Pet apparatus and method

Abstract

To maintaining TOF resolution while acquiring DOI information.SOLUTION: A PET apparatus according to an embodiment includes a PET detector and a processing unit. The PET detector includes: a detector crystal block comprising a plurality of detector crystals including a first detector crystal and a second detector crystal, and an inner reflector provided between the first detector crystal and the second detector crystal such that transparency of light varies depending on depth of the detector crystals; a first photosensor configured to detect a first intensity of light dependent on the transparency of the inner reflector; and a second photosensor configured to detect a second intensity of light dependent on the transparency of the inner reflector. The processing unit is configured to determine a first energy based on the first intensity, determine a second energy based on the second intensity, and determine, based on the first energy and the second energy, a depth of interaction (DOI) of a gamma ray in the detector crystal block.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The embodiments disclosed in this specification and the drawings relate to PET apparatuses and methods.

[0002] The present disclosure relates to methods and apparatuses for determining time-of-flight and depth of interaction using positron emission tomography, and to methods and apparatuses for using depth-of-interaction data acquired via detectors having reflectors in a PET scanner.

Background Art

[0003] The description of the background art described in this specification is for schematically showing the background of the present disclosure. The scope of work described in this chapter of the background art, and the work of the inventors of this application with respect to aspects of this specification that are not recognized as prior art at the time of filing, are not admitted, explicitly or implicitly, as prior art to the present disclosure.

[0004] Positron Emission Tomography (PET) is a functional imaging modality that enables imaging of the biochemical actions of humans or animals by using a radioactive tracer. In PET imaging, a tracer agent is taken into a patient to be imaged via injection, inhalation, or oral ingestion. After administration, due to its physical and biomolecular properties, the agent concentrates at specific locations in the patient's body. The actual spatial distribution of the agent, the concentration in the accumulation regions of the agent, and the dynamics of the process from administration until finally excreted are all factors that may have clinical significance.

[0005] During this process, the tracer bound to the agent emits positrons. When the emitted positrons collide with electrons, an annihilation event occurs, and the positrons and electrons combine. The annihilation event produces two gamma rays (511 keV) that travel substantially 180° apart. Time of Flight (TOF) and Depth of Interaction (DOI) are two metrics used to evaluate the performance of a PET scanner. Depending on the application, one method may be preferred over the other, but the use of multiple PET detectors may be required. PET detectors are expensive components in a whole-body (or total-body) PET system. Therefore, there is a desire for a detector that can measure both TOF and DOI without adding complex components or configuration / assembly steps to a conventional TOF detector.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to maintain TOF resolution while acquiring DOI information. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. The problems corresponding to the effects of each configuration shown in the embodiments described later can also be regarded as other problems.

Means for Solving the Problems

[0008] The PET device according to the embodiment includes a PET detector and a processing unit. The PET detector includes a detector crystal block including a plurality of detector crystals including a first detector crystal and a second detector crystal, and an inner reflector provided between the first detector crystal and the second detector crystal so that the light transmittance varies for each depth of the detector crystal, and a first optical sensor that detects a first intensity of light depending on the transmittance of the inner reflector, and a second optical sensor that detects a second intensity of light depending on the transmittance of the inner reflector. The processing unit determines a first energy based on the first intensity, determines a second energy based on the second intensity, and determines a depth of interaction (DOI) of gamma rays in the detector crystal block based on the first energy and the second energy.

Brief Description of Drawings

[0009]

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DETAILED DESCRIPTION OF THE INVENTION

[0010] The present disclosure relates to a PET device, the PET device including a mini-block (detector crystal block) including a plurality of detector crystals, wherein a first detector crystal and a second detector crystal of the plurality of detector crystals are separated by an inner reflector, the inner reflector having a depth-dependent transmittance, the mini-block, a first optical sensor configured to detect light from a gamma-ray detection event, a first intensity of the light detected by the first optical sensor depending on the depth-dependent transmittance of the inner reflector, a second optical sensor configured to detect light from a gamma-ray detection event, a second intensity of the light detected by the second optical sensor depending on the depth-dependent transmittance of the inner reflector, a detector block (PET detector) including the first and second optical sensors, a processing circuit (processing unit) configured to determine a first energy based on the detected first intensity, determine a second energy based on the detected second intensity, and determine a depth of interaction (DOI) of a gamma-ray detection event based on the first energy and the second energy.

[0011] The present disclosure further relates to a method including a mini-block (detector crystal block) having a plurality of detector crystals, wherein a first detector crystal and a second detector crystal of the plurality of detector crystals are separated by an inner reflector having a depth-dependent transmittance, detecting a first intensity of light from a gamma-ray detection event incident on the first detector crystal via a first optical sensor in a detector block (PET detector) including the mini-block, detecting a second intensity of light from a gamma-ray detection event incident on the second detector crystal via a second optical sensor in the detector block, determining a first energy based on the detected first intensity, determining a second energy based on the detected second intensity, and determining a DOI of a gamma-ray detection event based on the first energy and the second energy, wherein the first intensity of the light is determined by the depth-dependent transmittance of the inner reflector and the second intensity of the light is determined by the depth-dependent transmittance of the inner reflector.

[0012] Note that in the above Summary section of the invention, it should be noted that not all embodiments and / or incremental novel aspects of the present disclosure or the claimed invention are identified. Instead, this summary provides only a preliminary discussion of various embodiments. For further details and / or possible aspects of the present invention and embodiments, reference should be made to the Detailed Description section of the present disclosure and the corresponding drawings described below.

[0013] Various embodiments of the present disclosure presented as examples will be described in detail below with reference to the following drawings. Here, the same numbers mean the same elements.

[0014] The following disclosure presents many different embodiments, or examples, for implementing various features of the presented subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the configuration of the second mechanism in the following description, or the first mechanism mounted thereon, may include embodiments in which the first and second mechanisms are configured in a state of direct contact, and there may also be embodiments in which another mechanism is configured between the first and second mechanisms such that the first and second mechanisms are not in direct contact. In addition, the present disclosure may repeat reference numbers and / or reference characters in various examples. This repetition is for simplicity and clarity, but does not by itself define the relationship between the various embodiments and / or configurations being described. Further, to facilitate the description of the relationship of one element or the mechanism of another element or mechanism as shown in the figures, spatial relative terms such as "upper", "lower", "under", "downward", "lower side", "upper", "upper side", etc. may be used in this specification. The spatial relative terms are intended to encompass various directions of the device in use or operation in addition to the direction depicted in the figures. The system may be oriented in another way (rotated 90° or in other directions), and the spatial relative descriptions used in this specification may be interpreted accordingly.

[0015] As described in this specification, the order of description of different procedures is presented for clarity. Generally, these steps can be performed in any suitable order. Also, each of the different features, techniques, and configurations in this specification may be described at various places in the present disclosure, but each concept is intended to be executable independently of or in combination with each other. Therefore, the present invention can be embodied and considered in many different ways.

[0016] In a whole-body positron emission tomography (PET) scanner with a short axial field of view (AFOV), the time of flight (TOF) is more important than the depth of interaction (DOI) to improve the effective sensitivity of the system, and this has been shown to enable better image quality, shorter scan times, and lower radiation doses to patients. On the other hand, DOI information enables better image spatial resolution by correcting any parallax, which is important in PET scanners with a small bore diameter (e.g., for brain imaging) or a large axial acceptance angle (long-AFOV, whole-body scanners, etc.).

[0017] Furthermore, by measuring the DOI, the TOF resolution can also be improved. Therefore, a detector capable of measuring both TOF and DOI, preferably simultaneously, is desired.

[0018] In the use of a whole-body PET scanner (e.g., having a very long AFOV), DOI is becoming more important in order to correct for errors caused by very oblique lines of response along the axial direction. Thus, a PET scanner with both good TOF resolution and DOI information will further improve the performance of clinical PET scanners. Since PET detectors are expensive components of a whole-body (or full-body) PET system, a detector design that can measure TOF and DOI without adding complex components or assembly processes is also beneficial.

[0019] In particular, DOI information can be obtained from a PET detector having a specific design. As described herein, in the design of the PET detector according to this embodiment, a reflector shape that is particularly beneficial for implementation is used because of lower cost.

[0020] One challenge in applying DOI design from preclinical PET to clinical PET is to design a reflector to distinguish small crystals of preclinical PET detectors and direct scintillation light from one crystal to several different light sensors to achieve better crystal separation. However, separating scintillation light among several light sensors reduces the amount of scintillation light for each light sensor, which in turn reduces the photon statistics for each light sensor, increases the variation in photon travel distance, and causes timing jitter, resulting in degradation of TOF resolution. As described herein, careful design of the reflector shape can mitigate some degradation of TOF resolution and / or DOI resolution while acquiring DOI information for clinical PET scanners.

[0021] For this purpose, the PET apparatus according to the present embodiment includes a plurality of detector crystals including a first detector crystal and a second detector crystal, and an inner reflector provided between the first detector crystal and the second detector crystal so that the light transmittance varies for each depth of the detector crystal, and a detector crystal block including the inner reflector, a first photosensor that detects a first intensity of light depending on the transmittance of the inner reflector, and a second photosensor that detects a second intensity of light depending on the transmittance of the inner reflector. Further, the PET apparatus according to the present embodiment includes a processing unit that determines a first energy based on the first intensity, determines a second energy based on the second intensity, and determines a depth of interaction (DOI) of gamma rays in the detector crystal block based on the first energy and the second energy.

[0022] FIG. 1 is a diagram showing a PET detector 100 including a pixelated array of crystals (detector crystals) 105 connected to a pixelated array of photosensors 110 according to the present embodiment. In one embodiment, as shown in FIG. 1, the PET detector 100 includes a 4×4 array of crystals 105 disposed above or on top of a 4×4 array of photosensors 110 in a one-to-one arrangement, and the PET detector 100 is configured to provide single-ended readout. The photosensor 110 is configured to detect scintillation light from the corresponding crystal 105, and as a result, the best measurement conditions for TOF resolution are obtained. In particular, the reflector (the solid black line along the upper surface) separates each of the crystals 105. Note that the reflector disposed on the upper surface of the crystal 105 is not shown in the figure.

[0023] FIG. 2 is a schematic diagram showing a PET detector 200 including a mini-block (detector crystal block) design according to the present embodiment. In one embodiment, the PET detector 200 includes a crystal (detector crystal) 205 and a photosensor 210. In contrast to the PET detector 100 of FIG. 1, each crystal 205 is grouped together to form a mini-block 215 having two crystals 205 per mini-block 215. In this way, each of the PET detectors 200 includes a 2×4 array of mini-blocks 215. Here, each of the mini-blocks 215 includes two different types of reflectors, namely, an inner reflector 220 and an outer reflector 225.

[0024] In one embodiment, the inner reflector 220 separates the crystals 205 between each of the mini-blocks 215 and varies in transmittance along the z direction. DOI information with different light distribution patterns is encoded between each of the mini-blocks 215. The outer reflector 225 separates the mini-blocks 215 within the PET detector 200, and these are configured to prevent the mutual interference of light between the mini-blocks 215. That is, the outer reflector 225 is provided so as to surround the mini-blocks along the side surfaces of the mini-blocks 215. Since the scintillation light is confined to each of the mini-blocks 215, this helps to ensure that a high concentration of scintillation light reaches the photosensor 210 and maintains a higher timing resolution for TOF. It should be noted that although not shown, the design of the outer reflector 225 disposed on the upper surface of the crystal 205 may be included.

[0025] FIG. 3 is a schematic diagram showing the structure of the mini-block 215 according to the present embodiment. In one embodiment, one inner reflector 220 separates the two crystals 205, five outer reflectors 225 cover the four side surfaces and the top of the mini-block 215, and the bottom surfaces of the two crystals 205 are directly connected to one of the photosensors 210 for detecting scintillation light. The inner reflector 220 between the two crystals 205 is partially transmissive so that light is distributed or dispersed inside the mini-block 215. The outer reflector 225 can have a high reflectivity, thereby preventing the escape or leakage of light.

[0026] FIG. 4 is a schematic diagram showing the transmittance of the inner reflector 220 that changes according to depth in the present embodiment. In one embodiment, the transmittance (T inner ) can vary depending on the different depths (z-direction) of the crystal 205. Therefore, for gamma rays incident on the crystal 205 at different depths, the light distribution pattern inside the miniblock 215 becomes different, and thus DOI information can be extracted. The curve in FIG. 4 shows an example of the relationship between T inner and z, but the relationship can be generalized to T inner = f(z) for any function.

[0027] For example, the inner reflector 220 according to the present embodiment may be formed to have a plurality of openings that determine the light transmittance for each depth of the detector crystal (crystal 205). Here, the plurality of openings are divided into at least two sections along the inner reflector, and the first section of the at least two sections may have openings with different densities compared to the second section of the at least two sections. In this case, the first section may be disposed on the side opposite to the first optical sensor or the second optical sensor, even when the density of the openings is higher than the density of the openings in the second section. Also, in this case, the opening size of each opening of the plurality of openings may be the same. Further, the plurality of openings are separated into at least two sections along the inner reflector, and the first section of the at least two sections may have openings of different sizes compared to the second section of the at least two sections. In this case, the size of each opening in the first section may be larger than the size of each opening in the second section. Also, in this case, the number of openings in the first section may be the same as the number of openings in the second section.

[0028] FIG. 5 includes two schematic views showing various designs of the inner reflector 220 within the miniblock 215 according to this embodiment. In one embodiment, achieving z-direction dependent transmissivity with the inner reflector 220 can be accomplished by forming different patterns of openings (or holes) in or through the inner reflector 220. In one example, the left schematic view includes holes of the same size but different densities that vary in z-direction spacing or depth, while the right schematic view includes holes of different sizes that vary in z-direction spacing or depth. In one example, the holes can be of different sizes that are repeated or consistently spaced in z-direction depth. The shape of the holes can be circular, triangular, square, pentagonal, hexagonal, other n-gonal, or any combination thereof. In one example, the holes can be in a predetermined pattern while providing a target density to the target region. In one example, the holes can be in a random pattern while providing a target density to the target region. The pattern shown in FIG. 5 is symmetric about the z-axis, but this pattern can be asymmetric about the z-axis. That is, the density of the holes can vary along the y-axis. In one example, in a region of the inner reflector 220 that includes more holes, more light may pass through the inner reflector 220. At the same time, in a region of the inner reflector 220 that includes fewer holes, the transmissivity may be low. In one embodiment, the holes can be formed or fabricated via mechanical processes such as drilling, scribing, punching, stamping, etc. Similarly, the inner reflector 220 can also be fabricated to exclude material at a desired location via molding, sintering, other additive manufacturing, etc. In one embodiment, the holes can be formed via other processes such as chemical etching, plasma etching, laser etching, lithography, vapor deposition, etc.

[0029] Further, for example, the inner reflector 220 according to the present embodiment may be formed to include a first section having a first transmittance and a second section having a second transmittance. Here, the first transmittance may be determined by, for example, a first film applied to the first section of the inner reflector, and the second transmittance may be determined by a second film applied to the second section of the inner reflector. Further, the first section may be disposed on the opposite side of the first photosensor or the second photosensor, and the first transmittance may be higher than the second transmittance.

[0030] FIG. 6A is a schematic diagram showing various transmittances based on materials according to this embodiment. In one embodiment, different transmittances can be realized by using different materials along the z - direction. As shown in FIG. 6A, which can be regarded as a cross - sectional view through the inner reflector 220, the inner reflector 220 includes four sections, segments, or parts, which can be generalized to any other number of sections. In one example, the inner reflector 220 includes two sections, three sections, five sections, or generally, n sections. The shape of the cross - section of the section does not have to be four - sided as shown in the figure. The shapes of the sections can vary and be complementary to each other. In one example, the first section can be a convex pentagon, and at the same time, the adjacent second section can be a convex pentagon. Thus, a portion having convex and concave portions of the shape may have a composite transmittance with two different materials in the first and second sections. In one embodiment, the materials may be applied to each of the sections. In one example, a film or paint may be applied to each of the sections, where the film or paint for each section is a different material. In one example, various numbers of layers of film or paint may be applied to each of the sections, where the film or paint for each section is the same. Similarly, the film or paint for each section can also be a combination of different materials. As shown in FIG. 6A, the upper section can have a thin (or highly transmissive) film applied to promote light transmission, while the bottom section can have a thick (or low - transmissive) film applied to reduce light transmission. The material of the film or paint can be, for example, BaSO4.

[0031] In addition, in the inner reflector 220 according to the present embodiment, the first transmittance may be determined by the thickness of the first section of the inner reflector, and the second transmittance may be determined by the thickness of the second section of the inner reflector. In this case, the inner reflector 220 includes a bottom portion that is on the side of the first photosensor or the second photosensor, and an upper portion that is on the opposite side of the bottom portion. The thickness of the inner reflector increases from the upper portion toward the bottom portion, and the transmittance may be determined by the thickness of the inner reflector.

[0032] FIG. 6B is a schematic diagram showing that different transmittances can be achieved by changing the thickness of the inner reflector 220 according to the present embodiment. In one embodiment, the same material is used, but the transmittance can be changed by making the thickness of the inner reflector 220 different along the z direction. The cross-sectional view of FIG. 6B may be orthogonal to the cross-sectional views shown in FIGS. 5 and 6A. As shown in FIG. 6B, the upper section can be made thinner to promote higher light transmission, while the bottom section can be made thicker than the upper section to reduce light transmission. In one embodiment, the material of the inner reflector 220 can be polyester, polypropylene, polyphenylene, para-aramid, or the like.

[0033] In one embodiment, the inner reflector 220 can be fabricated or formed separately from the crystal 205 and disposed between two or more adjacent crystals 205. Additionally or alternatively, the inner reflector 220 can be fabricated or formed as part of the crystal 205. The length (or height) of the crystal 205 and the inner reflector 220 can be, for example, less than 100 mm, or less than 50 mm, or less than 25 mm, or 20 mm. The width of the crystal 205 and the inner reflector can be, for example, less than 50 mm, or less than 25 mm, or less than 15 mm, or less than 5 mm. In one example, the crystal 205 has a length of 20 mm and includes 10 sections, each section having a height of 2 mm. The diameter or width of the hole can be, for example, less than 2 mm, or less than 1 mm, or less than 500 um, or less than 100 um, or less than 1 um. The thickness of the thinnest section of the inner reflector 220 can be less than 5 mm, or less than 1 mm, or less than 500 um, or less than 100 um, or less than 500 nm. The thickness of the thickest section of the inner reflector 220 can be less than 15 mm, or less than 10 mm, or less than 5 mm, or less than 1 mm, or less than 100 um.

[0034] The above combinations of designs can be used as appropriate. In one example, the film may be applied to the inner reflector 220 with different hole densities formed therein. The film can be applied to the entire section or only to a part of the section. Similarly, the film can be applied to the inner reflector 220 whose thickness varies (along the length of the crystal 205) from the top to the bottom of the inner reflector. Similarly, the film can be applied to the inner reflector 220 whose thickness varies (along the length of the crystal 205) from the top to the bottom and at the same time has different hole densities formed therein.

[0035] FIG. 7 is a schematic diagram showing an electronic design for processing an analog signal from the optical sensor 210 according to the present embodiment. In one embodiment, each signal S ijIt can be transferred to two paths, namely, (i) a low-bandwidth current buffer, and then a low-speed path that is divided into three signals (E, x, y) for the determination of energy, DOI, and position information, and (ii) a high-pass filter (a small-capacity capacitor), and then to a high-speed path that forms timing information.

[0036] Figure 8 is a schematic diagram showing a method for decoding DOI information according to this embodiment. In one embodiment, for gamma rays incident on the crystal 205 at different depths, since the distribution of light between the odd-numbered crystals 205 (the crystals 205 to the left of the miniblock 215) and the even-numbered crystals (the crystals 205 to the right of the miniblock 215) is different, the ratio of the energies collected in the odd-numbered and even-numbered columns can be used to decode the DOI information. In particular, the energy signals from the odd-numbered and even-numbered columns of the optical sensor 210 are respectively summed by two analog-to-digital converters (ADCs). E L and E R The ratio between can provide a performance coefficient for decoding the DOI information. E L and E R The sum of (E = E L + E R ) can provide the total energy E of the scintillation event collected by the optical sensor 210.

[0037] In one example, the gamma rays are S 13 and S 14It may be detected by the miniblock 215 corresponding to the optical sensor 210. Depending on the position where the gamma ray is incident on the S13 crystal 205 along the z direction, different amounts of scintillation light leak through the inner reflector 220 to the S14 crystal 205. That is, since the transmittance of the inner reflector 220 depends on the z direction, the amount of light leaking from one crystal 205 to the other and detected varies according to the transmittance of the inner reflector 220 along the z direction, whereby the location where the gamma ray hits along the z direction can be specified. In one example, when the gamma ray is incident near the top of the left crystal 205 (S13), since the top of the inner reflector 220 is more transmissive, almost the same amount of scintillation light will reach the bottoms of these two crystals 205. Therefore, the right crystal 205 has a similar reading value and the ratio of E L and E R is close to 1. On the other hand, when the gamma ray is incident near the bottom of the left crystal 205, since the transmittance of the inner reflector 220 is lower towards the bottom, most of the scintillation light is collected by the optical sensor 210 (S 13 ) corresponding to the left crystal 205, whereby a higher E L is obtained. Therefore, depending on the values of E R and E L , the depth of the gamma ray collision can be determined. Note that in the above example, it is assumed that one gamma ray is incident on only one of the crystals 205.

[0038] FIG. 9 and FIG. 10 are schematic diagrams showing the electronic design of the PET detector 200 for determining the position (x, y) according to the present embodiment. In one embodiment, row and column processing can be used to decode the position of the scintillation event. FIG. 9 shows the decoding of the x position of the scintillation event, and FIG. 10 shows the decoding of the y position of the scintillation event.

[0039] FIG. 11 is a schematic diagram showing the electronic design of a timing path according to this embodiment. In one embodiment, each analog signal from the optical sensor 210 can be processed by a high-pass filter and combined at the input of one high-bandwidth transimpedance amplifier (TIA). The combined timing signal is sent to a high-speed comparator and digitized by a time-to-digital converter (TDC). The design shown in FIG. 11 has the fewest components required for extracting timing information and is the most economical (i.e., least expensive) approach, but it may be difficult to obtain fine-grained information, such as when multiple gamma rays are incident on the array of miniblocks 215.

[0040] FIG. 12 is a schematic diagram showing the electronic design of a timing path according to this embodiment. In one embodiment, each of the miniblocks 215 requires the most electronic components or includes the most expensive timing path. The advantages of this design are that (i) the number of interconnected optical sensors 210 is minimized, and thus the influence of dark counts on the timing signal is minimized, and (ii) for Compton scattering events that accumulate energy in different miniblocks 215, this design can generate several timing signals and use this additional information to better estimate the timing of the interaction. Thus, this information can be used to classify events into single miniblock 215 events and multiple miniblock 215 events, thereby reducing the degradation caused by Compton scattering events.

[0041] FIG. 13 is a schematic diagram showing the electronic design of a timing path according to this embodiment. In one embodiment, the design for the timing path shown in FIG. 13 is a compromise design between the designs of FIGS. 11 and 12. The design of FIG. 13 uses fewer TDCs than the design of FIG. 12 in terms of cost, but more TIAs and comparators than the design of FIG. 11. The design of FIG. 13 is intermediate between the performances of the designs of FIGS. 11 and 12 in terms of performance.

[0042] FIG. 14 is a schematic diagram showing the electronic design of a timing path according to this embodiment. In one embodiment, the design regarding the timing path shown in FIG. 14 is another compromise design of the designs in FIGS. 11 and 12. The design in FIG. 14 uses more TDCs than the design in FIG. 13 in terms of cost, but the number of TDCs used in the design in FIG. 14 can range from 1 to 8. The design in FIG. 14 is between the performances of the designs in FIGS. 12 and 13 in terms of performance.

[0043] FIGS. 15A and 15B are schematic diagrams showing a non-1:1 design of a crystal 205 with a smaller pitch size according to this embodiment. In one embodiment, FIG. 15A shows a design including a 6×6 array of crystals 205 connected to a 4×4 array of optical sensors 210. The 6×6 array of crystals 205 can be divided into 3×6 miniblocks 215 in a state where each of the miniblocks 215 includes a 2×1 crystal 205 divided by one of the inner reflectors 220. Thereby, optical distribution occurs. In one embodiment, FIG. 15B shows a design including a 6×6 array of crystals 205 connected to a 4×4 array of optical sensors 210. Here, as shown, the 6×6 array of crystals 205 can be divided into 3×3 miniblocks 215 in a state including 2×2 crystals 205 where each of the miniblocks 215 is divided by two inner reflectors 220 orthogonal to each other.

[0044] FIG. 16 is a diagram showing a non-limiting example of a flowchart of a method for determining DOI and TOF according to this embodiment.

[0045] In one embodiment, step 1605 is a miniblock having a plurality of detector crystals, wherein a first detector crystal and a second detector crystal of the plurality of detector crystals are divided by an inner reflector, and the inner reflector detects light from a gamma-ray detection event incident on the first (or second) detector crystal via a first optical sensor in a detector block including the miniblock having various transmittances.

[0046] In one embodiment, step 1610 detects light due to a gamma ray detection event incident on the first (or second) detector crystal via a second photosensor within the detector block.

[0047] In one embodiment, step 1615 determines a first energy based on the intensity of the light detected by the first photosensor.

[0048] In one embodiment, step 1620 determines a second energy based on the intensity of the light detected by the second photosensor.

[0049] In one embodiment, step 1625 determines a DOI along an inner reflector of the detected light based on the first energy and the second energy. For example, the processing unit determines the DOI based on the ratio of the first energy to the second energy.

[0050] In one embodiment, step 1630 determines a first TOF value based on the light detected by the first photosensor.

[0051] In one embodiment, step 1635 determines a second TOF value based on the light detected by the second photosensor.

[0052] In one embodiment, step 1640 determines a TOF value in the miniblock based on the first TOF value and the second TOF value.

[0053] Figures 17A and 17B show a non-limiting example of a PET scanner (PET device) 700 capable of implementing the above-described method. The PET scanner 700 includes a number of gamma-ray detectors (GRDs) (e.g., GRD1, GRD2 to GRDN) (PET detectors), each configured as a rectangular detector module. According to one implementation form, the detector ring includes 40 GRDs. In another implementation form, there are 48 GRDs, and when a larger number of GRDs are used, a PET scanner 700 with a larger inner diameter dimension is produced.

[0054] Each GRD may include a two-dimensional array of individual detector crystals that absorb gamma rays and emit scintillation photons. The scintillation photons can also be detected by a two-dimensional array of photomultiplier tubes (PMTs) arranged in the GRD. A light guide may be arranged between the detector crystal array and the PMT.

[0055] Alternatively, the scintillation photons can be detected by an array of silicon photomultipliers (SiPMs), and each of the individual detector crystals can have a corresponding SiPM.

[0056] Each photodetector (e.g., PMT or SiPM) can generate an analog signal indicating the energy of the gamma ray that causes a detection event when a scintillation event occurs. Further, photons emitted from one detector crystal can be detected by two or more photodetectors, and the detector crystal corresponding to the detection event can be determined based on the analog signals generated by each photodetector, for example, using Anger logic and crystal decoding.

[0057] Figure 17B shows a schematic diagram of a PET scanner system (PET device) having a gamma-ray (gamma ray) photon counting detector (GRD) configured to detect gamma rays emitted from an object OBJ. The GRD can measure the timing, position, and energy corresponding to each gamma-ray detector. In one implementation, the gamma-ray detectors are arranged within a ring as shown in FIGS. 17A and 17B. The detector crystal can be a scintillator crystal, which has individual scintillator elements arranged in a two-dimensional array, and the scintillator elements can be made of any known scintillation material. The PMTs can be arranged such that light from each scintillator element is detected by a plurality of PMTs, enabling the Anger arithmetic and crystal decoding of the scintillation event.

[0058] Figure 17B shows an example of the structure of a PET scanner 700 in which the object OBJ to be imaged is placed on a top plate 716, and GRD modules GRD1 to GRDN are arranged in a circumferential direction around the object OBJ and the top plate 716. The GRD can be fixedly coupled to an annular component 720 that is fixedly coupled to the gantry 740. The gantry 740 houses a number of components of the PET imaging device. The gantry 740 of the PET imaging device also includes an opening through which the object OBJ and the top plate 716 can pass, and gamma rays emitted from the object OBJ in the opposite direction by annihilation events can be detected by the GRD, and the timing information and energy information can be used to determine the coincidence counting of gamma-ray pairs.

[0059] In FIG. 17B, circuits and hardware for acquiring, storing, processing, and distributing gamma-ray detection data are also shown. These circuits and hardware include a processor 770 (processing unit), a network controller 774, a memory 778, and a data acquisition system (DAS) 776. The PET imaging device also includes a data channel that sends detection measurement results from the GRD to the DAS 776, the processor 770, the memory 778, and the network controller 774. The DAS 776 can control the acquisition, digitization, and transmission of detection data from the detector. In one implementation, the DAS 776 controls the movement of the top plate 716. The processor 770 performs functions including image reconstruction from detection data, pre-processing of detection data for reconstruction, and post-processing of image data, as discussed herein.

[0060] Processor 770 can be configured to implement various steps of the methods described herein and variations thereof. Processor 770 may include a CPU implemented as individual logic gates, 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 encoded in VHDL, Verilog, or any other hardware description language, and the code may be stored directly in the electronic memory within the FPGA or CPLD or as separate electronic memory. Further, the memory may be non-volatile memory such as ROM, EPROM, EEPROM, or FLASH memory. The memory can be volatile memory such as static or dynamic RAM, and a processor such as a microcontroller or microprocessor may be provided to manage the interaction between the electronic memory and the FPGA or CPLD and the memory.

[0061] Alternatively, the CPU of the processor 770 can execute a computer program including a set of computer-readable instructions for performing various steps of the method, and this program is stored in any one of the above-mentioned non-transitory electronic memory and / or hard disk drive, CD, DVD, FLASH drive or any other known storage medium. Further, the computer-readable instructions may be provided as a component of a utility application, a background daemon, or an operating system, or a combination thereof, and are executed in conjunction with a processor such as the Intel Xeon processor of the United States or the Opteron processor of AMD of the United States, and an operating system such as Microsoft's VISTA, UNIX (registered trademark), Solaris, LINUX (registered trademark), Apple's MAC-OS and other operating systems known to those skilled in the art. Further, the CPU may be implemented as a plurality of processors that cooperate in parallel to execute instructions.

[0062] The memory 778 can be a hard disk drive, a CD-ROM drive, a DVD drive, a FLASH drive, a RAM, a ROM, or any other electronic storage device known in the art.

[0063] A network controller 774, such as an Ethernet PRO network interface card of Intel Corporation in the United States, can interface between various components of the PET imaging device. Additionally, the network controller 774 can also interface with an external network. As understood, this external network can be a public network such as the Internet, or a private network such as a LAN or WAN network, or a combination thereof, and can also include a PSTN or ISDN subnet network. This external network can be a wired method such as an Ethernet (registered trademark) network, or a wireless method such as a cellular network including EDGE, 3G, 4G, and 5G wireless cellular systems. The wireless network can be WiFi, Bluetooth (registered trademark), or any other known wireless form of communication.

[0064] In the foregoing description, specific details, for example, a specific form of the processing system, descriptions of various components and processes used therein, are set forth. However, it should be understood that the techniques of this specification may be implemented in other embodiments departing from these specific details, and such details are for illustrative purposes and not limiting. The embodiments disclosed in this specification have been described with reference to the accompanying drawings. Similarly, for purposes of explanation, specific numbers, materials, and configurations are described to provide a complete understanding. Nevertheless, the embodiments may be implemented without such specific details. Components having substantially the same functional configuration are denoted by similar reference numerals, and thus any duplicate descriptions may be omitted.

[0065] Various techniques are described as a plurality of distinct operations to assist in the understanding of various embodiments. The order of the description should not be construed to mean that these operations necessarily follow an order. In fact, these operations need not be performed in the order described. The described operations may be performed in an order different from that of the above-described embodiments. Various additional operations may be performed, and / or the described operations may be omitted in additional embodiments.

[0066] Regarding embodiments of the present disclosure and the like, the following appendices are disclosed as an aspect of the invention and optional features.

[0067] (1) A PET device, comprising a miniblock (detector crystal block) including a plurality of detector crystals, wherein a first detector crystal and a second detector crystal of the plurality of detector crystals are separated by an inner reflector, the inner reflector having a depth-dependent transmittance, the miniblock, and a first optical sensor configured to detect light from a gamma-ray detection event, wherein a first intensity of the light detected by the first optical sensor depends on the depth-dependent transmittance of the inner reflector, the first optical sensor, and a second optical sensor configured to detect light from a gamma-ray detection event, wherein a second intensity of the light detected by the second optical sensor depends on the depth-dependent transmittance of the inner reflector, the second optical sensor, a detector block (PET detector) including, and based on the detected first intensity, determining a first energy, based on the detected second intensity, determining a second energy, and based on the first energy and the second energy, configured to determine a depth of interaction (DOI) of a gamma-ray detection event, a processing circuit including.

[0068] (2) The PET device according to (1), wherein the inner reflector includes a plurality of openings, and the depth-dependent transmittance of the inner reflector is determined by the plurality of openings.

[0069] (3) The plurality of openings are divided into at least two sections along the inner reflector, and the first section of the at least two sections has a different density of the plurality of openings compared to the second section of the at least two sections. The PET device according to any one of (1) or (2).

[0070] (4) The first section of the at least two sections is arranged towards the upper part of the inner reflector, the upper part of the inner reflector is arranged opposite to the bottom of the inner reflector, the bottom of the inner reflector is arranged near the first optical sensor or the second optical sensor, and the density of the plurality of openings in the first section of the at least two sections is greater than the density of the plurality of openings in the second section of the at least two sections. The PET device according to any one of (1) to (3).

[0071] (5) The opening size of each opening of the plurality of openings is the same. The PET device according to any one of (1) to (4).

[0072] (6) The plurality of openings are separated into at least two sections along the inner reflector, and the first section of the at least two sections has a different opening size for each opening of the plurality of openings compared to the second section of the at least two sections. The PET device according to any one of (1) to (5).

[0073] (7) The opening size of each opening of the plurality of openings in the first section of the at least two sections is larger than the opening size of each opening of the plurality of openings in the second section of the at least two sections. The PET device according to any one of (1) to (6).

[0074] (8) The number of the plurality of openings in the first section of the at least two sections is the same as the number of the plurality of openings in the second section of the at least two sections. The PET device according to any one of (1) to (7).

[0075] (9) The inner reflector includes a first section having a first constant transmittance and a second section having a second constant transmittance, and the PET device according to any one of (1) to (8).

[0076] (10) The first constant transmittance is determined by a first film applied to the first section of the inner reflector, and the second constant transmittance is based on a second film applied to the second section of the inner reflector, and the PET device according to any one of (1) to (9).

[0077] (11) The first section is arranged toward the upper part of the inner reflector, the upper part of the inner reflector is arranged opposite to the bottom of the inner reflector, the second section is arranged toward the bottom of the inner reflector, the bottom of the inner reflector is arranged near the first optical sensor or the second optical sensor, and the first constant transmittance is higher than the second constant transmittance, and the PET device according to any one of (1) to (10).

[0078] (12) The first constant transmittance is determined by the thickness of the first section of the inner reflector, and the second constant transmittance is determined by the thickness of the second section of the inner reflector, and the PET device according to any one of (1) to (11).

[0079] (13) The inner reflector includes an upper part and a bottom part, the upper part of the inner reflector is arranged opposite to the bottom of the inner reflector, the bottom of the inner reflector is arranged near the first optical sensor or the second optical sensor, the thickness of the inner reflector increases from the upper part of the inner reflector toward the bottom of the inner reflector, and the depth-dependent transmittance is determined by the thickness of the inner reflector, and the PET device according to any one of (1) to (12).

[0080] (14) The processing circuit is further configured to determine the DOI based on the ratio of the first energy to the second energy, and the PET device according to any one of (1) to (13).

[0081] (15) The processing circuit is further configured to determine a first time-of-flight (TOF) value based on the light detected by the first optical sensor, determine a second TOF value based on the light detected by the second optical sensor, and determine a mini-block TOF value based on the first TOF value and the second TOF value, for the PET device according to any one of (1) to (14).

[0082] (16) The mini-block includes an outer reflector surrounding the mini-block along the side surface of the mini-block, for the PET device according to any one of (1) to (15).

[0083] (17) The number of the plurality of detector crystals is the same as the number of the optical sensors, for the PET device according to any one of (1) to (16).

[0084] (18) Detecting a first intensity of light due to a gamma-ray detection event incident on the first or second detector crystal via a first optical sensor in a detector block (PET detector) including a mini-block (detector crystal block) having a plurality of detector crystals including a first detector crystal and a second detector crystal separated by an inner reflector having depth-dependent transmittance; detecting a second intensity of light from a gamma-ray detection event incident on the first or second detector crystal via a second optical sensor in the detector block; determining a first energy based on the detected first intensity of the light; determining a second energy based on the detected second intensity of the light; and determining a depth of interaction (DOI) of the gamma-ray detection event based on the first energy and the second energy.

[0085] (19) Further including determining a first time-of-flight (TOF) value based on the light detected by the first optical sensor, determining a second TOF value based on the light detected by the second optical sensor, and determining a mini-block TOF value based on the first TOF value and the second TOF value, for the method according to (18).

[0086] (20) The step of determining the DOI further includes determining the DOI based on the ratio of the first energy to the second energy, the method according to (18) or (19).

[0087] According to at least one embodiment described above, while acquiring DOI information, the TOF resolution can be maintained.

[0088] Those skilled in the art will also understand that there may be many variations made to the operation of the techniques described above while still achieving the same object of the present invention. Such variations are intended to be included within the scope of this disclosure. Thus, the above description of the embodiments of the present invention is not intended to be limiting. Rather, any limitations to the embodiments of the present invention are set forth in the following claims.

Description of Reference Numerals

[0089] 200 PET detector 205 Crystal 210 Optical sensor 215 Mini-block 220 Inner reflector 225 Outer reflector 700 PET scanner 770 Processor

Claims

1. A detector crystal block including a plurality of detector crystals including a first detector crystal and a second detector crystal, and an inner reflector provided between the first detector crystal and the second detector crystal so that the light transmittance varies for each depth of the detector crystal; A first optical sensor that detects a first intensity of light depending on the transmittance of the inner reflector; A second optical sensor that detects a second intensity of light depending on the transmittance of the inner reflector; A PET detector having the above; A processing unit that determines a first energy based on the first intensity, determines a second energy based on the second intensity, and determines a depth of interaction (Depth Of Interaction: DOI) of gamma rays in the detector crystal block based on the first energy and the second energy; A PET apparatus comprising the above.

2. The PET apparatus according to claim 1, wherein the inner reflector has a plurality of openings that determine the light transmittance for each depth of the detector crystal.

3. The PET apparatus according to claim 2, wherein the plurality of openings are divided into at least two sections along the inner reflector, and a first section of the at least two sections has the openings with a different density compared to a second section of the at least two sections.

4. The PET apparatus according to claim 3, wherein the first section is disposed on the opposite side of the first optical sensor or the second optical sensor side, and the density of the openings is higher than the density of the openings in the second section.

5. The PET apparatus according to claim 4, wherein the opening size of each opening of the plurality of openings is the same.

6. The PET apparatus according to claim 2, wherein the plurality of openings are separated into at least two sections along the inner reflector, and a first section of the at least two sections has openings of different sizes compared to a second section of the at least two sections.

7. The PET apparatus according to claim 6, wherein the size of each opening in the first section is larger than the size of each opening in the second section.

8. The PET apparatus according to claim 7, wherein the number of openings in the first section is the same as the number of openings in the second section.

9. The PET device according to claim 1, wherein the inner reflector includes a first section having a first transmittance and a second section having a second transmittance.

10. The PET device according to claim 9, wherein the first transmittance is determined by a first film applied to the first section of the inner reflector, and the second transmittance is determined by a second film applied to the second section of the inner reflector.

11. The PET device according to claim 10, wherein the first section is disposed on the side opposite to the first optical sensor or the second optical sensor, and the first transmittance is higher than the second transmittance.

12. The PET device according to claim 9, wherein the first transmittance is determined by the thickness of the first section of the inner reflector, and the second transmittance is determined by the thickness of the second section of the inner reflector.

13. The inner reflector includes a bottom portion on the side of the first optical sensor or the second optical sensor, and an upper portion on the side opposite to the bottom portion. The PET device according to claim 1, wherein the thickness of the inner reflector increases from the upper portion toward the bottom portion, and the transmittance is determined by the thickness of the inner reflector.

14. The PET device according to claim 1, wherein the processing unit determines the DOI based on a ratio of the first energy and the second energy.

15. The PET device according to claim 1, wherein the processing unit determines a first time-of-flight (TOF) value based on the light detected by the first optical sensor, determines a second TOF value based on the light detected by the second optical sensor, and determines a TOF value of a detector crystal block based on the first TOF value and the second TOF value.

16. The PET device according to claim 1, wherein the detector crystal block includes an outer reflector surrounding the detector crystal block along a side surface of the detector crystal block.

17. The PET device according to claim 1, wherein the number of the plurality of detector crystals is the same as the number of the optical sensors.

18. A first optical sensor in a PET detector including a detector crystal block including a plurality of detector crystals including a first detector crystal and a second detector crystal, and an inner reflector provided between the first detector crystal and the second detector crystal such that the light transmittance varies for each depth of the detector crystal, detects a first intensity of light depending on the transmittance of the inner reflector, a second optical sensor in the PET detector detects a second intensity of light depending on the transmittance of the inner reflector, determines a first energy based on the first intensity, determines a second energy based on the second intensity, and determines a depth of interaction (DOI) of gamma rays in the detector crystal block based on the first energy and the second energy. A method comprising the above.

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