Patent Publication Number: US-2022221595-A1

Title: Method and apparatus for positron emission tomography

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/079,542, filed Oct. 26, 2020, which is a continuation of U.S. patent application Ser. No. 16/422,499, filed May 24, 2019, which is a continuation of U.S. patent application Ser. No. 15/809,994, filed Nov. 10, 2017, which claims priority of PCT Application No. PCT/CN2017/098359, filed Aug. 21, 2017, the contents of each of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure generally relates to positron emission tomography (PET), and more specifically, relates to a method and apparatus for PET. 
     BACKGROUND 
     PET is a functional imaging technique in nuclear medicine that produces a three-dimensional image of functional processes in a living object. Typically, a short-lived radioactive isotope tracer, such as fluorodeoxyglucose (FDG), may be injected into the object. The tracer may undergo a positron emission decay (also known as the beta decay) and emit a positron. The positron may annihilate with an electron, generating a pair of annihilation photons (or gamma photons) that move in approximately opposite directions. 
     A PET system may include a PET detecting module to detect gamma rays. A PET detecting module may include a scintillator array and a plurality of optical channels (e.g., light guides). Each of the plurality of optical channels may guide a light signal to a photosensor. The optical channels may have various configurations. Each of plurality of optical channels may couple to a scintillator. An optical channel may couple to a row (or a column) of scintillators. Generally, with less optical channels, the cost and complexity of the PET system may be lower, but the detection performance of the PET system may be worse. It is desirable to seek a balance between maintaining a good performance and reducing the cost and complexity of the PET system. 
     SUMMARY 
     According to a first aspect of the present disclosure, a PET detecting module for detecting a radiation ray is provided. The PET detecting module may include a scintillator array, a first group of light guides and a second group of light guides. The scintillator array may be configured to receive a radiation ray and generate optical signals in response to the received radiation ray. The scintillator array may have a plurality of rows of scintillators arranged in a first direction and a plurality of columns of scintillators arranged in a second direction. The second direction may be approximately orthogonal to the first direction. The first group of light guides may be arranged on a top surface of the scintillator array along the first direction. The light guide count of the first group of light guides may be less than the row count of the plurality of rows of scintillators. The second group of light guides may be arranged on a bottom surface of the scintillator array along the second direction. The light guide count of the second group of light guides may be less than the column count of the plurality of columns of scintillators. 
     In some embodiments, at least one of the first group of light guides may be coupled to two adjacent rows of the plurality of rows of scintillators in the first direction. At least one of the second group of light guides may be coupled to two adjacent columns of the plurality of columns of scintillators in the second direction. 
     In some embodiments, the first group of light guides may extend in the first direction and distribute along the second direction. The second group of light guides may extend in the second direction and distribute along the first direction. 
     In some embodiments, a width of at least one of the first group of light guides may be less than a width of two adjacent rows of scintillators of the plurality of rows of scintillators. A width of at least one of the second group of light guides may be less than a width of two adjacent columns of scintillators of the plurality of rows of scintillators. 
     In some embodiments, the light guide count of the first group of light guides may be no less than a half of the row count of the plurality of rows of scintillators in the first direction. The light guide count of the second group of light guides may be no less than a half of the column count of the plurality of columns of scintillators in the second direction. 
     In some embodiments, the row count of the plurality of rows of scintillators in the first direction may equal the column count of the plurality of columns of scintillators in the second direction. 
     In some embodiments, the row count of the plurality of rows of scintillators in the first direction may be not equal to the column count of the plurality of columns of scintillators in the second direction. 
     In some embodiments, the first group of light guides may be physically connected to at least a portion of the top surface of the scintillator array. The second group of light guides may be physically connected to at least a portion of the bottom surface of the scintillator array. 
     In some embodiments, the first group of light guides may be coupled to a portion of the plurality of rows of scintillators in the first direction. The second group of light guides may be coupled to a portion of the plurality of columns of scintillators in the second direction. 
     In some embodiments, each of the first group of light guides may be coupled to at least one of the portion of the plurality of rows of scintillators in the first direction. Each of the second group of light guides may be coupled to at least one of the portion of the plurality of columns of scintillators in the second direction. 
     According to a second aspect of the present disclosure, a PET system is provided. The PET system may include a detector and at least one processor. The detector may be configured to receive radiation rays. The detector may include a detecting module. The detecting module may include a scintillator array, a first group of light guides and a second group of light guides. The scintillator array may be configured to receive a radiation ray and generate optical signals in response to the received radiation ray. The scintillator array may have a plurality of rows of scintillators arranged in a first direction and a plurality of columns of scintillators arranged in a second direction. The second direction may be approximately orthogonal to the first direction. The first group of light guides may be arranged on a top surface of the scintillator array. The second group of light guides may be arranged on a bottom surface of the scintillator array. The at least one processor may be configured to cause the system to: determine an intensity of an output from the first group of light guides according to the optical signals; determine an intensity of an output from the second group of light guides according to the optical signals; and identify, within the scintillator array, a scintillator that has interaction with the received radiation ray based on an intensity of the output from the first group of light guides and an intensity of the output from the second group of light guides. 
     In some embodiments, the first group of light guides may be arranged on a top surface of the scintillator array along the first direction. The second group of light guides may be arranged on a bottom surface of the scintillator array along the second direction. The light guide count of the first group of light guides may be less than the row count of the plurality of rows of scintillators, the light guide count of the second group of light guides may be less than the column count of the plurality of columns of scintillators. 
     In some embodiments, at least one of the first group of light guides may be coupled to two adjacent rows of the plurality of rows of scintillators in the first direction. At least one of the second group of light guides may be coupled to two adjacent columns of the plurality of columns of scintillators in the second direction. 
     In some embodiments, the system may further comprises one or more photosensors configured to convert the output from the first group of light guides and the output from the second group of light guides into electrical signals. The at least one processor may be configured to cause the PET system to: determine the intensity of the output from the first group of light guides and the intensity of the output from the second group of light guides according to the converted electrical signals. 
     In some embodiments, the one or more photosensors may include at least one silicon photomultiplier (SiPM). 
     In some embodiments, the at least one processor may be configured to cause the PET system to: determine a row number of the scintillator based on the intensity of the output from the first group of light guides; determine a column number of the scintillator based on the intensity of the output from the second group of light guides; and identify the scintillator based on the determined row number and the column number. 
     In some embodiments, the at least one processor may be configured to cause the PET system to determine a depth of the interaction with the received radiation ray in the identified scintillator based on the intensity of the output from the first group of light guides and the intensity of the output from the second group of light guides. 
     In some embodiments, the at least one processor may be configured to cause the PET system to reconstruct an image based, at least in part, on the row number of the identified scintillator, the column number of the identified scintillator, and the depth of the interaction with the received radiation ray in the identified scintillator. 
     In some embodiments, the at least one processor may be configured to cause the PET system to: detect an output component from each of the first group of light guides; determine an intensity component for each of the output components from the first group of light guides; and determine the intensity of the output from the first group of light guides according to the determined intensity components of the output components from the first group of light guides. 
     In some embodiments, the at least one processor may be configured to cause the PET system to: detect an output component from each of the second group of light guides; determine an intensity component for each of the output components from the second group of light guides; and determine the intensity of the output from the second group of light guides according to the determined intensity components of the output components from the second group of light guides. 
     According to a third aspect of the present disclosure, a method is provided. The method may be implemented on a computing device. The computing device may include at least one processor. The method may include one or more of the following operations. An intensity of an output from a first group of light guides of a scintillator array may be determined by the at least one processor according to optical signals generated by the scintillator in response to a received radiation ray. The first group of light guides may be arranged on a top surface of the scintillator array along a first direction. The scintillator array may have a plurality of rows of scintillators arranged in the first direction, a plurality of columns of scintillators arranged in a second direction. The second direction may be approximately orthogonal to the first direction. An intensity of an output from a second group of light guides of the scintillator array may be determined by the at least one processor according to the optical signals. The second group of light guides may be arranged on a bottom surface of the scintillator array along the second direction. A scintillator, within the scintillator array, that has interaction with the received radiation ray may be identified by the at least one processor based on the intensity of the output from the first group of light guides and the intensity of the output from the second group of light guides. The light guide count of the first group of light guides may be less than the row count of the plurality of rows of scintillators, the light guide count of the second group of light guides may be less than the column count of the plurality of columns of scintillators. 
     In some embodiment, at least one of the first group of light guides may be coupled to two adjacent rows of the plurality of rows of scintillators in the first direction. At least one of the second group of light guides may be coupled to two adjacent columns of the plurality of columns of scintillators in the second direction. 
     In some embodiments, electrical signals from one or more photosensors may be received. The electrical signals may be generated by the one or more photosensors by converting the output from the first group of light guides into the electrical signals. The intensity of the output from the first group of light guides may be determined according to the electrical signals. 
     In some embodiments, a row number of the scintillator may be determined based on the intensity of the output from the first group of light guides. A column number of the scintillator may be determined based on the intensity of the output from the second group of light guides. The scintillator may be identified based on the determined row number and the column number. 
     In some embodiments, a depth of the interaction with the received radiation ray in the identified scintillator may be determined. 
     Additional features will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the accompanying drawings or may be learned by production or operation of the examples. The features of the present disclosure may be realized and attained by practice or use of various aspects of the methodologies, instrumentalities and combinations set forth in the detailed examples discussed below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is further described in terms of exemplary embodiments. These exemplary embodiments are described in detail with reference to the drawings. These embodiments are non-limiting exemplary embodiments, in which like reference numerals represent similar structures throughout the several views of the drawings, and wherein: 
         FIG. 1  is a schematic diagram illustrating an exemplary PET system according to some embodiments of the present disclosure; 
         FIG. 2  is a schematic diagram illustrating an exemplary scintillator array according to some embodiments of the present disclosure; 
         FIG. 3A  is a schematic diagram illustrating an exemplary PET detecting module according to some embodiments of the present disclosure; 
         FIG. 3B  is a schematic diagram illustrating a group of exemplary PET detecting modules according to some embodiments of the present disclosure; 
         FIGS. 4A-4D  illustrate various views of an exemplary detecting module according to some embodiments of the present disclosure; 
         FIG. 5  is a block diagram illustrating an exemplary computing device according to some embodiments of the present disclosure; and 
         FIG. 6  is a flowchart illustrating an exemplary process for PET imaging according to some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant disclosure. However, it should be apparent to those skilled in the art that the present disclosure may be practiced without such details. In other instances, well-known methods, procedures, systems, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present disclosure. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present disclosure is not limited to the embodiments shown, but to be accorded the widest scope consistent with the claims. 
     The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise,” “comprises,” and/or “comprising,” “include,” “includes,” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     It will be understood that the term “system,” “engine,” “unit,” “module,” and/or “block” used herein are one method to distinguish different components, elements, parts, section or assembly of different level in ascending order. However, the terms may be displaced by other expression if they achieve the same purpose. 
     Generally, the word “module,” “unit,” or “block,” as used herein, refers to logic embodied in hardware or firmware, or to a collection of software instructions. A module, a unit, or a block described herein may be implemented as software and/or hardware and may be stored in any type of non-transitory computer-readable medium or other storage device. In some embodiments, a software module/unit/block may be compiled and linked into an executable program. It will be appreciated that software modules can be callable from other modules/units/blocks or themselves, and/or may be invoked in response to detected events or interrupts. Software modules/units/blocks configured for execution on a computing device (via, for example, computing device  140  as illustrated in  FIG. 1 ) may be provided on a non-transitory computer-readable medium, such as a compact disc, a digital video disc, a flash drive, a magnetic disc, or any other tangible medium, or as a digital download (and can be originally stored in a compressed or installable format that needs installation, decompression, or decryption prior to execution). Such software code may be stored, partially or fully, on a storage device of the executing computing device, for execution by the computing device. Software instructions may be embedded in firmware, such as an EPROM. It will be further appreciated that hardware modules/units/blocks may be included in connected logic components, such as gates and flip-flops, and/or can be included of programmable units, such as programmable gate arrays or processors. The modules/units/blocks or computing device functionality described herein may be implemented as software modules/units/blocks but may be represented in hardware or firmware. In general, the modules/units/blocks described herein refer to logical modules/units/blocks that may be combined with other modules/units/blocks or divided into sub-modules/sub-units/sub-blocks despite their physical organization or storage. The description may apply to a system, an engine, or a portion thereof. 
     It will be understood that when a unit, engine, module or block is referred to as being “on,” “connected to,” or “coupled to,” another unit, engine, module, or block, it may be directly on, connected or coupled to, or communicate with the other unit, engine, module, or block, or an intervening unit, engine, module, or block may be present, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     These and other features, and characteristics of the present disclosure, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, may become more apparent upon consideration of the following description with reference to the accompanying drawings, all of which form a part of this disclosure. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended to limit the scope of the present disclosure. It is understood that the drawings are not to scale. 
       FIG. 1  is a schematic diagram illustrating an exemplary imaging system  100  according to some embodiments of the present disclosure. In some embodiments, the imaging system  100  may be a single-modal system, such as positron emission tomography (PET) imaging system. Alternatively, the imaging system  100  may be a multi-modal system, such as a positron emission tomography PET-CT imaging system, a PET-MRI imaging system, etc. 
     In some embodiments, the imaging system  100  may include a scanner  110 , a network  120 , one or more terminals  130 , a computing device  140 , and a storage  150 . In some embodiments, the components of the imaging system  100  may be connected to each other via the network  120 . Alternatively or additionally, the components of the imaging system  100  may be directly connected to each other. 
     The scanner  110  may scan an object and generate scanning data corresponding to the object. The object may include but is not limited to one or more organs, one or more types of tissues, or the like, of a patient. In some embodiments, the scanner  110  may be a medical scanning device, for example, a PET device, a PET-CT device, a PET-MRI device, etc. The scanner  110  may include a gantry  111 , a detector  112 , a scanning area  113 , and a table  114 . An object may be placed on the table  114 . The table  114  may deliver the object to a target location in the scanning area  113 . The detector  112  may detect radiation rays (e.g., gamma photons) emitted from the object in the scanning area  113 . In some embodiments, the detector  112  may include a plurality of detection modules. The detection modules may be arranged in a suitable configuration, including but not limited to a ring (e.g., a detector ring), a rectangle, a triangle, or an array. Each of the plurality of detection modules may include a scintillator array, a first group of light guides, and a second group of light guides. 
     In application, a tracer (e.g., a radioactive isotope) may be injected into an object (via, for example, blood vessels of a patient). The atoms of the tracer may be converted into biologically active molecules. The molecules may gather in tissue of the patient. When a sufficient amount of the molecules are estimated to be gathered in the tissue (usually in an hour), the patient may be positioned on the table  114 . The radioactive isotope may undergo a positron emission decay (i.e., the beta decay) and emits positrons. The positrons may interact with electrons inside the tissue (the interaction between positrons and electrons is called annihilation). The annihilations of the electrons and positrons may each produce a pair of annihilation photons (also referred to as gamma photons) that move in approximately opposite directions. 
     The gamma photons may be detected by the detector  112 , and an image may be generated by the computing device  140  based on the information associated with the gamma photons. For example, the computing device  140  may determine the time-of-flight (time information) associated with each of the pairs of gamma photons. The computing device  140  may also determine the location where the annihilation happens based on the time-of-flight. After obtaining a plurality of locations of annihilations, the computing device  140  may generate a projection image (also referred to as a sonogram) based on the locations of the annihilations. The computing device  140  may reconstruct images based on the projection image and reconstruction techniques such as filtered back projection (FBP). The reconstructed images may indicate the tissue that contains a large number of biologically active molecules of the tracer. In some embodiments, the number of molecules of the tracer in a region may be related to biological functions of the tissues in the region. For example, if fluorodeoxyglucose (FDG) is used as the tracer in a PET scan, the number of tracer molecules in a region may be proportional to the rate of metabolism of glucose in the region. As tumors generally consume a huge amount of glucose, the region with a large number of molecules may be identified in a reconstructed image as tumor tissue. 
     The network  120  may include any suitable network that can facilitate the exchange of information and/or data between the components of the imaging system  100 . In some embodiments, one or more components of the imaging system  100  (e.g., the scanner  110 , the terminal  130 , the computing device  140 , the storage  150 , etc.) may communicate information and/or data with one or more other components of the imaging system  100  via the network  120 . For example, the computing device  140  may obtain image data (e.g., time information, energy information) from the scanner  110  via the network  120 . As another example, the computing device  140  may obtain user instructions from the terminal  130  via the network  120 . The network  120  may include a public network (e.g., the Internet), a private network (e.g., a local area network (LAN), a wide area network (WAN)), etc.), a wired network (e.g., an Ethernet network), a wireless network (e.g., an 802.11 network, a Wi-Fi network, etc.), a cellular network (e.g., a Long Term Evolution (LTE) network), a frame relay network, a virtual private network (“VPN”), a satellite network, a telephone network, routers, hubs, switches, server computers, and/or any combination thereof. Merely by way of example, the network  120  may include a cable network, a wireline network, a fiber-optic network, a telecommunications network, an intranet, a wireless local area network (WLAN), a metropolitan area network (MAN), a public telephone switched network (PSTN), a Bluetooth™ network, a ZigBee™ network, a near field communication (NFC) network, or the like, or any combination thereof. 
     The terminal  130  may include a mobile device  130 - 1 , a tablet computer  130 - 2 , a laptop computer  130 - 3 , or the like, or any combination thereof. In some embodiments, the mobile device  130 - 1  may include a smart home device, a wearable device, a mobile device, a virtual reality device, an augmented reality device, or the like, or any combination thereof. In some embodiments, the terminal  130  may be part of the computing device  140 . 
     The computing device  140  may process data and/or information obtained from the scanner  110 , the terminal(s)  130 , and/or the storage  150 . For example, the computing device  140  may process image data (including time information, energy information, etc.) and reconstruct an image based on the image data. In some embodiments, the computing device  140  may be a single server or a server group. The server group may be centralized or distributed. In some embodiments, the computing device  140  may be local or remote. For example, the computing device  140  may access information and/or data stored in the scanner  110 , the terminal(s)  130 , and/or the storage  150  via the network  120 . As another example, the computing device  140  may be directly connected to the scanner  110 , the terminal(s)  130  and/or the storage  150  to access stored information and/or data. In some embodiments, the computing device  140  may be implemented on a cloud platform. Merely by way of example, the cloud platform may include a private cloud, a public cloud, a hybrid cloud, a community cloud, a distributed cloud, an inter-cloud, a multi-cloud, or the like, or any combination thereof. In some embodiments, the computing device  140 , or a portion of the computing device  140  may be integrated into the scanner  110 . 
     The computing device  140  may include a processor, a storage module, an input/output (I/O) and a communication port. The processor may execute computer instructions (e.g., program code) and perform functions of the computing device  140  described herein. The computer instructions may include, for example, routines, programs, objects, components, data structures, procedures, modules, and functions, which perform particular functions described herein. The storage module may store data/information obtained from the scanner  110 , the terminal  130 , the storage  150 , and/or any other component of the imaging system  100 . In some embodiments, the storage module may include a mass storage, a removable storage, a volatile read-and-write memory, a read-only memory (ROM), or the like, or any combination thereof. The I/O may input and/or output signals, data, information, etc. In some embodiments, the I/O may enable a user interaction with the computing device  140 . In some embodiments, the I/O may include an input device and an output device. Examples of the input device may include a keyboard, a mouse, a touch screen, a microphone, or the like, or any combination thereof. Examples of the output device may include a display device, a loudspeaker, a printer, a projector, or the like, or any combination thereof. The communication port may be connected to a network (e.g., the network  120 ) to facilitate data communications. The communication port may establish connections between the computing device  140  and the scanner  110 , the terminal  130 , and/or the storage  150 . The connection may be a wired connection, a wireless connection, any other communication connection that can enable data transmission and/or reception, and/or any combination of these connections. 
     The storage  150  may store data, instructions, and/or any other information. In some embodiments, the storage  150  may store data obtained from the terminal(s)  130  and/or the computing device  140 . In some embodiments, the storage  150  may store data and/or instructions that the computing device  140  may execute or use to perform exemplary methods described in the present disclosure. In some embodiments, the storage  150  may store image data (e.g., time information, energy information) obtained from the scanner  110 . In some embodiments, the storage  150  may 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  150  may be connected to the network  120  to communicate with one or more other components of the imaging system  100  (e.g., the computing device  140 , the terminal(s)  130 , etc.). Alternatively or additionally, the storage  150  may be part of the computing device  140 . 
     It should be noted that the above description of the imaging system  100  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. For example, the assembly and/or function of the imaging system  100  may be varied or changed according to specific implementation scenarios. Merely by way of example, some other components may be added into the imaging system  100 , such as a patient positioning unit, data acquisition electronics, power supplies, and other devices or units. However, those variations and modifications do not depart from the scope of the present disclosure. 
       FIG. 2  is a schematic diagram illustrating an exemplary scintillator array according to some embodiments of the present disclosure. As shown in  FIG. 2 , a scintillator array  200  may include a plurality of scintillators  210 . The scintillators  210  may scintillate when a radiation ray (e.g., a gamma ray) photon collides the scintillator. The scintillators  210  may absorb the energy of the radiation ray photon and convert the absorbed energy into light signals. 
     In some embodiments, the scintillator array  200  may include a plurality of rows of scintillators (e.g., scintillators  210 ) arranged in a first direction (e.g., the direction of the X-axis) and a plurality of columns of scintillators arranged in a second direction (e.g., the direction of the Y-axis). The second direction may be approximately orthogonal to the first direction. In some embodiments, the row count of the rows of scintillators arranged in the X-axis direction (denoted as M) may equal the column count of the columns of scintillators arranged in the Y-axis direction (denoted as N). For example, both M and N may be in the range of 1 to 10. Merely by way of example, both M and N may be 6. In some embodiments, M may be different from N. For example, the scintillator array  410  may have a configuration of 3*4, 4*6, 6*5, 3*3, 5*5 scintillators, or the like. In some embodiments, the scintillator array  410  may include only one scintillator. 
     In some embodiments, the scintillators  210  in the scintillator array  200  may be of the same size. Alternatively, at least two scintillators in the scintillator array  200  may be of different sizes. In some embodiments, a scintillator  210  may have a shape of a cuboid, a cube, a cylinder, or other suitable configuration. 
     In some embodiments, a scintillator  210  may be coated with (or have a coating of) an optical glue, a reflective material, or the like, on at least part of a side of the scintillator. The surface areas of scintillators may be coated with different coating materials. 
     In some embodiments, the scintillator array  200  may include two flat surfaces (e.g., a top surface of the scintillator array or a bottom surface of the scintillator array). The first group of light guides may be arranged on the top surface. The second group of light guides may be arranged on the bottom surface. In some embodiments, a scintillator  210  may include at least one material including, for example, bismuth germanium oxide (BGO), lutetium-yttrium oxyorthosilicate (LYSO), lutetium oxyorthosilicate (LSO), or the like. 
       FIG. 3A  is a schematic diagram illustrating an exemplary detecting module  300  according to some embodiments of the present disclosure. The detecting module  300  may include a 4×4 scintillator array  310  (which may be an embodiment of the scintillator array  200  illustrated in  FIG. 2 ), the first group of light guides (e.g., light guide G Y1  and G Y2 ), and the second group of light guides (e.g., light guide G X1  and G X2 ). The first group of light guides may be arranged on the top surface of the 4×4 scintillator array  310  along the first direction (e.g., the direction of the X-axis). The second group of light guides may be arranged on the bottom surface of the 4×4 scintillator array  310  along the second direction (e.g., the direction of the Y-axis). In some embodiments, the light guide count of the first group of light guides may be less than the row count of the plurality of rows of scintillators. The light guide count of the second group of light guides may be less than the column count of the plurality of columns of scintillators. 
     In some embodiments, the first group of light guides may be physically (and/or directly) connected to at least a portion of the top surface of the scintillator array. For example, the first group of light guides may be coupled (i.e., optically coupled) to at least a portion of the top surface of the scintillator array. The second group of light guides may be physically (and/or directly) connected to at least a portion of the bottom surface of the scintillator array. In some embodiments, the first group of light guides may be coupled to a portion of the plurality of rows of scintillators in the first direction. The second group of light guides may be coupled to a portion of the plurality of columns of scintillators in the second direction. In some embodiments, each of the first group of light guides may be coupled to at least one of the portion of the plurality of rows of scintillators in the first direction. Each of the second group of light guides is coupled to at least one of the portion of the plurality of columns of scintillators in the second direction. More descriptions of the 4×4 scintillator array  310  may be found in  FIG. 4  and the description thereof. 
       FIG. 3B  is a schematic diagram illustrating a group of exemplary PET detecting modules  350  according to some embodiments of the present disclosure. The group of detecting modules  350  may include one or more detecting modules  300  (illustrated in  FIG. 3A ). For example, the group of detecting modules  350  may include 9 (arranged as 3×3) detecting modules  300 . Further, one or more groups of detecting modules  350  may constitute the detector  112 . As illustrated in  FIG. 3B , the group of detecting modules  350  may include a scintillator array (including 12×12 scintillators), with a 6×3 light guide array arranged on its top surface and a 3×6 light guide array arranged on its bottom surface. In some embodiments, the light guides in the same row (e.g., a light guide G 1 , a light guide G 2 , and a light guide G 3 ) may be integrated into one light guide. 
     It should be noted that the row counts or column counts mentioned in  FIGS. 3A and 3B , and the arrangement of the light guides are merely provided for the purpose of illustration, and not intended to limit the scope of the present disclosure. For example, the detecting module  300  may include 5×5 scintillators, 6×6 scintillators, 3×4 scintillators, etc. As another example, the group of detecting modules  350  may include 4×4 detecting modules  300 , 5×5 detecting modules  300 , 6×8 detecting modules  300 , or the like. 
       FIGS. 4A-4D  illustrate various views of an exemplary detecting module according to some embodiments of the present disclosure. In some embodiments, a detecting module  300  may be configured to receive a radiation ray and generate optical signals in response to the received radiation ray. The optical signals may be light rays emitted when a radiation ray interacts with a scintillator. As shown in  FIGS. 4A-4D , the detecting module  300  may include a scintillator array. The scintillator array may include a plurality of rows of scintillators arranged in a first direction (extending in the X-axis direction). The scintillator array may include a plurality of columns of scintillators arranged in a second direction (extending in the Y-axis direction). The second direction may be approximately orthogonal to the first direction. In some embodiments, the scintillator array may include a top surface and a bottom surface. The top surface and the bottom surface may be generally flat. The top surface or the bottom surface may face a detecting region of the PET system. In some embodiments, the first group of light guides may be arranged on a surface (e.g., the top surface) of the scintillator array. The light guides may be used to guide optical signals from the scintillators to a photosensor. In some embodiments, one of the first group of light guides may be coupled to two adjacent rows of the N rows of scintillators. The second group of light guides may be arranged on the opposite surface (e.g., the bottom surface) of the scintillator array. One of the second group of light guides may be coupled to two adjacent columns of the M columns of scintillators. In some embodiments, the first group of light guides may extend (i.e., prolongate) along the first direction and distribute in the second direction. The second group of light guides may extend along the second direction and distribute in the first direction. For example, as shown in  FIG. 4B , two light guides, G Y1  and G Y2 , may extend along the X-direction and distribute in the Y-direction. 
     In some embodiments, a width of one of the first group of light guides may be less than the total width of two adjacent rows of scintillators (i.e., the sum of the widths of two adjacent rows of scintillators). A width of one of the second group of light guides may be less than the total width of two adjacent columns of scintillators (i.e., the sum of the widths of two adjacent columns of scintillators). In some embodiments, the light guide count of the first group of light guides may be no less than a half of the row count of the plurality of rows of scintillators in the first direction. The light guide count of the second group of light guides may be no less than a half of the column count of the plurality of columns of scintillators in the second direction. 
       FIG. 4A  illustrates the top view of the detecting module  300 . In some embodiments, the row count of the plurality of rows of scintillators arranged in the X-direction (marked as N) may equal to the column count of the plurality of columns of scintillators arranged in the Y-direction (marked as M). For example, in the illustrated embodiment of  FIG. 4A , N is 4, and M is 4. As another example, both N and M may equal 2, 3, 5, 6, or the like. Alternatively, N may not equal M. For example, a scintillator array with N rows and M columns (marked as N*M) of scintillators may be 3*4, 4*6, 6*5, or the like. 
       FIG. 4B  illustrates the X-Y perspective view of the detecting module  300 . As shown in  FIG. 4B , the detecting module  300  may further include the first group of light guides (e.g., G Y1 , G Y2 ) extending along the X-direction. The light guide (G Y1  or G Y2 ) may be coupled to two adjacent rows of scintillators. For example, the light guide G Y1  may be coupled to the first row of the scintillators (e.g., S 11 , S 12 , S 13 , and S 14 ) and the second row of the scintillators (e.g., S 21 , S 22 , S 23 , and S 24 ). The light guide G Y1  may accumulate light signals from any of the 8 scintillators of the first and second rows of the scintillators. In some embodiments, if N is an even number, the light guide count of the first group of light guides may be a half of N. For example, if N equals 6, the light guide count of the first group of light guides may be 3. Similarly, if M is an even number, the light guide count of the second group of light guides may be a half of M. In some embodiments, if N is an odd number, the light guide count of the first group of light guides may be a half of N+1. For example, if N equals 7, the light guide count of the first group of light guides may be 4. Similarly, if M is an odd number, the light guide count of the second group of light guides may be a half of M+1. 
       FIG. 4C  shows a side view of the detecting module  300  seen in the Y-Z plane. Light guides G Y1  and G Y2  may be arranged on the top surface of the scintillator array. The light guide G X2  may be arranged on the bottom surface as well and coupled to the third column of the scintillators (including S 13 , S 23 , S 33  and S 43 ) and the fourth column of the scintillators (including S 14 , S 24 , S 34  and S 44 ). Although invisible in  FIG. 4C , the light guide G X1  may be arranged on the bottom surface. In this example, the light guides G Y1  and G Y2  may be orthogonal to the light guides G Y1  and G X2 .  FIG. 4D  shows a side view of the detecting module  300  seen in the X-Z plane. The light guides G Y1  and G Y2  may be on the top surface (although only G Y1  is visible in  FIG. 4D ). The light guides G X1  and G X2 , which may be orthogonal to G Y1  and G Y2 , may be arranged on the bottom surface. 
     In some embodiments, the computing device  140  may read the light guides, convert an output of the light guides into an electrical signal. The computing device  140  may identify which scintillator within the scintillator array may have a radiation ray (gamma ray) interaction, based on the electrical signals. The computing device  140  may further determine a depth of interaction of the received radiation ray in the identified scintillator. More details of the scintillator identification and the depth determination may be found in  FIG. 6  and the relevant description. 
       FIG. 5  is a block diagram illustrating an exemplary computing device according to some embodiments of the present disclosure. As shown in  FIG. 5 , the computing device  140  may include a detection module  510 , a determination module  520 , a reconstruction module  530 , and a storage module  540 . The detection module  510 , determination module  520 , reconstruction module  530 , and storage module  540  may refer to logic embodied in hardware or firmware, or to a collection of software instructions. The modules described herein may be implemented as software and/or hardware modules and may be stored in any type of non-transitory computer-readable medium or other storage device. In some embodiments, a software module may be compiled and linked into an executable program. It will be appreciated that software modules can be callable from other modules or from themselves, and/or can be invoked in response to detected events or interrupts. Software modules configured for execution on computing devices (e.g., a processor of computing device  140 ) can be provided on a computer readable medium, such as a compact disc, a digital video disc, a flash drive, a magnetic disc, or any other tangible medium, or as a digital download (and can be originally stored in a compressed or installable format that requires installation, decompression, or decryption prior to execution). Such software code can be stored, partially or fully, on a memory device of the executing computing device, for execution by the computing device. Software instructions can be embedded in a firmware, such as an EPROM. It will be further appreciated that hardware modules can be included of connected logic units, such as gates and flip-flops, and/or can be included of programmable units, such as programmable gate arrays or processors. The modules or computing device functionality described herein are preferably implemented as software modules, but can be represented in hardware or firmware. In general, the modules described herein refer to logical modules that can be combined with other modules or divided into sub-modules despite their physical organization or storage. 
     The detection module  510  may be configured to detect an output from light guides. For example, the detection module  510  may be configured to detect an output from the first group of light guides and an output from the second group of light guides. In some embodiments, the output from the first group of light guides or an output from the second group of light guides may be an optical signal including optical signals collected from the scintillators to which a light guide is coupled. 
     The determination module  520  may be configured to identify, within the scintillator array, a scintillator that has a radiation ray interaction with a received radiation ray. In some embodiments, the determination module  520  may determine a depth of interaction of the received radiation ray in the identified scintillator. The detection module  520  may determine the intensity of the output from the first group of light guides. The detection module  520  may also determine the intensity of the output from the second group of light guides. 
     The reconstruction module  530  may be configured to reconstruct a PET image based on the identified scintillators and depths of interaction of the received radiation ray in the identified scintillator. 
     The storage module  540  may be configured to store PET data, control parameters, processed PET data, or the like, or any combination thereof. In some embodiments, the storage module  540  may store one or more scanning protocols and/or encoded PET data. In some embodiments, the storage module  540  may store one or more programs and/or instructions that may be executed by the computing device  140  to perform exemplary methods described in this disclosure. 
     In some embodiments, one or more modules illustrated in  FIG. 5  may be implemented in at least a part of the exemplary PET system as illustrated in  FIG. 1 . For example, the acquisition module  510 , the control module  520 , the storage module  530 , and/or the processing module  540  may be integrated into a console (not shown). Via the console, a user may set parameters for scanning an object, controlling imaging processes, controlling parameters for reconstruction of an image, viewing reconstructed images, etc. In some embodiments, the console may be implemented via the computing device  140  and/or the terminal  160 . 
       FIG. 6  is a flowchart illustrating an exemplary process for PET imaging according to some embodiments of the present disclosure. In some embodiments, process  600  may be a process for reconstructing a PET image. The process  600  may be implemented by the computing device  140  and executed by a processor of the computing device  140 . 
     In  610 , a detector, including a plurality of detecting modules, may receive a plurality of radiation rays (gamma rays) that emitted from a subject. The plurality of detecting modules may be used to detect the radiation rays. Each of the plurality of detecting modules may include a scintillator array. Each of the plurality of detecting modules may include the first group of light guides and the second group of light guides. The scintillator array may have N rows of scintillators arranged in a first direction and M columns of scintillators arranged in a second direction. The second direction may be approximately orthogonal to the first direction. The detecting module may include the first group of light guides arranged on a top surface of the scintillator array and the second group of light guides arranged on a bottom surface of the scintillator array. In some embodiments, one light guide may be coupled to two adjacent rows of the plurality of rows of scintillators in the first direction. One light guide may be coupled to two adjacent columns of the plurality of columns of scintillators in the second direction. In some embodiments, N may equal M. For example, N=M=4. 
     In some embodiments, the width of one of the first group of light guides may be less than the total width of two adjacent rows of scintillators (i.e., the sum of the widths of two adjacent rows of scintillators), and the width of one of the second group of light guides may be less than the total width of two adjacent columns of scintillators (i.e., the sum of the widths of two adjacent columns of scintillators). In some embodiments, the width of each of the light guides may be a constant value. For example, the constant value may be the width of a scintillator. In some embodiments, the light guide count of the first group of light guides is no less than a half of N, and the light guide count of the second group of light guides is no less than a half of M. For example, when N=M=4, the light guide count of the first group of light guides may be 2, and the light guide count of the second group of light guides may be 2 as well. 
     In  620 , for a scintillator array, the detection module  510  may detect an output from the first group of light guides and an output from the second group of light guides. In some embodiments, a light guide may be coupled to two adjacent rows (or two adjacent columns) of scintillators. For example, two adjacent rows (or two adjacent columns) of scintillators may include 8 scintillators (as described in  FIGS. 4A-4D ). The output from the light guide may be an optical signal including optical signals from the scintillators to which the light guide is coupled. In some embodiments, the optical signals may be generated by the scintillator array  300  in response to a received radiation ray. 
     In some embodiments, one or more photosensors, arranged in the detecting module  510 , may be configured to convert the output from the first group of light guides and the second group of light guides into an electrical signal. The determination module  520  may determine the intensity of the output from the first group of light guides and the intensity of the output from the second group of light guides according to the electrical signal generated by the one or more photosensors. 
     In  630 , the determination module  520  may identify, within the scintillator array, a scintillator that has a radiation ray interaction with a received radiation ray based on the intensity of the output from the first group of light guides and the intensity of the output from the second group of light guides. For illustration and referring to  FIGS. 4A-4D , X1 may represent the intensity of the output from the light guide G X1 . X2 may represent the intensity of the output from the light guide G X2 . Y1 may represent the intensity of the output from the light guide G Y1 . Y2 may represent the intensity of the output from the light guide G Y2 . The location of the radiation ray interaction in the scintillator array may be determined according to equations (1) and (2): 
     
       
         
           
             
               
                 
                   
                     X 
                     = 
                     
                       X 
                       ⁢ 
                       
                         1 
                         / 
                         
                           ( 
                           
                             
                               X 
                               ⁢ 
                               1 
                             
                             + 
                             
                               X 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                           ) 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     Y 
                     = 
                     
                       Y 
                       ⁢ 
                       
                         1 
                         / 
                         
                           ( 
                           
                             
                               Y 
                               ⁢ 
                               1 
                             
                             + 
                             
                               Y 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                           ) 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where X1 represents the intensity of the output from the light guide G X1 , X2 represents the intensity of the output from the light guide G X2 , X represents a normalized location in the first direction of the radiation ray interaction, Y1 represents the intensity of the output from the light guide G Y1 , Y2 represents the intensity of the output from the light guide G Y2 , Y represents a normalized location in the second direction of the radiation ray interaction. The value of X may be used to determine which column of scintillators has radiation ray interaction. The value of Y may be used to determine which row of scintillators has radiation ray interaction. Take Y=Y1/(Y1+Y2) as an example. Three thresholds T1, T2, T3 may be designated for determining the scintillator(s) that has radiation ray interaction. If 0≤Y≤T1, the location of the radiation ray interaction may be determined in the fourth row of the scintillators (including S 41 , S 42 , S 43 , and S 44 ). If T1&lt;Y≤T2, the location of the radiation ray interaction may be determined in the third row of the scintillators (including S 31 , S 32 , S 33 , and S 34 ). If T2&lt;Y≤T3, the location of the radiation ray interaction may be determined in the second row of the scintillators (including S 21 , S 22 , S 23 , and S 24 ). If T3&lt;Y≤1, the location of the radiation ray interaction may be determined in the first row of the scintillators (including S 11 , S 12 , S 13 , and S 14 ). In some embodiments, the three threshold T1, T2, and T3 may be designated according to different situations (e.g., different width of the light guide). For example, T1 may equal 0.3, T2 may equal 0.5, and T3 may equal 0.7. Similarly, which column of the scintillators has the radiation ray interaction may be determined based on X=X1/(X1+X2) and the three thresholds T1, T2, and T3. In some embodiments, if M and/or N not equal 4, the number of the thresholds may be changed accordingly. For example, if both M and N equal 6, five thresholds may be designated for determining the scintillator(s) that has radiation ray interaction. 
     In  640 , the determination module  520  may determine a depth of interaction of the received radiation ray in the identified scintillator based on the intensity of the output from the first group of light guides and the intensity of the output from the second group of light guides. The depth of the radiation ray interaction in the scintillator array may be determined according to equation (3) 
     
       
         
           
             
               
                 
                   
                     Z 
                     = 
                     
                       
                         ( 
                         
                           
                             X 
                             ⁢ 
                             1 
                           
                           + 
                           
                             X 
                             ⁢ 
                             2 
                           
                         
                         ) 
                       
                       / 
                       
                         ( 
                         
                           
                             X 
                             ⁢ 
                             1 
                           
                           + 
                           
                             X 
                             ⁢ 
                             2 
                           
                           + 
                           
                             Y 
                             ⁢ 
                             1 
                           
                           + 
                           
                             Y 
                             ⁢ 
                             2 
                           
                         
                         ) 
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     where X1 represents the intensity of the output from the light guide G X1 , X2 represents the intensity of the output from the light guide G X2 , Y1 represents the intensity of the output from the light guide G Y1 , Y2 represents the intensity of the output from the light guide G Y2 , Z represents a normalized depth of the radiation ray interaction in the scintillator array. The value of Z may be in a range between 0 to 1. If Z is bigger than 0.5, the location of the interaction of the received radiation ray may be closer to the top surface. If Z is smaller than 0.5, the location of the interaction of the received radiation ray may be closer to the bottom surface. 
     In  650 , the reconstruction module  530  may reconstruct a PET image based on the identified scintillators and depths corresponding to each identified scintillators. In some embodiments, the reconstruction module  530  may reconstruct the image based on reconstruction techniques such as filtered back projection (FBP). A reconstructed image may illustrate the tissue that contains a large number of biologically active molecules of the tracer. 
     It should be noted that the above description of the processing module 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 or 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. For example, the weighted synthesis operation may be unnecessary. 
     Having thus described the basic concepts, it may be rather apparent to those skilled in the art after reading this detailed disclosure that the foregoing detailed disclosure is intended to be presented by way of example only and is not limiting. Various alterations, improvements, and modifications may occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested by this disclosure and are within the spirit and scope of the exemplary embodiments of this disclosure. 
     Moreover, certain terminology has been used to describe embodiments of the present disclosure. For example, the terms “one embodiment,” “an embodiment,” and/or “some embodiments” mean that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Therefore, it is emphasized and should be appreciated that two or more references to “an embodiment” or “one embodiment” or “an alternative embodiment” in various portions of this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the present disclosure. 
     Further, it will be appreciated by one skilled in the art, aspects of the present disclosure may be illustrated and described herein in any of a number of patentable classes or context including any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof. Accordingly, aspects of the present disclosure may be implemented entirely hardware, entirely software (including firmware, resident software, micro-code, etc.) or combining software and hardware implementation that may all generally be referred to herein as a “unit,” “module,” or “system.” Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable media having computer readable program code embodied thereon. 
     A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including electromagnetic, optical, or the like, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that may communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer readable signal medium may be transmitted using any appropriate medium, including wireless, wireline, optical fiber cable, RF, or the like, or any suitable combination of the foregoing. 
     Computer program code for carrying out operations for aspects of the present disclosure may be written in any combination of one or more programming languages, including an object oriented programming language such as JAVA, SCALA, SMALLTALK, EIFFEL, JADE, EMERALD, C++, C#, VB. NET, PYTHON or the like, conventional procedural programming languages, such as the “C” programming language, Visual Basic, Fortran 2013, PERL, COBOL 2012, PHP, ABAP, dynamic programming languages such as PYTHON, RUBY, and GROOVY, or other programming languages. The program code may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider) or in a cloud computing environment or offered as a service such as a Software as a Service (SaaS). 
     Furthermore, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations, therefore, is not intended to limit the claimed processes and methods to any order except as may be specified in the claims. Although the above disclosure discusses through various examples what is currently considered to be a variety of useful embodiments of the disclosure, it is to be understood that such detail is solely for that purpose and that the appended claims are not limited to the disclosed embodiments, but, on the contrary, are intended to cover modifications and equivalent arrangements that are within the spirit and scope of the disclosed embodiments. For example, although the implementation of various components described above may be embodied in a hardware device, it may also be implemented as a software only solution, for example, an installation on an existing server or mobile device. 
     Similarly, it should be appreciated that in the foregoing description of embodiments of the present disclosure, various features are sometimes grouped in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the various inventive embodiments. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed subject matter requires more features than are expressly recited in each claim. Rather, inventive embodiments lie in less than all features of a single foregoing disclosed embodiment. 
     In some embodiments, the numbers expressing quantities or properties used to describe and claim certain embodiments of the application are to be understood as being modified in some instances by the term “about,” “approximately,” or “substantially.” For example, “about,” “approximately,” or “substantially” may indicate ±20% variation of the value it describes, unless otherwise stated. Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. 
     Each of the patents, patent applications, publications of patent applications, and other material, such as articles, books, specifications, publications, documents, things, and/or the like, referenced herein is hereby incorporated herein by this reference in its entirety for all purposes, excepting any prosecution file history associated with same, any of same that is inconsistent with or in conflict with the present document, or any of same that may have a limiting affect as to the broadest scope of the claims now or later associated with the present document. By way of example, should there be any inconsistency or conflict between the description, definition, and/or the use of a term associated with any of the incorporated material and that associated with the present document, the description, definition, and/or the use of the term in the present document shall prevail. 
     In closing, it is to be understood that the embodiments of the application disclosed herein are illustrative of the principles of the embodiments of the application. Other modifications that may be employed may be within the scope of the application. Thus, by way of example, but not of limitation, alternative configurations of the embodiments of the application may be utilized in accordance with the teachings herein. Accordingly, embodiments of the present application are not limited to that precisely as shown and described.