DETECTOR MODULES FOR SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY IMAGING

A detector module for single SPECT may be provided. The detector module may include a semi-monolithic crystal and a plurality of SiPM photodetectors forming a photodetector array. The semi-monolithic crystal may include a plurality of monolithic crystal plates configured to receive gamma rays. The plurality of monolithic crystal plates may be arranged side by side along a thickness direction of the plurality of monolithic crystal plates. The photodetector array may include a plurality of columns arranged side by side along the thickness direction of the plurality of monolithic crystal plates. Each monolithic crystal plate may be in optical communication with one or more columns of SiPM photodetectors in the photodetector array, and the one or more columns of SiPM photodetectors may be configured to detect scintillation light produced by gamma ray interactions in the monolithic crystal plate.

TECHNICAL FIELD

The present disclosure generally relates to single photon emission computed tomography (SPECT) imaging, and in particular, to systems and methods for detector modules for SPECT imaging.

BACKGROUND

SPECT imaging is one of the nuclear medicine functional imaging techniques widely used in medical diagnosis (e.g., diagnosis of prostate cancer, neuroendocrine tumors, neuroblastoma, pheochromocytoma, or other diseases), preclinical scientific research, new drug development, etc. For example, a SPECT image may be indicative of some physiological parameters of tracer kinetics and can aid the evaluation of the physiology (or functionality) and/or anatomy (or structure) of a target organ or tissue, as well as its biochemical properties.

SUMMARY

According to an aspect of the present disclosure, a detector module for SPECT may be provided. The detector module may include a semi-monolithic crystal and a plurality of silicon photomultiplier (SiPM) photodetectors. The semi-monolithic crystal may include a plurality of monolithic crystal plates configured to receive gamma rays. The plurality of monolithic crystal plates may be arranged side by side along a thickness direction of the plurality of monolithic crystal plates. The plurality of SiPM photodetectors may form a photodetector array. The photodetector array may include a plurality of columns arranged side by side along the thickness direction of the plurality of monolithic crystal plates. For each of the plurality of monolithic crystal plates, the monolithic crystal plate may be in optical communication with one or more columns of SiPM photodetectors in the photodetector array, and the one or more columns of SiPM photodetectors may be configured to detect scintillation light produced by gamma ray interactions in the monolithic crystal plate.

In some embodiments, the detector module may be electronically connected to a processing device, and the processing device may be configured to perform the following operations. The processing device may receive readout signals from one or more target columns of SiPM photodetectors in the photodetector array that are in optical communication with a target monolithic crystal plate among the plurality of monolithic crystal plates. The processing device may further determine that a target gamma ray interaction occurs in the target monolithic crystal plate based on the readout signals.

In some embodiments, the one or more target columns of SiPM photodetectors include a plurality of rows arranged along a length direction of the target monolithic crystal plate, and the processing device may be further configured to perform the following operations. The processing device may determine a total signal intensity detected by each row of the plurality of rows based on the readout signals. The processing device may further determine position information of the target gamma ray interaction in the target monolithic crystal plate based on the total signal intensity received by each row of the plurality of rows.

In some embodiments, to determine position information of the target gamma ray interaction in the target monolithic crystal plate based on the total signal intensity received by each row of the plurality of rows, the processing device may be configured to perform the following operations. The processing device may determine a signal intensity distribution in the plurality of rows based on the total signal intensity received by each row of the plurality of rows. The processing device may further determine at least one of first position information or second position information based on the signal intensity distribution. The first position information may relate to the position of the target gamma ray interaction along the length direction of the target monolithic crystal plate, and the second position information may relate to the position of the target gamma ray interaction along a depth direction of the target monolithic crystal plate.

In some embodiments, to determine at least one of first position information or second position information based on the signal intensity distribution, the processing device may be configured to determine the at least one of the first position information or the second position information by processing the signal intensity distribution using a position information determination model.

In some embodiments, the position information determination model may be generated by a model training process. A plurality of training samples may be obtained. Each training sample may include a sample signal intensity distribution corresponding to a sample gamma ray interaction and reference position information of the sample gamma ray interaction. The position information determination model may be generated by training a preliminary model using the plurality of training samples.

In some embodiments, the detector module may further include a light guide disposed between the semi-monolithic crystal and the photodetector array, and configured to guide the scintillation light from the semi-monolithic crystal to the photodetector array.

In some embodiments, a material of the semi-monolithic crystal may include at least one of cesium iodide (CsI) or sodium iodide (NaI).

In some embodiments, a thickness of each of at least a portion of the plurality of monolithic crystal plates may be smaller than 1.3 millimeters.

In some embodiments, a distance between adjacent monolithic crystal plates among the plurality of monolithic crystal plates may be smaller than 0.1 millimeters.

In some embodiments, a size of each column in the photodetector array along the thickness direction of the plurality of monolithic crystal plates may be greater than a thickness of the monolithic crystal plate being in optical communication with the column.

In some embodiments, a signal readout sampling rate of each of the plurality of SiPM photodetectors may be in a range from 20 MHz to 150 MHz.

In some embodiments, a range of energy that the detector module focuses on may be a range from 20 kev to 1000 kev.

According to another aspect of the present disclosure, a SPECT device may be provided. The SPECT device may include a detector module and a collimator. The collimator may be configured to limit a range of photons entering the detector module. The detector module may be configured to detect photons. The detector module may include a semi-monolithic crystal and a plurality of silicon photomultiplier (SiPM) photodetectors. The semi-monolithic crystal may include a plurality of monolithic crystal plates configured to receive gamma rays. The plurality of monolithic crystal plates may be arranged side by side along a thickness direction of the plurality of monolithic crystal plates. The plurality of SiPM photodetectors may form a photodetector array. The photodetector array may include a plurality of columns arranged side by side along the thickness direction of the plurality of monolithic crystal plates. For each of the plurality of monolithic crystal plates, the monolithic crystal plate may be in optical communication with one or more columns of SiPM photodetectors in the photodetector array, and the one or more columns of SiPM photodetectors may be configured to detect scintillation light produced by gamma ray interactions in the monolithic crystal plate.

DETAILED DESCRIPTION

The term “image” in the present disclosure is used to collectively refer to imaging data (e.g., scan data, projection data) and/or images of various forms, including a two-dimensional (2D) image, a three-dimensional (3D) image, a four-dimensional (4D), etc. The term “pixel” and “voxel” in the present disclosure are used interchangeably to refer to an element of an image. The term “region,” “location,” and “area” in the present disclosure may refer to a location of an anatomical structure shown in the image or an actual location of the anatomical structure existing in or on a target object's body, since the image may indicate the actual location of a certain anatomical structure existing in or on the target object's body.

Conventionally, a detector module of a SPECT scanner includes an analog Anger detector module or a Cadmium zinc telluride (CZT) detector module. The analog Anger detector module includes a photomultiplier (PMT) photodetector and a monolithic scintillator. Due to a physical size limitation of the PMT photodetector and the use of the monolithic scintillator which results in a relatively large propagation range of scintillation photons, a spatial resolution of the analog Anger detector module is low. The CZT detector module has a compact and lightweight spatial structure, a high spatial resolution (e.g., a spatial resolution of 2.46 mm) and energy resolution, and a high scanning efficiency. However, the CZT detector module is usually used for high-energy quantitative detection, which may cause relatively great quantitative errors due to distortion. In addition, the cost of CZT detector module is relatively high.

An improved detector module for SPECT is needed to address the above-mentioned problems of conventional detector modules. One of the promising approaches is using silicon photomultiplier (SiPM) photodetectors. A size of a SiPM photodetector may be a millimeter-level. Conventional PMT photodetector normally has a size in a centimeter-level. Therefore, the size of the SiPM photodetector is much smaller than the size of the PMT photodetector. Therefore, at the same spatial resolution level, the detector module including the SiPM photodetectors has a much smaller size than a conventional detector module using PMT photodetectors. SiPM photodetectors have been widely used for positron emission tomography (PET) imaging. However, the SiPM photodetectors have not been used for SPECT imaging due to some reasons. For example, if the SiPM photodetectors are used for SPECT imaging, dark currents occur in the SiPM photodetectors will result in that an energy output signal (a sum of all signals detected by the SiPM photodetectors) of the detector module in the SPECT scanner has a non-negligible background noise, which reduces a signal-to-noise ratio of a resulting SPECT image and an energy resolution of the SiPM photodetectors. The reasons for the above problems may include: 1) In PET imaging, coincidence events need to be determined based on a nanosecond-level time window, for example, a coincidence event may be recorded when a pair of photons generated by a positron-electron annihilation are detected within a coincidence time window, e.g., within 6 to 12 nanoseconds. Since noises generated by the SiPM photodetectors occur randomly, the noises generated by the SiPM photodetectors may be eliminated after the coincidence event processing, so the background noise generated by the dark currents in the SiPM photodetectors does not affect PET imaging. However, there is no coincidence event processing in SPECT imaging, all events entering the SiPM photodetectors can be received, the background noise due to dark currents generated by the SiPM photodetectors will affect SPECT imaging; 2) SPECT imaging needs to focus on a wide range of energy (e.g., a range from 20 kev to 1000 kev), while PET imaging only focuses on a single 511 kev energy, so the dark current in the SiPM photodetectors has a greater impact on the energy resolution of SPECT imaging, especially the resolution of characteristic peaks with low energy; 3) In SPECT imaging, relatively few photons enter the detector module after passing through a collimator, so the background noise generated by the SiPM photodetectors can have a greater impact on SPECT imaging. Therefore, it is desirable to provide a detector module using SiPM photodetectors with a negligible background noise.

According to one aspect of the present disclosure, a detector module for SPECT may be provided. The detector module may include a semi-monolithic crystal and a plurality of SiPM photodetectors forming a photodetector array. The semi-monolithic crystal may include a plurality of monolithic crystal plates configured to receive gamma rays emitted by a radioactive tracer injected into a subject, and the plurality of monolithic crystal plates may be arranged side by side along a thickness direction of the plurality of monolithic crystal plates. The photodetector array may include a plurality of columns arranged side by side along the thickness direction of the plurality of monolithic crystal plates. For each of the plurality of monolithic crystal plates, the monolithic crystal plate may be in optical communication with one or more columns of SiPM photodetectors in the photodetector array, and the one or more columns of SiPM photodetectors may be configured to detect scintillation light produced by gamma ray interactions in the monolithic crystal plate. According to some embodiments of the present disclosure, the crystal in the detector module may be the semi-monolithic crystal including the plurality of monolithic crystal plates, which is different from the conventional monolithic scintillator. The scintillation light produced by gamma ray interactions in a specific monolithic crystal plate can only travel in the specific monolithic crystal plate and be detected by SiPM photodetectors being in optical communication with the specific monolithic crystal plate. In this way, only a small number of SiPM photodetectors are capable of detecting the scintillation light, the background noise caused by the dark currents in the small number of SiPM photodetectors is relatively small, thereby ensuring the signal-to-noise ratio of a resulting SPECT image and the energy resolution of the SiPM photodetectors, that is, the detector module of the present disclosure can effectively solve the problems caused by the use of SiPM photodetectors in SPECT imaging.

Compared with the conventional analog Anger detector module, the detector module of the present disclosure may have an improved spatial resolution by using the semi-monolithic crystal and the SiPM photodetectors with a size smaller than the PMT photodetectors.

Compared with the conventional CZT detector module, the cost of the detector module of the present disclosure is lower and the spatial resolution is higher.

FIG.1is a block diagram illustrating an exemplary SPECT imaging system100according to some embodiments of the present disclosure. As illustrated inFIG.1, the SPECT imaging system100may include a SPECT scanner110, a processing device120, and a storage device130. The components in the SPECT imaging system100may be connected in various ways. Merely by way of example, the SPECT scanner110may be connected to the processing device120through a network. As another example, the SPECT scanner110may be connected to the processing device120directly.

The SPECT scanner110may be configured to acquire scan data relating to an object. For example, the SPECT scanner110may scan the object or a portion thereof that is located within its detection region and generate scan data relating to the object or the portion thereof. The object may be a biological object (e.g., a patient, an animal) or a non-biological object (e.g., a phantom). In some embodiments, the object may include a specific part, organ, and/or tissue of the object. For example, the object may include the head, the bladder, the brain, the neck, the torso, a shoulder, an arm, the thorax, the heart, the stomach, a blood vessel, soft tissue, a knee, a foot, or the like, or any combination thereof, of a patient. In the present disclosure, “object” and “subject” are used interchangeably.

Before a scan performed by the SPECT scanner110, the object may be injected with a radioactive tracer. For example, the object may be scanned by the SPECT scanner110in a predetermined time period after the radioactive tracer is injected into the object. As another example, the object may be scanned by the SPECT scanner110in a certain time period after the radioactive tracer distribution in the object reaches equilibrium or steady-state. In some embodiments, the radioactive tracer may include technetium-99 (Tc-99), fluorine-18 (F-18), indium-111 (In-111), iodine-131 (I-131), or the like, or any combination thereof.

In some embodiments, the SPECT scanner110may include a single modality scanner or a multi-modality imaging device. For example, the SPECT scanner110may include a SPECT device, a SPECT-CT device, a SPECT-PET device, a SPECT-MR device, etc.

In some embodiments, the SPECT scanner110may include a gantry111, a collimator112, a detector module113, and/or other components not shown. The gantry111may support one or more parts of the SPECT scanner110, for example, the collimator112, the detector module113, and/or other components. The collimator112may limit a range of photons (e.g., γ photons) entering the detector module113. In some embodiments, the collimator112may be a multi-pinhole collimator having at least two sets of pinholes. Each set of pinholes may include one or more pinholes.

The detector module113may be configured to detect the photons collimated by the collimator and generate electrical signals. The detector module113may include a semi-monolithic crystal and a plurality of SiPM photodetectors. The semi-monolithic crystal may be configured to receive gamma rays emitted by the radioactive tracer injected into the subject. The SiPM photodetectors may form a photodetector array may be configured to detect scintillation light produced by gamma ray interactions in the semi-monolithic crystal. In some embodiments, the detector module113may have a relatively small size and be mounted on a specific position of the detection tunnel of the gantry111. In the SPECT scan, the gantry111may rotate around the object being scanned, and the detector module113may rotate with the gantry111to detect photons from different perspectives. In some embodiments, the detector module113may have a relatively big size that wraps around the detection tunnel of the gantry111. In the SPECT scan, the gantry111and the detector module113may remain still. More descriptions for the detector module113may be found elsewhere in the present disclosure (e.g.,FIGS.2-3Cand the descriptions thereof).

The processing device120may process data obtained from one or more components (e.g., the SPECT scanner110, or the storage device130) of the SPECT system100. For example, the processing device120may be electronically connected to the SPECT scanner110. The processing device120may receive readout signals from the photodetector array. Further, the processing device120may determine position information of a target gamma ray interaction in the semi-monolithic crystal based on the readout signals.

In some embodiments, the processing device120may be a single server or a server group. The server group may be centralized or distributed. In some embodiments, the processing device120may be local or remote. Merely for illustration, only one processing device120is described in the SPECT imaging system100. However, it should be noted that the SPECT imaging system100in the present disclosure may also include multiple processing devices. Thus operations and/or method steps that are performed by one processing device120as described in the present disclosure may also be jointly or separately performed by the multiple processing devices. For example, if in the present disclosure the processing device120of the SPECT imaging system100executes both process A and process B, it should be understood that the process A and the process B may also be performed by two or more different processing devices jointly or separately in the SPECT imaging system100(e.g., a first processing device executes process A and a second processing device executes process B, or the first and second processing devices jointly execute processes A and B).

The storage device130may store data and/or instructions. In some embodiments, the storage device130may store data obtained from the SPECT scanner110and/or the processing device120. In some embodiments, the storage device130may store data and/or instructions that the processing device120may execute or use to perform exemplary methods described in the present disclosure. In some embodiments, the storage device130may include a mass storage, removable storage, a volatile read-and-write memory, a read-only memory (ROM), or the like, or any combination thereof. In some embodiments, the storage device130may be implemented on the cloud platform described elsewhere in the present disclosure.

This description is intended to be illustrative, and not to limit the scope of the present disclosure. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments. However, those variations and modifications do not depart the scope of the present disclosure. Merely by way of example, the SPECT imaging system100may include one or more additional components and/or one or more components described above may be omitted. For example, the SPECT imaging system100may include a network. The network may include any suitable network that can facilitate the exchange of information and/or data for the SPECT imaging system100. In some embodiments, one or more components of the SPECT imaging system100(e.g., the SPECT scanner110, the processing device120, etc.) may communicate information and/or data with one or more other components of the SPECT imaging system100via the network.

FIG.2is a schematic diagram illustrating an exemplary detector module200for SPECT according to some embodiments of the present disclosure. In some embodiments, the detector module200may be an exemplary embodiment of the detector module113of the SPECT scanner110as described inFIG.1.

The detector module200may be configured to detect photons. In some embodiments, a range of energy that the detector module focuses on may be a range from 20 kev to 1000 kev. In some embodiments, the range of energy that the detector module focuses on is related to a radioactive tracer for SPECT scan. For example, if the radioactive tracer is iodine-131 (I-131), the range of energy that the detector module focuses on may be 364 keV. As another example, if the radioactive tracer is lutecium-177 (Lu-177), the range of energy that the detector module focuses on may be 208 keV.

As shown inFIG.2, the detector module200may include a semi-monolithic crystal210and a photodetector array220. The photodetector array220may be formed by a plurality of SiPM photodetectors.

As used herein, a semi-monolithic crystal refers a crystal that is not monolithic in at least one direction and is monolithic in one or more directions other than the at least one direction. For example, at least a portion of a monolithic crystal may be divided into multiple crystal plates arranged along the at least one direction to form the semi-monolithic crystal. As shown inFIG.2, the semi-monolithic crystal210may include a plurality of monolithic crystal plates211. A monolithic crystal plate211refers to a crystal whose one side is much shorter than other sides. For example, the monolithic crystal plate211may be a cuboid with one side much shorter than the other two sides. The plurality of monolithic crystal plates211may be configured to receive gamma rays emitted by a radioactive tracer injected into a subject. The plurality of monolithic crystal plates211may be arranged side by side along a thickness direction of the plurality of monolithic crystal plates211.

As used herein, a surface of a monolithic crystal plate211that receives gamma rays from the subject is referred to as an incident plane; the thickness direction of the monolithic crystal plate211refers to a direction along which the short side of the incident plane extends; the length direction of the monolithic crystal plate211refers to a direction along which the long side of the incident plane extends; and the depth direction of the monolithic crystal plate211refers to a direction along which a side of the monolithic crystal plate211perpendicular to the incident plane extends. For example, referring toFIG.2, the top surface of a monolithic crystal plate211is referred to as an incident plane, the thickness direction is parallel to an X-axis direction, the length direction is parallel to a Y-axis direction, and the depth direction is parallel to a Z-axis direction.

In some embodiments, the plurality of monolithic crystal plates211may include a plurality of columns along the thickness direction (i.e., the X-axis direction inFIG.2) and a plurality of rows along a length direction (i.e., the Y-axis direction inFIG.2) of the plurality of monolithic crystal plates211.

In some embodiments, a material of the semi-monolithic crystal210may include cesium iodide (CsI), sodium iodide (NaI), or the like, or any combination thereof. Since NaI is prone to deliquescence, the semi-monolithic crystal210may be sealed as soon as possible after the semi-monolithic crystal210is made using NaI.

In some embodiments, a length, a depth, and/or a thickness of each of at least a portion of the plurality of monolithic crystal plates211may be set according to a default setting of the SPECT imaging system100or an actual need. For example, the length of each of at least a portion of the plurality of monolithic crystal plates211may be greater than 10 millimeters (e.g., 15 millimeters, 20 millimeters, etc.). As another example, the depth of each of at least a portion of the plurality of monolithic crystal plates211may be greater than 5 millimeters (e.g., 8 millimeters, 10 millimeters, etc.). As still another example, the thickness of each of at least a portion of the plurality of monolithic crystal plates211may be smaller than 2 millimeters (e.g., 1.5 millimeters, 1.3 millimeters, etc.). In some embodiments, the smaller the thicknesses of the plurality of monolithic crystal plates211are, the greater the spatial resolution of the detector module200may be. In some embodiments, the thickness of each of at least a portion of the plurality of monolithic crystal plates211may be smaller than 1.3 millimeters.

In some embodiments, a distance between adjacent monolithic crystal plates may be set according to a default setting of the SPECT imaging system100or an actual need. For example, the distance between adjacent monolithic crystal plates211among the plurality of monolithic crystal plates211may be smaller than 0.5 millimeters (e.g., 0.2 millimeters, 0.1 millimeters, etc.). In some embodiments, the smaller the distance between adjacent monolithic crystal plates211among the plurality of monolithic crystal plates211is, the greater a sensitivity of the detector module200may be. In some embodiments, the distance between adjacent monolithic crystal plates211among the plurality of monolithic crystal plates211may be smaller than 0.1 millimeters. In some embodiments, the distance between adjacent monolithic crystal plates211may be set based on a separation layer arranged between adjacent monolithic crystal plates211.

The photodetector array220may include a plurality of columns arranged side by side along the thickness direction of the plurality of monolithic crystal plates211. For each monolithic crystal plate211, the monolithic crystal plate211may be in optical communication with one or more columns of SiPM photodetectors in the photodetector array220, and the one or more columns of SiPM photodetectors may be configured to detect scintillation light produced by gamma ray interactions in the monolithic crystal plate211. For example, each of some monolithic crystal plates211may be in optical communication with one column of SiPM photodetectors. As another example, each of some monolithic crystal plates211may be in optical communication with at least two columns of SiPM photodetectors. As still another example, a plurality of monolithic crystal plates211may be in optical communication with a same column of SiPM photodetectors.

Merely by way of example,FIGS.3A-3Cillustrates side views of exemplary detector modules300A,300B, and300C according to some embodiments of the present disclosure. The side views shown inFIGS.3A-3Care seen from a direction along the length direction of the monolithic crystal plates211(i.e., the Y direction). The detector modules300A,300B, and300C may be exemplary embodiments of the detector module200. As shown inFIG.3A-3C, the semi-monolithic crystal210may include four monolithic crystal plates211-1,211-2,211-3, and211-4. The photodetector array220may include ten columns S1-S10 of SiPM photodetectors.

As shown inFIG.3A, the monolithic crystal plates211-1,211-3, and211-4may be in optical communication with the columns S4, S5, and S6 of SiPM photodetectors, respectively. The monolithic crystal plate211-2may be in optical communication with both the columns S4 and S5 of SiPM photodetectors. As shown inFIG.3B, each monolithic crystal plate may be in optical communication with one column of SiPM photodetectors, that is, the monolithic crystal plates211-1,211-2,211-3, and211-4may be in optical communication with the columns S3, S4, S5, and S6 of SiPM photodetectors, respectively. As shown inFIG.3C, the monolithic crystal plates211-1and211-2may both be in optical communication with the column S5 of SiPM photodetectors. The monolithic crystal plates211-3and211-4may both be in optical communication with the column S6 of SiPM photodetectors.

Different connections between the monolithic crystal plates211and the columns of SiPM photodetectors may have different influences on the spatial resolution of the detector module200and subsequent determination of gamma ray interactions in the monolithic crystal plates211. If a plurality of monolithic crystal plates211are in optical communicate with only one column of SiPM photodetectors, the specific monolithic crystal plate where the gamma ray interaction occurs is not located based on readout signals from the columns of SiPM photodetectors, and in this connection manner, the spatial resolution of the detector module200may be reduced. In contrast, in other connection manners, the specific monolithic crystal plate where the gamma ray interaction occurs may be located based on readout signals from the columns of SiPM photodetectors. The connections between the monolithic crystal plates211and the columns of SiPM photodetectors may be determined according to actual requirements. Preferably, different columns of SiPM photodetectors may be in optical communicate with different monolithic crystal plates211and one column of SiPM photodetectors may be in optical communicate with only one monolithic crystal plate211, which may quickly locate the monolithic crystal plate where the gamma ray interaction occurs.

In some embodiments, a size of each column in the photodetector array220along the thickness direction of the plurality of monolithic crystal plates211may be greater than the thickness of the monolithic crystal plate being in optical communication with the column to facilitate the detection of the scintillation light.

In some embodiments, as shown inFIG.2, the photodetector array220may include a plurality of rows arranged side by side along the length direction (i.e., the Y-axis direction inFIG.2) of the plurality of monolithic crystal plates211, and each monolithic crystal plate211may correspond to the plurality of rows, which may facilitate to determine the position information of the gamma ray interaction along the length direction of the monolithic crystal plate described inFIG.5.

In some embodiments, at least one of a thickness, a length, or a height of each of the plurality of SiPM photodetectors may be smaller than 1 centimeter, that is, a size of each of the plurality of SiPM photodetectors may be a millimeter-level. Conventional PMT photodetector normally has a size in a centimeter-level. Therefore, the size of a SiPM photodetector is much smaller than the size of a PMT photodetector. Therefore, at the same spatial resolution level, the detector module200including the SiPM photodetectors has a much smaller size than a conventional detector module using PMT photodetectors (e.g., an analog Anger detector module). For example, a conventional ring detector module using PMT photodetectors may have a diameter of 2 meters, while a ring detector module using SiPM photodetectors may have a diameter of 80 centimeters. If the detector module200is made to have substantially the same as the size of the conventional detector module, the detector module200may have a higher spatial resolution than the conventional detector module.

In some embodiments, a separation layer may be arranged between each adjacent monolithic crystal plates211. The separation layer between an adjacent monolithic crystal plates211may be configured to block scintillation light transmission between the adjacent monolithic crystal plates211, so that the scintillation light produced by gamma ray interactions in a specific monolithic crystal plate can only travel in the specific monolithic crystal plate (that is, cannot travel through the separation layers to other monolithic crystal plates) and be detected by SiPM photodetector(s) in optical communication with the specific monolithic crystal plate. In this way, a target monolithic crystal plate in which a target gamma ray interaction occurs can be accurately determined, and a spatial resolution of the detector module200may be improved. In some embodiments, the separation layer may include a reflective film, a reflective foil, a reflective coating (e.g., a white reflective coating), or any other material that can prevent or substantially prevent light transmission.

In some embodiments, the detector module200may further include a light guide (e.g., a light guide230as shown inFIGS.3A-3C) disposed between the semi-monolithic crystal210and the photodetector array220. The light guide may be configured to guide scintillation light from the semi-monolithic crystal210to the photodetector array220. For example, if when scintillation light irradiates the gaps between SiPM photodetectors, the light guide may guide the scintillation light into a corresponding SiPM photodetectors, so that the scintillation light irradiating the gaps between SiPM photodetectors may be also detected. In some embodiments, the light guide may also be used to prevent moisture to protect the semi-monolithic crystal210. In some embodiments, the light guide may include a frosted glass. In some embodiments, the light guide may include a portion of the semi-monolithic crystal210. For example, a portion of the semi-monolithic crystal210away from the photodetector array220may be divided into the plurality of crystal plates211, and the other portion of the semi-monolithic crystal210close to the photodetector array220may be a monolithic crystal that is used as the light guide.

In some embodiments, the detector module200may be electronically connected to a processing device (e.g., the processing device120). The processing device may be configured to determine signal intensity information and/or position information relating to gamma ray interactions occur in the semi-monolithic crystal210. For example, after a target gamma ray interaction occurs in a target monolithic crystal plate among the plurality of monolithic crystal plates211, the scintillation light produced by target gamma ray interactions can only travel in the target monolithic crystal plate and be detected by one or more target columns of SiPM photodetectors in the photodetector array220that are in optical communication with the target monolithic crystal plate. The target column(s) of SiPM photodetectors may convert the detected scintillation light into electrical signals (also referred to as readout signals) and transmit the readout signals to the processing device. In some embodiments, a signal readout sampling rate of each of the plurality of SiPM photodetectors may be in a range from 20 MHz to 150 MHz. In some embodiments, the signal readout sampling rate of each of the plurality of SiPM photodetectors may be in a range from 25 MHz to 120 MHz.

After the readout signals are received from the target column(s) of SiPM photodetectors, the processing device may further determine the signal intensity information and/or the position information of the target gamma ray interaction based on the received readout signals. For example, the processing device may determine a sum of the signal intensities of the received readout signals as the signal intensity of the target gamma ray interaction. Merely by way of example, as shown inFIG.3A, if the target gamma ray interaction occurs in the monolithic crystal plate211-1, the processing device may determine a sum of the signal intensities of the readout signals received from the column S4 of SiPM photodetectors as the signal intensity of the target gamma ray interaction. As another example, as shown inFIG.3A, if the target gamma ray interaction occurs in the monolithic crystal plate211-2, the processing device may determine a sum of the signal intensities of the readout signals received from the columns S4 and S5 of SiPM photodetectors as the signal intensity of the target gamma ray interaction.

As another example, if the photodetector array220may include a plurality of rows arranged side by side along the length direction of the plurality of monolithic crystal plates211, the processing device may determine a total signal intensity detected by each row of the plurality of rows based on the readout signals. Further, the processing device may determine a signal intensity distribution in the plurality of rows based on the total signal intensity received by each row of the plurality of rows.

In some embodiments, the readout signal received from each SiPM photodetector in the one or more target columns of SiPM photodetectors may be transmitted respectively to the processing device using any suitable circuit, such as an application specific integrated circuit (ASIC). The processing device may determine a sum of the signal intensities of the received readout signals as the signal intensity of the target gamma ray interaction. In some embodiments, the readout signals from the one or more target columns of SiPM photodetectors may be superimposed to generate a combined readout signal, and then the combined readout signal may be transmitted to the processing device. The processing device may designate a signal intensity of the combined readout signal as the signal intensity of the target gamma ray interaction. Transmitting the combined readout signal may reduce a number of channels for signal transmission compared to transmitting each readout signal individually.

In some embodiments, the processing device may be also configured to determine position information of the target gamma ray interaction based on the signal intensity information of the target gamma ray interaction. The position information of the target gamma ray interaction may include position information of the target gamma ray interaction along one or more of the thickness direction, the length direction, and the depth direction of the plurality of monolithic crystal plates211.

Specifically, after the processing device receives the readout signals from the target column(s) of SiPM photodetectors, the processing device may determine that the target gamma ray interaction occurs in the target monolithic crystal plate based on the corresponding relationship between the SiPM photodetectors and the monolithic crystal plates, that is, the processing device may determine the position information of the target gamma ray interaction along the thickness direction of the plurality of monolithic crystal plates211. For example, as shown inFIG.3B, if there is no the light guide230, and the processing device receives the readout signals from the column S3 of SiPM photodetectors, the processing device may determine that a target gamma ray interaction occurs in the monolithic crystal plate211-1. As another example, as shown inFIG.3A, if the processing device receives the readout signals from the column S4 and S5 of SiPM photodetectors, the processing device may determine which monolithic crystal plate a target gamma ray interaction occurs in by looking up a preset table. The preset table may indicate a relationship between a monolithic crystal plate and corresponding column (s) of SiPM photodetectors detected scintillation light produced by a target gamma ray interaction that occurs in the monolithic crystal plate.

Further, the processing device may determine the position information of the target gamma ray interaction in the target monolithic crystal plate (i.e., the position information along the length direction of the monolithic crystal plates211and/or the position information along the depth direction of the monolithic crystal plates211) based on the readout signals. More descriptions for the determination of the position information of the target gamma ray interaction in the target monolithic crystal plate may be found elsewhere in the present disclosure (e.g.,FIG.5and the descriptions thereof).

As described elsewhere in the present disclosure, if the SiPM photodetectors are used for SPECT imaging, dark currents occur in the SiPM photodetectors will result in that an energy output signal (a sum of all signals detected by the SiPM photodetectors) of the detector module in the SPECT scanner has a non-negligible background noise, which reduces a signal-to-noise ratio of a resulting SPECT image and an energy resolution of the SiPM photodetectors. According to some embodiments of the present disclosure, the crystal in the detector module200is the semi-monolithic crystal210including the plurality of monolithic crystal plates211, which is different from the conventional monolithic scintillator. The scintillation light produced by gamma ray interactions in a specific monolithic crystal plate can only travel in the specific monolithic crystal plate and be detected by SiPM photodetector(s) in optical communication with the specific monolithic crystal plate. In this way, only a small number of SiPM photodetectors are capable of detecting the scintillation light of the specific monolithic crystal plate, the background noise caused by the dark currents in the small number of SiPM photodetectors is relatively small, thereby improving the signal-to-noise ratio of a resulting SPECT image and the energy resolution of the SiPM photodetectors. That is, the detector module200of the present disclosure can effectively solve the problems of using SiPM photodetectors in SPECT imaging.

In addition, some conventional detector modules (e.g., the analog Anger detector module) includes a PMT photodetector and a monolithic scintillator, which has a low resolution and a relatively big size. The CZT detector module is usually used for high-energy quantitative detection, it may cause relatively great quantitative errors due to distortion. In addition, the cost of CZT detector module is relatively high.

Compared with the conventional detector modules using PMT photodetectors and the monolithic scintillator, the detector module200may have an improved spatial resolution because the propagation range of scintillation photons may be smaller due to the use of the semi-monolithic crystal. Moreover, the spatial resolution of the detector module200may be further improved by using the SiPM photodetectors with a size smaller than the PMT photodetectors. In addition, the processing device only needs to receive readout signals from the small number of SiPM photodetectors, which only includes a small amount of data, thereby reducing the dead time of the SPECT imaging system during data transmission and improving the accuracy of the counting of the gamma ray interactions and the efficiency of the SPECT imaging.

Compared with the conventional CZT detector module, the cost of the detector module200is lower and the spatial resolution is higher. In general, a minimum of the spatial resolution of CZT detector module is 2.46 mm, while the spatial resolution of the detector module200may be smaller than or equal to 1.3 mm.

According to some embodiments of the present disclosure, the position information of the target gamma ray interaction (e.g., the position information of the target gamma ray interaction along the thickness direction, the length direction, and the depth direction of the plurality of monolithic crystal plates211) may be accurately determined due to using the detector module200, thereby improving the spatial resolution of the SPECT imaging system100, especially a pinhole imaging system.

FIG.4is a block diagram illustrating an exemplary processing device120according to some embodiments of the present disclosure. As illustrated inFIG.4, the processing device120may include an acquisition module402, a determination module404, and a model generation module406. As described inFIG.1, the SPECT imaging system100in the present disclosure may also include multiple processing devices, and the acquisition module402, the determination module404, and the model generation module406may be components of different processing devices. For example, the acquisition module and the determination module404may be components of a processing device120A, and the model generation module406may be a component of a processing device120B.

The acquisition module402may be configured to information relating to the SPECT imaging system100. For example, the acquisition module402may receive readout signals from target column(s) of SiPM photodetectors. More descriptions regarding the obtaining of the readout signals from target column(s) of SiPM photodetectors may be found elsewhere in the present disclosure. See, e.g., operation502inFIG.5, and relevant descriptions thereof.

The determination module404may be configured to determine a total signal intensity detected by each row of the plurality of rows based on the readout signals. The total signal intensity detected by a row may be a total value of the signal intensity detected by each SiPM photodetector in the row. More descriptions regarding the determination of the total signal intensity detected by each row of the plurality of rows based on the readout signals may be found elsewhere in the present disclosure. See, e.g., operation504inFIG.5, and relevant descriptions thereof.

The determination module404may be also configured to determine position information of the target gamma ray interaction in the target monolithic crystal plate based on the total signal intensity received by each row of the plurality of rows. More descriptions regarding the determination of the position information of the target gamma ray interaction in the target monolithic crystal plate may be found elsewhere in the present disclosure. See, e.g., operation506inFIG.5, and relevant descriptions thereof.

The model generation module406may be configured to generate one or more machine learning models (e.g., a position information determination model) by model training. More descriptions regarding the generation of the position information determination model may be found elsewhere in the present disclosure. See, e.g.,FIG.7, and relevant descriptions thereof.

It should be noted that the above description is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. In some embodiments, any one of the modules may be divided into two or more units. For instance, the acquisition module402may be divided into two units configured to acquire different data. In some embodiments, the processing device120may include one or more additional modules, such as a storage module (not shown) for storing data.

FIG.5is a flowchart illustrating an exemplary process for determining position information of a target gamma ray interaction according to some embodiments of the present disclosure. In some embodiments, process500may be executed by the SPECT imaging system100. For example, the process500may be implemented as a set of instructions (e.g., an application) stored in a storage device (e.g., the storage device130). In some embodiments, the processing device120(e.g., one or more modules illustrated inFIG.4) may execute the set of instructions and may accordingly be directed to perform the process500. The operations of the illustrated process presented below are intended to be illustrative. In some embodiments, the process500may be accomplished with one or more additional operations not described and/or without one or more of the operations discussed. Additionally, the order of the operations of process500illustrated inFIG.5and described below is not intended to be limiting.

In some embodiments, the target gamma ray interaction may be a gamma ray interaction (e.g., the latest gamma ray interaction) occur in a target monolithic crystal plate in a detector module. For example, the detector module may be the detector module200as described in connection withFIG.2. The detector module200may include a semi-monolithic crystal210that includes a plurality of monolithic crystal plates211, and the target monolithic crystal plate may be one of the plurality of monolithic crystal plates211. The detector module200may also include a photodetector array220. The photodetector array220may include a plurality of columns arranged side by side along the thickness direction of the plurality of monolithic crystal plates211and a plurality of rows arranged side by side along the length direction of the plurality of monolithic crystal plates211.

After the target gamma ray interaction occurs in the target monolithic crystal plate, the scintillation light produced by target gamma ray interactions can only travel in the target monolithic crystal plate and be detected by one or more target columns of SiPM photodetectors in the photodetector array220that are in optical communication with the target monolithic crystal plate. The target column(s) of SiPM photodetectors may convert the detected scintillation light into electrical signals (also referred to as readout signals) and transmit the readout signals to the processing device120. After the processing device120receives the readout signals from the target column(s) of SiPM photodetectors, the processing device120may determine that the target gamma ray interaction occurs in the target monolithic crystal plate based on the corresponding relationship between the SiPM photodetectors and the monolithic crystal plates.

In some embodiments, the target column(s) of SiPM photodetectors may include a plurality of rows arranged along the length direction of the target monolithic crystal plate. That is, the target column(s) of SiPM photodetectors may be a target photodetector array arranged in plurality of rows and one or more columns.

In502, the processing device120(e.g., the acquisition module402) may receive, from the target column(s) of SiPM photodetectors, readout signals.

In some embodiments, the readout signal received from each SiPM photodetector in the target column(s) of SiPM photodetectors may be transmitted respectively to the processing device120using any suitable circuit, such as an ASIC. The processing device120may receive the readout signals from the target column(s) of SiPM photodetectors. In some embodiments, the readout signals may be preprocessed (e.g., amplified), and the preprocessed readout signals may be transmitted to the processing device120for further processing. For illustration purposes, the following descriptions describe the processing of the readout signals.

In504, the processing device120(e.g., the determination module404) may determine, based on the readout signals, a total signal intensity detected by each row of the plurality of rows.

The total signal intensity detected by a row may be a total value of the signal intensity detected by each SiPM photodetector in the row. In some embodiments, for each row, the processing device120may determine a sum of one or more signal intensities of one or more readout signals from the row, and designate the sum of one or more signal intensities as the total signal intensity from the row.

For example, referring toFIG.3A, if the target gamma ray interaction occurs in the target monolithic crystal plate211-1, the target column(s) of SiPM photodetectors may be the column S3 of SiPM photodetectors. The column S3 of SiPM photodetectors may include multiple SiPM photodetectors each belonging to one row of SiPM photodetectors. For each row, the processing device120may directly designate the signal intensity of the readout signal received from the SiPM photodetector corresponding to the row as the total signal intensity detected by the row.

As another example, referring toFIG.3Aagain, if the target gamma ray interaction occurs in the target monolithic crystal plate211-2, the target column(s) of SiPM photodetectors may be the columns S4 and S5 of SiPM photodetectors. Each row of the columns S4 and S5 of SiPM photodetectors may include a first SiPM photodetector in the column S4 of SiPM photodetectors and a second SiPM photodetector in the column S5 of SiPM photodetectors. For each row, the processing device120may determine a sum of the signal intensities of the readout signals received from the first SiPM photodetector and the second SiPM photodetector corresponding to the row, and designate the sum of the signal intensities of the readout signals received from the first SiPM photodetector and the second SiPM photodetector corresponding to the row as the total signal intensity detected by the row.

In506, the processing device120(e.g., the determination module404) may determine, based on the total signal intensity received by each row of the plurality of rows, position information of the target gamma ray interaction in the target monolithic crystal plate.

In some embodiments, the processing device120may determine a signal intensity distribution (also referred to as a target signal intensity distribution) in the plurality of rows based on the total signal intensity received by each row of the plurality of rows. The signal intensity distribution may indicate total signal intensities corresponding to different rows along the length direction of the target monolithic crystal plate. Merely by way of example, the processing device120may establish a two-dimensional (2D) coordinate system including a first coordinate axis parallel to the length direction of the target monolithic crystal plate and a second coordinate axis parallel to a depth direction of the target monolithic crystal plate. For example, the 2D coordinate system may be the same as or similar to a 2D coordinate system including a Y-axis and a I-axis shown inFIG.6. The second coordinate axis may be configured to denote the total signal intensity received by each row of the plurality of rows. The first coordinate axis may be configured to denote a position of each row of the plurality of rows along the length direction of the target monolithic crystal plate. In some embodiments, the target signal intensity distribution may be represented by a target signal intensity curve in the 2D coordinate system. For example, the processing device120may determine a data point corresponding to each row, wherein the coordinate of the data point along the first coordinate axis is determined based on the position of the row along the length direction of the target monolithic crystal plate, and the coordinate of the data point along the second coordinate axis is determined based on the total signal intensity of the row. Further, the processing device120may perform a curve fit on a plurality of data points to determine the target signal intensity curve indicative of the target signal intensity distribution.

Further, the processing device120may determine at least one of first position information or second position information of the target gamma ray interaction based on the target signal intensity distribution. The first position information may relate to the position of the target gamma ray interaction along the length direction of the target monolithic crystal plate. The second position information may relate to the position of the target gamma ray interaction along the depth direction of the target monolithic crystal plate. For example, the first position information may be denoted by a first coordinate in the Y-axis, and the second position information may be denoted by a second coordinate in the Z-axis.

The position of the target gamma ray interaction along the length direction and the depth direction of the target monolithic crystal plate may affect the target signal intensity distribution (e.g., the shape of the signal intensity curve). For illustration purposes,FIG.6provides a schematic diagram illustrating exemplary reference gamma ray interactions and their respective reference signal intensity curves according to some embodiments of the present disclosure. As shown inFIG.6, the Y-axis denotes a position along the length direction of the target monolithic crystal plate, the Z-axis denotes a position along the depth direction of the target monolithic crystal plate, the I-axis denotes a total signal intensity received by each row of the plurality of rows, and a position point P refers to a position of a reference gamma ray interaction in a reference monolithic crystal plate where the reference gamma ray interaction occurs.

As shown inFIG.6, for each reference gamma ray interaction, a Y-axis coordinate of the corresponding position point P may substantially correspond to a peak of the corresponding reference signal intensity curves. Accordingly, a position of a gamma ray interaction along a length direction of a monolithic crystal plate where the gamma ray interaction occurs may be determined based on a peak of a signal intensity distribution corresponding to the gamma ray interaction. The processing device120may determine the first position information of the target gamma ray interaction according to a peak of the target signal intensity distribution. For example, the processing device120may designate a first coordinate of the peak of the target signal intensity distribution as the first position information of the target gamma ray interaction.

As shown inFIG.6, if the position point P is relatively far from the corresponding incident plane, the peak of the corresponding reference signal intensity curve may have a relatively sharp shape (i.e., the corresponding reference signal intensity curve may have a relatively sharp peak). Accordingly, a position of a gamma ray interaction along a depth direction of a monolithic crystal plate where the gamma ray interaction occurs may be determined based on a shape of a peak of a signal intensity distribution corresponding to the gamma ray interaction. The processing device120may determine the second position information of the target gamma ray interaction according to a shape of the peak of the target signal intensity distribution.

In some embodiments, the processing device120may obtain multiple reference gamma ray interactions and their corresponding reference signal intensity curves from a storage device (e.g., the storage device130). Each reference gamma ray interaction may have a known occurrence position. For each of the multiple reference signal intensity curves, the processing device120may determine a similarity between the reference signal intensity curve and the target signal intensity curve. Further, the processing device120may determine the first position information and/or the second position information based on the known occurrence position of a reference gamma ray interaction whose reference signal intensity curve has the maximum similarity to the target signal intensity curve.

In some determine, the processing device120may determine the first position information and/or the second position information by processing the target signal intensity distribution (e.g., the target signal intensity curve) using a position information determination model. The position information determination model may be a trained model (e.g., a machine learning model) configured to receive a signal intensity distribution corresponding to a gamma ray interaction as an input, and output position information of the gamma ray interaction. Merely by way of example, the target signal intensity curve may be input into the position information determination model, and the position information determination model may output the first position information and/or the second position information.

In some embodiments, the position information determination model may include a deep learning model, such as a Deep Neural Network (DNN) model, a Convolutional Neural Network (CNN) model, a Recurrent Neural Network (RNN) model, a Feature Pyramid Network (FPN) model, etc. Exemplary CNN models may include a V-Net model, a U-Net model, a Link-Net model, or the like, or any combination thereof. Since the position information determination model may learn the optimal mechanism for position information determination based on a large amount of data, the position information (e.g., the first position information, the second position information) of the target gamma ray interaction determined using the position information determination model may be relatively accurate.

In some embodiments, the processing device120may obtain the position information determination model from one or more components of the SPECT imaging system100(e.g., the storage device130) or an external source via a network. For example, the position information determination model may be previously trained by a computing device (e.g., the processing device120or a processing device of a model vendor), and stored in the storage device130. The processing device120may access the storage device130and retrieve the position information determination model. In some embodiments, the position information determination model may be generated according to a machine learning algorithm as described elsewhere in this disclosure (e.g.,FIG.4and the relevant descriptions).

In some embodiments, the position information determination model may be generated by performing process700as shown inFIG.7.

In702, the processing device120(e.g., the model generation module406) may obtain a plurality of training samples each of which includes a sample signal intensity distribution corresponding to a sample gamma ray interaction and reference position information of the sample gamma ray interaction.

In some embodiments, the plurality of training samples may be acquired based on a same sample SPECT scan using a sample detector module same as or similar to the detector module200. Alternatively, the plurality of training samples may be acquired based on different sample SPECT scans using the sample detector module or multiple sample detector modules. In some embodiments, the reference position information of the sample gamma ray interaction can be used as a ground truth (also referred to as a label) for model training. In some embodiments, the reference position information of a sample gamma ray interaction may be determined by a user manually. In some embodiments, the reference position information of a sample gamma ray interaction may include at least one of first sample position information or second sample position information of the sample gamma ray interaction. The first sample position information and the second sample position information may be similar to the first position information and the second position information described inFIG.5, respectively.

In some embodiments, the processing device120may obtain a training sample (or a portion thereof) from one or more components of the SPECT imaging system100(e.g., the storage device130) or an external source (e.g., a database of a third-party) via a network.

In704, the processing device120(e.g., the model generation module406) may generate the position information determination model by training a preliminary model using the plurality of training samples.

The preliminary model refers to a model to be trained. The preliminary model may be of any type of model (e.g., a machine learning model) as described elsewhere in this disclosure (e.g.,FIG.5and the relevant descriptions). In some embodiments, the processing device120may obtain the preliminary model from one or more components of the SPECT imaging system100or an external source (e.g., a database of a third-party) via a network. The preliminary model may include a plurality of model parameters. Before training, the model parameters of the preliminary model may have their respective initial values. For example, the processing device120may initialize parameter values of the model parameters of the preliminary model.

In some embodiments, the training of the preliminary model may include one or more iterations. For illustration purposes, the implementation of a current iteration is described hereinafter. In some embodiments, a same set or different sets of training samples may be used in different iterations in training the preliminary model. For the convenience of descriptions, a training sample used in the current iteration is referred to as a target training sample.

Merely by way of example, in the current iteration, the processing device120may obtain predicted position information of the sample gamma ray interaction of the target training sample based on an intermediate preliminary model. If the current iteration is the first iteration, the intermediate preliminary model may be the preliminary model. If the current iteration is an iteration other than the first iteration, the intermediate preliminary model may be an updated preliminary model generated in a previous iteration. For example, for the target training sample, the processing device120may generate a sample model input (e.g., a sample signal intensity distribution corresponding to the target training sample) and input the sample model input into the updated preliminary model. The updated preliminary model may output the predicted position information of the target training sample.

The processing device140B may further determine a value of a loss function based on the predicted position information of the target training sample. The loss function may be used to measure a discrepancy between a position information predicted by the preliminary model (or the updated preliminary model) in an iteration and the reference position information. Exemplary loss functions may include a focal loss function, a log loss function, a cross-entropy loss, a Dice ratio, or the like.

The processing device140B may then determine an assessment result of the intermediate preliminary model based on the value of the loss function. The assessment result may indicate whether the intermediate preliminary model is sufficiently trained. For example, the processing device120may determine whether a termination condition is satisfied in the current iteration based on the value of the loss function. Exemplary termination conditions may be that the value of the loss function in the current iteration is less than a threshold value, a difference between the values of the loss function obtained in a previous iteration and the current iteration (or among the values of the loss function within a certain number or count of successive iterations) is less than a certain threshold, a maximum number (or count) of iterations has been performed, or the like, or any combination thereof.

In response to determining that the termination condition is not satisfied in the current iteration, the processing device120may determine that the intermediate preliminary model is not sufficiently trained, and further update the intermediate preliminary model based on the value of the loss function. Merely by way of example, the processing device120may update at least some of the parameter values of the intermediate preliminary model according to, for example, a backpropagation algorithm. The processing device120may further perform a next iteration until the termination condition is satisfied. In response to determining that the termination condition is satisfied in the current iteration, the processing device120may determine that the intermediate preliminary model is sufficiently trained and terminate the training process. The intermediate preliminary model may be designated as the position information determination model.