JP6508343B2 - Radiation detector and detector module - Google Patents

Description

  The present invention relates to a radiation detector and a detector module used in a nuclear medicine diagnostic apparatus and the like taking a positron emission tomography apparatus (PET apparatus) as an example.

  Conventionally, as medical imaging methods, nuclear medicine diagnosis using positron emission tomography (PET) as an example is known. A positron emission tomography apparatus (PET apparatus) is an apparatus that generates a radiation image showing the distribution of a radiopharmaceutical labeled with a positron-emitting radionuclide in a subject.

  The PET apparatus comprises a plurality of radiation detectors arranged to surround the subject in a ring. The radioactive agent administered to the subject is accumulated at the site of interest and positrons are emitted from the accumulated agent. The emitted positrons annihilate with the electrons and produce a pair of gamma rays with opposite momentum. A pair of gamma rays are emitted in opposite directions to each other, and each gamma ray is simultaneously detected by the radiation detector. The position of the radioactive drug is calculated based on the information of the detected γ-ray, and a radiation image showing the distribution of the radioactive drug at the site of interest is provided by the PET device.

  The radiation detector includes a scintillator that absorbs radiation and converts it into light, and a photodetector using SiPM (Silicon Photo Multiplier) or the like. The SiPM has a configuration in which a large number of APDs (Avalanche Photo Diodes) are disposed as light receiving elements (photoelectric conversion elements), and the influence of the magnetic field is very small. Therefore, SiPM can also be used as a photodetector for PET-MR in which a magnetic resonance tomography apparatus (MR apparatus) suitable for anatomic diagnosis and a PET apparatus suitable for physiological function diagnosis are combined (for example, a patent) Reference 1).

  Here, the configuration of a conventional radiation detector using SiPM will be described with reference to the drawings. As shown in FIG. 10A, the conventional radiation detector 101 is configured by optically joining a scintillator 103 and a SiPM 105 that is a light detector. The scintillator 103 interacts with the γ ray to generate a large number of photons (photons). The SiPM 105 receives photons generated from the scintillator 103 and converts it into an electric signal. Then, as shown in FIG. 10A, a large number of radiation detectors 101 are arranged in a one-dimensional matrix form or a two-dimensional matrix form to constitute a detector module 101a.

  As shown in FIG. 10C, in the SiPM 105, a large number of microcells 107 are arranged in a two-dimensional matrix. Each microcell 107 is provided with APD109 which is a photoelectric conversion element, and quenching resistance 111, as shown in FIG.10 (d). That is, when photons are incident on the APD 109, the photons are converted into electric signals, and are output from the SiPM 105 as γ-ray detection signals. As shown in FIG. 10C, in the microcell 107, the area where the APD 109 is provided (area with halftone dots) is the light receiving area 107a.

  Each of the radiation detectors 101 includes a power source 121, a preamplifier 113, a comparator 115, and a shaping amplifier 117, as shown in FIGS. 11 (a) and 11 (b). The power supply 121 applies a bias voltage V required for the output of the γ-ray detection signal to each of the microcells 107 provided in the light detector 105. The preamplifier 113 is provided downstream of the SiPM 105, and amplifies an output signal from the SiPM 105 to convert it into a voltage. The comparator 115 and the shaping amplifier 117 are connected to the preamplifier 113, respectively. One of the amplified and converted output signals is input to the comparator 115, and the other of the output signals is input to the shaping amplifier 117.

  The comparator 115 derives, as timing information, information on the time when the γ ray is detected, based on the input output signal. That is, the electric signal indicating the timing information is output based on the time when the photon detection amount in the microcell 107 exceeds the predetermined threshold set in advance. The shaping amplifier 117 further amplifies and shapes the input output signal to acquire a pulse having a pulse height proportional to the energy of the incident γ-ray. Based on the pulse height of the pulse acquired by the shaping amplifier 117, information on the detected energy level of the γ ray is output as energy information.

  Thus, each of the radiation detectors 101 is configured to transmit the output signal to each of the comparator 115 and the shaping amplifier 117, thereby providing information on the time when the γ ray is detected (timing information) and the energy information of the detected γ ray. It can acquire (for example, refer nonpatent literature 1, 2). In recent years, the radiation detector 101 has often been used for a TOF (Time Of Flight) PET apparatus in order to detect the distribution of radiopharmaceuticals more precisely. Therefore, in the radiation detector 101, a demand for further improving the resolution (timing resolution) of timing information is increasing.

JP, 2008-311651, A

“Development of a PET Detector Module”, IEEE NSS and MIC 2014 N07-8 “Timing Resolution Dependency on MPPC Performance Parameters”, IEEE NSS and MIC 2014 N26-3

  However, in the case of the conventional example having such a configuration, there is a concern that it is difficult to improve the timing resolution while maintaining high energy information resolution (energy resolution). Hereinafter, problems in the conventional radiation detector will be described.

  The pulse height of the signal output from the SiPM 105 does not change with the number of photons incident on one microcell 107. Therefore, in order to maintain the linearity between the number of photons incident on the SiPM 105 and the pulse wave height output from the SiPM 105, it is necessary to increase the number of microcells 107 provided in the SiPM 105. That is, by increasing the number of microcells 107, simultaneous incidence of a plurality of photons on the same microcell 107 can be avoided, so that the linearity between the number of incident photons and the output can be suitably maintained. As a result, energy resolution in the radiation detector 101 can be improved.

  However, in the conventional radiation detector 101, when the pitch of the microcells 107 is reduced to increase the number of microcells 107 per unit area, there is a concern that the timing resolution may be degraded. That is, in each of the microcells 107, since the partition wall is provided on the peripheral edge portion 107b of the light receiving area 107a, the peripheral edge portion 107b of the microcell 107 becomes a photon insensitive portion. Then, as the number of microcells 107 provided in the SiPM 105 increases, the area of the light receiving area 107a decreases in the light detection surface (xy plane) of the SiPM 105, and thus the photon detection efficiency (PDE) of the SiPM 105 decreases.

  In order to improve the timing resolution of the radiation detector 101, from the time when photons are generated in the scintillator 103, the fluctuation of the time from when the photons reach the microcell 107 and the photon detection amount exceeds a predetermined threshold is reduced. is important. Therefore, when the photon detection efficiency of the SiPM 105 is lowered, the fluctuation of time until the photon detection amount exceeds the predetermined threshold value becomes large, and the timing resolution of the radiation detector 101 is lowered.

  On the other hand, when the pitch of the microcells 107 is increased to widen the light receiving area 107a of the microcell 107 per unit area in order to improve the timing resolution of the radiation detector 101, the number of microcells 107 per unit area decreases. Do. In this case, since the probability that two or more photons simultaneously enter the same microcell 107 increases, the linearity between the number of incident photons and the output deteriorates. As a result, the energy resolution in the radiation detector 101 is reduced.

  Thus, there is a contradiction between the specifications required to improve the energy resolution and the specifications required to improve the timing resolution. Therefore, in the conventional radiation detector 101, it is very difficult to improve both the energy resolution and the timing resolution.

  The present invention has been made in view of such circumstances, and can be used for PET devices such as TOF-PET devices, and is a radiation detector and detector having high energy resolution and high timing resolution. The purpose is to provide a module.

The present invention has the following configuration in order to achieve such an object.
That is, a radiation detector according to the present invention includes at least one scintillator that detects incident radiation and emits light, and a first light receiving element and a second light receiving element that convert light emitted from the scintillator into an electrical signal. At least one light detection means, each arranged in a matrix, optically coupled to the scintillator, and the electric signal converted by the first light receiving element, relates to the time when the radiation is incident on the scintillator The timing information acquisition circuit for acquiring timing information which is information, and the energy information acquisition circuit for acquiring energy information which is information related to the energy of the radiation incident on the scintillator based on the electric signal converted by the second light receiving element A first bias applying a first bias voltage to the first light receiving element A pressure supply, to said second light receiving element, and a second bias voltage supply source for applying a lower second bias voltage than said first bias voltage, for a single previous SL scintillator, at least one the first light receiving element and at least one of said second light receiving element is characterized in that it is light histological bound.

  [Operation / Effect] According to the X-ray imaging apparatus of the present invention, the light detection means is provided with the first light receiving element and the second light receiving element for converting the light emitted by the scintillator into an electric signal. The timing information acquisition circuit acquires timing information based on the electrical signal of the first light receiving element, and the energy information acquisition circuit acquires energy information based on the electrical signal of the second light receiving element.

  Each of the scintillators is optically coupled to each of the at least one first light receiving element and the at least one second light receiving element. That is, after the radiation incident on the scintillator is converted into light, a part becomes timing information through the first light receiving element, and the remaining part becomes energy information through the second light receiving element.

  That is, a first light receiving element which is a light receiving element for acquiring timing information and a second light receiving element which is a light receiving element for acquiring energy information are separately provided. In this case, it is possible to set the specification to improve the timing resolution for the first light receiving element, and to set the other specification to improve the energy resolution for the second light receiving element. Therefore, it is possible to preferably improve both the timing resolution and the energy resolution in the radiation detector.

The present invention may have the following configuration in order to achieve such an object.
That is, in the radiation detector according to the present invention, at least one scintillator for detecting incident radiation and emitting light, and a first light receiving element for converting the light emitted from the scintillator into an electric signal are arranged in a matrix And at least one first light detecting means optically coupled to the scintillator, and a second light receiving element for converting light emitted from the scintillator into an electric signal, which is disposed in a matrix, Timing information for acquiring timing information, which is information on the time when the radiation is incident on the scintillator, based on at least one second light detection unit optically coupled and the electric signal converted by the first light receiving element The radiation incident on the scintillator based on an acquisition circuit and an electrical signal converted by the second light receiving element. An energy information acquisition circuit that acquires energy information that is information related to the energy of the first light source; a first bias voltage supply power source that applies a first bias voltage to the first light receiving element; and a second bias voltage supply source for applying a lower than the first bias voltage second bias voltage, to one of the previous SL scintillator, at least one of said first light receiving element and at least one of said second light receiving element There characterized in that it optically histological bound.

  [Operation / Effect] According to the radiation detector of the present invention, the first light detection means comprises the first light receiving element, and the second light detection means comprises the second light receiving element. The timing information acquisition circuit acquires timing information based on the electrical signal of the first light receiving element, and the energy information acquisition circuit acquires energy information based on the electrical signal of the second light receiving element.

  Each of the scintillators is optically coupled to each of the at least one first light receiving element and the at least one second light receiving element. That is, after the radiation incident on the scintillator is converted into light, a part becomes timing information through the first light receiving element, and the remaining part becomes energy information through the second light receiving element.

  That is, a first light receiving element which is a light receiving element for acquiring timing information and a second light receiving element which is a light receiving element for acquiring energy information are separately provided. In this case, it is possible to set the specification to improve the timing resolution for the first light receiving element, and to set the other specification to improve the energy resolution for the second light receiving element. Therefore, it is possible to preferably improve both the timing resolution and the energy resolution in the radiation detector.

  The first light detection means having the first light receiving element and the second light detection means having the second light receiving element have different configurations. Therefore, the existing light detection means having a specification for improving the timing resolution as the first light detection means, and the existing light detection means having another specification for improving the energy resolution a second light detection Each can be diverted as a means. That is, since it is not necessary to newly manufacture the light detection means provided with the first light receiving element and the second light receiving element, the radiation detector according to the present invention can be manufactured more easily.

  [Operation and Effect] According to the radiation detector of the present invention, the first bias voltage supply power source applies the first bias voltage to the first light receiving element. The second bias voltage supply applies a second bias voltage lower than the first bias voltage to the second light receiving element. In such a configuration, a first bias voltage, which is a relatively high voltage, is applied to the first light receiving element. By increasing the bias voltage, the timing resolution obtained from the light receiving element is improved. Therefore, higher resolution timing information can be acquired based on the electrical signal output from the first light receiving element for acquiring timing information.

  On the other hand, a second bias voltage lower than the first bias voltage is applied to the second light receiving element. Lowering the bias voltage improves the energy resolution obtained from the light receiving element. Therefore, higher resolution energy information can be acquired based on the electrical signal output from the second light receiving element for acquiring energy information.

  In the invention described above, it is preferable that the area of the light receivable area per unit area of the first light receiving element is wider than the area of the light receivable area per unit area of the second light receiving element. .

  According to the radiation detector of the present invention, the area of the light receivable area per unit area of the first light receiving element is larger than the area of the light receivable area per unit area of the second light receiving element. Configured By widening the area of the light receivable region per unit area, the timing resolution acquired from the light receiving element is improved. Therefore, higher resolution timing information can be acquired based on the electrical signal output from the first light receiving element for acquiring timing information.

  On the other hand, as the area of the light receiving region of the second light receiving element per unit area is narrowed, the number of photons is decreased, and the energy resolution obtained from the light receiving element is slightly reduced. However, as described above, it is possible to prevent deterioration by devising the pitch of the microcell to improve the linearity, etc., and to obtain higher resolution energy information.

Further, in the invention described above, the area of the second light receiving element is preferably 2% to 40% of the area of the first light receiving element.

  According to the radiation detector of the present invention, the area of the second light receiving element in the light detection surface of the light detection means is 2% of the area of the first light reception element in the light detection surface of the light detection means 40%. In this case, the timing resolution acquired using the first light receiving element is suitably improved while maintaining the energy resolution acquired using the second light receiving element. Therefore, more accurate information can be acquired about the radiation which injects into a radiation detector.

  Also disclosed is a detector module in which a plurality of radiation detectors according to the present invention are arranged in one or two dimensions. Such a detector module has the effect of the radiation detector according to the invention and makes it possible to preferably improve both timing resolution and energy resolution. Therefore, by applying such a detector module to various PET devices, particularly TOF-PET, both energy resolution and timing resolution can be improved. As a result, in nuclear medicine diagnosis using a PET apparatus or the like, it is possible to perform more appropriate diagnosis by acquiring a radiation image that more accurately displays the distribution of a radiation drug.

  According to the radiation detector and the detector module according to the present invention, the light detection means includes the first light receiving element and the second light receiving element for converting the light emitted by the scintillator into an electric signal. The timing information acquisition circuit acquires timing information based on the electrical signal of the first light receiving element, and the energy information acquisition circuit acquires energy information based on the electrical signal of the second light receiving element.

  Each of the scintillators is optically coupled to each of the at least one first light receiving element and the at least one second light receiving element. That is, after the radiation incident on the scintillator is converted into light, a part becomes timing information through the first light receiving element, and the remaining part becomes energy information through the second light receiving element.

  That is, a first light receiving element which is a light receiving element for acquiring timing information and a second light receiving element which is a light receiving element for acquiring energy information are separately provided. In this case, it is possible to set the specification to improve the timing resolution for the first light receiving element, and to set the other specification to improve the energy resolution for the second light receiving element. Therefore, it is possible to preferably improve both the timing resolution and the energy resolution in the radiation detector.

FIG. 1 is a diagram showing an entire configuration of a radiation detector according to a first embodiment. (A) is a bird's-eye view showing the entire configuration of the radiation detector, (b) is a bird's-eye view showing the overall configuration of the detector module configured by arranging the radiation detector in a matrix, (c) FIG. 1 is a longitudinal sectional view showing the entire configuration of a PET apparatus configured using a detector module. FIG. 2 is a diagram showing a configuration of a light detector according to a first embodiment. (A) is a top view which shows the structure of a photodetector, (b) is a figure which shows the structure of a microcell. It is a top view which shows the example of the array pattern of microcells about the radiation detector which concerns on Example 1. FIG. (A) is a diagram showing a pattern in which microcells 15b are arrayed in a one-dimensional direction, (b) is a diagram showing a pattern in which microcells 15b are densely arranged in a two-dimensional matrix, and (c) is a diagram It is a figure which shows the pattern which the microcell 15a and the microcell 15b disperse | distribute and arrange. It is a figure which shows the structure which changes a specification with respect to each microcell about the radiation detector which concerns on Example 1. FIG. (A) is a bird's-eye view which shows the structure which applies a different bias voltage with respect to each microcell, (b) is a circuit diagram which shows the structure which applies a different bias voltage with respect to each microcell. It is a top view which shows the example of the array pattern of microcells about the radiation detector which concerns on Example 2. FIG. (A) is a diagram showing a pattern in which microcells 15b are arrayed in a one-dimensional direction, (b) is a diagram showing a pattern in which microcells 15b are densely arranged in a two-dimensional matrix, and (c) is a diagram It is a figure which shows the pattern which the microcell 15a and the microcell 15b disperse | distribute and arrange. It is a figure which shows the structure which changes a specification with respect to each microcell about the radiation detector which concerns on Example 2. FIG. (A) is a bird's-eye view which shows the structure which applies the same bias voltage with respect to each microcell, (b) is a circuit diagram which shows the structure which applies the same bias voltage with respect to each microcell, respectively. FIG. 7 is a diagram showing the configuration of a radiation detector according to a third embodiment. (A) is a bird's-eye view showing the entire configuration of the radiation detector, (b) is a view showing an example of an array pattern in which the pitch length of the microcell 15a is the same as the pitch length of the microcell 15b c) shows an example of an array pattern in which the pitch length of the microcell 15a is longer than the pitch length of the microcell 15b. It is a figure which shows the structure which changes a specification with respect to each microcell about the radiation detector which concerns on Example 3. FIG. (A) is a bird's-eye view which shows the structure which applies a different bias voltage with respect to each microcell, (b) is a circuit diagram which shows the structure which applies a different bias voltage with respect to each microcell. It is a figure showing the whole radiation detector composition concerning a modification. (A) is a bird's-eye view showing the entire configuration of the radiation detector, (b) is a bird's-eye view showing the overall configuration of the detector module configured by arranging the radiation detector in a matrix, (c) These are top views which show the example of the array pattern of microcell. It is a figure which shows the whole structure of the radiation detector which concerns on a prior art example. (A) is a bird's-eye view showing the entire configuration of the radiation detector, (b) is a bird's-eye view showing the overall configuration of the detector module configured by arranging the radiation detector in a matrix, (c) These are top views which show the structure of the photodetector in which a micro cell is arranged, (d) is a figure which shows the structure of a micro cell. It is a figure which shows the structure of the radiation detector which concerns on a prior art example. (A) is a bird's-eye view which shows the structure which applies a bias voltage with respect to each microcell, (b) is a circuit diagram which shows the structure which applies a bias voltage with respect to each microcell.

  The first embodiment of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1A, the radiation detector 1 according to the first embodiment is configured by optically joining the scintillator 3 and the light detector 5. The scintillator 3 is made of LYSO, LFS or the like, and generates a large number of photons by interaction with the incident γ-ray. The photodetector 5 detects photons generated from the scintillator 3 and converts it into an electrical signal. In the first embodiment, the light detector 5 corresponds to the light detection means in the present invention.

  An example of the light detector 5 includes SiPM configured by arranging light receiving elements in a matrix. The first embodiment will be described using SiPM as the light detector 5. As shown in FIG. 1B, the detector module 2 is configured by arranging a large number of radiation detectors 1 in the one-dimensional direction or two-dimensional direction on the substrate 6.

  The configuration of the PET device 7 provided with the radiation detector 1 according to the first embodiment is as shown in FIG. 1 (c). That is, the PET apparatus 7 is provided with a gantry 11 provided with an introduction hole 9 for introducing a subject. A housing 13 is provided inside the gantry 11. Inside the housing 13, the detector modules 2 are arranged in a ring shape so as to surround the introduction hole 9. Each of the radiation detectors 1 and the housing 13 are connected by a connection base 14. In FIG. 1C, the direction from the center Mo of the introduction hole 9 to the detection surface (xy plane) of the detector module 2 is the incident direction of the γ ray.

  Although the number of detector modules 2 arranged in a ring in FIG. 1C is eight, the number of detector modules 2 forming a ring structure may be changed as appropriate. Moreover, as PET apparatus 7 used as the application object of the radiation detector 1, various types of PET apparatuses, such as TOF-PET and PET-MR other than a normal PET apparatus, can be used.

  Next, the structure of the light detector 5 will be described. As shown in FIG. 2A, a large number of microcells 15 are arranged in a two-dimensional matrix, as shown in FIG. 2A. Each microcell 15 is provided with an APD 17 and a quenching resistor 19 as shown in FIG. 2 (b). The APD 17 is a photoelectric conversion element that converts light into electrical information, detects photons incident on the microcell 15, and converts the photon into an electrical signal. The microcell 15 corresponds to the light receiving element in the present invention.

  An area occupied by the APD 17 in the microcell 15 and capable of detecting photons is referred to as a light receiving area F. On the other hand, in the microcell 15, on the periphery of the light receiving area F, a partition made of a photon insensitive material is provided. An area in which such a partition wall is provided is referred to as a dead area N. As described above, in the radiation detector 1 according to the first embodiment, one photodetector 5 is optically coupled to one scintillator 3. Then, photons generated in one scintillator 3 are converted into electric signals by each of the plurality of microcells 15 arranged in the light detector 5, and are output from the light detector 5 as a γ-ray detection signal.

<Characteristic Configuration in Embodiment 1>
Here, the characteristic configuration of the radiation detector 1 according to the first embodiment will be described. The radiation detector 1 has a microcell 15 for acquiring information (timing information) of a time during which a γ ray is incident to one scintillator 3 and a microcell for acquiring information (energy information) regarding the energy of the incident γ ray. It has a configuration in which the cell 15 is separated.

  That is, as shown in FIG. 3A, the detection surface of the light detector 5 is disposed so that the microcell 15a used for acquiring timing information and the microcell 15b used for acquiring energy information are mixed. It is done. For convenience of explanation, in FIG. 3 and later, the microcell 15a indicates the light receiving area F by halftone dots, and the microcell 15b indicates the light receiving area F by hatching to distinguish them. Each of the microcells 15a corresponds to a first light receiving element in the present invention, and each of the microcells 15b corresponds to a second light receiving element in the present invention.

  The arrangement pattern of the microcells 15a and the microcells 15b on the detection surface of the photodetector 5 is not limited to the pattern shown in FIG. 3A, and may be changed as appropriate. That is, as shown in FIG. 3 (b), the microcells 15a may be densely arranged at appropriate positions such as the central region of the light detector 5. Further, as shown in FIG. 3C, each of the microcells 15a and each of the microcells 15b may be dispersed over the entire surface of the photon detection surface of the photodetector 5.

  In the light detector 5, the total area of the microcells 15b is preferably 2% to 40%, and more preferably 3% to 30% of the total area of the microcells 15a. The most preferable example is about 10%. In the first embodiment, the total area of the microcells 15b is about 10% of the total area of the microcells 15a.

  The radiation detector 1 further includes a first power supply 21, a second power supply 23, a first preamplifier 25, a second preamplifier 27, and a comparator 29, as shown in FIGS. 4 (a) and 4 (b). , Shaping amplifiers 31 respectively. The first power supply 21 and the second power supply 23 are voltage supply power supplies for applying a bias voltage. The first power supply 21 applies a bias voltage V1 to each of the microcells 15a. The first power supply 23 applies a bias voltage V2 to each of the microcells 15b. The height of the bias voltage V1 is adjusted to be higher than the height of the bias voltage V2.

  The first power supply 21 corresponds to a first bias voltage supply power supply in the present invention. The second power supply 23 corresponds to a second bias voltage supply in the present invention. The bias voltage V1 corresponds to the first bias voltage in the present invention. The bias voltage V2 corresponds to the second bias voltage in the present invention.

  The first preamplifier 25 is connected to the microcell 15a, and amplifies an output signal from the microcell 15a to convert it into a voltage. The second preamplifier 27 is connected to each of the microcells 15b, and amplifies the signal output from each of the microcells 15b and converts it into a voltage. The comparator 29 is connected to the first preamplifier 25 and outputs timing information based on the output signal amplified and converted by the first preamplifier 25. That is, the timing information is output from the comparator 29 based on the time when the photon detection amount in the microcell 15a exceeds a predetermined threshold. The first preamplifier 25 and the comparator 29 correspond to the timing information acquisition circuit in the present invention.

  The shaping amplifier 31 is connected to the second preamplifier 27 and outputs energy information based on the output signal amplified and converted by the second preamplifier 27. That is, by further amplifying and shaping the output signal of the second preamplifier 27, a pulse having a wave height proportional to the energy of photons incident on the microcell 15b is acquired. Based on the pulse height of the pulse acquired by the shaping amplifier 31, information on the height of the energy of the γ ray incident on the scintillator 3 is output from the shaping amplifier 31 as energy information. The second preamplifier 27 and the shaping amplifier 31 correspond to the energy information acquiring circuit in the present invention.

  Each of the timing information and energy information obtained for one scintillator 3 is sent to a coincidence circuit not shown. That is, timing information and energy information in each of the scintillators 3 provided in each of the detector modules 2 are transmitted to the coincidence circuit. Further, positional information of the scintillator 3 for outputting timing information and energy information is also transmitted to the coincidence circuit. The coincidence circuit detects the position information of the γ-ray electron pair generated by the annihilation of the same positron based on the timing information, energy information and position information of all the scintillators 3 provided in the PET device 7 . Then, based on the position information of the γ-ray electron pair, a radiation image representing the distribution of the radiation agent is generated.

  As described above, the radiation detector 1 includes the microcell 15a used for outputting timing information and the microcell 15b used for outputting energy information. Therefore, each of the microcells 15a and each of the microcells 15b can be set to different standards (specifications). That is, the microcell 15a can be set to a predetermined specification that improves the timing resolution, and the microcell 15b can be set to another specification that the energy resolution improves.

  The radiation detector 1 according to the first embodiment is configured to improve both the timing resolution and the energy resolution by setting the bias voltages to be applied to different heights. That is, the bias voltage V1 which is a relatively high voltage is applied by the first power supply 21 to each of the microcells 15a used for acquiring timing information among the plurality of microcells 15 optically coupled to one scintillator 3 Ru. On the other hand, a bias voltage V2, which is a relatively low voltage, is applied by the second power supply 23 to each of the microcells 15b used to acquire energy information.

  When raising the height of the bias voltage, the photon detection efficiency (PDE) is increased, so that the fluctuation of time until the photon detection amount exceeds the predetermined threshold value is reduced. Therefore, by applying a high voltage bias voltage V1 to the microcell 15a, the timing resolution acquired by the microcell 15a is improved.

  On the other hand, when raising the PDE, the probability that the same microcell 15 detects photons at the same time increases, and the energy resolution obtained based on the output of the microcell decreases. However, the microcell 15 a is a microcell used exclusively for acquiring timing information in the scintillator 3. Therefore, even if the PDE in the microcell 15a rises, the energy resolution in the scintillator 3 does not decrease. Therefore, by applying the high-voltage bias voltage V1 to the microcell 15a, the scintillator 3 can enjoy only the advantageous effect of improving the timing resolution.

  On the other hand, when the height of the bias voltage is lowered, the photon detection efficiency is lowered, so the probability that two or more photons are simultaneously detected in the same microcell can be reduced. Therefore, by applying a low voltage bias voltage V2 to the microcell 15b, the energy resolution obtained by the microcell 15b is improved.

  Note that the degradation of PDE reduces the timing resolution obtained based on the output of the microcell. However, the microcell 15 b is a microcell used exclusively for acquiring energy information in the scintillator 3. Therefore, even if the PDE in the microcell 15b decreases, the timing resolution in the scintillator 3 does not decrease. Therefore, by applying the relatively low voltage bias voltage V2 to the microcell 15b, only the advantageous effect of improving the energy resolution can be obtained in the scintillator 3.

  As described above, in the first embodiment, the specification is made such that the PDE is relatively high for the microcell 15a for timing information acquisition, and the PDE is relatively low for the microcell 15b for energy information acquisition. Set to another specification that you want to Specifically, by changing the height of the bias voltage (supply voltage) between the microcell 15a and the microcell 15b, it is possible to improve the energy resolution while improving the timing resolution.

<The effect by the structure of Example 1>
In the radiation detector 1 according to the first embodiment, the scintillator 3 and the photodetector 5 are optically coupled in a one-to-one manner. The photodetector 5 is provided with a microcell 15a used to acquire timing information and a microcell 15b used to acquire energy information.

  In the conventional radiation detector, as shown in FIGS. 11A and 11B, the electrical signals output from each of the microcells 107 are transmitted in parallel to the comparator 115 and the shaping amplifier 117. Then, timing information is acquired based on the output of the comparator 115, and energy information is acquired based on the output of the shaping amplifier 117. That is, the microcells 107 provided in the light detector 105 are both used for both acquisition of timing information and acquisition of energy information.

  Therefore, in the conventional radiation detector 101, it is difficult to achieve both high timing resolution and high energy resolution. That is, if the bias voltage V applied to all the microcells 107 is increased to improve the accuracy of timing information, the photon detection efficiency (PDE) is increased. As a result, the probability that the same microcell 107 detects two or more photons at the same time increases, and the accuracy of the energy information decreases. On the other hand, if the bias voltage V applied to all the microcells 107 is lowered to improve the accuracy of the energy information, the photon detection efficiency is lowered. As a result, since the fluctuation of time during which the photon detection amount exceeds the predetermined threshold value becomes large, the accuracy of the timing information decreases.

  Therefore, in the radiation detector 1 according to the first embodiment, among the plurality of microcells 15 provided in the light detector 5, some are microcells 15a exclusively used for acquiring timing information. The other part is a microcell 15b exclusively used for acquiring energy information. As described above, in the radiation detector 1, one microcell 15 a dedicated to acquiring timing information and one microcell 15 b dedicated to acquiring energy information are respectively optically coupled to one scintillator 3.

  A first power supply 21 applying a relatively high voltage bias voltage V1 is connected to the microcell 15a, and a second power supply 23 applying a relatively low voltage bias voltage V2 is connected to the microcell 15b. . Therefore, in the radiation detector 1, bias voltages different in height can be applied to each of the microcell 15a and the microcell 15b.

  By applying the bias voltage V1 of high voltage to the microcell 15a dedicated to timing information acquisition, it is possible to improve the accuracy of timing information while avoiding a decrease in energy resolution. Then, by applying a low voltage bias voltage V2 to the microcell 15b dedicated to energy information acquisition, it is possible to improve the accuracy of energy information while avoiding a decrease in timing resolution. As a result, it is possible to improve both the timing resolution and the energy resolution in the radiation detector 1.

  In recent years, a lutetium-based (Lu-based) material such as LYSO or LFS is used as the scintillator 3. Such a Lu-based scintillator has a luminescence amount about 10 times as large as that of a bismuth-based scintillator such as BGO used conventionally. Here, as a result of examination by the inventor, there was no difference in the energy resolution between the Lu-based scintillator and the bismuth-based scintillator, which was about 15%, although the light emission amount largely differs.

  That is, when the microcells contributing to the acquisition of energy information among all the microcells are about 10% of the microcells contributing to the acquisition of timing information, the timing resolution can be improved while maintaining the energy resolution of the radiation detector. It becomes. And as a result of further earnest examination, when the microcell 15b contributing to the acquisition of energy information is about 2% to 40% of the microcell 15a contributing to the acquisition of timing information, the effect of the present invention is suitably exhibited. found.

  Thus, the timing information and the energy information about the γ ray incident on the scintillator 3 can be obtained by the configuration in which one or more microcells 15a and one or more microcells 15b are optically coupled to one scintillator 3 respectively. Both can improve the accuracy. Then, by using the radiation detector 1 composed of the scintillator 3 and the light detector 5, it is possible to realize the PET device 7 in which high timing resolution and high energy resolution are compatible for γ-rays. As a result, a more accurate radiological image can be acquired for the distribution of the radiological drug, so that a more accurate diagnosis can be performed on the subject M.

  In recent years, in particular, there has been an increasing demand to realize a TOF-type PET apparatus (TOF-PET) having high resolution for timing information. Therefore, by applying the radiation detector 1 according to the first embodiment to TOF-PET, it is possible to realize TOF-PET in which the timing resolution is also improved while acquiring high-resolution energy information.

  A second embodiment of the present invention will now be described with reference to the drawings. The overall configuration of the radiation detector 1A according to the second embodiment is the same as the configuration of the radiation detector 1 according to the embodiment. That is, the radiation detector 1A has, similarly to the radiation detector 1, a configuration in which one photodetector 5A is optically coupled to one scintillator 3 (see FIG. 1A).

  However, in the light detector 5 according to the first embodiment, the area of the light receiving area F in each microcell 15 is the same. On the other hand, the photodetector 5A according to the second embodiment is different from the first embodiment in that the light receiving area F in each of the microcells 15a is wider than the light receiving area F in each of the microcells 15b. That is, as shown in FIG. 5A, the photodetector 5A is configured such that the pitch length T1 of the microcell 15a is longer than the pitch length T2 of the microcell 15b.

  By increasing the pitch length of the microcells 15, the area occupied by the insensitive regions N (partitions) formed between adjacent light receiving regions F is reduced. As a result, in the light detector 5A, the area of the light receiving area F per unit area in one microcell 15a is larger than the area of the light receiving area F per unit area in one microcell 15b.

  That is, in the first embodiment, by changing the height of the bias voltage to be applied, the specification of the microcell 15a used to acquire timing information is made different from the specification of the microcell 15b used to acquire energy information. On the other hand, in the second embodiment, the specification of the microcell 15a and the specification of the microcell 15b are made different by changing the area of the light receiving region F per unit area.

  Since the microcell 15a dedicated to timing information acquisition has a relatively large area of the light receiving area F per unit area, the photon detection efficiency is higher. As a result, higher resolution timing information can be acquired based on the output of the microcell 15a. On the other hand, since the area of the light receiving region F per unit area of the microcell 15b dedicated to acquiring energy information is relatively narrow, the photon detection efficiency is lower, but the linearity between the number of incident photons and the output is suitably maintained. As a result, energy information with higher resolution can be acquired based on the output of the microcell 15b.

  Further, by shortening the pitch length T2 of the microcells 15b relatively, the number of microcells 15b (number of pixels) per unit area increases. The increase in the number of pixels can more reliably prevent the same microcell 15b from simultaneously detecting two or more photons, thereby further improving energy resolution.

  As described above, in the radiation detector 1A according to the second embodiment, the microcell 15a is set relatively wide while the microcell 15b is set relatively narrow in the area of the light receiving region F per unit area in the microcell 15 . With such a configuration, as in the first embodiment, while the microcell 15a is set to a predetermined specification that improves the accuracy of timing information, the accuracy of energy information is improved for the microcell 15b. It can be set to another specification like this.

  As in the first embodiment, the arrangement pattern of the microcells 15a and the microcells 15b can be appropriately changed also in the second embodiment. That is, the arrangement of the microcells 15a may be set to be dense as shown in FIG. 5 (b) or may be dispersed as shown in FIG. 5 (c). Further, the shape of the light receiving area F is not limited to a rectangular shape, and the shape of the light receiving area F may be appropriately changed into a bowl shape or the like as in the microcell 15b shown in FIG. 5 (c).

  In the second embodiment, the specifications of the microcell 15a and the specifications of the microcell 15b are set to different specifications by changing the area of the light receiving region per unit area. Therefore, as shown in FIGS. 6 (a) and 6 (b), even if the same bias voltage V is applied to each of the microcell 15a and the microcell 15b from a single power supply 22, the timing resolution And energy resolution can both be improved. Therefore, it is not necessary to prepare multiple power sources for each radiation detector. In addition, since it is not necessary to change the circuit to connect each of the microcell 15a and each of the microcell 15b with different power supplies, the manufacturing cost of the radiation detector having the effects according to the present invention can be obtained. Can be further reduced.

  However, the radiation detector 1A according to the second embodiment is not limited to the structure shown in FIG. 6, and may have a structure including the first power supply 21 and the second power supply as shown in FIG. That is, while changing the area of the light receiving region of the microcell 15, the first power supply 21 applies a high voltage bias voltage V1 to the microcell 15a, and the first power supply 21 applies a high voltage bias voltage V1 to the microcell 15a It may be a configuration. In this case, since the microcell 15a has a wide light receiving area and a high bias voltage, the timing resolution can be further improved by the synergetic effect. On the other hand, since the microcell 15b has a narrow light receiving area and a low bias voltage, energy resolution can be further improved by a synergetic effect.

  A third embodiment of the present invention will now be described with reference to the drawings. In Embodiment 1 and Embodiment 2, the radiation detector 1 is configured by optically coupling one photodetector 5 to one scintillator 3. On the other hand, the radiation detector 1B according to the third embodiment has a configuration in which a plurality of photodetectors 5 are optically coupled to one scintillator 3 as shown in FIG. 7A. The detector modules 2 are configured by arranging the radiation detectors 1B in a one-dimensional matrix or two-dimensional matrix.

  In the third embodiment, it is assumed that two photodetectors 5 are optically coupled to one scintillator 3. As shown in FIG. 7B, one of the two light detectors 5 is a light detector 5L, and the other is a light detector 5R. In the photodetector 5L, microcells 15a used for acquiring timing information are arranged in a matrix, and in the photodetector 5R, microcells 15b used for acquiring energy information are arranged in a matrix. In the third embodiment, the light detector 5L corresponds to a first light detection means in the present invention, and the light detector 5R corresponds to a second light detection means in the present invention.

  As shown in FIGS. 8A and 8B, the radiation detector 1B includes the first power supply 21 and the second power supply 23 as in the first embodiment. The first power supply 21 applies a relatively high voltage bias voltage V1 to each of the microcells 15a, and the second power supply 23 applies a relatively low voltage bias voltage V2 to each of the microcells 15b. In this case, in the microcell 15a, the photon detection efficiency is increased by the bias voltage V1 of high voltage, so that the timing resolution is improved.

  On the other hand, in the microcell 15b, the photon detection efficiency is lowered by the low voltage bias voltage V2, so that the energy resolution is improved. By changing the bias voltage to be applied, while the microcell 15a is set to a predetermined specification that is advantageous for acquisition of timing information, another specification that is advantageous for acquisition of energy information for the microcell 15b It can be set to Therefore, it is possible to improve both the timing resolution and the energy resolution obtained for each of the radiation detectors 1B.

  In the third embodiment, a plurality of photodetectors 5 are optically coupled to one scintillator 3, and in each of the photodetectors 5, either one of the microcell 15a or the microcell 15b is formed in a matrix. It is arranged. In such a configuration, one of the first power supply 21 and the second power supply 23 is connected to each of the photodetectors 5. That is, since it is not necessary to connect a plurality of power supplies to one photodetector 5, circuit design is relatively easy.

  In each of the photodetectors 5, either the microcell 15a or the microcell 15b is arranged in a matrix. Therefore, the existing photodetector that is a specification that is advantageous for acquiring timing information is the photodetector 5L, and the existing photodetector that is another specification that is advantageous for acquiring energy information is a photodetector. Each can be diverted as 5R. That is, since it is not necessary to newly manufacture a photodetector including both the microcell 15a and the microcell 15b, the radiation detector according to the present invention can be manufactured more easily.

  The present invention is not limited to the above embodiment, and can be modified as follows.

  (1) In each of the embodiments described above, the method of changing the height of the bias voltage as a means for differentiating the specification of the microcell 15a and the specification of the microcell 15b (Example 1) and the light receiving area per unit area The method of changing the area of F (Example 2) has been described as an example. However, the means for differentiating the specifications is not limited to this, and the target of the change is the gain of the microcell 15, the resistance value of the quenching resistance 19, the capacitance value of SiPM 5 itself depending on the semiconductor manufacturing process, photon detection efficiency, The number of microcells (number of pixels) per unit area, crosstalk probability, dark count and the like can be mentioned.

  In general, when the gain is high, the photon detection efficiency is high, the number of pixels is small, the crosstalk probability is low, or the dark count is low, the energy resolution decreases while the timing resolution improves. On the other hand, when the gain is low, the photon detection efficiency is low, the number of pixels is large, the crosstalk probability is high, or the dark count is high, the energy resolution is improved while the timing resolution is lowered.

  Therefore, as an example, when differentiating specifications using gains, a microcell with a relatively high gain is used as the microcell 15a dedicated to timing information acquisition, and a microcell with a relatively low gain as microcell 15b dedicated to energy information acquisition. Use a cell. Even with such a configuration, it is possible to obtain timing information with improved resolution based on the output of the microcell 15a having a high gain in the microcell group optically coupled to the same scintillator 3. On the other hand, energy information with improved resolution can be obtained based on the output of the microcell 15b with low gain. As a result, in the radiation detector, it is possible to improve the accuracy of the energy information while improving the accuracy of the timing information.

  (2) In each of the embodiments described above, a configuration in which one or two or more photodetectors 5 are optically coupled to one scintillator 3 has been described as an example, but as shown in FIG. The radiation detector 1 </ b> C may be configured by optically coupling the scintillator 3 to one light detector 5. In the modification according to (2), the detector module 2C configured by the radiation detector 1C has a configuration as shown in FIG. 9 (b). The radiation detector 1C according to the modification of (2) has a configuration in which four scintillators 3a to 3d are optically coupled to one photodetector 5.

  In such a modification, at least one microcell 15a used to acquire timing information and one microcell 15b used to acquire energy information may be optically coupled to each scintillator 3, respectively. That is, in the light detector 5, regions where the scintillators 3a to 3d are optically coupled to each other are Pa to Pd, respectively (see FIG. 9B). Among the microcells 15 in each of the regions Pa to Pd, one or more of each of the microcell 15a (see FIG. 9B and halftone dots) and the microcell 15b (see diagonal lines and FIG. 9B) are included. It should be done.

  The microcell 15a is set to a specification that is advantageous for acquisition of timing information, and is set to another specification that is advantageous for acquisition of energy information. With such a configuration, for each of the γ rays incident on each of the scintillators 3a to 3d, it is possible to acquire timing information with improved resolution and energy information with improved resolution. Therefore, even with a radiation detector configured by optically coupling a plurality of scintillators to one photodetector, resolution can be improved for both timing information and energy information.

  (3) In the third embodiment described above, the bias voltage V1 is applied to the light detector 5L and the bias voltage V2 is applied to the light detector 5R to differentiate between the specifications of the microcell 15a and the specifications of the microcell 15b. But it is not limited to this. That is, as shown in FIG. 8C, the pitch length T1 of the microcell 15a provided in the light detector 5L is made longer than the pitch length T2 of the microcell 15b provided in the light detector 5R. May be

  By changing the pitch length, the area of the light receiving area F per unit area in the microcell 15a becomes wider than the area of the light receiving area F per unit area in the microcell 15b. As described above, as in the second embodiment, the specification of the microcell 15a and the specification of the microcell 15b can be differentiated by applying the configuration in which the area of the light receiving region per unit area is changed also in the third embodiment.

  In the modification according to (3), the pitch length of the microcell is changed for each light detector 5. That is, as an example, using the SiPM of a specification with a relatively long micro cell pitch length as the light detector 5L, and using the SiPM with a specification of a relatively short micro cell pitch length as the light detector 5R, A configuration similar to 2 can be realized. In this case, the resolution of both timing information and energy information can be improved by combining existing SiPMs and the like, so that the radiation detector according to the present invention can be relatively easily manufactured.

  In the configuration according to the third embodiment, other specifications such as gain and photon detection efficiency may be changed for each photodetector optically coupled to one scintillator 3. Further, in the configuration in which at least one microcell 15a and at least one microcell 15b are optically coupled to one scintillator 3, each of the photodetector 5L and the photodetector 5R includes the microcell 15a and the microcell 15b. And may be mixed.

  (4) In each of the embodiments described above, the scintillator 3 and the light detector 5 are directly coupled to each other. However, the present invention is not limited to this. That is, a light guide for transmitting light may be provided between the scintillator 3 and the light detector 5, and the scintillator 3 and the light detector 5 may be optically coupled indirectly.

1 ... radiation detector 2 ... detector module 3 ... scintillator 5 ... photodetector 7 ... PET device 15 ... micro cell (light receiving element)
17 ... APD
19 ... quenching resistance 21 ... first power supply (first bias voltage supply power)
23 ... 2nd power supply (2nd bias voltage supply)
25 ... 1st preamp 27 ... 2nd preamp 29 ... comparator 31 ... shaping amplifier

Claims (5)

At least one scintillator for detecting and emitting incident radiation;
At least one light detection means, each of a first light receiving element and a second light receiving element, arranged in a matrix and optically coupled to the scintillator, for converting light emitted from the scintillator into an electrical signal;
A timing information acquisition circuit that acquires timing information that is information related to the time when the radiation is incident on the scintillator based on the electrical signal converted by the first light receiving element;
An energy information acquisition circuit for acquiring energy information which is information related to the energy of the radiation incident on the scintillator based on the electric signal converted by the second light receiving element;
A first bias voltage supply power source for applying a first bias voltage to the first light receiving element;
A second bias voltage supply that applies a second bias voltage lower than the first bias voltage to the second light receiving element;
For one of the previous SL scintillator, the radiation detector, characterized in that at least one of said first light receiving element and at least one of said second light receiving element are optical histological bound. At least one scintillator for detecting and emitting incident radiation;
At least one first light detection means, arranged in a matrix, first light receiving elements arranged in a matrix, for converting light emitted from the scintillator into an electrical signal;
At least one second light detection means arranged in a matrix and second light receiving elements arranged in a matrix and optically coupled to the scintillator, for converting light emitted from the scintillator into an electrical signal;
A timing information acquisition circuit that acquires timing information that is information related to the time when the radiation is incident on the scintillator based on the electrical signal converted by the first light receiving element;
An energy information acquisition circuit for acquiring energy information which is information related to the energy of the radiation incident on the scintillator based on the electric signal converted by the second light receiving element;
A first bias voltage supply power source for applying a first bias voltage to the first light receiving element;
A second bias voltage supply that applies a second bias voltage lower than the first bias voltage to the second light receiving element;
For one of the previous SL scintillator, the radiation detector, characterized in that at least one of said first light receiving element and at least one of said second light receiving element are optical histological bound. In the radiation detector according to claim 1 or 2,
The radiation detector according to claim 1, wherein an area of the light receiving region per unit area of the first light receiving element is wider than an area of the light receiving region per unit area of the second light receiving element. The radiation detector according to any one of claims 1 to 3.
The area of the second light receiving element, the radiation detector is a 2% to 40% of the area of the first light receiving element.   A detector module configured by arranging a plurality of radiation detectors according to any one of claims 1 to 4 in a one-dimensional direction or a two-dimensional direction.

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