JP5009330B2 - Radiation detector - Google Patents

Description

  The present invention relates to a radiation detection apparatus for detecting radiation emitted from a radioisotope in a subject with a semiconductor detector and acquiring distribution information of the radioisotope in the subject, and more particularly to a polar generated in the semiconductor detector. The present invention relates to a semiconductor PET (Positron Emission Tomography) apparatus that can efficiently eliminate the activation.

  Conventionally, in a diagnostic method using a PET apparatus, first, a test drug labeled with a positron (positron) nuclide that is a radioisotope is introduced into the body of a subject by injection or inhalation. The test drug introduced into the body is accumulated in a specific part having a function corresponding to the test drug. For example, when a saccharide test drug is used, it is selectively accumulated at sites with high metabolism such as cancer cells. At this time, positrons are emitted from the positron nuclide of the test agent, and when the emitted positrons and surrounding electrons are combined and annihilated, two gamma rays are emitted in the direction of about 180 degrees. Therefore, the two gamma rays are simultaneously detected by a gamma ray detector arranged around the subject and processed by a computer or the like, thereby obtaining a positron nuclide distribution image (PET image) in the subject. The CT scan (computer tomography) apparatus used as a precision diagnostic apparatus can obtain structural information such as lesions in the body, whereas the PET apparatus can obtain functional information in the body of the subject, and thus various pathologies of intractable diseases. Elucidation becomes possible.

  In addition, the semiconductor PET device uses a semiconductor detector employing a semiconductor material such as CdTe (cadmium telluride), GaAs (gallium arsenide), TlBr (thallium bromide) as a gamma ray detector, and is a device using a scintillator. Compared to high spatial resolution.

  Among such semiconductor PET devices, a semiconductor PET device having a countermeasure against a polarization phenomenon called polarization is also known (see, for example, Patent Document 1).

  Polarization is a phenomenon that appears prominently in a Schottky CdTe semiconductor detector. When a bias voltage is continuously applied to the Schottky CdTe semiconductor detector, electrons are attracted to the vicinity of the electrode and an electric field in the detector is detected. Is a phenomenon in which the sensitivity of the detector decreases. Polarization is eliminated by setting the bias voltage applied to the semiconductor detector to zero or an extremely low voltage value over a predetermined time. The predetermined time depends on the magnitude of the bias voltage applied to the semiconductor detector and the time during which the application of the bias voltage is continued.

  The PET apparatus described in Patent Document 1 includes, for example, a power source (11), a protective resistor (12), a smoothing capacitor (13), a constant current diode (15, 16), a photo MOS relay (17), and a switch control device. A bias application circuit (106a) including (18) (see FIG. 1 of Patent Document 1), and after applying a bias voltage of 500 V to the semiconductor detector for 3 minutes, over a reset time of 0.2 seconds or more. Polarization is eliminated by repeating the operation of setting the bias voltage to zero and then returning the bias voltage to 500V.

JP 2006-184139 A

  However, the bias application circuit described in Patent Document 1 has a configuration in which six constant current diodes (15, 16) are connected in series, and if one of them fails, a large current is supplied to the power source (11). May flow. Further, the polarization is eliminated in a state in which the power source (11) and the semiconductor radiation detector (14) remain connected (current flows from the power source (11) to the semiconductor radiation detector (14)). Therefore, the polarization cannot be effectively eliminated (see FIG. 1 and paragraph [0020] of Patent Document 1).

  In view of the above, an object of the present invention is to provide a radiation detection apparatus capable of eliminating the polarization in a semiconductor detector while preventing adverse effects on a power supply that applies a bias voltage to the semiconductor detector.

  In order to achieve the above object, a radiation detection apparatus according to the present invention is a radiation detection apparatus including a semiconductor detector that detects radiation emitted from a radioisotope in a subject, the power source and the semiconductor detector. A contact switch element connected between the first switch element, one end connected to the first wiring connecting the contact switch element and the semiconductor detector, and the other end grounded; And a controller that controls opening and closing of the contact-type switch element and the first switch element. Thereby, the radiation detection apparatus according to the present invention can eliminate the polarization in the semiconductor detector while preventing the adverse effect on the power supply that applies the bias voltage to the semiconductor detector.

  Furthermore, a second wiring in which a resistor and a second switching element are connected in series, the second wiring having one end connected to the first wiring and the other end grounded, the second switching element, It is preferable that opening and closing is controlled by the controller. As a result, the radiation detection apparatus according to the present invention can prevent excessive fluctuation of the bias voltage and elimination of excessive discharge current from the smoothing capacitor when the polarization is eliminated.

  Furthermore, a voltage detector that detects that the voltage applied to the semiconductor detector has reached a predetermined pressure is further provided, and the controller controls opening and closing of each switch element based on an output of the voltage detector. Is preferred. As a result, the radiation detection apparatus according to the present invention can flexibly switch the switching timing of the switching element according to the change of the discharge characteristic even when the discharge characteristic of the smoothing capacitor changes according to the aging deterioration or the change of the environmental temperature. And can be appropriately adapted.

  Further, the first wiring preferably includes a coil in the wiring. Thereby, the radiation detection apparatus concerning this invention can remove the switching noise etc. which generate | occur | produce in a switch element.

  Further, the power source is preferably a variable DC voltage source. Thereby, the radiation detection apparatus according to the present invention can gradually decrease the bias voltage.

  In addition, the semiconductor detector includes a plurality of contacts, and the contact type switch element is connected between the power source and each of the plurality of semiconductor detectors, and the first switch element is the contact type switch. It is preferable that one end is connected to the first wiring connecting the element and the plurality of semiconductor detectors, and the other end is grounded. Thus, the radiation detection apparatus according to the present invention can further reduce the number of components and simplify the configuration.

  With the above-described means, the present invention can provide a radiation detection apparatus capable of eliminating the polarization in the semiconductor detector while preventing the adverse effect on the power supply that applies the bias voltage to the semiconductor detector.

It is a block diagram which shows the structural example of the radiation detection apparatus which concerns on this invention. It is the schematic which shows the structural example of the radiation detection apparatus which concerns on this invention. It is a circuit diagram (the 1) of the bias application circuit used with the radiation detection apparatus which concerns on this invention. It is a timing chart which shows the relationship between the opening / closing state of each switch element, and the bias voltage in a capacitor | condenser. It is a circuit diagram (the 2) of the bias application circuit used with the radiation detection apparatus which concerns on this invention. It is a circuit diagram (the 3) of the bias application circuit used with the radiation detection apparatus which concerns on this invention. It is a timing chart which shows the relationship between the switching state of each switch element, the output voltage of a variable DC voltage source, and the bias voltage in a capacitor | condenser. It is a circuit diagram in another example of composition of a radiation detection device concerning the present invention.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  FIGS. 1 and 2 are a block diagram and a schematic view showing a configuration example of a PET apparatus that is a radiation detection apparatus according to the present invention, respectively. The PET apparatus 100 includes a movable bed 50 on which a subject P is placed, A ring-shaped fixed gantry 30 is provided, and the movable bed 50 on which the subject P is placed is distributed over a wide range in the subject P while moving the movable bed 50 so as to pass through the ring of the fixed gantry 30. This is a device for detecting gamma rays emitted by positron nuclides, and comprises a control unit 1, an input unit 2, a semiconductor detector 3, a display unit 4, and an imaging range changing unit 5 as main components. The subject P is, for example, an experimental mouse.

  The control unit 1 is a computer including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), an NVRAM (Non-Volatile Random Access Memory), a timer, and the like. While the program corresponding to the image processing means 10 is stored in the ROM, the CPU executes the processing corresponding to the image processing means 10.

  The input unit 2 is a device for inputting various types of information to the control unit 1, and is, for example, a keyboard, a mouse, a touch panel, a voice recognition device, or the like.

  The semiconductor detector 3 is a device for detecting the spatial distribution and temporal distribution of gamma rays emitted from the subject P. For example, the semiconductor detector 3 is composed of a plate-like semiconductor crystal, and includes a ring-shaped fixed gantry 30. A plurality are arranged side by side along the circumference. Examples of the semiconductor crystal used in the semiconductor detector 3 include CdTe (cadmium telluride), GaAs (gallium arsenide), and TlBr (thallium bromide).

  Two gamma rays generated simultaneously when the positron from the positron nuclide disappears are emitted at an angle of about 180 degrees and enter the semiconductor detector 3 facing each other with the subject P interposed therebetween. Each of the two semiconductor detectors 3 on which the two gamma rays are incident generates an electrical signal (detection signal) in response to the incidence of the gamma rays and outputs the detection signal to the control unit 1.

  The display unit 4 is a device for displaying various types of information output by the control unit 1, and is a CRT monitor, a liquid crystal display, a projector, or the like, for example.

  The imaging range changing unit 5 is a mechanism for changing the imaging range of the PET apparatus 100, and is, for example, an electric motor for moving the movable bed 50 in the direction indicated by the bidirectional arrow AR in FIG.

  The image processing means 10 is a means for generating a PET image based on the detection signal output from each of the semiconductor detectors 3. For example, the image processing means 10 generates a PET image by coincidence detection and an image regeneration algorithm. In the coincidence detection, when there are two or more detection signals having substantially the same gamma ray incident times, the detection signals are determined to be valid and used as coincidence information. In the coincidence detection, a detection signal whose gamma ray incident times do not coincide is determined to be invalid and discarded.

  Further, the image processing means 10 uses a coincidence information and a position information of the semiconductor detector 3 that detects a gamma ray related to the coincidence information by a predetermined image regeneration algorithm (for example, expectation maximization (Expectation Maximization) method). A PET image is generated, and the generated PET image is output to the display unit 4.

  FIG. 3 is a circuit diagram of a bias application circuit used in the PET apparatus 100. The bias application circuit E1 includes a DC voltage source HV1, a capacitor C1, a voltage detection unit D1, resistors R1 and R2, switch elements SW1, SW2, And SW3, and the controller 20.

  The DC voltage source HV1 is a power source for generating a bias voltage that is a high-voltage DC voltage of, for example, 500 V to 1 kV, one end of which is grounded, and the other end is connected to the semiconductor detector 3 via the switch element SW1 and the resistor R1. Connected.

  The capacitor C1 is a smoothing capacitor for smoothing the bias voltage output from the DC voltage source HV1 and applying it to the semiconductor detector 3. For example, one end of the capacitor C1 is grounded and the other end is connected to the DC voltage source HV1 and the semiconductor detector. 3 is connected to a point on the wiring (hereinafter referred to as “first contact”). Thereby, the bias application circuit E1 can reduce the noise of the bias voltage applied to the semiconductor detector 3.

  The voltage detector D1 is an element for detecting whether or not the bias voltage applied to the capacitor C1 has reached a predetermined pressure. For example, when the bias voltage applied to the capacitor C1 exceeds or falls below a predetermined voltage value, the internal relay is activated. A meter relay that opens and closes, and outputs a detection result to the controller 20.

  In addition, the voltage detector D1 can monitor the deterioration of the semiconductor detector 3 by monitoring the bias voltage applied to the capacitor C1. If the semiconductor detector 3 is deteriorated due to aging or the like, a weak leakage current is generated even when no radiation is detected. For example, a voltage drop is generated at the resistor R1, thereby reducing the bias voltage applied to the capacitor C1. It is.

  The switch element SW1 is an element for directly grounding and discharging the capacitor C1 without any resistance, and is, for example, a contact reed relay having a high withstand voltage (for example, 5 kV), and one end thereof. Is connected to the ground, and the other end is connected to a point on the wiring between the DC voltage source HV1 and the semiconductor detector 3 (hereinafter referred to as “second contact”).

  The switch element SW2 is an element for grounding and discharging the capacitor C1 through the resistor R2. For example, like the switch element SW1, the switch element SW2 is a contact reed relay having a high withstand voltage (for example, 5 kV). Assuming a wire in which the resistor R2 and the switch element SW2 are connected in series, one end of the wire is grounded, and the other end of the wire is a point on the wire between the DC voltage source HV1 and the semiconductor detector 3 (hereinafter referred to as “wire”). , “Third contact”). Note that the arrangement of the resistor R2 and the switch element SW2 on the wiring is in no particular order.

  Further, the switch elements SW1 and SW2 may be contactless semiconductor switch elements such as photorelays, photocouplers, photoMOSs, etc., but contactless relays are more likely to be contactless semiconductor switch elements. This is more preferable because no voltage drop is generated when no ON resistance is present and the closed (energized) state is set.

  Further, the arrangement of the first contact, the second contact, and the third contact on the wiring between the DC voltage source HV1 and the semiconductor detector 3 is in no particular order.

  The switch element SW3 is a contact type switch element for preventing a short circuit between the DC voltage source HV1 and the ground via the resistor R1. For example, the switch element SW3 has a high withstand voltage (for example, 5 kV, as with the switch elements SW1 and SW2). In the case where the resistor R1 and the switch element SW3 are set in series, the set is connected in the wiring between the DC voltage source HV1 and the semiconductor detector 3. . Note that the arrangement of the resistor R1 and the switch element SW3 is in random order.

  In addition, one set of the resistor R1 and the switch element SW3 is disposed closer to the DC voltage source HV1 with respect to any of the first contact, the second contact, and the third contact.

  The resistor R1 is a resistor arranged to charge the capacitor C1 with a predetermined time constant, and the resistor R2 is a resistor arranged to discharge the capacitor C1 with a predetermined time constant.

  By selecting the size of the resistor R2, the bias application circuit E1 can discharge the bias voltage applied to the capacitor C1 at an arbitrary speed.

  The controller 20 is an element for controlling opening and closing of the switch elements SW1, SW2, and SW3. For example, the controller 20 is a programmable logic controller (PLC) or a dedicated electronic circuit, and switches based on the output of the voltage detection unit D1. Each of the elements SW1, SW2, and SW3 is opened and closed at a desired timing. Note that the controller 20 may be connected to the control unit 1 of the PET apparatus 100 and exchange various information with the control unit 1.

  In this embodiment, the bias voltage is 500 V, R1 is 100 kΩ, R2 is 1 MΩ, and the capacitor C1 is 1 nF. These values are appropriately selected according to the specifications of the amplifier AMP.

  The bias application circuit E1 is connected to the semiconductor detector 3 via the capacitor C1, and the semiconductor detector 3 outputs a detection signal to the control unit 1 of the PET apparatus 100 via the amplification amplifier AMP.

  The amplification amplifier AMP is for amplifying the detection signal output from the semiconductor detector 3, and is composed of, for example, an analog ASIC (Application Specific Integrated Circuit).

  Next, a process in which the controller 20 controls the opening and closing of the switch elements SW1, SW2, and SW3 will be described with reference to FIG. FIG. 4 is a timing chart showing the relationship between the open / close state of each switch element SW1, SW2, and SW3 and the bias voltage in the capacitor C1, and the horizontal axis shows the transition of time. In the present embodiment, the bias voltage adopts a positive value, but may adopt a negative value, and even when a negative value is adopted, the same explanation as below applies. Shall.

  First, when receiving a signal for starting PET image capturing from the control unit 1 of the PET apparatus 100, the controller 20 opens (shuts off) the switch elements SW1 and SW2. The switch elements SW1 and SW2 may be switched from the closed (energized) state to the open (shut-off) state at the same time, the switch element SW1 may be switched first, and the switch element SW2 may be switched. It may be the destination.

  Thereafter, when a sufficient time has elapsed for the switch elements SW1 and SW2 to switch to the open (shutoff) state, the controller 20 switches the switch element SW3 to the closed (energized) state and starts charging the capacitor C1.

  At this time, the bias voltage of the capacitor C1 rises to the same voltage of 500 V as that of the DC voltage source HV1 according to the time constant defined by the relationship with the resistor R1 (time constant of the RC primary delay circuit).

  When the voltage detection unit D1 detects that the bias voltage of the capacitor C1 exceeds a predetermined voltage (for example, 495V), the controller 20 notifies the semiconductor detector 3 that the detection is possible. May be output to the control unit 1 to start the image processing means 10 of the control unit 1.

  Thereafter, the controller 20 starts the polarization elimination process after continuing imaging for a period of time that does not cause excessive polarization in the semiconductor material in the semiconductor detector 3.

  In this case, the controller 20 may start the polarization elimination process when receiving a signal from the control unit 1 informing that a predetermined time (for example, 10 minutes) has elapsed since the start of imaging. Of course, the polarization elimination process may be started when it is detected that a predetermined time has elapsed since the start of shooting using the timer of the controller 20 itself.

  In the polarization elimination process, the controller 20 first switches the switch element SW3 to the open (shutoff) state. The DC voltage source HV1 and the switch elements SW1 and SW2 are physically separated (mechanically), and a large current is generated in the power supply HV1 due to dielectric breakdown or the like that may occur when a contactless semiconductor switch element is used. This is to prevent and protect the power supply HV1.

  Thereafter, the controller 20 switches the switch element SW2 to a closed (energized) state, and reduces (discharges) the bias voltage of the capacitor C1 in accordance with a time constant defined in relation to the resistor R2 (time constant of the RC first-order lag circuit). I will let you.

  Further, when the controller 20 detects that the bias voltage of the capacitor C1 has fallen below a predetermined voltage (for example, 250 V) by the voltage detection unit D1, the controller 20 switches the switch element SW1 to a closed (energized) state, The capacitor C1 is directly grounded without going through, and the bias voltage of the capacitor C1 is reduced (discharged) to zero.

  Thereafter, the controller 20 closes (energizes) each of the switch elements SW1, SW2, and SW3 until a sufficient time (for example, 0.4 seconds) elapses to cancel the polarization. (Electrification) state and open (shut off) state, and when sufficient time has passed to eliminate the polarization, switch elements SW1 and SW2 are switched to the open (shut off) state and the polarization elimination process is performed. Terminate.

  The switch elements SW1 and SW2 may be switched from the closed (energized) state to the open (shut-off) state at the same time, the switch element SW1 may be switched first, and the switch element SW2 may be switched. It may be the destination. In addition, the controller 20 may set the switch element SW2 in an open (cut-off) state before a sufficient time has passed to cancel the polarization after the switch element SW1 is closed (energized). This is because the polarization can be eliminated as long as the switch element SW1 is in a closed (energized) state.

  Thereafter, the controller 20 switches the switch element SW3 to a closed (energized) state, and increases the bias voltage of the capacitor C1 to 500 V again according to the time constant defined by the relationship with the resistor R1 (the time constant of the RC first-order lag circuit) ( Charging), and thereafter the above-described processing is repeated.

  With the above configuration, the bias application circuit E1 switches the switch element SW3 to an open (cut-off) state before discharging the capacitor C1, and physically disconnects the DC voltage source HV1. Polarization in the semiconductor detector 3 can be eliminated while reliably preventing adverse effects on the direct current voltage source HV1.

  Further, since the bias application circuit E1 switches the switch elements SW1 and SW2 to the open (cut off) state before bringing the switch element SW3 into the closed (energized) state, it physically separates the ground by them (mechanical). The capacitor C1 can be charged while reliably preventing adverse effects on the DC voltage source HV1 due to the elements for eliminating the polarization (switch elements SW1 and SW2).

  The bias application circuit E1 does not switch the switch element SW1 to the closed (energized) state at a fixed timing registered in advance, but detects that the bias voltage applied to the capacitor C1 has reached a predetermined pressure by the voltage detection unit D1. In addition, since the switch element SW1 is switched to the closed (energized) state, even if the discharge characteristic of the capacitor C1 changes in accordance with the aging deterioration or the change in environmental temperature, the change in the discharge characteristic changes. The switching timing of the switch element SW1 from the open (cut off) state to the closed (energized) state can be flexibly and appropriately adapted without generating an excessive discharge current and adversely affecting the amplification amplifier AMP. Polarization can be eliminated.

  In addition, the bias application circuit E1 grounds the capacitor C1 via the resistor R2 and reduces the bias voltage at the capacitor C1 to a predetermined voltage, and then directly grounds the capacitor C1 without any resistor and further discharges it. Therefore, excessive fluctuation of the bias voltage in the capacitor C1 and generation of excessive discharge current from the capacitor C1 can be prevented, and the amplification amplifier AMP can be protected.

  Next, another bias application circuit E2 used in the PET apparatus 100 will be described with reference to FIG. FIG. 5 is a circuit diagram of the bias application circuit E2.

  The bias application circuit E2 is different from the bias application circuit E1 in that the coil L1 and the resistor R3 are provided on the wiring between the DC voltage source HV1 and the semiconductor detector 3, but the bias application circuit E2 is common to the bias application circuit E1 in other points. To do. Therefore, the coil L1 and the resistor R3, which are different points, will be described while omitting the description regarding the common points.

  The coil L1 is an element for reducing noise in the bias voltage. For example, the coil L1 is suitable for removing high-frequency components in switching noise generated in the switch elements SW1, SW2, or SW3.

  The resistor R3 is an element for preventing an excessive charge current from flowing into the capacitor C1 or an excessive discharge current from flowing out from the capacitor C1, and includes a DC voltage source HV1 and a semiconductor detector. 3 between the first contact and the second contact on the wiring between the first and second contacts.

  With the above configuration, the bias application circuit E2 performs the polarization in the semiconductor detector 3 while reliably preventing variations in the bias voltage and the generation of excessive current in the amplifier AMP in addition to the above-described effects of the bias application circuit E1. Can be resolved.

  Next, still another bias application circuit E3 used in the PET apparatus 100 will be described with reference to FIG. FIG. 6 is a circuit diagram of the bias application circuit E3.

  The bias application circuit E3 includes a variable DC voltage source HV2 instead of the DC voltage source HV1 and is different from the bias application circuit E1 in that the switch element SW2 and the resistor R2 are omitted. In other points, the bias application circuit E3 differs from the bias application circuit E1. Common. Therefore, the variable DC voltage source HV2, which is a difference, will be described while omitting the description regarding the common points.

  The variable DC voltage source HV2 is a DC voltage source that can control the magnitude of the bias voltage to be output. For example, the variable DC voltage source HV2 can decrease the output voltage in accordance with a control signal output from the controller 20.

  By decreasing the output voltage of the variable DC voltage source HV2, the bias application circuit E3 can decrease the bias voltage applied to the capacitor C1 at an arbitrary speed.

  FIG. 7 is a timing chart showing the relationship between the open / close states of the switch elements SW1 and SW3, the output voltage of the variable DC voltage source HV2, and the bias voltage at the capacitor C1.

  First, when receiving a signal for starting PET image capturing from the control unit 1 of the PET apparatus 100, the controller 20 opens (cuts off) the switch element SW1.

  Thereafter, when a sufficient time has elapsed for the switch element SW1 to switch to the open (shutoff) state, the controller 20 switches the switch element SW3 to the closed (energized) state and starts charging the capacitor C1.

  At this time, the bias voltage of the capacitor C1 rises to a voltage of 500 V, which is the same as that of the DC voltage source HV2, in accordance with a time constant defined by the relationship with the resistor R1 (time constant of the RC primary delay circuit).

  Thereafter, the controller 20 starts the polarization elimination process after continuing imaging for a period of time that does not cause excessive polarization in the semiconductor material in the semiconductor detector 3.

  In the polarization elimination process, the controller 20 first outputs a control signal to the DC voltage source HV2, gradually decreases the output voltage of the DC voltage source HV2, and reduces (discharges) the bias voltage of the capacitor C1. To do.

  Thereafter, when the voltage detection unit D1 detects that the bias voltage of the capacitor C1 has fallen below a predetermined voltage (for example, 250 V), the controller 20 switches the switch element SW3 to an open (cut-off) state. This is because the DC voltage source HV2 and the switch element SW1 are physically separated.

  Thereafter, the controller 20 switches the switch element SW1 to the closed (energized) state, directly grounds the capacitor C1 without any resistance, and reduces (discharges) the bias voltage of the capacitor C1 to zero.

  At this time, although the discharge current from the capacitor C1 increases rapidly, the bias voltage of the capacitor C1 is already less than the predetermined voltage, so that it does not increase so as to adversely affect the amplification amplifier AMP.

  Thereafter, the controller 20 outputs a control signal to the DC voltage source HV2 so as to increase the output of the DC voltage source HV2 to the original 500V. This is to prepare for the next charging of the capacitor C1.

  Thereafter, the controller 20 closes (energizes) and opens (cuts off) the switch elements SW1 and SW3 until a sufficient time (for example, 0.4 seconds) elapses to eliminate the polarization. When a sufficient time has passed for canceling the polarization, the switch element SW1 is switched to the open (shut off) state and the polarization canceling process is terminated.

  Thereafter, the controller 20 switches the switch element SW3 to a closed (energized) state, and increases the bias voltage of the capacitor C1 to 500 V again according to the time constant defined by the relationship with the resistor R1 (the time constant of the RC first-order lag circuit) ( Charging), and thereafter the above-described processing is repeated.

  With the above configuration, the bias application circuit E3 physically switches the variable DC voltage source HV2 by switching the switch element SW3 to the open (cut-off) state before directly discharging the capacitor C1 without grounding any resistor. Since it is separated mechanically, the polarization in the semiconductor detector 3 can be eliminated while reliably preventing the adverse effect on the variable DC voltage source HV2 due to the polarization elimination process.

  In addition, the bias application circuit E3 switches the switch element SW1 to the open (cut off) state before switching the switch element SW3 to the closed (energized) state and physically (mechanically) separates the ground. The capacitor C1 can be charged while reliably preventing the adverse effect on the DC voltage source HV2 by the element for switching (switch element SW1).

  The bias application circuit E3 does not switch the switch element SW1 to the closed (energized) state at a fixed timing registered in advance, but detects that the bias voltage applied to the capacitor C1 has reached a predetermined pressure by the voltage detection unit D1. In addition, since the switch element SW1 is switched to the closed (energized) state, even if the discharge characteristic of the capacitor C1 changes in accordance with the aging deterioration or the change in environmental temperature, the change in the discharge characteristic changes. The switching timing of the switch element SW1 from the open (cut off) state to the closed (energized) state can be flexibly and appropriately adapted without generating an excessive discharge current and adversely affecting the amplification amplifier AMP. Polarization can be eliminated.

  In addition, since the bias application circuit E3 decreases the output of the variable DC voltage source HV2 to a predetermined voltage and then discharges the capacitor C1 directly to ground without passing through any resistor, the bias voltage in the capacitor C1 is excessive. Therefore, the amplification amplifier AMP can be protected by preventing excessive fluctuations and generation of excessive discharge current from the capacitor C1.

  Next, another embodiment of the PET apparatus according to the present invention will be described with reference to FIG. FIG. 8 is a circuit diagram of a bias application circuit (the same bias application circuit as the bias application circuit E1 in FIG. 3 and the reference symbol E1 is used as it is) in the PET apparatus 200, and one bias application. One bias application circuit E1 is one semiconductor detector in that the circuit E1 is connected to a plurality of semiconductor detectors 3-1 to 3-n (n is a natural number excluding zero) and is multi-channeled. 3 is the same as the PET apparatus 100 in other respects.

  With the configuration shown in FIG. 8, the PET apparatus 200 can collectively perform the polarization elimination processing for the plurality of semiconductor detectors 3-1 to 3-n with one bias application circuit E 1. Compared with the PET apparatus 100 including the bias application circuit E1 corresponding to each of the detectors 3, the number of components such as a switch element, a capacitor, and a resistor can be significantly reduced.

  This configuration can be similarly applied even when the bias application circuit E2 or E3 is used as the bias application circuit.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, in the above-described embodiment, the control unit 1 or the controller 20 opens (cuts off) the switch element SW3 during the polarization elimination process, and the DC voltage source HV1 or HV2 and the semiconductor detector 3 or amplification amplifier. A part other than the voltage source such as AMP is physically separated from the physical source (mechanical), but an abnormality has occurred in the DC voltage source HV1 or HV2 based on the output of the voltage detection unit D1 or the like, or the voltage source When it is detected that an abnormality has occurred in a part other than the DC voltage source HV1 or HV2 and the part other than the voltage source are physically (mechanically) separated by opening (cutting off) the switch element SW3. May be. This is in order to reliably protect the parts having no abnormality.

  In the present embodiment, the bias application circuits E1 to E3 are used to eliminate the polarization in the semiconductor detectors of the PET apparatuses 100 and 200. However, a CT (Computerized Tomography) apparatus, a PET-CT apparatus, You may utilize in order to eliminate the polarization in other radiation detection apparatuses provided with semiconductor detectors, such as a PET-MRI (Magnetic Resonance Imaging) apparatus or a radiation monitor apparatus.

DESCRIPTION OF SYMBOLS 1 Control part 2 Input part 3, 3-1 to 3-n Semiconductor detector 4 Display part 5 Imaging | photography range change part 10 Image processing means 20 Controller 30 Fixed gantry 50 Movable bed 100, 200 PET apparatus AMP, AMP1-AMPn Amplification amplifier C1 Capacitor D1 Voltage detection unit E1-E3 Bias application circuit HV1, HV2 DC voltage source L1 Coil R1-R3 Resistance SW1-SW3 Switch element

Claims (6)

A radiation detection apparatus comprising a semiconductor detector for detecting radiation emitted by a radioisotope in a subject,
A contact-type switch element connected between a power source and the semiconductor detector;
A first switch element having one end connected to the first wiring connecting the contact switch element and the semiconductor detector and the other end grounded;
A controller for controlling opening and closing of the contact-type switch element and the first switch element;
A radiation detection apparatus comprising: A second wiring in which a resistor and a second switch element are connected in series, and includes the second wiring having one end connected to the first wiring and the other end grounded,
The second switch element is controlled to be opened and closed by the controller.
The radiation detection apparatus according to claim 1. A voltage detector for detecting that the voltage applied to the semiconductor detector has reached a predetermined pressure;
The controller controls opening and closing of each switch element based on the output of the voltage detection unit,
The radiation detection apparatus according to claim 1, wherein: The first wiring includes a coil in the wiring,
The radiation detection apparatus according to any one of claims 1 to 3, wherein The power source is a variable DC voltage source.
The radiation detection apparatus according to any one of claims 1 to 4, wherein the radiation detection apparatus includes: The semiconductor detector is plural,
The contact type switch element is connected between the power source and each of the plurality of semiconductor detectors,
The first switch element has one end connected to the first wiring connecting the contact type switch element and the plurality of semiconductor detectors, and the other end grounded.
The radiation detection apparatus according to any one of claims 1 to 5, wherein the radiation detection apparatus includes:

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