Patent Description:
In a positron emission tomography (PET) apparatus, a substance labeled with a radioisotope (RI) that emits positrons is applied to a subject as a tracer. Then, a radiation detector measures a pair of γ-rays generated by annihilation of the positron emitted from the RI substance and the electron in the normal substance, thereby obtaining information about the subject.

In a measurement apparatus, such as the PET apparatus, a radiation detector used for detecting radiation rays, such as γ-rays, is appropriately configured by combining, for example, a scintillator that generates scintillation light in response to incidence of a radiation ray and a photodetector that detects the scintillation light and outputs a detection signal (see, for example, Patent Document <NUM>).

In a radiation detector used in a PET apparatus, it is important to determine at which position the γ-ray incident on the detector has interacted with a scintillator and detected. In particular, when the γ-ray is detected at a position around the visual field of the detector (a position away from the center), a parallax error occurs and causes a problem that the spatial resolution of γ-ray detection is lowered. In order to prevent the spatial resolution of radiation detection from being lowered, a phoswich type detector has been proposed.

In the phoswich type radiation detector, a scintillator used for radiation detection is configured by stacking two types of scintillator units having detection signal time constants different from each other. With this configuration, it is possible to determine which scintillator unit detects the radiation ray, based on information on the time waveform of the detection signal, for example, the time constant of the time waveform. This phoswich type detector can be used as a depth of interaction (DOI) detector.

As a method for obtaining a parameter indicating a time waveform, such as a time constant of a detection signal output from a detector, for example, a configuration in which waveform sampling for the time waveform of the detection signal is performed can be used. However, with the configuration of performing the waveform sampling of the detection signal, while a lot of information on the detection signal is obtained, it is unsuitable for radiation measurement at a high count rate, and power consumption is hardly reduced.

Further, Patent Document <NUM> and Non Patent Document <NUM> disclose the configurations in which the detection signal is compared with a threshold voltage, and a time during which the voltage value of the signal exceeds the threshold voltage (Time over Threshold: ToT) is obtained. However, with these configurations, the time constant itself of the detection signal is not obtained, and it is difficult to determine the time waveform of the detection signal with sufficient accuracy. Further, the problem of acquisition and determination of such information on the time waveform of the detection signal similarly occurs in radiation detectors other than the phoswich type detector described above. The article of <NPL>, discloses a radiation detection device comprising:a scintillator and a photodetector, first and second comparators, a first time width measurement device and a second time width measurement device; andan analysis unit for obtaining a time constant indicating a time waveform of the detection signal based on the first time width and the second time width. The same is also known from another article, i.e.<NPL>.

The present invention has been made to solve the above problem, and an object thereof is to provide a radiation detection device capable of appropriately acquiring and determining information on a time waveform of a detection signal output from a radiation detector including a scintillator and a photodetector.

A radiation detection device according to the present invention is defined in the independent claim. Further advantageous embodiments are defined in dependent claims.

In the above radiation detection device, the first comparator and the second comparator in which threshold voltages different from each other are set are provided for the detection signal output from the radiation detector including the scintillator and the photodetector. Then, the different time widths of the first and second digital signals output from the two comparators are measured by the first and second time width measurement devices, and the time constant which is a parameter indicating the time waveform of the detection signal in response to the radiation detection is obtained based on the obtained first time width and second time width. With this configuration, it is possible to appropriately acquire and determine information on the time waveform of the detection signal with a simple configuration.

According to a radiation detection device of the present invention, by providing, for a detection signal output from a radiation detector including a scintillator and a photodetector, first and second comparators in which different threshold voltages are set, measuring time widths of first and second digital signals output from the comparators with first and second time width measurement devices, and obtaining, based on the obtained first and second time widths, a time constant indicating the time waveform of the detection signal, it is possible to appropriately acquire and determine information on the time waveform of the detection signal with a simple configuration.

Hereinafter, embodiments of a radiation detection device according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference signs, without redundant description. Further, the dimensional ratios in the drawings are not always coincident with those in the description.

<FIG> is a diagram schematically illustrating a configuration of a radiation detection device of a first embodiment. A radiation detection device 1A according to the present embodiment includes a radiation detector <NUM>, a time waveform measurement unit <NUM>, and an analysis unit <NUM>.

The radiation detector <NUM> detects an incident radiation ray and outputs a generated electric signal (voltage signal) as a detection signal. The radiation detector <NUM> in this configuration example includes a scintillator <NUM> and a photodetector <NUM>. The scintillator <NUM> is made of a predetermined scintillation material, and generates scintillation light in response to incidence of a radiation ray to be detected. The time waveform of the scintillation light generated in the scintillator <NUM> is a predetermined waveform determined depending on the light emission characteristics of the scintillation material. Further, the radiation ray to be detected by the scintillator <NUM> is, for example, a γ ray, an X ray, an electron, a charged particle, a cosmic ray, or the like.

The photodetector <NUM> detects the scintillation light output from the scintillator <NUM> and outputs a detection signal. As the photodetector <NUM>, for example, a photomultiplier tube (PMT), a silicon photomultiplier (SiPM), a multi-pixel photon counter (MPPC), or the like can be used. Further, if the output from the photodetector <NUM> is a current signal, it is preferable to perform current voltage conversion with an amplifier or the like to generate a detection signal that is a voltage signal. The time waveform of the detection signal is a predetermined waveform determined depending on the time waveform of the scintillation light described above, the light detection characteristics of the photodetector <NUM>, and the like. A detection signal S0 generated by the photodetector <NUM> is output from the output terminal <NUM> to the time waveform measurement unit <NUM> of the subsequent stage.

The time waveform measurement unit <NUM> is a measurement circuit unit that measures the time waveform of the detection signal S0 output from the output terminal <NUM> of the photodetector <NUM>. The time waveform measurement unit <NUM> in the present configuration example includes a first comparator <NUM>, a second comparator <NUM>, a first time width measurement device <NUM>, and a second time width measurement device <NUM>. The detection signal S0 output from the photodetector <NUM> is branched at a branch point <NUM>, and the branched detection signals S0 are respectively input to the first comparator <NUM> and the second comparator <NUM>.

To the first comparator <NUM>, a first threshold voltage V1 is applied. The first comparator <NUM> compares the detection signal S0, which is a voltage signal, with the first threshold voltage V1, and outputs a first digital signal S1 having a first time width T1 corresponding to a time during which the voltage value of the detection signal S0 exceeds the threshold voltage V1. Further, to the second comparator <NUM>, a second threshold voltage V2 having a voltage value different from that of the first threshold voltage V1 is applied. The second comparator <NUM> compares the detection signal S0 with the second threshold voltage V2, and outputs a second digital signal S2 having a second time width T2 corresponding to a time during which the voltage value of the detection signal S0 exceeds the threshold voltage V2.

The first time width measurement device <NUM> measures the first time width T1 of the first digital signal S1 output from the first comparator <NUM>, and outputs the obtained data on the first time width T1 to the analysis unit <NUM> of the subsequent stage. Further, the second time width measurement device <NUM> measures the second time width T2 of the second digital signal S2 output from the second comparator <NUM>, and outputs the obtained data on the second time width T2 to the analysis unit <NUM>. Each of the first time width measurement device <NUM> and the second time width measurement device <NUM> is preferably configured by a time to digital converter (TDC).

The analysis unit (analysis device) <NUM> obtains, based on the first time width T1 and the second time width T2 respectively input from the first and second time width measurement devices <NUM> and <NUM>, a time constant τ, which is a parameter indicating the time waveform of the detection signal S0. The time constant τ is, for example, a fall time τd of the time waveform of the detection signal S0 to be described later. Further, the analysis unit <NUM> may obtain, as the time constant τ, a parameter indicating the time waveform other than the fall time τd. Further, the analysis unit <NUM> may further obtain a pulse height E of the time waveform of the detection signal S0 based on the time constant τ as necessary. As the analysis unit <NUM>, a computer including a CPU and a memory, a field programmable gate array (FPGA), or the like can be used, for example.

A display unit (display device) <NUM> and a storage unit (storage device) <NUM> are connected to the analysis unit <NUM>. The display unit <NUM> displays an analysis result of the detection signal S0 by the analysis unit <NUM>, such as the time constant τ derived as described above, as necessary. The storage unit <NUM> stores data on the first and second time widths T1 and T2 input to the analysis unit <NUM>, data on the analysis result, such as the time constant τ derived by the analysis unit <NUM>, and the like.

The effect of the radiation detection device 1A according to the above embodiment is described.

In the radiation detection device 1A illustrated in <FIG>, the first comparator <NUM> and the second comparator <NUM> in which the threshold voltages V1 and V2 different from each other are set are provided for the detection signal S0 output from the radiation detector <NUM> including the scintillator <NUM> and the photodetector <NUM>. Then, different time widths of the first and second digital signals S1 and S2 respectively output from the two comparators <NUM> and <NUM> are measured by the first and second time width measurement devices <NUM> and <NUM>, and the time constant τ indicating the time waveform of the detection signal S0 in response to the radiation detection is obtained by the analysis unit <NUM> based on the obtained first time width T1 and second time width T2. With this configuration, it is possible to appropriately acquire and determine information on the time waveform of the detection signal S0 with a simple configuration without performing waveform sampling or the like.

Further, in the above detection device 1A, the analysis unit <NUM> may further obtain, based on the time constant τ, the pulse height E of the time waveform of the detection signal S0 in addition to the time constant τ. With this configuration, it is possible to easily obtain the pulse height E of the detection signal S0 at high speed with low power consumption without providing a pulse height measurement device, such as an analog to digital converter (ADC), separately from the time waveform measurement unit <NUM> including the comparators <NUM> and <NUM> and the time width measurement devices <NUM> and <NUM>. In addition, the pulse height E may not be obtained if unnecessary.

<FIG> is a flowchart illustrating a radiation detection method performed in the radiation detection device 1A illustrated in <FIG>. Further, <FIG> is a graph illustrating the time waveform of the detection signal S0 output from the photodetector <NUM>. Further, <FIG> is a graph illustrating the first and second time widths T1 and T2 obtained by applying the first and second threshold voltages V1 and V2 to the detection signal S0. In the following, a radiation detection method according to the present embodiment will be described together with specific examples of the time waveform of the detection signal S0 and a method of deriving the time constant τ and the like.

In the radiation detection method illustrated in <FIG>, first, a radiation ray is detected by the radiation detector <NUM> including the scintillator <NUM> and the photodetector <NUM>, and a detection signal S0 is output from the output terminal <NUM> of the photodetector <NUM> in response to the incidence of the radiation ray (step S11). <FIG> schematically illustrates an example of the time waveform of the detection signal S0 output from the photodetector <NUM>. In the graph of <FIG>, the horizontal axis indicates time, and the vertical axis indicates the voltage value of the detection signal S0.

In the time waveform of the detection signal S0 illustrated in <FIG>, the part before a signal peak Sp is a signal rising part Sr, and the part after the signal peak Sp is a signal falling part Sd. Further, the time waveform of the detection signal S0 having a shape illustrated in <FIG> can be expressed by, for example, the following Formula (<NUM>). [Formula <NUM>] <MAT> Here, in Formula (<NUM>), E represents a pulse height that is a voltage value at the signal peak Sp, τr represents a rise time (rise time constant) of the signal rising part Sr, and τd represents a fall time (fall time constant) of the signal falling part Sd.

The detection signal S0 output from the radiation detector <NUM> is input to the first and second comparators <NUM> and <NUM> in the time waveform measurement unit <NUM>. The first comparator <NUM> compares the detection signal S0 with the first threshold voltage V1 and outputs the first digital signal S1 having the first time width T1 corresponding to a time during which the voltage value of the detection signal S0 exceeds the threshold voltage V1, as illustrated in the graph of <FIG>. Further, the second comparator <NUM> compares the detection signal S0 with the second threshold voltage V2 and similarly outputs the second digital signal S2 having the second time width T2 corresponding to a time during which the voltage value of the detection signal S0 exceeds the threshold voltage V2 (step S12). The first and second time widths T1 and T2 are respectively measured by the first and second time width measurement devices <NUM> and <NUM> (step S13).

In addition, <FIG> and <FIG> illustrate that the signal peak Sp of the time waveform of the detection signal S0 is in the positive direction with respect to the voltage, but if the signal peak Sp of the detection signal S0 is in the negative direction with respect to the voltage, the time width is only required to be, for example, a time width corresponding to a time during which the voltage value of the detection signal S0 the positive/negative of which is inverted exceeds the threshold voltage. This corresponds to a time during which the voltage value of the original detection signal is below the threshold voltage.

The analysis unit <NUM> derives the time constant τ indicating the time waveform of the detection signal S0 based on the first and second time widths T1 and T2 and the like measured by the first and second time width measurement devices <NUM> and <NUM> (step S14). Further, the analysis unit <NUM> derives the pulse height E of the time waveform of the detection signal S0 based on the first and second time widths T1 and T2, the time constant τ, and the like, as necessary (step S15).

Here, in the time waveform of the detection signal S0 output from the photodetector <NUM>, if the rise time τr is sufficiently shorter than the fall time τd, the first time width T1 of the detection signal S0 for the first threshold voltage V1 is expressed by the following Formula (<NUM>). [Formula <NUM>] <MAT> Further, the second time width T2 of the detection signal S0 for the second threshold voltage V2 is similarly expressed by the following Formula (<NUM>). [Formula <NUM>] <MAT>.

Thus, when the time constant τ derived by the analysis unit <NUM> as a parameter of the time waveform is the fall time τd of the time waveform of the detection signal S0, the time constant τ is obtained with the following Formula (<NUM>). [Formula <NUM>] <MAT> With Formula (<NUM>), it is possible to appropriately easily obtain the time constant τ of the detection signal S0.

Further, when the analysis unit <NUM> obtains the pulse height E of the detection signal S0 in addition to the time constant τ, the pulse height E can be obtained with the following Formula (<NUM>) using the fall time τd obtained as the time constant τ. [Formula <NUM>] <MAT> In addition, the first and second threshold voltages V1 and V2 in the first and second comparators <NUM> and <NUM> can be arbitrarily set and adjusted so as to easily obtain the time constant τ and the like.

Further, regarding the above waveform condition that the rise time τr is sufficiently shorter than the fall time τd in the detection signal S0, specifically, it is preferable that, for example, the rise time τr of the time waveform of the detection signal S0 with the fall time τd satisfies the following condition.

Here, <FIG> is a table showing rise times τr and fall times τd of time waveforms of scintillation light output from scintillators. <FIG> shows rise times τr and fall times τd of time waveforms of existing scintillators of LSO, LYSO, LaBr3, GSO, and GAGG used in PET apparatuses. These scintillators are considered to sufficiently satisfy the above condition that the rise time τr is sufficiently shorter than the fall time τd.

The radiation detection device 1A having the configuration illustrated in FTG. <NUM> can be suitably applied to, for example, a PET apparatus. <FIG> is a diagram illustrating a configuration of a PET apparatus to which the radiation detection device illustrated in <FIG> is applied. A PET apparatus 2A is configured by arranging a plurality of radiation detectors <NUM> each including the scintillator <NUM> and the photodetector <NUM> so as to surround a subject P. Further, for the detection signal S0 output from each radiation detector <NUM>, a signal processing unit <NUM> including the time waveform measurement unit <NUM> and the analysis unit <NUM> illustrated in <FIG> is provided.

In the PET apparatus 2A, a pair of γ rays generated by annihilation of the positron inside the subject P is detected by the radiation detectors <NUM>. In the example illustrated in <FIG>, a pair of γ rays generated at a measurement point P1 inside the subject P is detected by radiation detectors <NUM> and <NUM>. Further, a pair of γ rays generated at a measurement point P2 is detected by radiation detectors <NUM> and <NUM>.

The detection signal S0 output from the radiation detector <NUM> is input to the signal processing unit <NUM>, and the signal processing unit <NUM> measures the first and second time widths T1 and T2 of the detection signal S0 and derives the time constant τ of the time waveform, as described above with reference to <FIG>. Further, based on the obtained time constant τ, the characteristics of the radiation detector <NUM>, such as the characteristics of the scintillator <NUM>, are derived. Information on the derived characteristic of the radiation detector <NUM> can be used, for example, to improve the performance of the PET apparatus 2A.

<FIG> is a diagram schematically illustrating a configuration of a radiation detection device of a second embodiment. A radiation detection device 1B according to the present embodiment includes a radiation detector 10B, a time waveform measurement unit <NUM>, and an analysis unit <NUM>. Among these, the configurations of the time waveform measurement unit <NUM> and the analysis unit <NUM> are similar to those illustrated in <FIG>. Further, in <FIG>, a display unit <NUM> and a storage unit <NUM> connected to the analysis unit <NUM> are not illustrated.

The radiation detector 10B in this configuration example includes a scintillator <NUM> and a photodetector <NUM>. Further, the scintillator <NUM> is configured by arranging a first scintillator unit <NUM> and a second scintillator unit <NUM> in this order from the photodetector <NUM>.

The first scintillator unit <NUM> is made of a first scintillation material, and generates scintillation light having a predetermined time waveform in response to incidence of a radiation ray. The second scintillator unit <NUM> is made of a second scintillation material different from the first scintillation material, and generates scintillation light having a time waveform different from that of the first scintillator unit <NUM> in response to incidence of a radiation ray. The photodetector <NUM> detects the scintillation light output from the first scintillator unit <NUM> or the second scintillator unit <NUM>, and outputs a detection signal S0 via the output terminal <NUM> and an amplifier <NUM>. At this time, the time waveform of the detection signal S0 output from the photodetector <NUM> varies depending on whether the detected radiation ray has interacted with the first scintillator unit <NUM> or the second scintillator unit <NUM>.

<FIG> is a flowchart illustrating a radiation detection method performed in the radiation detection device 1B illustrated in <FIG>. In the radiation detection method illustrated in <FIG>, first, a radiation ray is detected by the radiation detector 10B constituted by the scintillator <NUM> including the first and second scintillator units <NUM> and <NUM>, and the photodetector <NUM>, and the detection signal S0 is output from the output terminal <NUM> of the photodetector <NUM> (step S21).

The detection signal S0 is input to the first and second comparators <NUM> and <NUM> in the time waveform measurement unit <NUM> via the amplifier <NUM> and the branch point <NUM>. The first comparator <NUM> compares the detection signal S0 with the first threshold voltage V1 and outputs the first digital signal S1 having the first time width T1. Further, the second comparator <NUM> compares the detection signal S0 with the second threshold voltage V2 and outputs the second digital signal S2 having the second time width T2 (step S22). The first and second time widths T1 and T2 are respectively measured by the first and second time width measurement devices <NUM> and <NUM> (step S23).

The analysis unit <NUM> derives the time constant τ indicating the time waveform of the detection signal S0 based on the first and second time widths T1 and T2 measured by the first and second time width measurement devices <NUM> and <NUM> (step S24). Further, the analysis unit <NUM> determines, based on the obtained time constant τ, whether the detection signal S0 output from the photodetector <NUM> is caused by scintillation light generated in the first scintillator unit <NUM> or the second scintillator unit <NUM>, that is, whether the radiation ray is detected by the first scintillator unit <NUM> or the second scintillator unit <NUM> (step S25).

In this manner, with the configuration for obtaining the time constant τ of the detection signal S0 based on the first and second time widths T1 and T2 as described above, it is possible to determine, based on the obtained time constant τ, whether the radiation ray is detected by the first scintillator unit <NUM> or the second scintillator unit <NUM>, in the case where the scintillator <NUM> includes the first and second scintillator units <NUM> and <NUM>. Further, it is possible to similarly perform such determination of the scintillator unit when the scintillator includes three or more scintillator units.

A measurement experiment on the determination of the scintillator units based on the time constant τ of the detection signal S0 was performed. <FIG> is a diagram illustrating a measurement experiment performed using the radiation detector 10B illustrated in <FIG>. In this measurement experiment, the radiation detector 10B was placed in a thermostatic chamber <NUM> at a temperature of <NUM>. Regarding the configuration of the radiation detector 10B, a <NUM>×<NUM>×<NUM><NUM> GSO scintillator was used as the first scintillator unit <NUM>, and a <NUM>×<NUM>×<NUM><NUM> GAGG scintillator was used as the second scintillator unit <NUM>.

Further, S13360-<NUM> manufactured by Hamamatsu Photonics was used as the MPPC of the photodetector <NUM>. The light receiving surface size of this MPPC is <NUM>×<NUM><NUM>, and the array pitch of a plurality of photodetection pixels arrayed two-dimensionally is <NUM>. Further, regarding the voltage applied to the MPPC, the voltage exceeding the breakdown voltage was set to Vexcess = <NUM> V. Further, a <NUM>Na radiation source was disposed as a radiation source <NUM> at a position separated by <NUM> from the scintillator <NUM> including the first and second scintillator units <NUM> and <NUM>, and the γ rays from the radiation source <NUM> were detected by the radiation detector 10B.

Further, in this measurement experiment, an oscilloscope <NUM> instead of the time waveform measurement unit <NUM> illustrated in <FIG> was provided for the detection signal S0 output from the output terminal <NUM> of the photodetector <NUM>, and the time waveform data measured by the oscilloscope <NUM> was taken into the computer (PC) of the analysis unit <NUM>, and then the first and second time widths T1 and T2, the time constant τ and the like of the time waveform of the detection signal S0 were analyzed by software. Further, as the oscilloscope <NUM>, DSO-S404A manufactured by Keysight Corporation was used.

<FIG> is a graph illustrating the time waveform and the first and second time widths T1 and T2 of the detection signal S0 obtained in the measurement experiment illustrated in <FIG>. Here, the analysis unit <NUM> performed fitting to time waveform data S6 of the detection signal S0 obtained by the oscilloscope <NUM> with a theoretical formula, and a time waveform S7 was obtained as a fitting result. Further, numerical analysis was performed for the time waveform S7 by setting the first and second threshold voltages V1 and V2 to obtain the first time width T1 and the second time width T2. Further, the time constant τ of the detection signal S0 was obtained based on the first and second time widths T1 and T2.

<FIG> is a graph illustrating determination of the scintillator unit based on the time constant τ of the detection signal S0 obtained in the measurement experiment illustrated in <FIG>. In the graph of <FIG>, the horizontal axis indicates the fall time τd (ns) of the detection signal S0 obtained as the time constant τ. In the experimental result illustrated in <FIG>, the detection data by the GSO scintillator distributed in a region R1 in which the fall time τd is short and the detection data by the GAGG scintillator distributed in a region R2 in which the fall time τd is long can be clearly determined. Such a determination function of the scintillator can be applied to, for example, determining scintillator units in a phoswich type detector configured by stacking a plurality of types of scintillator units having different time constants of a detection signal, and thus, it is possible to achieve a detection device capable of supporting a high count rate and reducing power consumption.

<FIG> is a diagram schematically illustrating a configuration of a radiation detection device of a third embodiment. A radiation detection device 1C according to the present embodiment includes a radiation detector 10C, a time waveform measurement unit <NUM>, and an analysis unit <NUM>. Among these, the configurations of the time waveform measurement unit <NUM> and the analysis unit <NUM> are similar to those illustrated in <FIG>. Further, in <FIG>, a display unit <NUM> and a storage unit <NUM> connected to the analysis unit <NUM>, and a scintillator <NUM> included in the radiation detector 10C are not illustrated.

The radiation detector 10C in this configuration example includes a scintillator <NUM> and a photodetector <NUM>. Further, as the photodetector <NUM>, a photodetector <NUM> configured as an MPPC including a plurality of photodetection pixels (photodetection units) is used. <FIG> is a plan view illustrating a configuration of the photodetector <NUM> in the radiation detection device 1C illustrated in <FIG>. Further, <FIG> is a plan view illustrating the configuration of the partially enlarged photodetector <NUM> illustrated in <FIG>. <FIG> is an enlarged view of a central region <NUM> of the photodetector <NUM> illustrated in <FIG>.

The photodetector <NUM> includes N photodetection pixels (micropixels) <NUM> that are arranged one-dimensionally or two-dimensionally and each generate a detection signal S0 in response to incidence of light, and a single output terminal <NUM> that outputs the detection signal S0 generated in each of the N photodetection pixels <NUM> to the outside. Here, N is an integer of <NUM> or more. Further, regarding a specific configuration of the MPPC, Patent Document <NUM> can be referred to, for example.

In the configuration example illustrated in <FIG> and <FIG>, the N photodetection pixels <NUM> are two-dimensionally arranged on the detector chip of the photodetector <NUM>. Further, at the center of the detector chip, a common electrode <NUM> for collecting the detection signals S0 from the photodetection pixels <NUM> is disposed. In addition, in <FIG>, the photodetection pixels <NUM> are illustrated only in the vicinity of both ends of the detector chip in order for the common electrode <NUM> to be easily recognized and the like.

Each of the N photodetection pixels <NUM> of the photodetector <NUM> includes an avalanche photodiode (APD) <NUM> that operates in Geiger mode, and a quenching resistor <NUM> connected in series to the APD <NUM>. Further, the quenching resistor <NUM> is connected to the common electrode <NUM> via a signal line <NUM> as illustrated in <FIG>. The detection signal S0 generated by each photodetection pixel <NUM> is output from the output terminal <NUM> to the outside via the signal line <NUM> and the common electrode <NUM>.

Further, the N photodetection pixels <NUM> of the photodetector <NUM> are configured to output detection signals S0 having time waveforms different from each other (time constants different from each other). Specifically, in the present configuration example, the photodetector <NUM> is configured such that the quenching resistors <NUM> that determine, in the N photodetection pixels <NUM>, the time waveforms and time constants of the detection signals have resistance values different from each other.

<FIG> is a flowchart illustrating a radiation detection method performed in the radiation detection device 1C illustrated in <FIG>. In the radiation detection method illustrated in <FIG>, first, a radiation ray is detected by the radiation detector 10C constituted by the scintillator <NUM> and the photodetector <NUM> including the N photodetection pixels <NUM>, and a detection signal S0 is output from the output terminal <NUM> of the photodetector <NUM> (step S31).

The detection signal S0 is input to the first and second comparators <NUM> and <NUM> in the time waveform measurement unit <NUM> via the amplifier <NUM> and the branch point <NUM>. The first comparator <NUM> compares the detection signal S0 with the first threshold voltage V1 and outputs the first digital signal S1 having the first time width T1. Further, the second comparator <NUM> compares the detection signal S0 with the second threshold voltage V2 and outputs the second digital signal S2 having the second time width T2 (step S32). The first and second time widths T1 and T2 are respectively measured by the first and second time width measurement devices <NUM> and <NUM> (step S33).

The analysis unit <NUM> derives the time constant τ indicating the time waveform of the detection signal S0 based on the first and second time widths T1 and T2 measured by the first and second time width measurement devices <NUM> and <NUM> (step S34). Further, the analysis unit <NUM> determines, based on the obtained time constant τ, which one of the N photodetection pixels (photodetection units) has output the detection signal S0 (step S35).

In this manner, with the configuration for obtaining the time constant τ of the detection signal S0 based on the first and second time widths T1 and T2 as described above, it is possible to determine, based on the obtained time constant τ, which one of the N photodetection pixels <NUM> has output the detection signal S0, in the case where the photodetector <NUM> includes the N photodetection pixels (photodetection units) <NUM>.

In addition, in this configuration example, the photodetector <NUM> includes the N photodetection pixels <NUM> as described above, and the number of the photodetection pixels (photodetection units) <NUM> is arbitrarily set to two or more. For example, when the photodetector <NUM> includes a first photodetection unit that outputs a detection signal having a predetermined time waveform, and a second photodetection unit that outputs a detection signal having a time waveform different from that of the first photodetection unit, it is possible to determine, based on the obtained time constant τ, whether the detection signal S0 is output from the first photodetection unit or the second photodetection unit.

Further, regarding the configuration of the N photodetection pixels <NUM> of the photodetector <NUM> that output detection signals having time waveforms different from each other, various configurations other than the configuration illustrated in <FIG> is applicable.

<FIG> is a diagram schematically illustrating a configuration of a first modification of the photodetector <NUM> in the radiation detection device 1C illustrated in <FIG>. In the present configuration example, the photodetector <NUM> is configured as a photodetector 50A including N photodetection pixels <NUM> and a single output terminal <NUM>.

Each of the N photodetection pixels <NUM> of the photodetector 50A includes an APD <NUM> that operates in Geiger mode, a quenching resistor <NUM> connected in series to the APD <NUM>, and a frequency filter <NUM> connected in series between the quenching resistor <NUM> and the output terminal <NUM>.

Further, in this configuration example, the photodetector 50A is configured such that the frequency filters <NUM> of the N photodetection pixels <NUM> have frequency characteristics different from each other. Thus, the N photodetection pixels <NUM> of the photodetector 50A output detection signals S0 having time waveforms different from each other. The frequency filters <NUM> of the N photodetection pixels <NUM> are, for example, high-pass filters, low-pass filters, or band-pass filters having cutoff frequencies different from each other.

<FIG> is a diagram schematically illustrating a configuration of a second modification of the photodetector <NUM> in the radiation detection device 1C illustrated in <FIG>. In the present configuration example, the photodetector <NUM> is configured as a photodetector 50B including N photodetection pixels <NUM> and a single output terminal <NUM>.

Each of the N photodetection pixels <NUM> of the photodetector 50B includes an APD <NUM> that operates in Geiger mode, a quenching resistor <NUM> connected in series to the APD <NUM>, and a capacitor <NUM> connected in parallel to the APD <NUM>.

Further, in this configuration example, the photodetector 50B is configured such that the capacitors <NUM> of the N photodetection pixels <NUM> have capacitance values different from each other. Thus, the N photodetection pixels <NUM> of the photodetector 50B output detection signals S0 having time waveforms different from each other.

The radiation detection device according to the present invention is not limited to the above embodiments and configuration examples, and can be variously modified. For example, in the configurations illustrated in <FIG> and <FIG>, the amplifier <NUM> is provided for the detection signal S0 output from the photodetector <NUM>, however, this amplifier <NUM> may not be provided if unnecessary.

Further, regarding the time constant τ indicating the time waveform of the detection signal S0 obtained by the analysis unit <NUM>, the fall time τd is used as the time constant τ in the above configuration example, but another parameter related to the time waveform may be obtained as the time constant τ as long as the time waveform of the detection signal S0 can be determined. Further, regarding the time width of the detection signal S0 used for deriving the time constant τ, the first and second time widths T1 and T2 are measured in the above configuration example, but three or more types of time widths may be measured, for example.

The radiation detection device of the above embodiment is configured to include (<NUM>) a scintillator for generating scintillation light in response to incidence of a radiation ray, (<NUM>) a photodetector for detecting the scintillation light output from the scintillator and outputting a detection signal, (<NUM>) a first comparator for comparing the detection signal with a first threshold voltage and outputting a first digital signal having a first time width corresponding to a time during which a voltage value of the detection signal exceeds the first threshold voltage, (<NUM>) a first time width measurement device for measuring the first time width of the first digital signal, (<NUM>) a second comparator for comparing the detection signal with a second threshold voltage different from the first threshold voltage and outputting a second digital signal having a second time width corresponding to a time during which the voltage value of the detection signal exceeds the second threshold voltage, (<NUM>) a second time width measurement device for measuring the second time width of the second digital signal, and (<NUM>) an analysis unit for obtaining a time constant indicating a time waveform of the detection signal based on the first time width and the second time width.

Here, in the above detection device, the scintillator may include a first scintillator unit for generating scintillation light having a predetermined time waveform, and a second scintillator unit for generating scintillation light having a time waveform different from that of the first scintillator unit. Further, in this case, the analysis unit may determine, based on the obtained time constant, whether the detection signal output from the photodetector is caused by the scintillation light generated in the first scintillator unit or the second scintillator unit. With this configuration, it is possible to reliably determine the scintillator unit based on the time constant of the detection signal.

Further, in the above detection device, the photodetector may include a first photodetection unit for outputting a detection signal having a predetermined time waveform, and a second photodetection unit for outputting a detection signal having a time waveform different from that of the first photodetection unit. Further, in this case, the analysis unit may determine, based on the obtained time constant, whether the detection signal is output from the first photodetection unit or the second photodetection unit. With this configuration, it is possible to reliably determine the photodetection unit based on the time constant of the detection signal.

Regarding a specific configuration of the detection device, each of the first time width measurement device and the second time width measurement device may include a time to digital converter. Thus, it is possible to appropriately measure the first and second time widths of the detection signal.

In the above detection device, a rise time τr in the time waveform of the detection signal with a fall time τd may satisfy a condition, <MAT> Further, in the above detection device, the analysis unit obtains the time constant τ with a formula, <MAT> where V1 is the first threshold voltage, T1 is the first time width, V2 is the second threshold voltage, and T2 is the second time width. With these configurations, it is possible to appropriately obtain the time constant τ of the detection signal.

Further, in the above detection device, the analysis unit may further obtain a pulse height of the time waveform of the detection signal based on the time constant. With this configuration, it is possible to appropriately obtain the pulse height of the detection signal without providing a pulse height measurement device separately from the time waveform measurement unit including the comparator and the time width measurement device.

Claim 1:
A radiation detection device comprising:
a scintillator (<NUM>) for generating scintillation light in response to incidence of a radiation ray;
a photodetector (<NUM>) for detecting the scintillation light output from the scintillator and outputting a detection signal;
a first comparator (<NUM>) for comparing the detection signal with a first threshold voltage and outputting a first digital signal having a first time width corresponding to a time during which a voltage value of the detection signal exceeds the first threshold voltage;
a first time width measurement device (<NUM>) for measuring the first time width of the first digital signal;
a second comparator (<NUM>) for comparing the detection signal with a second threshold voltage different from the first threshold voltage and outputting a second digital signal having a second time width corresponding to a time during which the voltage value of the detection signal exceeds the second threshold voltage;
a second time width measurement device (<NUM>) for measuring the second time width of the second digital signal; and
an analysis unit (<NUM>) for obtaining a time constant indicating a time waveform of the detection signal based on the first time width and the second time width,
characterized in that the analysis unit (<NUM>) obtains the time constant τ with a formula, <MAT>
where V1 is the first threshold voltage, T1 is the first time width, V2 is the second threshold voltage, and T2 is the second time width.