WO2015114740A1 - 放射線検出器 - Google Patents
放射線検出器 Download PDFInfo
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- WO2015114740A1 WO2015114740A1 PCT/JP2014/051863 JP2014051863W WO2015114740A1 WO 2015114740 A1 WO2015114740 A1 WO 2015114740A1 JP 2014051863 W JP2014051863 W JP 2014051863W WO 2015114740 A1 WO2015114740 A1 WO 2015114740A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/20—Measuring radiation intensity with scintillation detectors
- G01T1/208—Circuits specially adapted for scintillation detectors, e.g. for the photo-multiplier section
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/20—Measuring radiation intensity with scintillation detectors
- G01T1/2018—Scintillation-photodiode combinations
- G01T1/20184—Detector read-out circuitry, e.g. for clearing of traps, compensating for traps or compensating for direct hits
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/20—Measuring radiation intensity with scintillation detectors
- G01T1/2018—Scintillation-photodiode combinations
- G01T1/20185—Coupling means between the photodiode and the scintillator, e.g. optical couplings using adhesives with wavelength-shifting fibres
Definitions
- the present invention relates to a radiation detector that detects radiation through fluorescence, and more particularly, to a radiation detector that can identify an incident position of fluorescence.
- a conventional positron emission tomography apparatus for imaging the distribution of radiopharmaceuticals will be described.
- a conventional PET apparatus is provided with a detector ring in which radiation detectors for detecting radiation are arranged in an annular shape. This detector ring detects a pair of ⁇ -rays (an annihilation radiation pair) emitted from the radiopharmaceutical in the subject and in opposite directions.
- the radiation detector 51 includes a scintillator 52 in which scintillator crystals are arranged two-dimensionally, a photodetector 53 that detects fluorescence emitted from ⁇ rays absorbed by the scintillator 52, And a position calculation unit 54 for specifying the generation position.
- the photodetector 53 has a detection surface in which detection elements are arranged in a matrix. And the detection surface of the photodetector 53 and one surface of the scintillator 52 are optically connected (for example, refer patent document 1).
- the radiation incident on the scintillator 52 is converted into a large number of photons and travels toward the photodetector 53. At this time, the photons travel through the scintillator 52 while spatially spreading and enter the detection surfaces of the photodetectors 53 arranged in a matrix. That is, a large number of photons due to fluorescence are simultaneously distributed to and detected by a plurality of detection elements.
- the radiation detector 51 is configured to know where the fluorescence is emitted from the scintillator 2 using the fluorescence detection data captured by the plurality of detection elements. That is, the radiation detector 51 obtains the position of the center of gravity of the fluorescent light flux on the detection surface by a plurality of detection elements.
- the position of the center of gravity means the position where fluorescence is generated. This position data is used when mapping the radiopharmaceutical of the subject.
- a method by which the conventional radiation detector 51 calculates the center of fluorescence is described.
- the detection surface of the photodetector 53 is composed of 2 ⁇ 2 detection elements as shown in FIG.
- the fluorescence detection signals output from the detection elements a1... A4 are denoted by A1.
- A1... A4 indicates the intensity of the fluorescence detected by each detection element a1.
- the conventional radiation detector 51 calculates the center of gravity of the fluorescence based on such a principle, and distinguishes which of the scintillator crystals constituting the scintillator 52 emitted the fluorescence.
- the photodetector 53 detects the detection data Xa, Xb, Ya. Yb is sent to the position calculation unit 54.
- the position calculation unit 54 calculates X and Y, which are fluorescence generation positions in the radiation detector 51, based on the above-described equations (1) and (2).
- the conventional radiation detector has the following problems. That is, the conventional radiation detector has a problem that the circuit is complicated.
- detection data Xa, Xb, Ya, Yb is generated for one fluorescence and simultaneously sent to the position calculation unit 54. Therefore, a dedicated line is provided for each of the detection data Xa, Xb, Ya, Yb between the photodetector 53 and the position calculation unit 54.
- the detection data output from the photodetector 53 is analog data.
- these detection data must be converted into digital data. Since the detection data Xa, Xb, Ya, Yb are sent from the photodetector 53 at the same time, it is necessary to digitize each detection data at the same time.
- an A / D conversion circuit is required for each detection data as shown in FIG.
- Symbol ENG in FIG. 9 is analog data indicating the intensity of fluorescence. Since this analog data is also sent from the photodetector 53 simultaneously with the detection data Xa, Xb, Ya, Yb, an A / D conversion circuit is also required for this analog data.
- a / D conversion circuit is a complicated circuit. According to the conventional configuration, a plurality of such complex A / D conversion circuits (five in the example of FIG. 9) are required. In some PET apparatuses, for example, 100 radiation detectors 51 may need to be arranged, and the number of A / D conversion circuits included in the PET apparatus is considerable. Such a situation is undesirable from the viewpoint of miniaturization and cost reduction of the PET apparatus.
- the A / D conversion circuit requires a large amount of power for operation. Therefore, a PET apparatus having many A / D conversion circuits is not desirable from the viewpoint of suppressing power consumption.
- the detection data Xa, Xb, Ya, Yb are simultaneously output from the photodetector 53, a plurality of A / D conversion circuits must be operated at the same time.
- the power consumption of the radiation detector 51 suddenly increases.
- Such a change in power consumption hinders stable operation of the A / D conversion circuit, and the digital data relating to the output does not become a correct value.
- Such disturbance of digital data is also caused by a clock signal supplied to the A / D conversion circuit.
- the clock signal is absolutely necessary when a plurality of A / D conversion circuits are driven in synchronism, and this signal cannot be omitted.
- the present invention has been made in view of such circumstances, and an object of the present invention is to reduce the number of A / D conversion circuits so as to reduce the number of A / D conversion circuits and to provide a radiation detector that performs accurate operation with low power consumption. It is to provide.
- the radiation detector according to the present invention includes a scintillator that converts radiation into fluorescence, a photodetector that outputs a plurality of analog signals indicating the fluorescence generation position of the scintillator and an analog signal indicating the intensity of the fluorescence, A / D conversion circuit that converts each analog signal into a digital signal, and output from the photodetector at the same time by extending the time until the analog signal output from the photodetector is input to the A / D conversion circuit
- Signal delay means for sequentially inputting each analog signal to the A / D conversion circuit, and position calculation means for calculating where in the scintillator fluorescence is generated based on each of the digital signals.
- the radiation detector of the present invention it is possible to provide a radiation detector that is compact, consumes less power, and operates accurately by suppressing the number of A / D conversion circuits. That is, the present invention extends the time until the analog signal output from the photodetector is input to the A / D conversion circuit, thereby sequentially converting the analog signals output from the photodetector in order to A / D. It is configured to be input to the D conversion circuit. In this way, all analog signals output from the photodetector can be digitized by a single A / D conversion circuit.
- the radiation detector it is not necessary to provide the radiation detector with a plurality of A / D conversion circuits, so that power consumption can be suppressed and noise can be reduced accordingly. Further, according to the radiation detector according to the present invention, the clock signal for synchronizing the A / D conversion circuit is not necessary, so that noise derived from the clock signal does not occur.
- the A / D conversion circuit sets the signal intensity during which tailing that the signal intensity does not gradually change as the attenuation of the input analog signal progresses is set as the baseline to the next digitization. It is more desirable to perform the operation.
- the signal delay means does not operate for analog signals that are first input to the A / D conversion circuit among the analog signals that are simultaneously output by the photodetector that detects fluorescence. desirable.
- the signal delay means does not delay the signal for the analog signal that is first input to the A / D conversion circuit, it is possible to provide a radiation detector that does not delay as much as possible and has a good response.
- the signal delay means shift the timing at which each analog signal is input to the A / D conversion circuit by delaying each analog signal by a predetermined time.
- the signal delay means delays each analog signal by a predetermined time. If the predetermined time is determined in this way, it is not necessary to set the delay time individually for each analog signal.
- the present invention it is possible to provide a radiation detector that is compact, consumes less power, and operates accurately by suppressing the number of A / D conversion circuits. That is, the present invention extends the time until the analog signal output from the photodetector is input to the A / D conversion circuit, thereby sequentially converting the analog signals output from the photodetector in order to A / D. It is configured to be input to the D conversion circuit. In this way, all analog signals output from the photodetector can be digitized by a single A / D conversion circuit.
- FIG. 1 is a functional block diagram illustrating an overall configuration of a radiation detector according to Embodiment 1.
- FIG. FIG. 3 is a plan view illustrating the configuration of the photodetector according to the first embodiment.
- 4 is a time course illustrating an analog signal according to the first embodiment. It is a time course explaining a mode that the analog signal which concerns on Example 1 is emitted simultaneously. It is a time course explaining a mode that each of the analog signal which concerns on Example 1 is delayed by a different space
- 3 is a time course for explaining the pileup of fluorescence according to Example 1.
- FIG. 1 is a functional block diagram illustrating an overall configuration of a radiation detector according to Embodiment 1.
- FIG. 3 is a plan view illustrating the configuration of the photodetector according to the first embodiment.
- 4 is a time course illustrating an analog signal
- FIG. 3 is a time course for explaining the resetting of the baseline of the A / D conversion circuit according to the first embodiment. It is a schematic diagram explaining the radiation detector which concerns on a conventional structure. It is a schematic diagram explaining the radiation detector which concerns on a conventional structure.
- the radiation detector 1 is provided with a scintillator 2 configured by arranging scintillator crystals C vertically and horizontally, and a lower surface of the scintillator 2, and detects fluorescence emitted from the scintillator 2.
- positioned in the position interposed between the scintillator 2 and the light detector 3 are provided.
- Each of the scintillator crystals C is composed of Lu 2 (1-X) Y 2X SiO 5 (hereinafter referred to as LYSO ) in which Ce is diffused. When radiation enters the scintillator 2, the radiation is converted into fluorescence.
- the photodetector 3 outputs an analog signal necessary for discriminating the position of incident fluorescence with respect to x and y. More specifically, the photodetector 3 has a detection surface 3b in which detection elements 3a are arranged in a matrix of, for example, 8 ⁇ 8, and the detection surface 3b is optically connected to the scintillator 2. Yes. When fluorescence is generated, each of the detection elements 3a detects fluorescence. The photodetector 3 outputs analog signals Xa, Xb, Ya, Yb indicating the generation position of the fluorescence and an analog signal ENG indicating the intensity of the fluorescence based on the fluorescence detection result of the detection element 3a.
- the analog signal output from the photodetector 3 will be described.
- the center point of the detection surface 3b is set as the origin, and the fluorescence generation position is indicated on the basis of this.
- the left region as viewed from the origin is designated as RXa, and the right region as seen from the origin is designated as RXb.
- the upper region viewed from the origin is designated as RYa, and the lower region seen from the origin is designated as RYb.
- the photodetector 3 obtains a total value by summing the fluorescence detection intensities output from the detection element 3a for the four regions of the region RXa, the region RXb, the region RYa, and the region RYb while performing a predetermined weighting calculation. This total value will be referred to as analog signals Xa, Xb, Ya, Yb.
- the photodetector 3 also outputs an analog signal ENG indicating the fluorescence intensity in addition to the above-described analog signal relating to the fluorescence generation position. Since this analog signal ENG is a result of fluorescence detection on the entire detection surface 3b, it does not have information on the position where fluorescence is generated. Instead, the analog signal ENG has information about the energy of the radiation associated with the fluorescence.
- the light guide 4 is provided to guide the fluorescence generated in the scintillator 2 to the photodetector 3. Therefore, the light guide 4 is optically coupled to the scintillator 2 and the photodetector 3.
- FIG. 3 conceptually shows the digitization process for the analog signal Xa.
- the analog signal Xa is a pulse-like signal, and the intensity of the analog signal Xa integrated by time means the fluorescence intensity in the region RXa. Therefore, the A / D conversion circuit 13 integrates the analog signal Xa with respect to time and outputs the result as a digital signal DXa.
- the A / D conversion circuit 13 integrates the analog signals Xb, Ya, Yb, ENG in terms of time and outputs the results as digital signals DXb, DYa, DYb, DENG.
- the signal delay unit 11 is provided so that the analog signals are not simultaneously input to the A / D conversion circuit 13.
- the signal delay unit 11 extends each analog signal output from the photodetector 3 by extending the time until the analog signal output from the photodetector 3 is input to the A / D conversion circuit 13.
- the A / D conversion circuit 13 is sequentially input.
- the delay circuit A delays the input analog signal Xb by 0.5 ⁇ s and inputs it to the A / D conversion circuit 13.
- the delay circuit B delays the input analog signal Ya by 1 ⁇ s and inputs it to the A / D conversion circuit 13
- the delay circuit C delays the input analog signal Yb by 1.5 ⁇ s to A
- the signal is input to the / D conversion circuit 13.
- the delay circuit D delays the input analog signal ENG by 2 ⁇ s and inputs it to the A / D conversion circuit 13.
- the signal delay unit 11 corresponds to the signal delay means of the present invention.
- FIG. 5 shows the output of the signal delay unit 11.
- the signal delay unit 11 delays the analog signal Xb by 0.5 ⁇ s, the analog signal Ya by 1 ⁇ s, the analog signal Xb by 1.5 ⁇ s, and the analog signal ENG by 2 ⁇ s with respect to the analog signal Xa.
- the signal is input to a circuit related to the A / D conversion circuit 13 through the wiring.
- analog signals are sequentially input to the A / D conversion circuit 13 in the order of Xa, Xb, Ya, Yb, and ENG as shown in FIG. 6, and the analog signals do not overlap each other.
- the radiation count rate is sufficiently low, and the radiation is detected within 100 ⁇ s only during 10 ⁇ s. Therefore, even in a configuration that requires five times as long as the conventional configuration in digitizing the radiation detection data shown in FIG. 5, the digitization operation can be performed with sufficient time.
- each analog signal is delayed by the signal delay unit 11 by a different inherent time with respect to a certain analog signal.
- the signal delay unit 11 shifts the timing at which each analog signal is input to the A / D conversion circuit 13 by delaying each analog signal by a predetermined time (0.5 ⁇ s in the above example). In this way, it is not necessary to set the delay time individually for each analog signal.
- the analog signal that is not delayed is Xa, but the present invention can prevent other analog signals from being delayed.
- the delay times of 0.5 ⁇ s, 1 ⁇ s, 1.5 ⁇ s, and 2 ⁇ s correspond to the analog signals Xb, Ya, Yb, and ENG.
- the present invention appropriately changes this correspondence. Can do.
- Each analog signal is delayed by 0.5 ⁇ s, but this value can be changed as appropriate.
- the analog signal Xa is input to the A / D conversion circuit 13 without passing through any of the delay circuits A to D. Accordingly, the signal delay unit 11 has a number of delay circuits that is one less than the type of analog signal output by the photodetector 3. The number of delay circuits is such that a plurality of analog signals are sequentially input to the A / D conversion circuit 13 as long as other analog signals are appropriately delayed with respect to one type of analog signal. Because it ’s enough to make it happen. In this way, the signal delay unit 11 does not operate on the analog signals that are first input to the A / D conversion circuit 13 among the analog signals that are simultaneously output by the photodetector 3 that has detected the fluorescence. In this way, since the signal delay unit 11 does not delay the signal for the analog signal first input to the A / D conversion circuit 13, the operation is not delayed as much as possible, and the response as the detector as the detector. Will be better.
- the delay circuits A to D included in the signal delay unit 11 have a simple structure and less power consumption than the circuit that realizes the A / D conversion circuit 13. Therefore, the radiation detector according to the present invention is more compact and consumes less power than a conventional configuration having A / D conversion units corresponding to the number of types of analog signals.
- Each analog signal Xa, Xb, Ya, Yb, ENG passes through the filter unit 12 and is converted into a digital signal DXa, DXb, DYa, DYb, DENG by the A / D conversion circuit 13.
- digital signals DXa, DXb, DYa, and DYb related to the position specification of the fluorescence are sent to the position calculation unit 14.
- the position calculation unit 14 calculates the fluorescence generation position (X, Y) based on the following two equations.
- the position calculation unit 14 calculates where in the scintillator 2 the fluorescence is generated based on each of the digital signals.
- the filter unit 12 corresponds to the filter unit of the present invention
- the position calculation unit 14 corresponds to the position calculation unit of the present invention.
- X (DXa ⁇ DXb) / (DXa + DXb)
- Y (DYa ⁇ DYb) / (DYa + DYb)
- Fluorescence generation position (X, Y) and fluorescence energy DENG are grouped with data indicating the fluorescence generation time, and are output from the radiation detector 1 as a data set indicating the fluorescence detection results.
- the pileup determination unit 15 determines whether a pileup has occurred. First, the phenomenon called pile-up will be described. When radiation enters the scintillator 2, fluorescence is generated and the scintillator 2 emits light. This light emission continues for a while while gradually fading, and it takes a certain time to settle.
- the analog signal output from the photodetector 3 has a trailing pulse shape as shown in FIG. 3 indicates that the light emission of the scintillator 2 is weakened.
- the pileup determination unit 15 corresponds to a pileup determination unit of the present invention.
- FIG. 7 shows the change over time of the fluorescence emission intensity measured by the photodetector 3 separately from the analog signals Xa, Xb, Ya, Yb, and ENG when the radiation is incident on the scintillator 2 where the emission is not sufficiently settled. It is represented by The phenomenon in which two fluorescences overlap as shown in the figure is derived from the fact that a plurality of radiations enter the scintillator 2 of the radiation detector 1 in a short time, and is called pile-up.
- the photodetector 3 sequentially monitors the fluorescence emission intensity, and generates a trigger signal Tr when the emission intensity rises to a certain threshold value a. This trigger signal Tr is sent to the pile-up determination unit 15.
- the pile-up determination unit 15 waits until the next trigger signal Tr is sent. Then, the pile-up determining unit 15 determines that the pile-up has occurred when the interval T from the time when the previous trigger signal Tr is sent to the time when the next trigger signal Tr is sent is equal to or shorter than a predetermined time. And the determination result Dp is sent to the filter unit 12.
- the filter unit 12 discards each analog signal related to the pileup sent from the filter unit 12 so as not to send it to the A / D conversion circuit 13 in the subsequent stage. In this way, the filter unit 12 discards the signal related to the pile-up output from the photodetector 3 and does not input it to the A / D conversion circuit 13.
- the filter unit 12 sends a signal indicating that a part of the signal is discarded to the A / D conversion circuit 13 and the position calculation unit 14.
- a digital signal such as an analog signal Xa related to pileup that has reached the A / D conversion circuit 13 before the occurrence is determined is discarded.
- the pile-up determination unit 15 is based on the time interval from when the photodetector 3 inputs the trigger signal Tr indicating that the scintillator 2 has generated fluorescence to when the next trigger signal Tr is input. In the course of the decay of the fluorescence generated when the radiation is incident on the scintillator 2, it is determined whether or not there is a pile-up that is a phenomenon in which the radiation is incident again on the scintillator 2 and the intensity of the fluorescence that has been attenuated is increased again. To do.
- the trigger signal Tr is used for determining the pileup, but it can also be used as a signal indicating the start of operation of the A / D conversion circuit 13 and the position calculation unit 14.
- FIG. 8 represents an analog signal Xa and an analog signal Xb that are input to the A / D conversion circuit 13 with a time difference.
- FIG. 8 is a time course showing a signal input to the A / D conversion circuit 13, and is different from FIG. 7 showing the time course of the emission intensity detected by the photodetector 3, so care should be taken.
- the analog signal Xa when the analog signal Xa is sent to the A / D conversion circuit 13, the input of the A / D conversion circuit 13 does not readily become 0 even after the strength is considerably reduced. That is, the analog signal Xa causes tailing, and the influence is not easily contained on the input side of the A / D conversion circuit 13. If this tailing is ignored and the next analog signal Xb is sent to the A / D conversion circuit 13, as shown in the upper side of FIG. 8, the A / D conversion circuit 13 receives the signal related to the analog signal Xb and the analog signal Xa. A signal obtained by summing up signals related to tailing is input. In such a situation, as shown in the upper side of FIG. 8, when the analog signal Xb is A / D converted, the signal intensity derived from the analog signal Xa indicated by hatching is greatly estimated.
- the A / D conversion circuit 13 of the present invention resets the baseline for the purpose of solving such a problem.
- the baseline is a signal strength defined as 0 when the A / D conversion circuit 13 receives an analog signal, and is adjusted by the A / D conversion circuit 13 setting a bias for the input.
- This baseline initially corresponds to a state where no current is input to the A / D conversion circuit 13 (or no voltage is applied). Based on this baseline, the A / D conversion circuit 13 recognizes the strength of the analog signal Xa. After measuring the magnitude of the analog signal Xa, the A / D conversion circuit 13 measures the magnitude of the current (or the magnitude of the voltage) input before the next analog signal Xb is input.
- the baseline is reset so as to newly set the size and the like of the baseline.
- the A / D conversion circuit 13 of the present invention is configured to reset the base line on the input side immediately before the analog signals Ya, Yb, ENG are input, as indicated by the arrows in the lower part of FIG. .
- the timing at which each analog signal Xb, Ya, Yb, ENG is input to the A / D conversion circuit 13 can be known based on the analog signal Xa. That is, the setting of the signal delay unit 11 determines that each analog signal is input at a timing delayed by a specific delay time from the reception of the analog signal Xa.
- the A / D conversion circuit 13 of the present invention resets the baseline of the analog signal Xb based on the setting of the signal delay unit 11 after 0.5 ⁇ s has elapsed since the input of the analog signal Xa started. Do it before you do it. It is desirable to reset the baseline when a time has elapsed as much as possible after the input of the previous analog signal Xa has started. This is because the tailing component of the previous analog signal Xa gradually settles with time.
- the A / D conversion circuit 13 also completes the resetting of the baselines for the other analog signals Ya, Yb, and ENG until 1 ⁇ s, 1.5 ⁇ s, and 2 ⁇ s elapse from the time when the input of the analog signal Xa is started. In this way, the A / D conversion circuit 13 sets the signal strength during tailing in which the signal strength does not gradually change as the attenuation of the input analog signal progresses to the baseline, and executes the next digitization operation. .
- each of the units 12, 14, 15 is realized by an arithmetic device provided in the radiation detector 1.
- Each of these units may be realized by a CPU.
- the present invention it is possible to provide the radiation detector 1 that is compact, consumes less power, and operates accurately by suppressing the number of A / D conversion circuits 13.
- the present invention increases the time until the analog signal output from the photodetector 3 is input to the A / D conversion circuit 13, thereby sequentially switching the analog signals output simultaneously from the photodetector 3.
- the A / D converter circuit 13 is configured to input to the A / D converter circuit 13. In this way, all analog signals output from the photodetector 3 can be digitized by the single A / D conversion circuit 13.
- the present invention since it is not necessary to provide a plurality of A / D conversion circuits 13 in the radiation detector, power consumption can be suppressed, and noise can be reduced accordingly. Further, according to the radiation detector 1 according to the present invention, a clock signal that synchronizes the A / D conversion circuit 13 is not necessary, so that noise derived from the clock signal does not occur.
- the signal strength related to tailing generated by the previous analog signal is set to the input baseline, and the next analog signal is set. If the signal is digitized, the next analog signal is not often estimated due to the influence of tailing.
- the present invention is not limited to the above-described configuration, and can be modified as follows.
- Each set value in each embodiment is an example. Accordingly, each set value can be freely changed.
- the scintillator crystal referred to in each of the above embodiments is composed of LYSO.
- LGSO Li 2 (1-X) G 2X SiO 5
- GSO Ga 2
- the scintillator crystal may be made of other materials such as SiO 5 ). According to this modification, it is possible to provide a method of manufacturing a radiation detector that can provide a cheaper radiation detector.
- the photodetector may be a photomultiplier tube, or a photodiode, an avalanche photodiode, a semiconductor detector, or the like may be used.
- the present invention is suitable for medical devices.
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Abstract
Description
X={(A1+A3)-(A2+A4)}/{(A1+A2+A3+A4)}……(1)
Y={(A1+A2)-(A3+A4)}/{(A1+A2+A3+A4)}……(2)
すなわち、従来構成の放射線検出器は、回路が複雑であるという問題点がある。
すなわち、本発明に係る放射線検出器は、放射線を蛍光に変換するシンチレータと、シンチレータの蛍光の発生位置を示した複数のアナログ信号および蛍光の強度を示したアナログ信号を出力する光検出器と、各アナログ信号をデジタル信号に変換するA/D変換回路と、光検出器から出力されたアナログ信号がA/D変換回路に入力されるまでの時間を延長することにより、光検出器から同時に出力された各アナログ信号を順番にA/D変換回路に入力させる信号遅延手段と、デジタル信号の各々に基づいて蛍光がシンチレータのどこで発生したかを算出する位置算出手段とを備えることを特徴とするものである。
上述の構成によれば、信号遅延手段が最初にA/D変換回路に入力されるアナログ信号については信号の遅延を行わないので、極力動作が遅れず、レスポンスがよい放射線検出器を提供できる。
上述の構成によれば、信号遅延手段が各アナログ信号を所定の時間ずつ遅延させる構成となっている。このように所定の時間を決めるようにすれば、各アナログ信号について個別に遅延時間を設定しなくてもよくなる。
図1に示すように、実施例1に係る放射線検出器1は、シンチレータ結晶Cが縦横に配列されて構成されたシンチレータ2と、シンチレータ2の下面に設けられ、シンチレータ2から発する蛍光を検知する光検出器3と、シンチレータ2と光検出器3との間に介在する位置に配置されたライトガイド4とを備える。シンチレータ結晶Cの各々は、Ceが拡散したLu2(1-X)Y2XSiO5(以下、LYSOとよぶ)によって構成されている。シンチレータ2に放射線が入射すると、放射線は蛍光に変換される。
この様なアナログ信号Xa,Xb,Ya,Yb,ENGは、種々の計算処理を行う前段階としてA/D変換回路13によりデジタル信号に変換される。図3は、アナログ信号Xaについてのデジタル化処理を概念的に表している。アナログ信号Xaは、パルス状の信号であり、アナログ信号Xaの強度を時間で積分したものが領域RXaにおける蛍光の強度を意味している。したがって、A/D変換回路13は、アナログ信号Xaを時間的に積分してその結果をデジタル信号DXaとして出力するようになっている。この様な事情は他のアナログ信号Xb,Ya,Yb,ENGについても同じである。A/D変換回路13は、アナログ信号Xb,Ya,Yb,ENGを時間的に積分してその結果をデジタル信号DXb,DYa,DYb,DENGとして出力するようになっている。
光検出器3は、蛍光を検出するとアナログ信号Xa,Xb,Ya,Yb,ENGを出力する。そして、各アナログ信号の出力のタイミングは、図4のタイムコースが示すように同時となっている。各アナログ信号は、共通の蛍光についての出力だからである。このような事情を考慮せずにアナログ信号Xa,Xb,Ya,Yb,ENGをA/D変換回路13に入力させると、各アナログ信号の合計に相当する信号がA/D変換されるだけで、各アナログ信号に対応するデジタル信号DXa,DXb,DYa,DYb,DENGは得られない。
そこで、本発明によれば、信号遅延部11を備え、各アナログ信号をA/D変換回路13に同時に入力させないようにしている。この信号遅延部11は、光検出器3から出力されたアナログ信号がA/D変換回路13に入力されるまでの時間を延長することにより、光検出器3から同時に出力された各アナログ信号を順番にA/D変換回路13に入力させる構成となっている。
各アナログ信号Xa,Xb,Ya,Yb,ENGは、フィルタ部12を通過しA/D変換回路13によりデジタル信号DXa,DXb,DYa,DYb,DENGに変換される。これらのうち蛍光の位置特定に係るデジタル信号DXa,DXb,DYa,DYbは、位置算出部14に送出される。位置算出部14は、次の2式に基づいて、蛍光の発生位置(X,Y)を算出する。このように、位置算出部14は、デジタル信号の各々に基づいて蛍光がシンチレータ2のどこで発生したかを算出する。フィルタ部12は、本発明のフィルタ手段に相当し、位置算出部14は、本発明の位置算出手段に相当する。
X=(DXa-DXb)/(DXa+DXb)
Y=(DYa-DYb)/(DYa+DYb)
パイルアップ判定部15は、パイルアップが発生したかどうかを判定している。まずは、このパイルアップという現象について説明する。放射線がシンチレータ2に入射すると、蛍光が発生し、シンチレータ2が発光する。この発光は、次第に弱まりながらもしばらく続き、収まるまでに一定の時間がかかる。光検出器3が出力するアナログ信号が図3のような尾を引くパルス状となるのは、シンチレータ2の発光が弱まっていく様子を表しているのである。パイルアップ判定部15は、本発明のパイルアップ判定手段に相当する。
続いて、本発明の特徴の一つであるA/D変換回路13が行うベースラインのリセットについて説明する。上述のように、シンチレータ2で発生した蛍光が完全に収まるのに時間がかかるので、蛍光の強度を反映したアナログ信号Xa,Xb,Ya,Yb,ENGも完全に0になるのに時間がかかる。図8上側は、A/D変換回路13に時間差をもって入力されるアナログ信号Xaとアナログ信号Xbとを表している。図8は、A/D変換回路13に入力される信号を表したタイムコースであり、光検出器3が検出した発光強度のタイムコースを示した図7とは異なるので注意が必要である。
3 光検出器
11 信号遅延部(信号遅延手段)
12 フィルタ部(フィルタ手段)
13 A/D変換回路
14 位置算出部(位置算出手段)
15 パイルアップ判定部(パイルアップ判定手段)
Claims (5)
- 放射線を蛍光に変換するシンチレータと、
前記シンチレータの蛍光の発生位置を示した複数のアナログ信号および蛍光の強度を示したアナログ信号を出力する光検出器と、
各アナログ信号をデジタル信号に変換するA/D変換回路と、
前記光検出器から出力されたアナログ信号が前記A/D変換回路に入力されるまでの時間を延長することにより、前記光検出器から同時に出力された各アナログ信号を順番に前記A/D変換回路に入力させる信号遅延手段と、
デジタル信号の各々に基づいて蛍光が前記シンチレータのどこで発生したかを算出する位置算出手段とを備えることを特徴とする放射線検出器。 - 請求項1に記載の放射線検出器において、
前記光検出器が前記シンチレータで蛍光が発生したことを示すトリガー信号を入力してから次のトリガー信号を入力するまでの経時的間隔に基づいて、放射線が前記シンチレータに入射して生じた蛍光が減衰していく過程で放射線が前記シンチレータに再び入射し、減衰しつつあった蛍光の強度が再び強まる現象であるパイルアップの発生の有無を判定するパイルアップ判定手段と、
前記光検出器から出力されたパイルアップに係る信号を破棄して前記A/D変換回路に入力させないフィルタ手段とを備えることを特徴とする放射線検出器。 - 請求項1または請求項2に記載の放射線検出器において、
前記A/D変換回路は、入力したアナログ信号の減衰が進むにつれ信号強度が次第に変化しなくなるテーリングが発生中の信号強度をベースラインに設定して次回のデジタル化動作を実行することを特徴とする放射線検出器。 - 請求項1ないし請求項3のいずれかに記載の放射線検出器において、
前記信号遅延手段は、蛍光を検出した前記光検出器が同時に出力する各アナログ信号のうち、最初に前記A/D変換回路に入力されるものについては動作しないことを特徴とする放射線検出器。 - 請求項1ないし請求項4のいずれかに記載の放射線検出器において、
前記信号遅延手段は、各アナログ信号を所定の時間ずつ遅延させることにより各アナログ信号が前記A/D変換回路に入力するタイミングをずらすことを特徴とする放射線検出器。
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PCT/JP2014/051863 WO2015114740A1 (ja) | 2014-01-28 | 2014-01-28 | 放射線検出器 |
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JPH10221455A (ja) * | 1997-02-05 | 1998-08-21 | Jeol Ltd | X線発生検出装置 |
JPH1123721A (ja) * | 1997-07-07 | 1999-01-29 | Hamamatsu Photonics Kk | 放射線位置検出装置 |
WO2012032689A1 (ja) * | 2010-09-06 | 2012-03-15 | 株式会社島津製作所 | 放射線検出器 |
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JPS63295985A (ja) * | 1987-05-28 | 1988-12-02 | Shimadzu Corp | シンチレ−シヨンカメラ |
JPH10221455A (ja) * | 1997-02-05 | 1998-08-21 | Jeol Ltd | X線発生検出装置 |
JPH1123721A (ja) * | 1997-07-07 | 1999-01-29 | Hamamatsu Photonics Kk | 放射線位置検出装置 |
WO2012032689A1 (ja) * | 2010-09-06 | 2012-03-15 | 株式会社島津製作所 | 放射線検出器 |
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JP2023517792A (ja) * | 2020-01-02 | 2023-04-27 | レイキャン テクノロジー シーオー., エルティーディー. (スーチョウ) | 信号サンプリング方法及び再構成方法、並びに装置 |
JP7418871B2 (ja) | 2020-01-02 | 2024-01-22 | レイキャン テクノロジー シーオー., エルティーディー. (スーチョウ) | 信号サンプリング方法及び再構成方法、並びに装置 |
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