Positron emission tomography system, positron emission tomography method, and gamma-ray detector

Abstract

To provide both good time-of-flight resolution and interaction depth information. [Solution] The positron emission tomography apparatus according to the embodiment comprises a scintillation array and a photosensor array. The scintillation array includes a plurality of scintillator crystal units individually separated by a reflective material, and each scintillator crystal unit is configured to generate scintillation light in response to gamma-ray interactions within the scintillator crystal unit caused by gamma-ray irradiation from a subject, and has a substructure for decoding two or more depths within the scintillator crystal unit such that gamma-ray interactions at different depths cause scintillation light to escape from the photo-escape plane of the scintillator crystal unit in different patterns. The photosensor array converts the scintillation light received from the scintillation array into an electrical signal.

Description

Technical Field

[0001] The embodiments disclosed in this specification and the drawings relate to a positron emission tomography device, a positron emission tomography method, and a gamma-ray detector.

Background Art

[0002] A positron emission tomography (PET) device is a functional imaging modality that can image the biochemical processes of humans or animals using radioactive tracers. In PET imaging, a tracer agent is administered to the patient to be imaged by injection, inhalation, or ingestion. After administration, due to the physical and biomolecular properties of the agent, the agent accumulates in specific locations within the patient's body. The actual spatial distribution of the agent, the intensity of the agent accumulation region, and the dynamics of the process from administration to final excretion are all factors that can have clinical significance.

[0003] During this process, the tracer attached to the agent emits positrons. When the emitted positrons collide with electrons, an annihilation event occurs where the positrons and electrons combine. The annihilation event generates two gamma-ray photons that travel substantially 180 degrees apart (at 511 keV).

[0004] Time-of-flight (TOF) and depth-of-interaction (DOI) are two important measurement criteria for evaluating the performance of a PET scanner. In different applications, it may be preferable to prioritize one over the other.

[0005] In clinical PET scanners, TOF is more emphasized than DOI. The TOF function can improve the system's effective sensitivity and is essential for clinical applications. This improvement can achieve better image quality and a reduction in the radiation dose administered to the patient. In clinical PET scanners, since the bore diameter is relatively large, DOI does not play such an important role.

[0006] Conversely, in preclinical PET scanners, which are characterized by small bore diameters, the importance of DOI information increases. The DOI function plays a crucial role in improving spatial resolution by correcting parallax errors, which are a particular concern in preclinical applications.

[0007] Furthermore, DOI information has been shown to contribute to improving TOF resolution. In addition, DOI becomes even more important in correcting errors caused by the significant tilt of the response line along the axial direction when the axial length of clinical PET scanners is long, such as whole-body scanners.

[0008] To improve the overall performance of clinical PET scanners, there is a need for scanners that possess both good TOF resolution and DOI capabilities. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent Application Publication No. 2012 / 0235047 [Patent Document 2] U.S. Patent Application Publication No. 2016 / 0170040 [Patent Document 3] U.S. Patent Application Publication No. 2022 / 0214464 [Patent Document 4] European Patent Application Publication No. 4163678 [Overview of the project] [Problems that the invention aims to solve]

[0010] One of the problems that the embodiments disclosed herein and in the drawings aim to solve is to provide both good TOF resolution and DOI information. However, the problems that the embodiments disclosed herein and in the drawings aim to solve are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0011] The positron emission tomography (PET) apparatus according to this embodiment comprises a scintillation array, a photosensor array, and a processing circuit. The scintillation array is a scintillation array including a plurality of scintillator crystal units individually separated by a reflective material, wherein each scintillator crystal unit is configured to generate scintillation light in response to gamma-ray interactions within the scintillator crystal unit caused by gamma-ray irradiation from a subject, and has a substructure for decoding two or more depths within the scintillator crystal unit such that gamma-ray interactions at different depths produce scintillation light escaping from the photo-escape plane of the scintillator crystal unit in different patterns. The photosensor array is coupled to the scintillation array and converts the scintillation light received from the scintillation array into an electrical signal. The processing circuit extracts information representing the interaction depth of the gamma-ray interactions within the scintillation array from the electrical signal and reconstructs an image of the subject based on the extracted information. [Brief explanation of the drawing]

[0012] Various embodiments of the present disclosure, proposed as examples, will be described in detail with reference to the following figures. Here, similar reference numerals indicate similar elements.

[0013] [Figure 1] Figure 1 shows the parallax error caused by oblique line-of-response (LOR) in a pair of pixels of a positron emission tomography (PET) detector that does not have interaction depth (DOI) functionality. [Figure 2] Figure 2 shows a typical single-ended readout configuration in which the pixelation array of the scintillator crystal unit is coupled to the top of the pixelation array of the photosensor. [Figure 3]FIG. 3 is a diagram showing a modified single-ended readout configuration according to an embodiment of the present disclosure, in which each scintillator crystal unit of the pixelated array has a sub-structure for decoding DOI information. [Figure 4] FIG. 4 is a diagram showing an exemplary sub-structure design inside a scintillator crystal unit according to an embodiment of the present disclosure. [Figure 5A] FIG. 5A is a diagram showing an exemplary sub-structure design inside a scintillator crystal unit according to an embodiment of the present disclosure. [Figure 5B] FIG. 5B is a diagram showing an exemplary sub-structure design inside a scintillator crystal unit according to an embodiment of the present disclosure. [Figure 6A] FIG. 6A is a diagram showing an exemplary scintillator crystal unit including four segments according to an embodiment of the present disclosure. [Figure 6B] FIG. 6B is a diagram showing a flood histogram formed by irradiating gamma rays onto the four segments shown in FIG. 6A. [Figure 7A] FIG. 7A is a diagram showing an exemplary scintillator crystal unit including eight segments according to an embodiment of the present disclosure. [Figure 7B] FIG. 7B is a diagram showing a flood histogram formed by irradiating gamma rays onto the eight segments shown in FIG. 7A. [Figure 8] FIG. 8 is a diagram showing an exemplary scenario in which a pixelated optical sensor array is directly coupled to a pixelated array of a scintillator crystal unit according to an embodiment of the present disclosure. [Figure 9] FIG. 9 is a diagram showing an exemplary electronic device design for obtaining information (t, x, y, e) of timing, position, and energy from a pixelated optical sensor array according to an embodiment of the present disclosure. [Figure 10] FIG. 10 is a flowchart showing an exemplary procedure 1000 for extracting DOI information according to an embodiment of the present disclosure. [Figure 11A] FIG. 11A is a diagram showing a perspective view of a PET scanner that can be used with the technology of the present disclosure. [Figure 11B] FIG. 11B is a diagram showing a schematic view of a PET scanner that can be used in the technology of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present disclosure relates to a positron emission tomography (PET) device. The PET device includes a scintillation array, an optical sensor array, and a processing circuit. The scintillation array includes a plurality of scintillator crystal units individually separated by a reflective material. Each of the plurality of scintillator crystal units is configured to generate scintillation light in response to a gamma-ray interaction within the scintillator crystal unit caused by gamma-ray irradiation from an imaging subject. Each scintillator crystal unit includes a substructure for decoding two or more depths within the scintillator crystal unit, whereby gamma-ray interactions at different depths result in scintillation light escaping from the light extraction surface of the scintillator crystal unit in different patterns. The optical sensor array is coupled to the scintillation array and converts the scintillation light received from the scintillation array into an electrical signal. The processing circuit is configured to extract information representing the interaction depth of gamma-ray interactions within the scintillation array from the electrical signal and reconstruct an image of the imaging subject based on the extracted information.

[0015] This disclosure further relates to a method for extracting DOI information in a PET imaging system. The method includes generating scintillation light in response to gamma-ray interactions within a scintillation array caused by gamma-ray irradiation from an imaging subject, via a scintillation array. The scintillation array includes a plurality of scintillator crystal units individually separated by a reflective material. Each scintillator crystal unit has substructures for decoding two or more depths within the scintillator crystal unit, thereby resulting in scintillation light from which gamma-ray interactions at different depths escape from the photo-escape plane of the scintillator crystal unit in different patterns. The method also includes converting the scintillation light received from the scintillation array into an electrical signal via an optical sensor array coupled to the scintillation array. The method further includes extracting information from the electrical signal that represents the interaction depth of the gamma-ray interactions within the scintillation array. The method further includes reconstructing an image of the imaging subject based on the extracted information.

[0016] This disclosure further relates to a gamma-ray detector used in a PET imaging system. The gamma-ray detector includes a scintillation array comprising a plurality of scintillator crystal units individually separated by a reflective material. Each of the plurality of scintillator crystal units is configured to generate scintillation light in response to gamma-ray interactions within the scintillator crystal unit caused by gamma-ray irradiation from an imaging subject. Each scintillator crystal unit includes a substructure for decoding two or more depths within the scintillator crystal unit, so that gamma-ray interactions at different depths result in scintillation light escaping from the photo-escape plane of the scintillator crystal unit in different patterns.

[0017] The above summary does not prescribe all embodiments and / or additional novel aspects of the invention described in this disclosure or claims. Instead, the above summary merely provides a preliminary description of different embodiments and corresponding points of novelty. Additional details and / or possible perspectives of the invention and embodiments are shown in the detailed description of this disclosure and the corresponding figures, which are further described below.

[0018] The following disclosure provides embodiments or examples for carrying out different features of the subject matter provided. For the sake of simplicity, specific examples of components and arrangements are described below. Naturally, these are merely examples and are not intended to be limiting.

[0019] For example, the order in which the different steps described below are presented is for clarity. In general, these steps can be performed in any suitable order. Furthermore, although each of the different features, techniques, structures, etc. of this specification may be described in different parts of this disclosure, it is intended that each of these concepts can be performed independently of or in combination with one another. Accordingly, the present invention can be embodied and considered in many different ways.

[0020] Furthermore, when used below, words such as "one" generally mean "one or more" unless otherwise specified.

[0021] To achieve high sensitivity, positron emission tomography (PET) imaging scanners typically use thick detectors to provide the necessary stopping power for 511 keV gamma photons. However, uncertainty in the depth of interaction (DOI) information in these thick detectors can lead to parallax errors. Such parallax degradation can worsen as the radial position within the PET field of view increases.

[0022] Figure 1 illustrates a scenario in which parallax errors arise from oblique response lines (LORs) in PET detector pixels without DOI information. Without DOI functionality, gamma-ray interactions occurring at all depths within the detector pixel are assumed to have occurred at a single location. For example, in Figure 1, the dashed line represents the estimated LOR, which is identical for all coincidence events between two detector pixels. The solid line represents the true LOR, which can be accurately depicted when DOI information for a specific coincidence event is available. Such parallax errors can lead to artifacts and image degradation.

[0023] Figure 2 shows a typical single-ended readout configuration. In this configuration, the pixelated array of scintillator crystal units is coupled to the top of the pixelated array of the photosensors. Specifically, the scintillator crystal units of a 4x4 crystal array are matched one-to-one with the photosensors of a 4x4 photosensor array. This configuration is optimal for TOF resolution because the individual photosensors can effectively capture most of the scintillation light emitted from the corresponding scintillator crystal units. However, a drawback of this design is the lack of DOI information, and the challenge is to acquire DOI information without compromising TOF resolution or significantly increasing system cost.

[0024] Figure 3 shows an exemplary single-ended readout configuration according to an embodiment of the present disclosure. As shown in Figure 3, a 4×4 crystal array is coupled to the top of an 8×8 photosensor array. Here, the 4×4 crystal array is an example of a scintillation array. The photosensor array is composed at a finer granularity level compared to the crystal array. Each scintillator crystal unit of the pixelation array has a substructure designed to direct the scintillation light generated in the scintillator crystal unit to a different location in the photosensor array than the others. This design makes it possible to distinguish gamma-ray interactions occurring at different depths within individual scintillator crystal units, thereby enabling the extraction of DOI information.

[0025] Figure 4 shows an exemplary substructure design within a scintillator crystal unit according to an embodiment of the present disclosure. This design involves inscribing microcracks into the interior of a crystal (crystal bulk) using a high-power laser. The created microcracks form an optical barrier that defines the light propagation path within the crystal.

[0026] For example, these laser-induced optical barriers (LIOBs) may be arranged as follows: In the upper one-third of the scintillator crystal unit, an optical barrier surface is formed in the center of the crystal unit along the y-axis, and in the lower two-thirds of the crystal unit, an optical barrier surface is formed in the center of the crystal unit along the x-axis. This design changes the light distribution at the photoescape plane (i.e., the lower end surface of the crystal unit where scintillation light is detected by the photosensor) for gamma-ray interactions at different depths within the crystal unit.

[0027] The details shown in Figure 4 are not limiting. For example, the upper optical barrier may be located in the upper two-thirds of the crystal unit, and the lower optical barrier may be located in the lower one-third of the crystal unit. Other divisions, proportions, and arrangements may be used without departing from the spirit and scope of this disclosure.

[0028] Similarly, although the upper and lower optical barriers are shown as being perpendicular to each other, the angle between the optical barriers may be other than 90 degrees.

[0029] Figures 5A and 5B show two exemplary substructure designs within a scintillator crystal unit according to the embodiments of this disclosure. Both designs use four subcrystals to form individual crystal units. In the upper one-third of the crystal unit, a reflective material (such as an Enhanced Specular Reflector (ESR) film or BaSO4 film) is applied to the central surface along the y-axis. In the lower two-thirds of the crystal unit, a reflective material is applied to the central surface along the x-axis. Optical adhesives are used at other contact surfaces between the subcrystals to allow light to pass through the crystal unit. Thus, these contact surfaces, to which the reflective material and optical adhesive are applied, define the optical path within the scintillator crystal unit.

[0030] Similar to the example shown in Figure 4, the details in Figures 5A and 5B are illustrative and not limiting. Those skilled in the art will be able to recognize various modifications and variations applicable to the illustrated designs.

[0031] Figure 6A shows an exemplary scintillator crystal unit including four segments according to an embodiment of the present disclosure. Figure 6B shows a flood histogram formed by gamma-ray irradiation of the four segments shown in Figure 6A. The four segments can be realized by the microcrack approach shown in Figure 4, or by the subcrystal approach shown in Figures 5A and 5B. Note that the distances between segments in the drawings do not represent the actual physical spacing, but are for the purpose of making their positions easier to see.

[0032] When gamma rays irradiate different segments in Figure 6A, the scintillation photons are distributed differently as they exit the scintillation crystal unit through the optical readout surface (e.g., the bottom surface of the crystal unit). As shown in Figure 6B, four dots A, B, C, and D can be formed on the crystal flood histogram, corresponding to four different gamma-ray interaction regions A, B, C, and D within the crystal unit, respectively. In this way, DOI information can be encoded into the crystal flood histogram and determined based on the crystal flood histogram.

[0033] The configurations shown in Figures 4, 5A, 5B, and 6A can all decode two depth locations. Different crystal substructure designs enable decoding of three or more depth locations. For example, Figure 7A shows a scintillator crystal unit containing eight segments according to an embodiment of this disclosure. Figure 7B shows a flood histogram formed by gamma-ray irradiation of the eight segments shown in Figure 7A. As shown in Figure 7B, eight dots A to H, corresponding to eight different gamma-ray interaction regions A to H within the crystal unit, can be formed on the crystal flood histogram. Based on the crystal flood histogram, it is possible to determine four different depths.

[0034] Furthermore, the scintillator crystal units can be separated using highly reflective materials. For example, each crystal unit can be wrapped in an ESR film or a BaSO4 film. This approach maintains the intensity of scintillation light from individual crystal units, as in the PET detector design shown in Figure 2, thereby resulting in high TOF resolution. This is a clear advantage compared to other designs where the amount of scintillation light on individual photosensors may be diminished by light sharing or the use of absorbent materials within the crystal array.

[0035] Figure 8 shows an exemplary scenario in which a pixelated photosensor array is directly coupled to a pixelated scintillator crystal array according to an embodiment of the present disclosure. Since each crystal unit in this arrangement is coupled to multiple photosensors to achieve DOI decoding, there is no need to arrange an optical waveguide between the crystal array and the photosensor array.

[0036] Figure 9 shows an exemplary electronic device design for acquiring timing, position, and energy information (t, x, y, e) from a pixelated optical sensor array according to an embodiment of the present disclosure. As described above, if there is no optical waveguide between the crystal array and the optical sensor array, the scintillation light leaving each scintillator crystal unit spreads to a small portion of the optical sensor array, for example, four optical sensors located beneath the crystal unit. The high-speed outputs of these four optical sensors can be connected to a single timing channel. In the case of a 4x4 optical sensor array, there are four timing channels, as shown in Figure 9. The low-speed components from the anode terminals of the four optical sensors can be used to extract position and energy information (x, y, e).

[0037] Each crystal unit generates a timing signal. In situations where multiple crystal units are irradiated with gamma rays due to the Compton scattering effect, an averaged timing signal can be calculated using energy-weighted averaging.

[0038] Various methods can be applied to decode DOI information from crystal flood histograms. In one embodiment, information on gamma-ray interactions within a scintillation array, namely DOI, interaction crystal, interaction energy, and interaction time, can be determined using timing, position, and energy information acquired via the Anger Logic electronic device shown in Figure 9. For example, DOI information can be extracted by inputting timing, position, and energy information into a pre-trained neural network. For example, information on the interaction crystal, interaction energy, and / or interaction time can be obtained from the output of the neural network along with the DOI information.

[0039] Figure 10 shows a flowchart of an exemplary procedure 1000 for extracting DOI information according to an embodiment of this disclosure.

[0040] In step S1010, scintillation light is generated via a scintillation array in response to gamma-ray interactions within the scintillation array. In step S1020, the scintillation light generated in the scintillation array is converted into an electrical signal via a photosensor array. In step S1030, information (t, x, y, e) regarding the timing, position, and energy of the gamma-ray interactions within the scintillation array is derived by Anger logic calculation based on the converted electrical signal. In step S1040, the derived information (t, x, y, e) can be used to determine information regarding the gamma-ray interactions within the scintillation array, namely the DOI, interaction crystal, interaction energy, and interaction time.

[0041] Subsequently, the extracted DOI information can be used in the image reconstruction process to mitigate parallax errors and improve the image quality of the PET scanner. Furthermore, by incorporating the extracted DOI information into the timing calibration process, the TOF resolution of the PET scanner can be further improved.

[0042] Figures 11A and 11B show embodiments of a PET apparatus 1100, including a PET scanner capable of carrying out the method described herein. The PET scanner includes a plurality of gamma-ray detectors (GRDs) (e.g., GRD1, GRD2 to GRDN), each configured as a rectangular detector module.

[0043] Each GRD may include a two-dimensional array of individual detector crystals that absorb gamma rays and emit scintillation photons. These scintillation photons can be detected by a two-dimensional array of photodetectors or optical sensors, such as photomultiplier tubes (PMTs) or silicon photomultiplier tubes (SiPMs). Optical waveguides can be placed between the array of detector crystals and the photodetectors.

[0044] Each photodetector (e.g., PMT or SiPM) can generate an analog signal indicating when a scintillation event occurs, as well as the energy of the gamma rays that generate the detection event. Furthermore, photons emitted from one detector crystal can be detected by two or more photodetectors, and based on the analog signals generated by each photodetector, the detector crystal corresponding to the detection event can be determined, for example, using Anger logic and crystal decoding.

[0045] Figure 11B shows an example of a PET scanner configuration, where the subject OBJ to be imaged is placed on a bed 1116, and GRD modules GRD1 to GRDN are arranged circumferentially around the subject OBJ and bed 1116. The GRDs can be fixedly connected to annular components 1120 which are fixedly connected to a gantry 1140. The gantry 1140 houses many of the components of the PET scanner. The gantry 1140 of the PET scanner also includes an opening through which the subject OBJ and bed 1116 can pass, allowing the GRDs to detect gamma rays emitted in the opposite direction from the subject OBJ due to annihilation events, and to determine the coincidence of gamma ray pairs using timing and energy information.

[0046] Figure 11B also shows the circuitry and hardware for acquiring, storing, processing, and distributing gamma-ray detection data. This circuitry and hardware includes a processor 1170, a network controller 1174, a memory 1178, and a Data Acquisition System (DAS) 1176. The PET scanner also includes data channels that route detection measurement results from the GRD to the DAS 1176, processor 1170, memory 1178, and network controller 1174. The DAS 1176 can control the acquisition, digitization, and routing of detection data from the detector. In one embodiment, the DAS 1176 controls the movement of the bed 1116. The processor 1170 performs functions including image reconstruction from detection data, pre-reconstruction processing of detection data, and post-reconstruction processing of image data, as described herein. Here, the processor 1170 is an example of a processing circuit.

[0047] The processor 1170 can be configured to perform various steps and variations thereof of the method described herein. The processor 1170 may include a CPU that can be implemented as individual logic gates, such as an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), or other Complex Programmable Logic Device (CPLD). The FPGA or CPLD implementation may be coded in VHDL, Verilog, or other hardware description language, and the code may be stored directly in the electronic memory within the FPGA or CPLD, or in a separate electronic memory. Furthermore, the memory may be non-volatile, such as ROM, EPROM, EEPROM, or flash memory. The memory may also be volatile, such as static RAM or dynamic RAM, and a processor, such as a microcontroller or microprocessor, may be provided to manage the electronic memory and manage the interaction between the FPGA or CPLD and the memory.

[0048] Alternatively, the CPU within processor 1170 may execute a computer program comprising a set of computer-readable instructions that perform various steps of the described method, the program being stored in any of the non-transient electronic memory and / or hard disk drives, CDs, DVDs, flash drives, or other known storage media described above. Furthermore, the computer-readable instructions may be provided as utility applications, background daemons, or components of an operating system, or a combination thereof, and may be executed in cooperation with processors such as Intel Xeon or AMD Opteron processors, and Microsoft Vista, UNIX®, Solaris, LINUX®, Apple, MAC-OS, and other operating systems known to those skilled in the art. Furthermore, the CPU may be implemented as multiple processors that operate concurrently and cooperatively to execute instructions.

[0049] The memory 1178 may be a hard disk drive, CD-ROM drive, DVD drive, flash drive, RAM, ROM, or other electronic storage device known in the art.

[0050] Network controllers 1174, such as Intel Ethernet® PRO network interface cards manufactured by Intel Corporation in the United States, can interface between various parts of the PET scanner. Furthermore, network controller 1174 can also interface with an external network. As can be understood, the external network can be a public network such as the Internet, a private network such as a LAN or WAN network, or any combination thereof, and may include a PSTN or ISDN subnetwork. The external network can be wired, such as an Ethernet® network, or wireless, such as a cellular network including EDGE, 3G, and 4G wireless cellular systems. The wireless network may be WiFi, Bluetooth®, or other known wireless communication formats.

[0051] To aid in understanding the various embodiments, various techniques have been described as multiple separate operations. The order of the description should not be interpreted as meaning that these operations are necessarily order-dependent. In fact, these operations do not need to be performed in the order presented. The described operations may be performed in a different order than in the embodiments described. In additional embodiments, various additional operations may be performed, and / or the described operations may be omitted.

[0052] In light of the above teachings, numerous modifications and variations of the embodiments presented herein are possible. Therefore, it should be understood that within the scope of the claims, this application may be implemented in ways other than those specifically described herein. The present invention is not limited to the embodiments described herein. In particular, features of the illustrated embodiments can be combined in variations not shown.

[0053] Furthermore, embodiments of this disclosure may be described in the following appendix.

[0054] (1) A positron emission tomography (PET) apparatus comprising: (1) a scintillation array including a plurality of scintillator crystal units individually separated by a reflective material, each of the plurality of scintillator crystal units configured to generate scintillation light in response to gamma-ray interactions within the scintillator crystal unit caused by gamma-ray irradiation from an imaging subject, each scintillator crystal unit having a substructure for decoding two or more depths within the scintillator crystal unit, thereby resulting in scintillation light from which gamma-ray interactions at different depths escape from the photo-escape plane of the scintillator crystal unit in different patterns; a photosensor array coupled to the scintillation array to convert scintillation light received from the scintillation array into an electrical signal; and a processing circuit configured to extract information representing the interaction depth of gamma-ray interactions within the scintillation array from the electrical signal, and to reconstruct an image of the imaging subject based on the extracted information.

[0055] (2) The apparatus according to (1), wherein the substructure of each scintillator crystal unit includes a crystal bulk body having an optical barrier disposed therein, the optical barrier being a microcrack inside the crystal bulk body formed by a laser engraving process.

[0056] (3) The apparatus according to (2), wherein in the substructure of each scintillator crystal unit, an optical barrier separates the crystal bulk into four parts, thereby resulting in gamma-ray interactions in the four parts producing scintillation light that escapes from the optical escape plane of the scintillator crystal unit in four different patterns.

[0057] (4) The apparatus according to (2), wherein in the substructure of each scintillator crystal unit, an optical barrier separates the crystal bulk into eight parts, thereby resulting in gamma-ray interactions in the eight parts producing scintillation light that escapes from the optical escape plane of the scintillator crystal unit in eight different patterns.

[0058] (5) The apparatus according to (1), wherein the substructure of each scintillator crystal unit comprises a plurality of subcrystals, and the plurality of subcrystals have a reflective material and an optical adhesive applied to different contact interfaces between the plurality of subcrystals.

[0059] (6) The apparatus as in (5), wherein the substructure of each scintillator crystal unit includes four subcrystals, thereby resulting in scintillation light escaping from the photo-escape plane of the scintillator crystal unit in four different patterns due to gamma-ray interactions in the four subcrystals.

[0060] (7) The apparatus as in (5), wherein the substructure of each scintillator crystal unit includes eight subcrystals, thereby resulting in scintillation light escaping from the photo-escape plane of the scintillator crystal unit in eight different patterns due to gamma-ray interactions in the eight subcrystals.

[0061] (8) The apparatus according to (1), wherein the processing circuit is further configured to perform a process to derive information (t, x, y, e) of the timing, position, and energy of the gamma-ray interaction in the scintillation array based on an electrical signal, and to determine information representing the interaction depth of the gamma-ray interaction in the scintillation array based on the derived information (t, x, y, e).

[0062] (9) The apparatus according to (8), wherein the processing circuit is further configured to determine information representing the interaction crystal, interaction energy, and interaction time related to the gamma-ray interaction in the scintillation array based on the derived information (t, x, y, e).

[0063] (10) The apparatus described in (1), wherein the optical sensor array is composed of finer particles compared to the scintillation array.

[0064] (11) A method for extracting interaction depth (DOI) information in positron emission tomography (PET), comprising: generating scintillation light in response to gamma-ray interactions in a scintillation array caused by gamma-ray irradiation from an imaging subject via a scintillation array, wherein the scintillation array comprises a plurality of scintillator crystal units individually separated by a reflective material, each scintillator crystal unit having a substructure for decoding two or more depths within the scintillator crystal unit, thereby generating scintillation light such that gamma-ray interactions at different depths escape from the photo-escape plane of the scintillator crystal unit in different patterns; converting the scintillation light received from the scintillation array into an electrical signal via an optical sensor array coupled to the scintillation array; extracting information representing the interaction depth of gamma-ray interactions in the scintillation array from the electrical signal; and reconstructing an image of the imaging subject based on the extracted information.

[0065] (12) The method according to (11), wherein the substructure of each scintillator crystal unit comprises a crystal bulk body having an optical barrier disposed therein, the optical barrier being a microcrack inside the crystal bulk body formed by a laser engraving process.

[0066] (13) The method according to (12), wherein in the substructure of each scintillator crystal unit, an optical barrier separates the crystal bulk into four parts, thereby resulting in gamma-ray interactions in the four parts causing scintillation light to escape from the photo-escape plane of the scintillator crystal unit in four different patterns.

[0067] (14) The method according to (12), wherein in the substructure of each scintillator crystal unit, an optical barrier separates the crystal bulk into eight parts, thereby resulting in gamma-ray interactions in the eight parts causing scintillation light to escape from the photo-escape plane of the scintillator crystal unit in eight different patterns.

[0068] (15) The apparatus according to (11), wherein the substructure of each scintillator crystal unit comprises a plurality of subcrystals, the plurality of subcrystals having a reflective material and an optical adhesive applied to different contact interfaces between the plurality of subcrystals.

[0069] (16) The method according to (15), wherein the substructure of each scintillator crystal unit comprises four subcrystals, thereby resulting in scintillation light escaping from the photo-escape plane of the scintillator crystal unit in four different patterns due to gamma-ray interactions in the four subcrystals.

[0070] (17) The method according to (15), wherein the substructure of each scintillator crystal unit comprises eight subcrystals, thereby resulting in scintillation light escaping from the photo-escape plane of the scintillator crystal unit in eight different patterns due to gamma-ray interactions in the eight subcrystals.

[0071] (18) The method of (11), further comprising: extracting information (t, x, y, e) of the timing, position, and energy of the gamma-ray interaction in the scintillation array based on an electrical signal; and determining information representing the interaction depth of the gamma-ray interaction in the scintillation array based on the extracted information (t, x, y, e).

[0072] (19) The method of (18), further comprising determining, based on derived information (t, x, y, e), information representing the interaction crystal, interaction energy, and interaction time related to the gamma-ray interaction in the scintillation array.

[0073] (20) A gamma-ray detector for use in a positron emission tomography (PET) imaging system, comprising a scintillation array including a plurality of scintillator crystal units individually separated by a reflective material, wherein each of the plurality of scintillator crystal units is configured to generate scintillation light in response to gamma-ray interactions within the scintillator crystal unit caused by gamma-ray irradiation from an imaging subject, and each scintillator crystal unit has a substructure for decoding two or more depths within the scintillator crystal unit, thereby resulting in a scintillation array in which gamma-ray interactions at different depths result in scintillation light escaping from the photo-escape plane of the scintillator crystal unit in different patterns.

[0074] In light of the above teachings, numerous modifications and variations of the embodiments presented herein are possible. Therefore, it should be understood that, within the scope of the claims, this disclosure may be implemented in ways other than those specifically described herein.

[0075] According to at least one embodiment described above, both good TOF resolution and DOI information can be provided.

[0076] While several embodiments have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be implemented in a variety of other forms, and various omissions, substitutions, modifications, and combinations of embodiments are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0077] 1100 Positron Emission Tomography (PET) System 1170 Processor GRD1, GRD2~GRDN Gamma-ray detectors

Claims

1. A scintillation array comprising a plurality of scintillator crystal units individually separated by a reflective material, wherein each scintillator crystal unit is configured to generate scintillation light in response to gamma-ray interactions within the scintillator crystal unit caused by gamma-ray irradiation from a subject, and the scintillation array having a substructure for decoding two or more depths within the scintillator crystal unit such that gamma-ray interactions at different depths cause scintillation light to escape from the photo-escape surface of the scintillator crystal unit in different patterns, A photosensor array coupled to the scintillation array converts scintillation light received from the scintillation array into an electrical signal, A processing circuit extracts information representing the interaction depth of the gamma-ray interaction within the scintillation array from the electrical signal, and reconstructs an image of the subject based on the extracted information. A positron emission tomography (PTMO) scanner equipped with the following features.

2. Each of the scintillator crystal units comprises a substructure containing a crystalline bulk body having an optical barrier disposed within the substructure, wherein the optical barrier is a microcrack formed inside the crystalline bulk body through a laser engraving process. The positron emission tomography apparatus according to claim 1.

3. The substructure of each scintillator crystal unit is configured such that the optical barrier separates the crystalline bulk into four parts, and the gamma-ray interaction in the four parts generates scintillation light escaping from the optical escape plane of the scintillator crystal unit in four different patterns. The positron emission tomography apparatus according to claim 2.

4. The substructure of each scintillator crystal unit is configured such that the optical barrier separates the crystal bulk into eight parts, and the gamma-ray interactions in the eight parts cause scintillation light to escape from the photo-escape plane of the scintillator crystal unit in eight different patterns. The positron emission tomography apparatus according to claim 2.

5. The substructure of each scintillator crystal unit comprises a plurality of subcrystals, and the plurality of subcrystals have a reflective material and an optical adhesive applied to different contact interfaces between the plurality of subcrystals. A positron emission tomography apparatus according to any one of claims 1 to 4.

6. The substructure of each scintillator crystal unit comprises four subcrystals, and the gamma-ray interactions in the four subcrystals are configured to produce scintillation light escaping from the photo-escape plane of the scintillator crystal unit in four different patterns. The positron emission tomography apparatus according to claim 5.

7. The substructure of each scintillator crystal unit comprises eight subcrystals, and the gamma-ray interactions in the eight subcrystals are configured to produce scintillation light escaping from the photo-escape plane of the scintillator crystal unit in eight different patterns. The positron emission tomography apparatus according to claim 5.

8. The aforementioned processing circuit is Based on the aforementioned electrical signals, information (t, x, y, e) regarding the timing, position, and energy of the gamma-ray interaction within the scintillation array is derived. Based on the derived information (t, x, y, e), information representing the interaction depth of the gamma-ray interaction within the scintillation array is determined. A positron emission tomography apparatus according to any one of claims 1 to 4.

9. The processing circuit determines information representing the interaction crystal, interaction energy, and interaction time related to the gamma-ray interaction within the scintillation array based on the derived information (t, x, y, e). The positron emission tomography apparatus according to claim 8.

10. The aforementioned optical sensor array is composed of finer particles compared to the scintillation array. A positron emission tomography apparatus according to any one of claims 1 to 4.

11. A positron emission tomography (PT) method applied to a positron emission tomography apparatus comprising: a scintillation array including a plurality of scintillator crystal units individually separated by a reflective material, wherein each scintillator crystal unit is configured to generate scintillation light in response to gamma-ray interactions within the scintillator crystal unit caused by gamma-ray irradiation from a subject, and the scintillation array having a substructure for decoding two or more depths within the scintillator crystal unit such that gamma-ray interactions at different depths cause scintillation light to escape from the photo-escape plane of the scintillator crystal unit in different patterns; a photosensor array coupled to the scintillation array; and a processing circuit. The scintillator crystal unit included in the scintillation array generates scintillation light in response to gamma-ray interactions within the scintillator crystal unit, The optical sensor array performs the step of converting scintillation light received from the scintillation array into an electrical signal, The processing circuit performs the steps of: extracting information representing the interaction depth of the gamma-ray interaction in the scintillation array from the electrical signal, and reconstructing an image of the subject based on the extracted information; Positron emission tomography (PTMO) methods, including those mentioned above.

12. A gamma-ray detector used in a positron emission tomography (PTMO) scanner, A scintillation array comprising a plurality of scintillator crystal units individually separated by a reflective material, wherein each scintillator crystal unit is configured to generate scintillation light in response to gamma-ray interactions within the scintillator crystal unit caused by gamma-ray irradiation from a subject, and the scintillation array having a substructure for decoding two or more depths within the scintillator crystal unit such that gamma-ray interactions at different depths cause scintillation light to escape from the photo-escape plane of the scintillator crystal unit in different patterns. A gamma-ray detector equipped with the following features.

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