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

Abstract

The present application discloses an image reconstruction method, system, detection equipment, electronic equipment and storage medium, which relate to the field of data processing. The image reconstruction method includes: obtaining the TOF resolution of some response lines based on prior information; obtaining the time resolution of all scintillation crystals based on the TOF resolution of the said part of the response line and the incident angle of the corresponding photon; obtaining the TOF resolution of the remaining response lines based on the time resolution of all scintillation crystals and the incident angle of the photon; and reconstructing the image based on all TOF resolutions and a first preset algorithm. The solution of the present application performs differentiated processing on the TOF resolutions of different response lines, especially associating the TOF resolution of the response line with the time resolution of the corresponding scintillation crystal and the incident angle of the photon, accurately estimating the TOF resolution of the response line, and effectively improving the quality of image reconstruction.

Description

Technical Field

[0001] 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

[0002] 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.

[0003] In the early days of PET, the main information used for image reconstruction was the number of coincident events on the lines connecting each detector pair. However, the photon time-of-flight (TOF) resolution performance of early detectors was insufficient, bringing almost no gain to image reconstruction. However, with the development of PET detector technology in recent years, the TOF resolution of PET detectors has reached 200ps-600ps. With the support of this TOF information, the quality of TOF image reconstruction has been significantly improved compared to non-TOF image reconstruction. TOF resolution has also become a key indicator for evaluating PET system performance, and TOF image reconstruction has also been widely used.

[0004] The existing method divides the number of coincident events on a line of response (LOR) into different time groups (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 ijk It 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.

[0005] 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

[0006] 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.

[0007] 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 time resolution of all scintillation crystals based on the TOF resolution of the some response lines and the incident angles of the corresponding photons; obtaining the TOF resolution of the remaining response lines based on the time resolution of all scintillation crystals and the incident angles of the photons; and reconstructing an image based on all TOF resolutions and a first preset algorithm.

[0008] In the embodiment of the present application, the TOF resolution of the partial response line and the incident angle of the corresponding photon satisfy the relationship:

[0009]

[0010] 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.

[0011] In an embodiment of the present application, obtaining the time resolution of all scintillation crystals based on the TOF resolution of the partial response line and the incident angle of the corresponding photon includes: inputting the TOF resolution of the partial response line and the incident angle of the corresponding photon as input values ​​into the relationship to obtain the time resolution of all scintillation crystals;

[0012] Obtaining the TOF resolutions of the remaining response lines based on the time resolutions of all scintillation crystals and the incident angles of photons includes: listing the time resolutions corresponding to two scintillation crystals located on the same response line into a group, and inputting the time resolutions and the incident angles of photons of each group as input values ​​into the relationship to obtain the TOF resolutions of all the response lines.

[0013] In the embodiment of the present application, the prior information is obtained according to the following steps:

[0014] Perform image detection tests under experimental conditions to obtain the number of coincidence events on all response lines and the time difference between the two crystals in each coincidence event;

[0015] Selecting a response line whose number of matching events reaches a first preset threshold as a target response line;

[0016] The TOF resolutions of all the target response lines are obtained as the prior information according to a second preset algorithm and the time differences of the respective coincident events.

[0017] In the embodiment of the present application, the second preset algorithm is:

[0018]

[0019] 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'.

[0020] In an embodiment of the present application, the first preset threshold is greater than or equal to 5.

[0021] In the examples of this application, the test conditions include:

[0022] Selecting a source that emits only positrons as the target source; and / or,

[0023] The shape of the target radiation source includes a shell source, a line source or a point source.

[0024] In an embodiment of the present application, when the target radiation source is the shell source, before selecting the response line whose number of coincidence events exceeds a first preset threshold as the target response line, the step of obtaining the prior information further includes:

[0025] Response lines whose distance from the central axis of the shell source reaches a second preset threshold are excluded.

[0026] In the embodiment of the present application, the second preset threshold is 80% of the maximum distance corresponding to the detection ring field of view.

[0027] In an embodiment of the present application, when the target radiation source is the shell source, before selecting the response line whose number of coincidence events exceeds a first preset threshold as the target response line, the step of obtaining the prior information further includes:

[0028] All coincidence events are time-of-flight compensated using a pre-set method.

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

[0030] 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;

[0031] A time difference spectrum is drawn based on the time difference of the matching event to obtain two peaks, which correspond to the two intersection points of the response line and the shell source respectively; the matching event is classified into one of the two peaks using the k-mean algorithm; and the flight time difference of the matching event is compensated based on the intersection point to which the matching event belongs and the calculated flight time difference.

[0032] 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.

[0033] In the embodiment of the present application, the preset requirements include:

[0034] The thickness of the shell source is less than or equal to 1 cm; or,

[0035] The diameter of the line source is less than or equal to 1 cm; or

[0036] The diameter of the point source is less than or equal to 0.5 cm.

[0037] 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.

[0038] 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.

[0039] In the embodiment of the present application, the target radiation source includes 18 F. 22 Na or 68 Ge.

[0040] In the embodiment of the present application, the first preset algorithm is:

[0041]

[0042] 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, S is the set of response line numbers and time bin numbers where all tabular data events are located, and H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0043] In the embodiment of the present application, the first preset algorithm is:

[0044]

[0045] 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 timebin number k of all tabular data events in the lth subset, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0046] In the embodiment of the present application, the first preset algorithm is:

[0047]

[0048] 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 ith response line, and are the numbers of all H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0049] In the embodiment of the present application, the first preset algorithm is:

[0050]

[0051] 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, H ij is the system matrix for non-TOF reconstruction, H ijkSystem matrix for TOF reconstruction.

[0052] In the embodiments of this application,

[0053] H ijk =H ij K ijk

[0054]

[0055] 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.

[0056] In a second aspect, an image reconstruction system is provided, comprising: an acquisition unit for acquiring the TOF resolution of a portion of the response lines based on prior information; a calculation unit for obtaining the time resolution of all scintillation crystals based on the TOF resolution of the portion of the response lines and the incident angle of the corresponding photons, and obtaining the TOF resolution of the remaining response lines based on the time resolution of all the scintillation crystals and the incident angle of the photons; and a reconstruction unit for reconstructing an image based on all the TOF resolutions and a first preset algorithm.

[0057] In an embodiment of the present application, the calculation unit is used to group the time resolutions corresponding to two scintillation crystals located on the same response line into one group, and obtain the TOF resolutions of all the response lines based on the relationship between each group of time resolutions and the incident angle of the photon.

[0058] In a third aspect, a detection device is provided, comprising the image reconstruction system described in the second aspect.

[0059] 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 image reconstruction method described in the embodiment of the present application when running the computer program.

[0060] 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 image reconstruction method described in the embodiment of the present application when executed.

[0061] 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 and the incident angle of the photon, accurately estimating the TOF resolution of the response line, and effectively improving the quality of image reconstruction.

[0062] 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

[0063] 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:

[0064] Figure 1 A flowchart of an image reconstruction method according to an embodiment of the present application is shown;

[0065] Figure 2 A flowchart of an image reconstruction method according to an embodiment of the present application is shown;

[0066] Figure 3 shows a cross-sectional schematic diagram of a shell source and a detector according to an embodiment of the present application;

[0067] Figure 4 shows a cross-sectional schematic diagram of a line source / point source and a detector according to an embodiment of the present application;

[0068] Figure 5 shows the original time difference distribution diagram on a response line in the shell source according to an embodiment of the present application;

[0069] Figure 6 shows a distribution diagram after flight time difference compensation on a response line in a shell source according to an embodiment of the present application;

[0070] Figure 7 A simulated time-of-flight diagram of a shell source detection test according to an embodiment of the present application is shown;

[0071] Figure 8 shows a structural block diagram of an image reconstruction system according to an embodiment of the present application;

[0072] Figure 9 A schematic diagram of an electronic device according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] The image reconstruction method, system, detection device, electronic device and storage medium provided in this application particularly relate to positron emission tomography (PET) technology.

[0079] As previously mentioned, in existing technologies known to the present inventors, TOF image reconstruction typically assumes 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.

[0080] In this regard, the present application provides an image reconstruction method. Figure 1 As shown, the image reconstruction method provided by this application generally includes the following steps:

[0081] S110: Obtaining the TOF resolution of some response lines according to prior information.

[0082] 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.

[0083] It should be noted that, in general, the 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 includes an array of several detection units, each detection unit includes a scintillation crystal and other devices. When the line connecting any two scintillation crystals passes through the field of view of the detection ring, it may form a response line. That is, a response line is connected to a scintillation crystal at each end. In this application, it is required that the scintillation crystals connected at both ends of the partial response line need 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 lines) is sufficient to smoothly obtain the TOF resolution of all response lines, and balance the response line acquisition amount and the TOF resolution calculation amount. When the number of partial response lines is large, the calculation amount of the TOF resolution of the remaining response lines can be reduced, and vice versa, the calculation amount of the TOF resolution of the remaining response lines will be increased. However, when the number of partial response lines is large, the amount of data of the prior information is also required to be large enough, so the number or proportion of partial response lines should be appropriate.

[0084] S120: Obtaining the time resolution of all scintillation crystals according to the TOF resolution of the partial response line and the incident angle of the corresponding photon.

[0085] Exemplarily, step S120 may further include:

[0086] The time resolution of all scintillation crystals is obtained according to the TOF resolution of the partial response line and the incident angle of the corresponding photon.

[0087] 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.

[0088] In practice, the inventors found that the TOF resolution of the response line is affected by the scintillation crystal and the incident angle of the photons.

[0089] Exemplarily, the TOF resolution of the response line and the incident angle of the corresponding photon satisfy the following relationship:

[0090]

[0091] 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.

[0092] 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 from experience that r and the variable δ r The relationship between them can be obtained by indexing the variable δ through r. r .

[0093] When the time resolution of the scintillation crystal and the TOF resolution of the response line are obtained by the above formula (1), since the TOF resolution of the response line is associated with the incident angle of the scintillation crystal and the photon, the accurate time resolution of the scintillation crystal can be obtained, and thus the accurate TOF resolution of the response line can be obtained, which is beneficial to the performance of image reconstruction.

[0094] For the solution of the above formula (1), the time resolution of all scintillation crystals can 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 kFor example, the solution to the system of simultaneous equations may be achieved by using methods such as Preconditioned Conjugate Gradient (PCG), Minimum Residuals (MINRES), or Least Squares QR-factorization (LSQR). These methods may be described in detail in the prior art and will not be described in detail in this application.

[0095] S130: Obtain the TOF resolutions of the remaining response lines according to the time resolutions of all scintillation crystals and the incident angles of the photons.

[0096] Exemplarily, step S130 may further include:

[0097] The time resolutions corresponding to the two scintillation crystals on the same response line are grouped together, and the time resolutions of each group and the incident angle of the photon are input as input values ​​into the above formula (1) to obtain the TOF resolutions of all the response lines.

[0098] For example, all scintillation crystals are arranged in pairs to form several groups, one group corresponds to one LOR, and all groups correspond to all LORs. Each group and the incident angle of the photon are substituted into the above formula (1) as input values, and the TOF resolution of all response lines can be finally obtained.

[0099] 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.

[0100] S140: Reconstructing an image according to all TOF resolutions and a first preset algorithm.

[0101] The first preset algorithm may adopt any algorithm in the field of TOF image reconstruction that can realize image reconstruction.

[0102] In one example, the first preset algorithm is, for example, a list-mode maximum-likelihoodexpectation-maximization (LM-MLEM) algorithm, and the specific algorithm is as shown in the following formula (2).

[0103]

[0104] 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 ikare 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, and H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0105] 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 (3):

[0106]

[0107] 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 ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0108] 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 (4):

[0109]

[0110] 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, and H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0111] 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 (5):

[0112]

[0113] 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.

[0114] In the above example, H ijk =H ij K ijk , K ijk It can be calculated using the following formula (6).

[0115]

[0116] Wherein, 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 can be the data obtained by formula (1) in the above step S130.

[0117] Compared with the existing technology, the image reconstruction method provided by this application differentiates 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 and the incident angle of the photon, accurately estimating the TOF resolution of the response line, and effectively improving the quality of image reconstruction.

[0118] Regarding the prior information, in this application, it can be obtained in a variety of ways, for example, through simulation experiments. For example, Figure 2 As shown, the prior information is obtained by following the steps below:

[0119] 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.

[0120] Regarding the test conditions, there are two aspects to consider: one is the choice of detector, and the other is the choice of radiation source.

[0121] 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.

[0122] 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.

[0123] In this application, the core considerations for selecting the target radiation source are the shape and the position of the source in the detector.

[0124] Regarding the shape, the target source includes a shell source, a line source, or a point source. For a schematic diagram of the cross section of a shell source, see Figure 3 The shell source 31 is placed in the detector ring 10. The straight line is the response line 20. Usually, there are at least two lines connecting a single detector unit and two other detector units at different positions passing through the radiation source. The cross-sectional diagram of the line source and the point source can be seen in FIG. Figure 4 The point inside detector ring 10 represents 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 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. Regarding shell sources, those skilled in the art will understand that, as the name implies, a shell source comprises a generally elongated cylindrical shell with an inner and outer wall. The target source is placed between the inner and outer walls. The shell source thickness represents the difference in radius between the inner and outer walls in cross-section.

[0125] The target radiation source is positioned within the detector in such a way that the line connecting any single detection unit to 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 non-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 non-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 the point source achieves the goal of at least three non-collinear and at least four non-coplanar intersections with the line source on the cross-section of the detection ring.

[0126] 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.

[0127] 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.

[0128] S220: Selecting the response line whose number of matching events reaches a first preset threshold as the target response line.

[0129] 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 greater than or equal to 5 matching events is selected as the target response line.

[0130] 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:

[0131] Response lines whose distance from the central axis of the shell source reaches a second preset threshold are excluded.

[0132] 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.

[0133] In addition, when the target radiation source is a shell source, after step S220, the step of obtaining the prior information further includes:

[0134] All coincidence events are time-of-flight compensated using a pre-set method.

[0135] Compensating the time of flight for coincident events can eliminate the influence of flight time on time difference. The preset method can be an existing time compensation method. In one example, the flight time difference caused by two annihilation positions is calculated based on the geometric relationship, and then the time difference is used to compensate the coincident event. The distribution of time difference on a response line of the original shell source has two peaks, see Figure 5 , becomes a peak after compensation, see Figure 6 .

[0136] Specifically, in one example of this application, the preset method is:

[0137] 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;

[0138] 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;

[0139] The k-mean algorithm is used to classify the matching events into one of the two peaks;

[0140] 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.

[0141] More specifically, in one example, for a particular LOR, there are two intersections with the shell source. The flight time differences of the coincident events produced by the annihilation of these two intersections are quite different, so two "peaks" can be seen on the time difference spectrum, for example Figure 5 We compensate for the flight time of each eligible event by the following method:

[0142] 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:

[0143] 1.1) Initialize the center positions of the two peaks T1 and T2 to -1 and 1;

[0144] 1.2) When i = 1, 2, ..., N;

[0145] 1.2.1) If |Δt i -T1|≤|Δt i -T2|, then the i-th matching event belongs to the first set S1;

[0146] 1.2.2) If |Δt i -T1|>|Δt i -T2|, then the i-th matching event belongs to the second set S2;

[0147] 1.3) Recalculate the center position,

[0148] 1.4) Repeat steps 1.2 and 1.3 3 to 5 times;

[0149] 1.5) Output the center positions T1, T2 and the sets S1, S2.

[0150] 2. Let the length of the chord where the LOR intersects the shell source be L, and the speed of light be c, such as Figure 7 As shown, the flight time difference of each coincident event after flight time compensation is calculated:

[0151] 2.1) When i = 1, 2, ..., N;

[0152] 2.1.1) If i∈S1, then the time difference after compensation Δt' i =Δt i +L / c;

[0153] 2.1.2) If i∈S2, then the time difference after compensation Δt' i =Δt i -L / c.

[0154] 3. Time difference Δt' after the above processing i , i=1,2,…,N The time difference spectrum drawn has only one peak, for example Figure 6 .

[0155] 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).

[0156] 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.

[0157] The second preset algorithm may be:

[0158]

[0159] 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'.

[0160] 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.

[0161] Corresponding to the above image reconstruction method, the present application also provides an image reconstruction system. Figure 8 As shown, 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 some response lines based on prior information; the calculation unit 720 obtains the time resolution of all scintillation crystals based on the TOF resolution of the partial response lines and the incident angle of the corresponding photons, and obtains the TOF resolution of the remaining response lines based on the time resolution of all scintillation crystals and the incident angle of the photons; the reconstruction unit 730 is used to reconstruct the image based on all TOF resolutions and a first preset algorithm.

[0162] 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 electrical structures. When the line connecting any two scintillation crystals passes through the field of view of the detection ring, it may form 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.

[0163] Exemplarily, the calculation unit 720 is configured to obtain the time resolution of all scintillation crystals based on the TOF resolution of the partial response line and the incident angle of the corresponding photon, and group the time resolutions corresponding to two scintillation crystals located on the same response line into a group, and use the time resolution of each group and the incident angle of the photon as input values ​​to obtain the TOF resolution of all the response lines through formula (1).

[0164] Exemplarily, the corresponding relationship between the TOF resolution of the partial response line and the incident angle of the corresponding photon can be expressed as:

[0165]

[0166] 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.

[0167] 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 from experience that r and the variable δ r The relationship between the variables δ can be obtained by indexing r. r .

[0168] When the time resolution of the scintillation crystal and the TOF resolution of the response line are obtained by the above formula (1), since the TOF resolution of the response line is associated with the incident angle of the scintillation crystal and the photon, the accurate time resolution of the scintillation crystal can be obtained, and thus the accurate TOF resolution of the response line can be obtained, which is beneficial to the performance of image reconstruction.

[0169] For the solution of the above formula (1), the time resolution of all scintillation crystals can 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 For example, the solution to the system of simultaneous equations may be achieved by using methods such as Preconditioned Conjugate Gradient (PCG), Minimum Residuals (MINRES), or Least Squares QR-factorization (LSQR). These methods may be described in detail in the prior art and will not be described in detail in this application.

[0170] The first preset algorithm may adopt any algorithm in the field of TOF image reconstruction that can realize image reconstruction.

[0171] In one example, the first preset algorithm is, for example, a list-mode maximum-likelihoodexpectation-maximization (LM-MLEM) algorithm, and the specific algorithm is as shown in the following formula (2).

[0172]

[0173] 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.

[0174] 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 (3):

[0175]

[0176] 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 ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0177] 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 (4):

[0178]

[0179] 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, and H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

[0180] 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 (5):

[0181]

[0182] 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.

[0183] In the above example, H ijk =H ij K ijk , K ijk It can be calculated using the following formula (6).

[0184]

[0185] Wherein, 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 can be the data obtained by formula (1) in the above step S130.

[0186] 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 time resolution of the corresponding scintillation crystal and the incident angle of the photon, accurately estimating the TOF resolution of the response line, and effectively improving the quality of image reconstruction.

[0187] For the prior information, please refer to the description of the above image reconstruction method, which will not be repeated here.

[0188] 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.

[0189] like Figure 9 As shown, the electronic device is 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, etc. Among them, the memory 820 stores program code, and the program code can be executed by the processor 810, so that the processor 810 performs the methods described in this specification according to various exemplary embodiments of the present application. For example, the processor 810 can execute the following Figures 1 and 2 The method shown in .

[0190] 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 .

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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++, etc., and 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 stand-alone 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 through 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).

[0198] 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.

[0199] 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.

[0200] Those skilled in the art will appreciate that the modules described above 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 embodiment can be combined into one module, or one module can be further divided into multiple sub-modules.

[0201] 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.

[0202] 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.

[0203] 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: include: Obtain TOF resolution of some response lines based on prior information; The time resolution of all scintillation crystals is obtained according to the TOF resolution of the partial response line and the incident angle of the corresponding photon; The TOF resolution of the remaining response lines is obtained based on the time resolution of all scintillation crystals and the incident angle of the photons; reconstructing an image according to the TOF resolution of all response lines and a first preset algorithm; The prior information is obtained by following the steps below: Perform image detection tests under experimental conditions to obtain the number of coincidence events on all response lines and the time difference between the two crystals in each coincidence event; Selecting a response line whose number of matching events reaches a first preset threshold as a target response line; Obtaining the TOF resolution of all the target response lines as the prior information according to a second preset algorithm and the time difference of each coincident event; The prior information is the correspondence between the target response line and the TOF resolution. The corresponding TOF resolution can be indexed through the response line that is the same as the target response line.

2. The image reconstruction method according to claim 1, wherein: The TOF resolution of the partial response line and the incident angle of the corresponding photon satisfy the relationship: 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.

3. The image reconstruction method according to claim 2, wherein: The time resolution of all scintillation crystals obtained based on the TOF resolution of the partial response line and the incident angle of the corresponding photon includes: The TOF resolution of the partial response line and the incident angle of the corresponding photon are input as input values ​​into a relationship formula to obtain the time resolution of all scintillation crystals; The TOF resolution of the remaining response lines obtained according to the time resolution of all scintillation crystals and the incident angle of the photons includes: The time resolutions corresponding to two scintillation crystals on the same response line are grouped together, and the time resolutions of each group and the incident angle of the photon are input as input values ​​into the relationship formula to obtain the TOF resolutions of all the response lines.

4. The image reconstruction method according to claim 1, wherein: The second preset algorithm is: 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 of the target response line, and the TOF resolution of the target response line is 2.355σ ’ .

5. The image reconstruction method according to claim 1, wherein: The first preset threshold is greater than or equal to 5.

6. The image reconstruction method according to claim 1, wherein: The test conditions include: Selecting a source that emits only positrons as the target source; and / or, The shape of the target radiation source includes a shell source, a line source or a point source.

7. The image reconstruction method according to claim 6, characterized in that: When the target radiation source is the shell source, before selecting the response line whose number of coincidence events exceeds a first preset threshold as the target response line, the step of acquiring the prior information further includes: Response lines whose distance from the central axis of the shell source reaches a second preset threshold are excluded.

8. The image reconstruction method according to claim 7, characterized in that: The second preset threshold is 80% of the maximum distance corresponding to the detection ring field of view.

9. The image reconstruction method according to claim 6, wherein: When the target radiation source is the shell source, after selecting the response line whose number of coincidence events exceeds a first preset threshold as the target response line, the step of acquiring the prior information further includes: All coincidence events are time-of-flight compensated using a pre-set method.

10. The image reconstruction method according to claim 9, 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 coincident events generated by annihilation of the two intersection points; 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; The k-mean algorithm is used to classify the matching events into one of the two peaks; 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.

11. The image reconstruction method according to claim 6, wherein: The test conditions also include: the size of the target radiation source is smaller than a preset requirement.

12. The image reconstruction method according to claim 11, wherein: 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.

13. The image reconstruction method according to claim 8, wherein: The test conditions also include: the position of the target radiation source satisfies the requirement that a line connecting any single detection unit and at least two detection units at different positions passes through the target radiation source.

14. The image reconstruction method according to claim 13, wherein: The height of the shell source is parallel to the axis of the PET; or, Among the intersection points of the cross section of the detection ring with the line source, at least three points are not colinear; or, at least four of the point sources are not coplanar.

15. The image reconstruction method according to claim 6, characterized in that: The target radiation source includes 18 F. 22 Na or 68 Ge.

16. The image reconstruction method according to claim 1, wherein: The first preset algorithm is: 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 group of the i-th response line, S is the set of response line numbers and time group numbers where all tabular data events are located, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

17. The image reconstruction method according to claim 1, wherein: The first preset algorithm is: 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 group of the i-th response line, S l is the set of response line number i and time group number k of all tabular data events in the lth subset, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

18. The image reconstruction method according to claim 1, wherein: The first preset algorithm is: 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 group of the i-th response line, respectively, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

19. The image reconstruction method according to claim 1, wherein: The first preset algorithm is: 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 group of the i-th response line, S l is the set of response lines numbered i in the lth subset, H ij is the system matrix for non-TOF reconstruction, H ijk System matrix for TOF reconstruction.

20. The image reconstruction method according to any one of claims 16 to 19, characterized in that: H ijk =H ij K ijk Where T0 is the start time of the kth time group, T1 is the end time of the kth time group, t is the integration variable, and σ represents the TOF resolution of the response line.

21. An image reconstruction system, characterized in that: include: An acquisition unit, configured to acquire the TOF resolution of a portion of the response line based on 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 the incident angle of the corresponding photons, and to obtain the TOF resolution of the remaining response lines according to the time resolution of all scintillation crystals and the incident angle of the photons; a reconstruction unit, configured to reconstruct an image according to all TOF resolutions and a first preset algorithm; The prior information is obtained by following the steps below: Perform image detection tests under experimental conditions to obtain the number of coincidence events on all response lines and the time difference between the two crystals in each coincidence event; Selecting a response line whose number of matching events reaches a first preset threshold as a target response line; Obtaining the TOF resolution of all the target response lines as the prior information according to a second preset algorithm and the time difference of each coincident event; The prior information is the correspondence between the target response line and the TOF resolution. The corresponding TOF resolution can be indexed through the response line that is the same as the target response line.

22. The image reconstruction system according to claim 21, wherein: The calculation unit is used to group the time resolutions corresponding to two scintillation crystals located on the same response line into one group, and obtain the TOF resolutions of all the response lines according to different relationship equations corresponding to the time resolutions of each group and the incident angle of the photon.

23. A detection device, characterized in that: The method comprises the image reconstruction system as claimed in any one of claims 21 to 22.

24. An electronic device, characterized in that: include: A processor and a memory storing a computer program, wherein the processor is configured to implement the image reconstruction method according to any one of claims 1 to 20 when running the computer program.

25. A storage medium, characterized in that The storage medium stores a computer program, and the computer program is configured to implement the image reconstruction method according to any one of claims 1 to 20 when executed.

Images