represents the temporal resolution of scintillation crystal i, σ j represents the temporal resolution of scintillation crystal j, σ ij It represents the TOF resolution of the response line formed by scintillation crystals i and j.

[0073] In practice, the time resolution of all scintillation crystals can be obtained by solving a set of simultaneous equations. For example, when σ is known, ij , σ ik , σ jk When ……, by solving the above formula (1) for the simultaneous equation system, we can get σ i , σ j , σ k .... Exemplarily, the solution to the system of simultaneous equations may adopt methods such as Preconditioned Conjugate Gradient (PCG), Minimum Residuals (MINRES) or Least Squares QR-factorization (LSQR). These methods can be referred to the records of the prior art and will not be described in detail in this application.

[0074] It should be understood by those skilled in the art that the preset model may be other models or algorithms besides the above formula (1). As long as the model or algorithm can obtain the TOF resolution of all response lines based on the TOF resolution of some response lines, it can be applied to the present application. For example, in a further example of the present application, the above formula (1) can be extended and expanded. In practice, the inventors found that the TOF resolution of the response line is not only affected by the scintillation crystal, but also by the incident angle of the photons. Therefore, the variable δ can be further introduced on the basis of the above formula (1). r , where r is the distance between the response line and the center of the field of view (FOV) on the longitudinal plane of the detection ring. The incident angle of the photon depends on r. It can be obtained empirically that r and the variable δ rThe relationship between the variables δ can be obtained by indexing r. r Specifically, the above formula (1) can be transformed into the following formula (2):

[0075] Among them, σ i , σ j and σ ij The meaning of δ is the same as that of the above formula (1), r Represents a variable related to the incident angle of the photon.

[0076] When the above formula (2) is used as a preset model to obtain the time resolution of the scintillation crystal and the TOF resolution of the response line, since it not only associates the TOF resolution of the response line with the scintillation crystal, but also further associates the TOF resolution of the response line with the incident angle of the photon, it can obtain a more accurate time resolution of the scintillation crystal than the above formula (1), thereby obtaining a more accurate TOF resolution of the response line, which is more conducive to the performance of image reconstruction.

[0077] For the solution of the above formula (2), the time resolution of all scintillation crystals can also be obtained by the method of simultaneous equations. For example, when σ is known ij , σ ik , σ jk When ……, by performing simultaneous equations on the above formula (2), we can get σ i , σ j , σ k .... Exemplarily, the solution to the system of simultaneous equations may adopt methods such as Preconditioned Conjugate Gradient (PCG), Minimum Residuals (MINRES) or Least Squares QR-factorization (LSQR). These methods can be referred to the records of the prior art and will not be described in detail in this application.

[0078] S130: Obtain the TOF resolutions of the remaining response lines according to the time resolutions of all scintillation crystals and the preset model.

[0079] It can be understood that the partial response lines in the above step S110 and the remaining response lines in step S130 together constitute all the response lines.

[0080] Exemplarily, step S130 may further include: grouping the time resolutions corresponding to two scintillation crystals on the same response line into one group, and inputting all groups of time resolutions as input values ​​into the preset model to obtain the TOF resolutions of the remaining response lines.

[0081] For example, taking the preset model as the above formula (1), all scintillation crystals are arranged and combined in pairs to form several groups, one group corresponds to one LOR, and all groups correspond to all LORs. Each group is substituted into the above formula (1) as an input value, and the TOF resolution of the remaining response lines can be finally obtained.

[0082] It can be understood that, under normal circumstances, the preset models used in step S120 and step S130 are the same. However, it is not ruled out that in some cases, the preset models used by the two are different. For example, the preset model in step S120 adopts formula (1), and the preset model in step S130 adopts formula (2). It can also be the other way around, or step S120 and step S130 respectively adopt other algorithms that can be applied to this application as preset models.

[0083] S140: Reconstructing an image according to the TOF resolution and a first preset algorithm.

[0084] The first preset algorithm may adopt any algorithm in the field of TOF image reconstruction that can realize image reconstruction.

[0085] In one example, the first preset algorithm is, for example, a list-mode maximum-likelihood expectation-maximization (LM-MLEM) algorithm, and the specific algorithm is as shown in the following formula (3).

[0086] in, is the j-th pixel value of the n-th iteration, N i and A i are the normalization factor and attenuation factor of the i-th LOR, r ik and s ik are the number of random and scattered coincident events on the kth time bin of the i-th LOR, S is the set of LOR numbers and time bin numbers of all list-mode events, H ij is the system matrix for non-TOF reconstruction, H ijk The system matrix needs to be supplemented for TOF reconstruction.

[0087] In another example, the first preset algorithm is, for example, a list-mode ordered-subsets expectation-maximization (LM-OSEM) algorithm, and the specific algorithm is as shown in the following formula (4):

[0088] in, is the jth pixel value of the lth subset in the nth iteration, N iand A i are the normalization factor and attenuation factor of the i-th LOR, r ik and s ik are the number of random and scattered coincidence events on the kth time bin of the i-th LOR, S l is the set of LOR number i and time bin number k of all list-mode events in the lth subset, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0089] In another example, the first preset algorithm is, for example, a maximum-likelihood expectation-maximization (MLEM) algorithm, and the specific algorithm is as shown in the following formula (5):

[0090] in, is the j-th pixel value of the n-th iteration, N i and A i are the normalization factor and attenuation factor of the i-th LOR, r ik and s ik are the number of random and scattered coincidence events on the kth time bin of the i-th LOR, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0091] In another example, the first preset algorithm is, for example, an ordered-subsets expectation-maximization (OSEM) algorithm, and the specific algorithm is as shown in the following formula (6):

[0092] in, is the jth pixel value of the lth subset in the nth iteration, N i and A i are the normalization factor and attenuation factor of the i-th LOR, r ik and s ik are the number of random and scattered coincidence events on the kth time bin of the i-th LOR, S l is the set of LOR number i in the lth subset, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0093] In the above example, H ijk =H ij Kijk , K ijk It can be calculated using the following formula (7).

[0094] Wherein, T0 is the start time of the kth time bin, T1 is the end time of the kth time bin, t is the integral variable, and σ can adopt the data obtained by the preset model in the above step S130.

[0095] Compared with the existing technology, the image reconstruction method provided by the present application performs differentiated processing on the TOF resolution of different response lines, especially correlating the TOF resolution of the response line with the temporal resolution of the corresponding scintillation crystal, accurately estimating the TOF resolution of the response line, and using it in TOF image reconstruction, which can effectively improve the quality of image reconstruction.

[0096] Regarding the prior information, in this application, a variety of methods can be used to obtain it, for example, it can be obtained through simulation experiments. For example, as shown in Figure 2, the prior information is obtained according to the following steps:

[0097] S210: Performing an image detection test under the test conditions to obtain the number of coincidence events on all response lines and the time difference between the two crystals in each coincidence event.

[0098] Regarding the test conditions, there are two main aspects to consider: one is the selection of detectors, and the other is the selection of radiation sources.

[0099] The detector selection is typically the same as that used in actual image detection, including its shape and structure. This eliminates the need to calibrate prior information due to detector differences, reduces computational workload, and significantly ensures the accuracy of prior information.

[0100] Regarding the selection of radiation sources, in this application, a radiation source that only emits positrons is selected as the target radiation source. That is, the target radiation source is required not to emit gamma photons in the energy range of 400keV-650keV to avoid affecting the detection of positron annihilation. For example, the target radiation source is: 18 F. 22 Na or 68 Ge.

[0101] In this application, the core considerations for selecting the target radiation source are the shape and the position of the source in the detector.

[0102] Regarding shape, the target source can be a shell source, a line source, or a point source. A cross-sectional schematic diagram of a shell source is shown in Figure 3 . Shell source 31 is placed within detector ring 10. The straight line represents response line 20. Typically, at least two lines connecting a single detector unit to two other detector units at different locations pass through the source. Cross-sectional schematic diagrams of line and point sources are shown in Figure 4 . The points within detector ring 10 represent the cross-section of line source 32 or point source 33. The target source is required to be sufficiently thin, meaning its dimensions must be smaller than a preset requirement. For example, the shell source's thickness is less than or equal to 1 cm, the line source's diameter is less than or equal to 1 cm, or the point source's diameter is less than or equal to 0.5 cm. Regarding shell sources, those skilled in the art will understand that, as the name implies, a shell source consists of a generally elongated cylindrical shell with an inner and outer wall. The target source is placed between these two walls. The shell source's thickness represents the difference in radius between the inner and outer walls in cross-section.

[0103] The target radiation source is positioned within the detector in a manner that ensures that the line connecting any single detection unit and at least two detection units at different locations passes through the target radiation source. The detector comprises a plurality of detection units, each of which includes a scintillator crystal and a photoelectric converter. Specifically, when the target radiation source is a shell source, the height of the shell source is parallel to the axis of the PET. When the target radiation source is a line source, at least three of the intersections with the line source on the cross-section of the detection ring are not collinear. This can be achieved by providing at least three line sources or by rotating the line source. When the target radiation source is a point source, at least four of the point sources are not coplanar. This can be achieved by providing at least four point sources or by rotating and / or moving the point source. In some examples, there is only one line source and one point source, and rotating the line source and point source ensures that at least three of the intersections with the line source on the cross-section of the detection ring are not collinear and at least four of the point sources are not coplanar.

[0104] In addition, the shell source activity range is 0.4mCi-2mCi, and the scanning time is 1 hour to 2 hours; the line source activity range is 50μCi-1000μCi, and the single position scanning time is 5 minutes to 20 minutes; the point source activity range is 10μCi-200μCi, and the single position scanning time is 1 minute to 5 minutes.

[0105] In step S210, the test conditions can be selected as described above and the test can be started. During the test, information such as the number of coincident events and the time difference between the two crystals in a single coincident event is acquired and recorded. It should be noted that a single coincident event consists of two single-photon events detected by the scintillation crystals at the two ends of the same response line. For each coincident event, a photon detection time difference corresponding to the single-photon events at the two ends of the response line can be obtained.

[0106] S220: Selecting the response line whose number of matching events reaches a first preset threshold as the target response line.

[0107] During detection, some response lines may have fewer matching events, or even no matching events detected. Due to the small amount of data, subsequent information acquisition may be impossible. Therefore, it is necessary to select a target response line based on the number of matching events. For example, the first preset threshold is greater than or equal to 5, meaning that a response line with more than 5 matching events is selected as the target response line.

[0108] When the target source is a point source or a line source, the TOF resolution of the response line can be directly calculated. However, when the target source is a shell source, it is impossible to distinguish which intersection of the shell source and the response line the event originated from. Therefore, before step S220, the step of obtaining prior information also includes:

[0109] Response lines whose distance from the central axis of the shell source reaches a second preset threshold are excluded.

[0110] The second preset threshold is 80% of the maximum distance corresponding to the detection ring field of view, that is, the response line whose distance from the central axis of the shell source exceeds 80% of the maximum distance corresponding to the detection ring field of view is not the target response line.

[0111] In addition, when the target radiation source is a shell source, after step S220, the step of obtaining the prior information further includes:

[0112] All coincidence events are time-of-flight compensated using a pre-set method.

[0113] Compensating coincident events for flight time can eliminate the impact of flight time on the time difference. The pre-set method can be an existing time compensation method. In one example, the flight time difference caused by two annihilation locations is calculated based on the geometric relationship, and then used to compensate for the coincident event. As shown in Figure 5, the time difference distribution on a response line of the shell source originally had two peaks. As shown in Figure 6, after compensation, it has become a single peak.

[0114] Specifically, in one example of this application, the preset method is:

[0115] Obtaining two intersection points of the response line and the shell source and the time-of-flight difference of coincident events generated by annihilation of the two intersection points;

[0116] A time difference spectrum is drawn according to the time difference of the event to obtain two peaks, wherein the two peaks correspond to two intersection points of the response line and the shell source respectively;

[0117] The k-mean algorithm is used to classify the matching events into one of the two peaks;

[0118] The flight time difference of the event is compensated according to the intersection point to which the event belongs and the calculated flight time difference.

[0119] More specifically, in one example, a particular LOR has two intersections with the shell source. The flight time differences between the coincident events generated by the annihilation of these two intersections are quite different, resulting in two "peaks" visible on the time difference spectrum, as shown in Figure 5. We compensate the flight time of each coincident event by the following method:

[0120] 1. Assume that N coincident events are detected on the LOR, and the flight time difference between each coincident event is Δt i , i = 1, 2, ..., N, calculate the center positions of the two peaks using the k-mean algorithm:

[0121] 1.1) Initialize the center positions of the two peaks T1 and T2 to -1 and 1;

[0122] 1.2) When i = 1, 2, ..., N;

[0123] 1.2.1) If |Δt i -T1|≤|Δt i -T2|, then the i-th matching event belongs to the first set S1;

[0124] 1.2.2) If |Δt i -T1|>|Δt i -T2|, then the i-th matching event belongs to the second set S2;

[0125] 1.3) Recalculate the center position,

[0126] 1.4) Repeat steps 1.2 and 1.3 3 to 5 times;

[0127] 1.5) Output the center positions T1, T2 and the sets S1, S2.

[0128] 2. Let the length of the chord where the LOR intersects the shell source be L and the speed of light be c, as shown in Figure 7. Calculate the flight time difference of each coincident event after flight time compensation:

[0129] 2.1) When i = 1, 2, ..., N;

[0130] 2.1.1) If i∈S1, then the time difference after compensation Δt′ i =Δt i +L / c;

[0131] 2.1.2) If i∈S2, then the time difference after compensation Δt′ i =Δt i -L / c.

[0132] 3. Time difference Δt′ after the above processing i , the time difference spectrum drawn when i = 1, 2, ..., N has only one peak, such as Figure 6.

[0133] 4. Perform the above processing on all valid LORs (ie, LORs whose distance from the central axis of the shell source is less than a second preset threshold).

[0134] S230: Obtaining the TOF resolutions of all the target response lines as the prior information according to a second preset algorithm and the time differences of the respective coincident events.

[0135] The second preset algorithm may be:

[0136] Where n is the total number of coincidence events on a target response line, Δt i is the time difference of the i-th matching event, is the mean of the time difference on the target response line, σ is the standard deviation of the time difference on the target response line, and the TOF resolution of the target response line is 2.355σ.

[0137] It should be noted that the prior information obtained in step S230 is generally the correspondence between the target response line and the TOF resolution. In step S110, the corresponding TOF resolution can be indexed by the response line that is identical to the target response line. In actual detection, any response line that is identical to the target response line can be directly indexed to obtain the TOF resolution.

[0138] Corresponding to the above-mentioned image reconstruction method, the present application also provides an image reconstruction system. As shown in FIG8 , the image reconstruction system provided by the present application generally includes: an acquisition unit 710, a calculation unit 720, and a reconstruction unit 730. The acquisition unit 710 is used to obtain the TOF resolution of a portion of the response line based on prior information; the calculation unit 720 is used to obtain the time resolution of all scintillation crystals based on the TOF resolution of the portion of the response line and a preset model, and to obtain the TOF resolution of the remaining response lines based on the time resolution of all scintillation crystals and the preset model; and the reconstruction unit 730 is used to reconstruct the image based on all TOF resolutions and a first preset algorithm.

[0139] Among them, the number or proportion of partial response lines is required to meet the requirement of being able to obtain the time resolution of all scintillation crystals based on the TOF resolution of the partial response line. It should be noted that, in general, the image detection device includes a number of detectors. For example, all detectors are combined to form at least one detection ring. Each detector includes an array of a number of scintillation crystals and other device structures. When the line connecting any two scintillation crystals passes through the field of view of the detection ring, it may constitute a response line. That is, a scintillation crystal is connected to each end of a response line. In this application, the scintillation crystals connected to both ends of the partial response line are required to cover all scintillation crystals. In reverse expression, each scintillation crystal corresponds to at least one response line. The purpose of setting the number or proportion of partial response lines in this application is to ensure that the basic data (TOF resolution of the partial response line) is sufficient to smoothly obtain the TOF resolution of all response lines, and to balance the response line acquisition amount and the TOF resolution calculation amount, that is, the number or proportion of partial response lines should be appropriate.

[0140] Exemplarily, the calculation unit 720 is used to input the TOF resolutions of the partial response lines as input values ​​into the preset model to obtain the time resolutions of all scintillation crystals, and to group the time resolutions corresponding to two scintillation crystals located on the same response line into a group, and input all groups of time resolutions as input values ​​into the preset model to obtain the TOF resolutions of the remaining response lines.

[0141] For example, the preset model is:

[0142] Among them, σ i represents the temporal resolution of scintillation crystal i, σ j represents the temporal resolution of scintillation crystal j, σ ij It represents the TOF resolution of the response line formed by scintillation crystals i and j.

[0143] In practice, the time resolution of all scintillation crystals can be obtained by solving a set of simultaneous equations. For example, when σ is known, ij , σ ik , σ jk When ..., by solving the simultaneous equations of the preset model, we can get σ i , σ j , σ k .... Exemplarily, the solution to the system of simultaneous equations may adopt methods such as Preconditioned Conjugate Gradient (PCG), Minimum Residuals (MINRES), or Least Squares QR-factorization (LSQR).

[0144] It should be understood by those skilled in the art that the preset model may be other models or algorithms besides the above formula (1). As long as the model or algorithm can obtain the TOF resolution of all response lines based on the TOF resolution of some response lines, it can be applied to the present application. For example, in a further example of the present application, the above formula (1) can be extended and expanded. In practice, the applicant found that the TOF resolution of the response line is not only affected by the scintillation crystal, but also by the incident angle of the photon. Therefore, the variable δ can be further introduced on the basis of the above formula (1). r , where r is the distance between the response line and the center of the field of view (FOV) on the longitudinal plane of the detection ring. The incident angle of the photon depends on r. It can be obtained empirically that r and the variable δ r The relationship between the variables δ can be obtained by indexing r. r Specifically, the above formula (1) can be transformed into the following formula (2):

[0145] Among them, σ i , σ j and σ ij The meaning of δ is the same as that of the above formula (1), r Represents a variable related to the incident angle of the photon.

[0146] When the above formula (2) is used as a preset model to obtain the time resolution of the scintillation crystal and the TOF resolution of the response line, since it not only associates the TOF resolution of the response line with the scintillation crystal, but also further associates the TOF resolution of the response line with the incident angle of the photon, it can obtain a more accurate time resolution of the scintillation crystal than the above formula (2), thereby obtaining a more accurate TOF resolution of the response line, which is more conducive to the performance of image reconstruction.

[0147] For the solution of the above formula (2), the time resolution of all scintillation crystals can also be obtained by the method of simultaneous equations. For example, when σ is known ij , σ ik , σ jk When ……, by solving the above formula (1) for the simultaneous equation system, we can get σ i , σ j , σ k.... Exemplarily, the solution to the system of simultaneous equations may adopt methods such as Preconditioned Conjugate Gradient (PCG), Minimum Residuals (MINRES) or Least Squares QR-factorization (LSQR). These methods can be referred to the records of the prior art and will not be described in detail in this application.

[0148] The first preset algorithm may adopt any algorithm in the field of TOF image reconstruction that can realize image reconstruction.

[0149] In one example, the first preset algorithm is, for example, a list-mode maximum-likelihood expectation-maximization (LM-MLEM) algorithm, and the specific algorithm is as shown in the following formula (3).

[0150] in, is the j-th pixel value of the n-th iteration, N i and A i are the normalization factor and attenuation factor of the i-th LOR, r ik and s ik are the number of random and scattered coincident events on the kth time bin of the i-th LOR, S is the set of LOR numbers and time bin numbers of all list-mode events, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0151] In another example, the first preset algorithm is, for example, a list-mode ordered-subsets expectation-maximization (LM-OSEM) algorithm, and the specific algorithm is as shown in the following formula (4):

[0152] in, is the jth pixel value of the lth subset in the nth iteration, N i and A i are the normalization factor and attenuation factor of the i-th LOR, r ik and s ik are the number of random and scattered coincidence events on the kth time bin of the i-th LOR, S l is the set of LOR number i and time bin number k of all list-mode events in the lth subset, H ijis the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0153] In another example, the first preset algorithm is, for example, a maximum-likelihood expectation-maximization (MLEM) algorithm, and the specific algorithm is as shown in the following formula (5):

[0154] in, is the j-th pixel value of the n-th iteration, N i and A i are the normalization factor and attenuation factor of the i-th LOR, r ik and s ik are the number of random and scattered coincidence events on the kth time bin of the i-th LOR, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0155] In another example, the first preset algorithm is, for example, an ordered-subsets expectation-maximization (OSEM) algorithm, and the specific algorithm is as shown in the following formula (6):

[0156] in, is the jth pixel value of the lth subset in the nth iteration, N i and A i are the normalization factor and attenuation factor of the i-th LOR, r ik and s ik are the number of random and scattered coincidence events on the kth time bin of the i-th LOR, S l is the set of LOR number i in the lth subset, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0157] In the above example, H ijk =H ij K ijk , K ijk It can be calculated using the following formula (7).

[0158] Wherein, T0 is the start time of the kth time bin, T1 is the end time of the kth time bin, t is the integral variable, and σ can adopt the data obtained by the preset model in the above step S130.

[0159] Compared with the existing technology, the image reconstruction system provided by the present application performs differentiated processing on the TOF resolution of different response lines, especially correlating the TOF resolution of the response line with the temporal resolution of the corresponding scintillation crystal, accurately estimating the TOF resolution of the response line, and using it in TOF image reconstruction, which can effectively improve the quality of image reconstruction.

[0160] For the prior information, please refer to the description of the above image reconstruction method, which will not be repeated here.

[0161] In some embodiments, an electronic device is provided, which may include a processor and a memory storing a computer program, wherein the processor is configured to execute the method of any embodiment of the present application when running the computer program.

[0162] As shown in Figure 9, the electronic device is presented in the form of a general-purpose computing device. The components of the electronic device may include, but are not limited to, at least one processor 810, at least one memory 820, a bus 830 connecting different system components (including the memory 820 and the processor 810), a display unit 840, and the like. Among them, the memory 820 stores program code, and the program code can be executed by the processor 810, so that the processor 810 executes the method described in this specification according to various exemplary embodiments of the present application. For example, the processor 810 can execute the method shown in Figures 1 to 2.

[0163] The memory 820 may include a readable medium in the form of a volatile memory unit, such as a random access memory unit (RAM) 8201 and / or a cache memory unit 8202 , and may further include a read-only memory unit (ROM) 8203 .

[0164] The memory 820 may also include a program / utility 8204 having a set (at least one) of program modules 8205, such program modules 8205 including but not limited to: an operating system, one or more application programs, other program modules, and program data, each of which or some combination may include an implementation of a network environment.

[0165] Bus 830 may represent one or more of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, a processing unit, or a local bus using any of a variety of bus architectures.

[0166] The electronic device can also communicate with one or more external devices 800 (e.g., a keyboard, a pointing device, a Bluetooth device, etc.), one or more devices that enable a user to interact with the electronic device, and / or any device that enables the electronic device to communicate with one or more other computing devices (e.g., a router, a modem, etc.). Such communication can occur via an input / output (I / O) interface 850. Furthermore, the electronic device can communicate with one or more networks (e.g., a local area network (LAN), a wide area network (WAN), and / or a public network such as the Internet) via a network adapter 960. The network adapter 860 can communicate with other modules of the electronic device via a bus 830. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with the electronic device, including but not limited to microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage systems.

[0167] Through the description of the above embodiments, it is easy for those skilled in the art to understand that the example embodiments described here can be implemented by software or by combining software with necessary hardware. The technical solution according to the embodiment of the present application can be embodied in the form of a software product, which can be stored in a computer-readable storage medium (which can be a CD-ROM, a USB flash drive, a mobile hard disk, etc.) or on a network, and includes a number of computer program instructions to enable a computing device (which can be a personal computer, a server, or a network device, etc.) to perform the above method according to the embodiment of the present application.

[0168] The software product can adopt any combination of one or more readable media. The readable medium can be a readable signal medium or a readable storage medium. The readable storage medium can be, for example, but not limited to, a system, device or component of electricity, magnetism, light, electromagnetic, infrared, or semiconductor, or any combination thereof. More specific examples (non-exhaustive list) of readable storage media include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof.

[0169] Computer-readable storage media may include a data signal propagated in baseband or as part of a carrier wave, which carries readable program code. Such propagated data signals may take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. The readable storage medium may also be any readable medium other than a readable storage medium, which may send, propagate, or transmit a program for use by or in conjunction with an instruction execution system, apparatus, or device. The program code contained on the readable storage medium may be transmitted using any appropriate medium, including but not limited to wireless, wired, optical cable, RF, etc., or any suitable combination thereof.

[0170] The program code for performing the operations of the present application can be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java, C++, and the like, as well as conventional procedural programming languages ​​such as C or similar programming languages. The program code can be executed entirely on the user computing device, partially on the user device, as a standalone software package, partially on the user computing device and partially on a remote computing device, or entirely on a remote computing device or server. In the case of a remote computing device, the remote computing device can be connected to the user computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0171] The computer-readable medium carries one or more program instructions. When the one or more program instructions are executed by a device, the computer-readable medium implements the aforementioned functions.

[0172] Through the description of the above embodiments, it is easy for those skilled in the art to understand that the example embodiments described here can be implemented by software or by combining software with necessary hardware. The technical solution according to the embodiment of the present application can be embodied in the form of a software product, which can be stored in a computer-readable storage medium (which can be a CD-ROM, a USB flash drive, a mobile hard disk, etc.) or on a network, and includes a number of computer program instructions to enable a computing device (which can be a personal computer, a server, or a network device, etc.) to perform the above method according to the embodiment of the present application.

[0173] Those skilled in the art will appreciate that the above modules can be distributed in the device as described in the embodiment, or can be modified accordingly to be used in one or more devices that are uniquely different from the embodiment. The multiple modules of the above embodiments can be combined into one module, or one module can be further divided into multiple submodules.

[0174] Although the present application provides the method operation steps described in the above embodiments or flow charts, more or fewer operation steps may be included in the method based on routine or no creative work. In the steps where there is no necessary causal relationship in logic, the execution order of these steps is not limited to the execution order provided in the embodiments of the present application.

[0175] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0176] The embodiments of the present application are described in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only intended to help understand the method and core ideas of the present application. At the same time, changes or modifications made by those skilled in the art based on the ideas of the present application, the specific implementation methods, and the scope of application of the present application, all fall within the scope of protection of the present application. In summary, the contents of this specification should not be construed as limiting the present application.

Claims

1. An image reconstruction method, characterized in that, Including: Obtaining the TOF resolution of partial response lines according to prior information; Obtaining the time resolution of all scintillation crystals according to the TOF resolution of the partial response lines and a preset model; Obtaining the TOF resolution of the remaining response lines according to the time resolution of all scintillation crystals and the preset model; Reconstructing an image according to all TOF resolutions and a first preset algorithm.

2. The image reconstruction method according to claim 1, wherein The obtaining the time resolution of all scintillation crystals according to the TOF resolution of the partial response lines and the preset model includes: Taking the TOF resolution of the partial response lines as input values respectively and inputting them into the preset model to obtain the time resolution of all scintillation crystals; The obtaining the TOF resolution of the remaining response lines according to the time resolution of all scintillation crystals and the preset model includes: Listing the time resolutions corresponding to two scintillation crystals on the same response line as a group, and taking all groups of time resolutions as input values and inputting them into the preset model to obtain the TOF resolution of the remaining response lines.

3. The image reconstruction method according to claim 1, wherein The preset model is as follows: Among them, σ i represents the time resolution of the scintillation crystal i, σ j represents the time resolution of the scintillation crystal j, and σ ij represents the TOF resolution of the response line formed by the scintillation crystal i and the scintillation crystal j.

4. The image reconstruction method according to claim 1, wherein The preset model is as follows: Among them, σ i represents the time resolution of the scintillation crystal i, and σ j represents the time resolution of the scintillation crystal j. δ r represents a variable related to the photon incident angle, and σ ij represents the TOF resolution of the response line formed by the scintillation crystal i and the scintillation crystal j.

5. The image reconstruction method according to claim 1, characterized in that The prior information is obtained according to the following steps: Conducting an image detection experiment under experimental conditions, and obtaining the number of coincidence events on all response lines and the time difference between two crystals in each coincidence event; Selecting the response lines with the number of coincidence events reaching a first preset threshold as target response lines; Obtaining the TOF resolution of all the target response lines according to a second preset algorithm and the time difference of each coincidence event as the prior information.

6. The image reconstruction method according to claim 5, wherein The second preset algorithm is as follows: where n is the total number of coincidence events on a certain target response line, and Δt i is the time difference of the i-th coincidence event, is the mean of the coincidence time differences of the target response line, σ is the standard deviation of the time differences of the target response line, and the TOF resolution of the target response line is 2.355σ.

7. The image reconstruction method according to claim 5, wherein The first preset threshold is greater than or equal to 5.

8. The image reconstruction method according to claim 5, wherein The experimental conditions include: Selecting a radiation source that only emits positrons as the target radiation source; and / or, The shape of the target radiation source includes a shell source, a line source or a point source.

9. The image reconstruction method according to claim 8, characterized in that, When the target radiation source is the shell source, before selecting the response lines with the number of coincidence events exceeding the first preset threshold as target response lines, the steps for obtaining the prior information further include: Excluding the response lines with the distance from the central axis of the shell source reaching a second preset threshold.

10. The image reconstruction method according to claim 9, characterized in that, The second preset threshold is 80% of the maximum distance corresponding to the detection ring field of view.

11. The image reconstruction method according to claim 8, wherein When the target radiation source is the shell source, after selecting the response lines with the number of coincidence events exceeding the first preset threshold as target response lines, the steps for obtaining the prior information further include: Performing time-of-flight compensation on all coincidence events by using a preset method.

12. The image reconstruction method according to claim 11, characterized in that, The preset method is: Obtaining two intersection points of the response line and the shell source and the time-of-flight difference of the coincidence events generated by the annihilation of the two intersection points; Drawing a time-difference spectrum according to the time difference of the coincidence events to obtain two peaks, and the two peaks respectively correspond to the two intersection points of the response line and the shell source; Using the k-mean algorithm to classify the coincidence events into one of the two peaks; Compensating the time-of-flight difference of the coincidence events according to the intersection point to which the coincidence events belong and the calculated time-of-flight difference.

13. The image reconstruction method according to claim 8, wherein The experimental conditions further include: the size of the target radiation source is less than a preset requirement.

14. The image reconstruction method according to claim 13, wherein The preset requirement includes: The thickness of the shell source is less than or equal to 1 cm; or, The diameter of the line source is less than or equal to 1 cm; or, The diameter of the point source is less than or equal to 0.5 cm.

15. The image reconstruction method according to claim 8, characterized in that, The test conditions further include: the position of the target radiation source satisfies ensuring that the connection lines between any single detection unit and at least two detection units at different positions all pass through the target radiation source.

16. The image reconstruction method according to claim 15, characterized in that, The height of the shell source is parallel to the axis of the PET; or, Among the intersection points of the line source on the cross-section of the detection ring, at least three points are not collinear; or, At least four of the point sources are not coplanar.

17. The image reconstruction method according to claim 8, wherein The target radiation source includes 18 F,[[]] 22 Na or 68 Ge.[[]] 18. The image reconstruction method according to claim 1, wherein The first preset algorithm is as follows: Among them, is the j-th pixel value of the n-th iteration, N i and A i are the normalization factor and attenuation factor of the i-th response line, r ik and s ik are the number of random and scattered coincidence events in the k-th time bin of the i-th response line, S is the set of response line numbers and time bin numbers where all list-mode events are located, H ij is the system matrix for non-TOF reconstruction, H ijk is the system matrix for TOF reconstruction.

19. The image reconstruction method according to claim 1, characterized in that, The first preset algorithm is as follows: Among them, is the j-th pixel value of the l-th subset for the n-th iteration, N i and A i are the normalization factor and the attenuation factor of the i-th response line, r ik and s ik are the number of random and scattered coincidence events in the k-th time bin of the i-th response line, S l is the set of response line numbers i and time bin numbers k where all list-mode events in the l-th subset are located, H ij is the system matrix for non-TOF reconstruction, H ijk is the system matrix for TOF reconstruction.

20. The image reconstruction method according to claim 1, wherein The first preset algorithm is as follows: Among them, is the j-th pixel value for the n-th iteration, N i and A i are the normalization factor and attenuation factor of the i-th response line, r ik and s ik are the numbers of random and scattered coincidence events in the k-th time bin of the i-th response line, H ij is the system matrix for non-TOF reconstruction, H ijk is the system matrix for TOF reconstruction.

21. The image reconstruction method according to claim 1, wherein The first preset algorithm is as follows: Among them, is the j-th pixel value of the l-th subset for the n-th iteration, N i and A i are the normalization factor and attenuation factor of the i-th response line, r ik and s ik are the number of random and scattered coincidence events in the k-th time bin of the i-th response line, S l is the set of response line numbers i in the l-th subset, H ij is the system matrix for non-TOF reconstruction, H ijk is the system matrix for TOF reconstruction.

22. The image reconstruction method according to any one of claims 18 to 21, characterized in that H ijk = H ij K ijk Wherein, T0 is the start time of the k-th time bin, T1 is the end time of the k time bins, t is the integration variable, and σ represents the TOF resolution of the response line.

23. An image reconstruction system, characterized in that, Comprising: An acquisition unit, configured to acquire the TOF resolution of partial response lines according to prior information; A calculation unit, configured to obtain the time resolution of all scintillation crystals according to the TOF resolution of the partial response lines and a preset model, and obtain the TOF resolution of the remaining response lines according to the time resolution of all scintillation crystals and the preset model; A reconstruction unit, configured to reconstruct an image according to all TOF resolutions and a first preset algorithm.

24. The image reconstruction system according to claim 23, wherein, The calculation unit is configured to input the TOF resolutions of the partial response lines into the preset model respectively as input values to obtain the time resolution of all scintillation crystals, list the time resolutions corresponding to two scintillation crystals located on the same response line as a group, and input the time resolutions of all groups into the preset model respectively as input values to obtain the TOF resolution of the remaining response lines.

25. A detection device, characterized in that, Comprising the image reconstruction system according to any one of claims 23 to 24.

26. An electronic device, characterized in that, Comprising: A processor and a memory storing a computer program, the processor being configured to implement the method according to any one of claims 1 to 22 when the computer program is running.

27. A storage medium, characterized in that, The storage medium stores a computer program, the computer program being configured to implement the method according to any one of claims 1 to 22 when running.

Images