JP2015040791A - Radiation detection apparatus, and radiation inspection apparatus and radiation imaging apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation detector capable of suppressing an influence of energy resolution or the like on performance by suppressing characteristic change of a semiconductor radiation detection unit, and a radiation inspection apparatus and a radiation imaging apparatus each using the radiation detector.SOLUTION: A radiation detector includes: a plurality of semiconductor radiation detection units each detecting a radiation; a power supply applying a bias voltage to the semiconductor radiation detection units; and an application-direction switching mechanism switching a direction of the bias voltage applied to the semiconductor radiation detection units from the power supply over between a forward direction and an opposite direction, only the bias voltage in the forward direction being applied to the semiconductor radiation detection units when detection processing for detecting the radiation is carried out, and characteristic recovery processing involving application of the bias voltage at least in the opposite direction being carried out at timing other than timing of the detection processing.

Description

  The present invention relates to a radiation detection apparatus using a semiconductor radiation detector, and a radiation inspection apparatus and a radiation imaging apparatus using the radiation detection apparatus.

  Examples of application fields of gamma ray measurement include gamma camera devices, single photon emission tomography (SPECT) devices, and positron emission type devices that emit gamma rays emitted from radiopharmaceuticals administered into the body of a subject. Examples include a nuclear medicine diagnostic apparatus that measures with a tomographic imaging (PET) apparatus. Other application fields include radiation bomb terrorism dosimeters using radiation measurement devices and gamma cameras for nuclear power plants.

  Conventionally, a semiconductor radiation detector mounted on such a radiation detection apparatus is a combination of a scintillator that converts radiation into light and a photomultiplier tube that detects and amplifies the light. In recent years, a structure that directly converts electric charges generated by the interaction between radiation such as γ-rays and a semiconductor crystal into an electric signal has high expectations for a semiconductor radiation detector that has high energy resolution and can be miniaturized. It is growing.

  Examples of semiconductor crystals used in semiconductor radiation detectors include silicon (Si) and germanium (Ge), cadmium telluride (CdTe), cadmium zinc telluride (CZT), gallium arsenide (GaAs), and the like. In particular, thallium bromide (TlBr) is expected to have a large linear attenuation coefficient due to the photoelectric effect due to its large atomic number and density, and it can be expected to obtain γ-ray sensitivity equivalent to other semiconductor crystals with thinner crystals. Yes.

  The thallium bromide radiation detector is used in a configuration in which charges are collected by forming an electrode so that a semiconductor crystal is sandwiched between electrode materials such as gold, platinum, and palladium, and applying a bias voltage between the two electrodes. However, when a bias voltage is applied to the semiconductor radiation detector having such a configuration and operated for a long time, accumulation of cations such as Tl + (thallium ion) near the cathode electrode, It is known that the element characteristics of a semiconductor radiation detector, which is considered to be caused by accumulation of anions such as Br- (bromine ion), change, and affect performance such as energy resolution.

  For the purpose of suppressing such a characteristic change of the semiconductor radiation detector, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2009-156800), an element is formed by inserting a thallium layer into an electrode of a thallium bromide radiation detector. Technology that attempts to suppress changes in characteristics over a long period of time, and attempts to enable long-term use by reversing the positive and negative bias voltages for charge collection applied to the thallium bromide radiation detector at regular intervals. Techniques to do this are disclosed.

JP 2009-156800 A

  However, the above prior art has the following problems.

  In semiconductor radiation detectors, since the mobility and lifetime of electrons and holes are different, the signal waveform is detected depending on whether the gamma rays have reacted near the + side or the near side of the semiconductor radiation detector. Changes. For example, when gamma rays are incident from a direction perpendicular to the electrode surface, the amount of reaction near the incident surface is large due to the attenuation effect in the semiconductor radiation detector, and the number of reactions on the opposite surface is small. The characteristics vary greatly depending on the direction of voltage application. Also, depending on the electrode structure of the semiconductor radiation detector, a dead area where gamma rays cannot be detected appears only on the + side or the − side. Therefore, if the bias voltage application direction is reversed, the sensitivity of the semiconductor radiation detector changes. That is, when gamma rays are likely to hit a specific location in the semiconductor radiation detector, the element characteristics change depending on the direction of the bias voltage applied to the semiconductor radiation detector, and the characteristics such as energy resolution change. There was a problem of end.

  The present invention has been made in view of the above, and a radiation detection apparatus capable of suppressing an influence on performance such as energy resolution by suppressing a change in characteristics of a semiconductor radiation detector, and a radiation inspection using the same The object is to provide a device and radiation.

  To achieve the above object, the present invention provides a plurality of semiconductor radiation detectors for detecting radiation, a power source for applying a bias voltage to the semiconductor radiation detector, and applied from the power source to the semiconductor radiation detector. An application direction switching mechanism for switching the direction of the bias voltage between the forward direction and the reverse direction, and only the forward bias voltage is applied to the semiconductor radiation detector when performing the detection process for detecting radiation, and other than during the detection process. Is provided with a control unit that controls the application direction switching mechanism so as to perform at least a characteristic recovery process involving application of a bias voltage in the reverse direction.

  According to the present invention, the influence on the performance such as energy resolution can be suppressed by suppressing the characteristic change of the semiconductor radiation detector.

It is a figure which shows the whole structure of the radiography apparatus shown as an example of the apparatus provided with the radiation detection apparatus which concerns on 1st Embodiment. It is a figure which shows schematically the structure of the camera in 1st Embodiment. It is a figure which shows schematically the electronic circuit of the camera in 1st Embodiment. It is a functional block diagram which shows typically the structure of the control part in 1st Embodiment. It is a flowchart which shows operation | movement of the radiation detection apparatus in 1st Embodiment. It is a figure which shows the change with time passage of the bias voltage applied to a detector in 1st Embodiment. It is a figure which shows schematically the electronic circuit of the camera in 2nd Embodiment. It is a functional block diagram which shows typically the structure of the control part in 2nd Embodiment. It is a figure which shows the opening-and-closing state of each switch in 2nd Embodiment, and the voltage applied with time passage. It is a figure which shows the opening-and-closing state of each switch in 3rd Embodiment, and the voltage applied with time passage.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing an overall configuration of a radiation inspection apparatus shown as an example of an apparatus provided with a radiation detection apparatus according to the present embodiment. 2 is a diagram schematically showing the configuration of the camera, and FIG. 3 is a diagram schematically showing an electronic circuit of the camera. FIG. 4 is a functional block diagram schematically showing the configuration of the control unit.

  In FIG. 1, a single photon emission tomography apparatus which is a kind of radiation inspection apparatus according to the present embodiment includes a gantry 10, two cameras 11A and 11B supported by the gantry 10 facing each other, and a radiation inspection apparatus. It is schematically configured to include a control unit 12 that controls the overall operation, a display device 13 that displays various setting screens, inspection results, and the like.

  The gantry 10 is provided with a bed 14 on which a subject 15 by a radiological examination apparatus is placed, and has a structure in which the subject 15 can be moved relative to the gantry 10. The subject 15 placed on the bed 14 is administered with a radiopharmaceutical containing 99 mTc having a half-life of 6 hours, for example, as a source of γ-rays detected by the cameras 11A and 11B. The cameras 11A and 11B are installed so as to be able to be driven in the radial direction and the circumferential direction of the gantry 10, and at the time of tomographic imaging, the camera 11 rotates around the subject 15 around the gantry mounting portion. Then, γ rays emitted from the radiopharmaceutical (99mTc) accumulated in the tumor or the like in the body of the subject 15 are detected by the cameras 11A and 11B, and the detection result is processed by the control unit 12, whereby the tomographic image of the subject 15 is obtained. Is generated.

  In FIG. 2, the cameras 11A and 11B respectively select a plurality of collimators 26 that select γ rays emitted from the body of the subject 15 and pass only γ rays in a certain direction, and γ that have passed through each collimator 26. A plurality of detectors (semiconductor radiation detectors) 21 for detecting the line, a temperature detector 39 for detecting the temperature of the detector 21, and a γ-ray detection signal detected by the plurality of detectors 21 are amplified and digitally converted. The data including the ID of the detector 21 that has detected the γ-ray, the peak value of the γ-ray, and the detection time is collected by processing the analog front-end circuit 25 and the signal from the analog front-end circuit 25 to collect the signal. And a data collection circuit 27 to be sent to the control unit 12. The plurality of detectors 21 are arranged side by side with a collimator 26 on a detection board 23, and the analog front end circuit 25 and the data collection circuit 27 are arranged on a measurement board 24 connected to the detection board 23. Yes.

  The detector 21, the detector board 23, the circuit board 24, and the collimator 26 constituting the cameras 11A and 11B are covered with a light-shielding / γ-ray / electromagnetic shield 29 formed of iron, lead, or the like. Extra light, gamma rays, electromagnetic waves, etc. are blocked.

  The data integrated circuit 27 is configured by, for example, an FPGA (Field Programmable Gate Array) or the like in consideration of a function change or the like. Further, the analog front-end circuit 25 needs to process a fine analog signal for a large number of channels, and is configured by, for example, an application specific integrated circuit (ASIC).

  The detector 21 in the present embodiment is a radiation detector formed of thallium bromide crystals. For example, an electrode (not shown) is sandwiched between electrode materials such as gold, platinum, palladium, and the like. And charge collection by applying a bias voltage between the two electrodes.

  In FIG. 3, one end (one electrode) of a plurality of detectors 21 arranged on the detection substrate 23 of the cameras 11 </ b> A and 11 </ b> B is connected to a high voltage power line 34. The high voltage power line 34 is connected to a high voltage power supply 32A that applies a positive voltage via a high voltage switch 33A, and is connected to a high voltage power supply 32B that applies a negative voltage via a high voltage switch 33B.

  The other end (the other electrode) of the detector 21 is connected to the analog front end circuit 25. A plurality of charge amplifiers 35 are provided in the analog front end circuit 25, and the plurality of detectors 21 are connected to the corresponding charge amplifiers 35.

  Each output of the charge amplifier 35 is connected to a corresponding shaping amplifier 36. The charged signal output from the detector 21 by the incidence of γ rays is converted into a voltage signal by the charge amplifier 35 and the shaving amplifier 36, amplified, and output to the multiplexer 37.

  The multiplexer 37 processes the outputs of the plurality of shaving amplifiers 36 to convert them into one signal, and outputs it to the A / D converter 38. The operations of the multiplexer 37 and the A / D converter 38 are controlled by the data acquisition circuit 27. The data acquisition circuit 27 controls the multiplexer 37 and the A / D converter 38 in the analog front-end circuit 25 during the radiation detection process, reads out the peak value of the necessary channel (detector), and outputs it to the control unit 12. To do.

  Here, in the present embodiment, the bias voltage when applying a positive voltage (+ voltage) to one (one electrode) of the detector 21 is the forward bias voltage, and one (one) of the detector 21. The bias voltage when a negative voltage (− voltage) is applied to the negative electrode) is defined as a reverse bias voltage.

  In this embodiment, since the thallium bromide element (crystal) constituting the detector 21 has no polarity, the bias voltage in any direction may be defined as the forward direction or the reverse direction. The form is defined as described above for explanation. In this embodiment, a separate power source is prepared for each direction of the bias voltage applied to the detector 21. For example, one insulated power source is used, and both sides of the power source are switched by a switch. May be configured. Further, the positive and negative voltages may be different, and in that case, the application time is appropriately configured so as to change according to the voltage.

  In FIG. 4, the control unit 12 has a function of controlling the operation of the entire radiation examination apparatus and also functions as a data processing apparatus in the radiation detection apparatus.

  The control unit 12 includes a storage unit 12A that stores various programs, setting values, examination results (tomographic image information, tomographic images, etc.), the peak value of γ rays detected by the cameras 11A and 11B, detection time, and A tomographic image information creating unit 12B that takes in data including a detector (channel) ID, generates a planar image, generates tomographic image information (tomographic image) by image reconstruction, and displays it on the display device 13, and a detector 21 includes an application time measuring unit 12 </ b> C that measures the time during which forward and reverse bias voltages are applied.

  FIG. 5 is a flowchart illustrating the operation of the radiation detection apparatus according to the present embodiment, and FIG. 6 is a diagram illustrating a change of the bias voltage applied to the detector with time.

  In FIG. 5, when the operation of the radiation detection apparatus is instructed together with the operation of the radiation inspection apparatus, the control unit 12 first switches the switches 33A and 33A as preview operations for previewing data for patient positioning and apparatus operation confirmation. By alternately opening and closing 33B, the bias voltage to be applied to the detector 21 is alternately applied at a constant cycle in the forward direction and the reverse direction (see step S100, the pre-bye mode in FIG. 6). Note that the reverse bias voltage is applied to the detector 21 only during the preview period, and there is no problem with a decrease in measurement accuracy caused by applying the reverse bias voltage.

  Subsequently, in the measurement period, a forward bias voltage is applied to the detector 21 as a measurement operation (see step S110, the collection mode in FIG. 6). Since data such as uniformity is measured in accordance with the forward bias voltage, accurate data acquisition is possible.

  Subsequently, when the measurement period ends and a monitoring period (including a preview period) for confirming the measurement result is reached, a measurement time (a time during which a bias voltage is applied) is used as a characteristic recovery process for recovering the characteristics of the detector 21. In response to this, a reverse bias voltage is applied (see step S120, the characteristic recovery process in FIG. 6).

  Thereafter, it is determined whether or not to end the measurement operation (step S130). If the determination result is NO, the mode is switched to a mode (preview mode) in which the direction of the bias voltage is periodically switched. If the determination result is YES Ends the operation.

  Since the detector 21 is deteriorated and recovered in a short time when the temperature is high, the temperature is measured using the thermometer 39 built in the cameras 11A and 11B, and the reverse direction in the characteristic recovery process is determined according to the measurement result. Adjust the bias voltage application time.

  Further, in the single photon emission tomography apparatus, since measurement is not performed when moving a patient or a detector, it is possible to restore the characteristics of the detector 21 by applying a reverse bias voltage during that period. It is.

  Moreover, in thallium bromide, the deterioration of the detector remains for a long time even when the power is turned off, so if the power is turned off during the recovery of the detector, it will affect after the next measurement. Therefore, for example, the application time of the forward and reverse bias voltages is stored in the non-volatile memory, and when the operation is forcibly terminated due to an unexpected power shutdown or the like, the characteristic recovery processing operation is carried over from the next time onward. You may comprise as follows. Further, when the characteristic recovery of the detector 21 by the characteristic recovery process cannot be sufficiently performed, a warning may be issued.

  The effect of the present embodiment configured as described above will be described.

  The thallium bromide radiation detector is used in a configuration in which charges are collected by forming an electrode so that a semiconductor crystal is sandwiched between electrode materials such as gold, platinum, and palladium, and applying a bias voltage between the two electrodes. However, when a bias voltage is applied to the semiconductor radiation detector having such a configuration and operated for a long time, accumulation of cations such as Tl + (thallium ion) near the cathode electrode, It is known that the element characteristics of a semiconductor radiation detector, which is considered to be caused by accumulation of anions such as Br- (bromine ion), change, and affect performance such as energy resolution.

  In the prior art, by inserting a thallium layer into the electrode of the thallium bromide radiation detector, a technique for suppressing changes in device characteristics over a long period of time, or a charge collection bias applied to the thallium bromide radiation detector It was intended to enable long-term use by using the voltage with the voltage reversed at regular intervals.

  However, in semiconductor radiation detectors, the mobility and lifetime of electrons and holes are different, so gamma rays are detected depending on whether they react near the + side or minus side of the semiconductor radiation detector. The signal waveform changes. For example, when gamma rays are incident from a direction perpendicular to the electrode surface, the amount of reaction near the incident surface is large due to the attenuation effect in the semiconductor radiation detector, and the number of reactions on the opposite surface is small. The characteristics vary greatly depending on the direction of voltage application. Also, depending on the electrode structure of the semiconductor radiation detector, a dead area where gamma rays cannot be detected appears only on the + side or the − side. Therefore, if the bias voltage application direction is reversed, the sensitivity of the semiconductor radiation detector changes. That is, when gamma rays are likely to hit a specific location in the semiconductor radiation detector, the element characteristics change depending on the direction of the bias voltage applied to the semiconductor radiation detector, and the characteristics such as energy resolution change. There was a problem of end.

  In contrast, in the present embodiment, a plurality of semiconductor radiation detectors that detect radiation, a power source that applies a bias voltage to the semiconductor radiation detector, and a direction of a bias voltage that is applied from the power source to the semiconductor radiation detector And an application direction switching mechanism for switching between forward and reverse directions, and only a forward bias voltage is applied to the semiconductor radiation detector when performing a detection process for detecting radiation, and at least reverse except during the detection process. Since the characteristic recovery process with application of the direction bias voltage is performed, the influence on the performance such as the energy resolution can be suppressed by suppressing the characteristic change of the semiconductor radiation detector.

  A second embodiment of the present invention will be described with reference to the drawings.

  In the present embodiment, the leakage current is measured for each of the plurality of detectors in the first embodiment, and the characteristic recovery process is performed based on the measurement result.

  FIG. 7 is a diagram schematically showing the electronic circuit of the camera in the present embodiment, and FIG. 8 is a functional block diagram schematically showing the configuration of the control unit. FIG. 9 is a diagram showing the open / closed state of each switch in FIG. 7 and the applied voltage over time. In the figure, the same members as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In FIG. 7, one end (one electrode) of a plurality of detectors 21 arranged on the detection board 23 of the cameras 11 </ b> A and 11 </ b> B is connected to a high voltage power line 34. The high voltage power line 34 is connected to a high voltage power source 32A that applies a positive voltage via a high voltage switch 33A, and is connected to a high voltage power source 32B that applies a negative voltage via a high voltage switch 33B, and is connected to a ground switch 33C. Is grounded.

  The other end (the other electrode) of the detector 21 is connected to the analog front end circuit 25. A plurality of charge amplifiers 35 are provided in the analog front end circuit 25, and the plurality of detectors 21 are connected to the corresponding charge amplifiers 35 via input switches 42. The transmission line connecting the detector 21 and the input switch 42 is connected to the power source of the front end circuit 25 via the bias voltage switch 41A and grounded via the bias voltage switch 41B.

  The charge amplifier 35 is provided with a discharge switch 43 that connects both ends of the feedback capacitor 45 in order to release the charge of the feedback capacitor 45 connected for charge storage. Normally, a resistor is provided in parallel with the feedback capacitor 45 in order to stabilize the operation of the charge amplifier 35, but the illustration is omitted. If this resistor also hinders operation, it can be considered to switch in series so that it can be disconnected. In addition, a leakage current canceller or a protection circuit may be connected to the input of the charge amplifier 35 so that the leakage current generated in the detector 21 does not affect the measurement. Is configured so as to be disconnected from the input of the charge amplifier 35.

  Each output of the charge amplifier 35 is connected to a corresponding shaping amplifier 36. The charged signal output from the detector 21 by the incidence of γ rays is converted into a voltage signal by the charge amplifier 35 and the shaving amplifier 36, amplified, and output to the multiplexer 37.

  The multiplexer 37 processes the outputs of the plurality of shaving amplifiers 36 to convert them into one signal, and outputs it to the A / D converter 38. The operations of the multiplexer 37 and the A / D converter 38 are controlled by the data acquisition circuit 27. During the radiation detection process, the data collection circuit 27 controls the multiplexer 37 and the A / D converter 38 in the analog front end circuit 25 to read out the necessary peak value of the channel (detector) and output it to the control unit 120. To do.

  In FIG. 8, the control unit 120 of the present embodiment has a function of controlling the operation of the entire radiation inspection apparatus and also functions as a data processing device in the radiation detection apparatus.

  The control unit 120 includes a storage unit 12A for storing various programs, set values, examination results (tomographic image information, tomographic images, etc.), the peak value of γ rays detected by the cameras 11A and 11B, detection time, and A tomographic image information creating unit 12B that takes in data including a detector (channel) ID, generates a planar image, generates tomographic image information (tomographic image) by image reconstruction, and displays it on the display device 13, and a detector 12C includes an application time measuring unit 12C that measures the time during which the forward and reverse bias voltages are applied to 21 and a deterioration state determination mechanism 12D that determines the deterioration state of the characteristics of each of the plurality of detectors 21. .

  As shown in FIG. 9, in the measurement operation of the present embodiment, the voltage is periodically inverted during the preview period, and a forward bias voltage is applied during the measurement period. This is the same as in the first embodiment. At this time, in order to measure the charge signal from the detector 1, the input switch 42 connecting the charge amplifier 35 and the detector 21 is in an ON state (closed state), and the other switches are in an OFF state (open state). ).

  When the measurement is completed and the apparatus can be stopped, first, a characteristic recovery operation is performed in which a reverse bias voltage is applied in accordance with the measurement time (forward bias voltage application time).

  Here, an operation of individual correction processing for correcting each characteristic variation of the plurality of detectors 21 is performed.

  In the individual correction process, first, the leakage current of each detector 21 is measured. The following processing will be described as being performed individually for each detector 21 unless otherwise described. At the time of measurement of each detector 21, the input switch 42 is turned off (opened) so that the fluctuating current generated when switching the high voltage power supply does not affect the charge amplifier 35. At the same time, the bias voltage switch 41A is turned on (closed) in order to release the leakage current. The bias voltage switch 41B may be turned on (closed state), or a system in which current is released to the power supply or ground by a protective diode without using a switch may be used. Further, it is desirable to reduce noise at the start of current integration by making the destination of leakage current the same as the voltage during normal operation of the charge amplifier 35.

  The charge amplifier 35 and the detector 21 are disconnected by opening the input switch 42, and at the same time, the discharging switch 43 is turned ON (closed state). As a result, the charges accumulated in the hoodback capacitor 45 are discharged.

  Subsequently, when the voltage applied to the high-voltage power supply line 34 is stabilized, the leakage current is measured. In order to connect the charge amplifier 35 and the detector 21, the input switch 41 is turned on (closed) at the same time as the bias voltage switch 41 </ b> B that has leaked the leakage current is turned off (open). Furthermore, integration of the leakage current is started by turning off the discharge switch 43 (open state). When the bias voltage is + (forward direction) and the leak current flows into the front end circuit 25, the charge amplifier 35 performs a feedback operation so that the voltage of the input unit becomes constant, and thus the output voltage decreases. For example, when a leak current of 1 nA flows in the feedback capacitor 1 pF, a voltage drop of 1 V occurs at the output of the charge amplifier 35 after 1 msec.

  After integrating the current for a certain period, the leakage current is measured when a reverse bias voltage is applied. At the same time that the input switch 42 is turned off (opened), the bias voltage switch 41A is turned on (closed). At the normal bias voltage, the discharge switch 43 is also in the ON state (closed state), but remains in the OFF state (open state) in order to store the previous leakage current amount. After reversing the voltage applied to the high-voltage power line, the leakage current integration is resumed.

  The input switch 42 is turned on (closed), and the bias voltage switch 41A is turned off (open). As a result, the leak current of the detector 21 is integrated by the charge amplifier 35. When a bias voltage of − (reverse direction) is applied to the detector 21, current flows out from the front end circuit 25. For this reason, the voltage of the charge amplifier 35 rises. It is possible to take a difference in current by integrating the current for the same time as in the case of + voltage (when a forward bias voltage is applied).

  Next, correction for each detector 21 is performed. The deterioration state determination unit 12D determines and extracts the detector 21 that is considered to have deteriorated characteristics based on the measurement result of the leakage current described above. Various methods can be considered for determining the deterioration of the characteristics. For example, when the calculated absolute value of the leakage current is equal to or greater than a predetermined threshold, it can be determined that the characteristics of the detector 21 are deteriorated. . By applying a reverse bias voltage to the detector 21 determined to have deteriorated characteristics, the characteristics of the plurality of detectors 21 are individually recovered. When the voltage applied to the high-voltage power supply line 34 is set to 0 V and the bias voltage switch 41B is turned on (closed), a reverse bias voltage is applied from the front end circuit 25 to the detector 21. When the bias voltage switch 41A is turned on (closed), no voltage is applied to the detector 21. In this way, a reverse bias voltage is applied only to the detector 21 whose deterioration has progressed to restore the characteristics. The connection destination of the bias voltage switch 41B can be connected to the power supply line of the front end circuit 25 or a higher power supply line, or the high voltage power supply line can be set to 0 V or less to give a larger reverse bias voltage. It is. The measurement of the leak current and the individual correction process are repeated, and the process is repeated until there is no detector 21 that should perform the specified number of times correction or characteristic correction.

  In addition, when each of the characteristic variations of the detectors of the plurality of detectors 21 is corrected as in the present embodiment, the two processes of measuring the leakage current of the detector 21 and the correction process are performed for each detector 21. Therefore, it is desirable to perform the operation at the time of starting up, shutting down, or performing maintenance.

  Other configurations are the same as those of the first embodiment.

  Also in the present embodiment configured as described above, the same effects as in the first embodiment can be obtained.

  A third embodiment of the present invention will be described with reference to the drawings.

  This embodiment is configured so as to divide and measure the leakage current of each detector in the second embodiment.

  FIG. 10 is a diagram showing the open / closed state of each switch in FIG. 7 and the applied voltage over time. In the figure, members similar to those of the second embodiment are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 10, in the measurement operation of the present embodiment, the leakage current is measured for the three states of the positive side, the negative side, and the zero point while changing the voltage applied to the high-voltage power supply line 34. Do. And it calculates based on the measurement result of the leakage current in three states, and calculates the target detector 21 leakage current by calculation.

  In the leakage current measurement, the voltage applied to the high-voltage power supply line 34 is set to + (the high-voltage switch 33A is closed), and the discharge switch 43 of the charge amplifier 35 is turned on (closed). After the voltage applied to the high-voltage power line 34 is stabilized, the discharge switch 43 is turned off (opened). In this state, the charge amplifier 35 is charged by the leak current of the detector 21, and the output voltage gradually decreases (similar to the second embodiment).

  After a predetermined time has elapsed, the input switch 42 is turned off (opened). As a result, the inflow of leak current to the charge amplifier 35 is stopped, and the voltage fluctuation of the charge amplifier 35 does not occur. In this state, the voltage of the charge amplifier 35 is A / D converted and stored as a digital value. Next, in order to measure the leakage current on the negative side, the discharge switch 43 is turned on (closed), the voltage of the charge amplifier 35 is returned, and a negative bias voltage is applied to the high-voltage power supply line 34 (high-voltage switch 33B). Is closed).

  After the applied voltage is stabilized, the discharge switch 43 is turned off (opened), and the current is integrated for a certain time. Thereafter, the input switch 42 is turned off (opened), and the voltage of the charge amplifier 35 is measured.

  The same measurement is also performed when the voltage of the high-voltage power supply line 34 is set to 0 V (when the ground switch 33C is closed). Generation of noise in the switch operation can be canceled by using measurement data when the voltage of the high-voltage power supply line 34 is 0V.

  Thereafter, the deterioration state of each detector 21 is calculated from the leakage current obtained from the three measurements.

  Only the detector 21 that can be determined to be deteriorated by turning on one of the bias voltage switches 41A and 41B (closed state) is recovered.

  In the present embodiment, the measurement of the leakage current is performed three times. However, the leakage current may be measured a plurality of times in order to reduce errors.

  Other configurations are the same as those of the second embodiment.

  Also in the present embodiment configured as described above, the same effects as those of the first and second embodiments can be obtained.

  In the above, the case where the radiation detection apparatus according to the present embodiment is used in a single photon emission tomography apparatus, which is a kind of radiation inspection apparatus, has been described as an example. Needless to say, the present invention can be applied to a radiation imaging apparatus.

DESCRIPTION OF SYMBOLS 10 Gantry 11A, 11B Camera 12,120 Control part 13 Display apparatus 14 Bed 15 Subject 21 Detector 23 Detection board 24 Measurement board 25 Analog front end circuit 26 Collimator 27 Data collection circuit 32A, 32B High voltage power supply 33A, 33B High voltage switch 34 High voltage Power line 35 Charge amplifier 36 Shaving amplifier 37 Multiplexer 38 A / D converter 39 Temperature detector 41A, 41B Bias voltage switch 42 Input switch

Claims (10)

A plurality of semiconductor radiation detectors for detecting radiation;
A power supply for applying a bias voltage to the semiconductor radiation detector;
An application direction switching mechanism for switching a direction of a bias voltage applied from the power source to the semiconductor radiation detector between a forward direction and a reverse direction;
Only a forward bias voltage is applied to the semiconductor radiation detector when performing a detection process for detecting radiation, and at least a characteristic recovery process involving application of a bias voltage in the reverse direction is performed other than during the detection process. A radiation detection apparatus comprising: a control unit that controls the application direction switching mechanism. The radiation detection apparatus according to claim 1,
A voltage application time measuring unit for measuring the time of applying a forward bias voltage and a reverse bias voltage to the semiconductor radiation detector,
The said control part controls the application time of the reverse bias voltage in the said characteristic recovery process based on the measurement result by the said voltage application time measurement part, The radiation detection apparatus characterized by the above-mentioned. The radiation detection apparatus according to claim 1,
A voltage application time measuring unit for measuring the time of applying a forward and reverse bias voltage to the semiconductor radiation detector, and
A temperature detector for detecting the ambient temperature of the semiconductor radiation detector,
The control unit performs the characteristic recovery processing based on the application time of the forward bias voltage to the semiconductor radiation detector measured by the voltage application time measurement unit and the detection result of the temperature detector. A radiation detection apparatus for controlling a time during which a reverse bias voltage is applied to a radiation detector. The radiation detection apparatus according to claim 3.
The control unit applies only a forward bias voltage to the semiconductor radiation detector when performing a detection process for detecting radiation, and at least a characteristic recovery process involving applying a bias voltage in the reverse direction other than during the detection process And the application direction switching mechanism is controlled so as to alternately apply a forward bias voltage and a reverse bias voltage in cases other than the detection process and other than the characteristic recovery process. apparatus. The radiation detection apparatus according to any one of claims 1 to 4,
The semiconductor radiation detector is formed of thallium bromide crystal. The radiation detection apparatus according to any one of claims 1 to 4,
A deterioration state determination mechanism for determining a deterioration state of characteristics for each of the plurality of semiconductor radiation detectors;
An applied voltage switching mechanism that applies different voltages to each of the plurality of semiconductor radiation detectors,
The said control part controls the said application direction switching mechanism and the said applied voltage switching mechanism based on the determination result from the said deterioration state determination mechanism, The radiation detection apparatus characterized by the above-mentioned. The radiation detection apparatus according to claim 6.
The degradation state detection mechanism includes a leakage current detector that detects a leakage current of the semiconductor radiation detector, and detects a degradation state of characteristics of the semiconductor radiation detector based on the leakage current. Radiation detection device. The radiation detection apparatus according to claim 6.
The degradation state detection mechanism has a leakage current detector that detects a leakage current of the semiconductor radiation detector, and based on a difference between a forward leakage current and a backward leakage current of the semiconductor radiation detector. A radiation detection apparatus for detecting a deterioration state of characteristics of a semiconductor radiation detector.   A radiation inspection apparatus comprising the radiation detection apparatus according to claim 1.   A radiation imaging apparatus comprising the radiation detection apparatus according to claim 1.

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