JP5577507B2 - Radiation imaging device - Google Patents

Description

  The present invention relates to a radiation imaging apparatus.

  As a conventional technique, a time for applying a bias voltage is determined in accordance with a distance between an anode electrode and a cathode electrode of a CdTe semiconductor element and a magnitude of a bias voltage applied between these electrodes. A radiation detection method is known in which, after measurement is performed by applying a voltage, the application of the bias voltage is stopped to make the bias voltage zero (see, for example, Patent Document 1).

  The radiation detection method described in Patent Document 1 can recover the phenomenon in which the height and frequency of current pulses decrease in continuous measurement by pausing the application of a bias voltage for several seconds.

Japanese Patent No. 3151487

  However, in the radiation detection method described in Patent Document 1, when the number of CdTe semiconductor elements to which a bias voltage is applied by a bias power supply increases, the current required for the bias power supply to discharge and charge the bias voltage in a short time. There is a problem that the capacity increases.

  Accordingly, an object of the present invention is to provide a radiation imaging apparatus capable of reducing the current capacity required for a bias power source.

  In order to achieve the above object, the present invention provides a plurality of radiation detector groups having semiconductor elements for detecting radiation, a bias power source for supplying a bias voltage to each of the plurality of radiation detector groups, a bias power source, and a plurality of bias power sources. A second state is provided between each of the radiation detector groups and is in a first state in which a bias voltage is not supplied by an input first signal, and in which a bias voltage is supplied by an input second signal. A plurality of refresh units that are subjected to refresh processing of the target radiation detector group by being in the state, and a plurality of refresh units are output by outputting the first signal or the second signal to the plurality of refresh units Provided is a radiation imaging apparatus including a refresh control unit for controlling.

  In addition, it is preferable that a plurality of detector heads including at least one of the plurality of radiation detector groups are provided, and the number of bias power supplies is the same as the number of the plurality of detector heads.

  Moreover, it is preferable that said refresh control part outputs the 1st signal for performing a refresh process to each of several radiation detector groups to each refresh part according to a predetermined period.

  Moreover, it is preferable that said refresh control part outputs a 1st signal and a 2nd signal according to the period of a refresh process.

  The refresh control unit preferably generates a dummy event signal.

  Further, it is preferable that the refresh control unit adds time stamp information indicating a time when the first signal or the second signal is generated to the dummy event signal.

  The refresh control unit preferably outputs the first signal and the second signal to the refresh unit based on the acquired control signal.

  In addition, when the data collection time is shorter than the time required for the refresh process, the refresh process is preferably performed before the start of data collection or after the end of data collection.

  When the sum of the data collection time and the time required for the refresh process is shorter than the period, it is preferable that the refresh process period changes for each frame.

  In addition, when the time when the measurement of n frames following the first frame ends is shorter than the cycle, the refresh control unit satisfies that the time when the measurement of n frames ends is shorter than the cycle. Preferably, the refresh unit performs the refresh process before the start of the (n + 1) th measurement after the end of the measurement of the nth frame.

  With the radiation imaging apparatus according to the present invention, the current capacity required for the bias power supply can be reduced.

FIG. 1 is a schematic diagram of a nuclear medicine diagnostic apparatus according to the first embodiment. FIG. 2 is a perspective view of a detector head configured by arranging a plurality of radiation detectors according to the first embodiment. FIG. 3 is a perspective view of the radiation detector according to the first exemplary embodiment. FIG. 4 is a block diagram showing an outline of a circuit configuration of the nuclear medicine diagnosis apparatus according to the first embodiment. FIG. 5 is a block diagram of a radiation detection circuit mounted on the radiation detector according to the first embodiment and its peripheral circuits. FIG. 6 is a block diagram relating to a group of detectors according to the first embodiment. FIG. 7A is a schematic diagram relating to the first refresh processing according to the first embodiment, FIG. 7B is a schematic diagram relating to the second refresh processing, and FIG. It is the schematic regarding a refresh process. FIG. 8 is a block diagram showing an outline of a circuit configuration of the nuclear medicine diagnosis apparatus according to the second embodiment. FIG. 9 is a block diagram relating to a group of detectors according to the second embodiment. FIG. 10 is a block diagram of a radiation detection circuit and its peripheral circuits mounted on the radiation detector according to the third embodiment. FIG. 11 is a schematic diagram regarding dynamic scan data collection according to the first modification. FIG. 12 is a schematic diagram regarding static scan data collection according to the second modification. FIG. 13 is a schematic diagram regarding data collection in the ECG gate measurement mode according to the third modification. FIG. 14 is a schematic diagram regarding data collection by a SPECT scan according to the fourth modification. FIG. 15 is a schematic diagram regarding data collection in the high-speed fanning scan mode by the SPECT scan according to the fifth modification.

[Summary of embodiment]
A radiation imaging apparatus according to an embodiment includes a plurality of radiation detector groups having semiconductor elements that detect radiation, a bias power source that supplies a bias voltage to each of the plurality of radiation detector groups, a bias power source, and a plurality of radiations A second state is provided between each of the detector groups and is in a state in which a bias voltage is not supplied by an input first signal, and in which a bias voltage is supplied by an input second signal. By controlling the plurality of refresh units by outputting the first signal or the second signal to the plurality of refresh units and the plurality of refresh units that are subjected to the refresh process of the target radiation detector group by entering the state A refresh control unit.

[First Embodiment]
(Outline of the configuration of the nuclear medicine diagnostic apparatus 1)
FIG. 1 is a schematic diagram of a nuclear medicine diagnostic apparatus according to the first embodiment. The nuclear medicine diagnostic apparatus 1 as a radiation imaging apparatus detects, for example, radiation emitted from a drug administered to a subject, generates a reconstructed image obtained by reconstructing an image based on the detection result, and displays the display unit 91. Is displayed.

  For example, as shown in FIG. 1, the nuclear medicine diagnostic apparatus 1 arranges at least one detector head 3 rotatably in the opening 21, supports the detector head 3, and rotates it around the subject. A radiation detection apparatus 2 having a gantry 20 including a mechanism unit and a bed 22 for transporting a subject to an opening 21 of the gantry 20, imaging conditions, processing of collected data, formation of a reconstructed image, analysis of image data And the like, a control unit 8 that controls the image capturing conditions, image processing conditions, display conditions, an input unit 90 for inputting various instructions to the control device 8, and a display unit 91 for displaying reconstructed images and various instruction input information. And is schematically configured.

  The radiation detection device 2 and the control device 8 are connected by a communication cable 7. A radiation detection signal generated by detecting radiation emitted from the subject is output from the detector head 3 to the control device 8 via the gantry 20 by the communication cable 7. Various control signals are transmitted and received between the radiation detection device 2 and the control device 8.

(Configuration of detector head 3)
FIG. 2 is a perspective view of a detector head configured by arranging a plurality of radiation detectors according to the first embodiment. FIG. 3 is a perspective view of the radiation detector according to the first exemplary embodiment.

  The detector head 3 according to the present embodiment is configured by holding a plurality of radiation detectors 5 by a radiation detector stand 300 as shown in FIG. Specifically, a plurality of supports in which a plurality of grooves 311 into which the plurality of radiation detectors 5 are inserted are arranged at a predetermined distance according to the interval at which the plurality of radiation detectors 5 are arranged. 31, radiation detection comprising a base 30 on which the support 31 is mounted, and a plurality of connectors 32 provided between the plurality of supports 31 to which the card edge portions 60 of the plurality of radiation detectors 5 are respectively connected. A plurality of radiation detectors 5 are held in the instrument stand 300. A plurality of radiation detectors 5 according to the present embodiment are inserted and fixed in each of the plurality of grooves 311 of the support 31 to constitute the detector head 3 as shown in FIG.

  The plurality of supports 31 are provided on the base 30 with an interval corresponding to the width of the radiation detector 5. Each of the plurality of supports 31 has a plurality of wall portions 310, and a groove 311 is formed between the wall portions 310. The wall portion 310 is provided with a recessed portion 312 on one surface, and the other surface is a flat surface 313. The elastic member mounting portion 55 of the radiation detector 5 shown in FIG. 3 includes, for example, an elastic member 56 formed using sheet metal, and the radiation detector 5 is inserted into the groove 311 of the support 31. The radiation detector 5 is fixed to the support 31 by pressing the radiation detector 5 against the flat surface 313 of the wall portion 310 by the elastic member 56. Each of the plurality of supports 31 can be formed from a metal material by cutting or the like.

  The collimator 4 has a plurality of openings and is provided above the plurality of radiation detectors 5, that is, on the opposite side of the base 30 of the radiation detector 5. By using the collimator 4, only the radiation 6 from a specific direction can be detected by a CdTe element described later. As an example, the plurality of openings of the collimator 4 are formed in a substantially square shape.

(Configuration of radiation detector 5)
The radiation detector 5 according to the present embodiment is a radiation detector that detects radiation 6 such as γ-rays and X-rays. In FIG. 3, the radiation 6 enters from the upper side to the lower side of the page. That is, the radiation 6 propagates along the direction from the CdTe element 50 as a semiconductor element of the radiation detector 5 toward the card holder 53 and enters the radiation detector 5.

  In the radiation detector 5, the radiation 6 is incident on each side surface of the CdTe element 50 (that is, the surface facing upward in FIG. 3). Therefore, each side surface of the CdTe element 50 is an incident surface for the radiation 6. A radiation detector in which the side surface of the semiconductor element is the incident surface of the radiation 6 is referred to as an edge-on type radiation detector.

  The radiation detector 5 emits the radiation 6 via the collimator 4 having a plurality of openings through which the incident radiation 6 passes along a specific direction (for example, a direction from the subject toward the radiation detector 5). To detect. The collimator 4 is a perforated parallel collimator, but is not limited to this, and a pinhole collimator or the like may be used. The present embodiment can also be applied to a radiation detector that is not an edge-on type. In addition, the radiation detector 5 according to the present embodiment has a card shape.

  Further, the substrate 51 of the radiation detector 5 is sandwiched and supported by the card holder 53 and the card holder 54. The card holder 53 and the card holder 54 are formed to have the same shape, and the protruding portion 57 of the card holder 54 is fitted into the grooved hole 58 of the card holder 53 and the grooved portion of the card holder 54 has. The protrusions 59 included in the card holder 53 are fitted into holes (not shown) to support the substrate 51.

  The elastic member mounting portion 55 presses and fixes the radiation detector 5 against the radiation detector stand 300 when the radiation detector 5 is inserted into the radiation detector stand 300 that supports the plurality of radiation detectors 5. This is a portion where the elastic member 56 is provided. The radiation detector stand 300 has a connector 32 into which the card edge portion 60 is inserted. The radiation detector 5 is formed on the card edge portion 60 by inserting the card edge portion 60 into the connector 32. The pattern 60a and the connector 32 are electrically connected.

  In the radiation detector 5, for example, four CdTe elements 50 are arranged at a constant interval on one side of the substrate 51, and four CdTe elements 50 are arranged at a constant interval on the other side.

  The flexible substrate 52 is a substrate formed using, for example, a film-like resin (for example, polyimide).

  The flexible substrate 52 has connection portions 520 to 523 having a substantially semicircular shape at a lower portion with respect to the paper surface of FIG. The connection parts 520 to 523 are patterns formed using a conductive material, and are formed using Cu or the like, for example. As shown in FIG. 3, the connection part 520 is configured to be electrically connected to the substrate terminal 510. Similarly, the connection portion 521 is electrically connected to the substrate terminal 511, the connection portion 522 is electrically connected to the substrate terminal 512, and the connection portion 523 is electrically connected to the substrate terminal 513. In FIG. 3, illustration of a substrate terminal electrically connected to the flexible substrate on the opposite side of the flexible substrate 52 and the flexible substrate on the opposite side is omitted.

  A plurality of grooves (not shown) provided in the CdTe element 50 are provided on the element surface at substantially equal intervals. Furthermore, the CdTe element 50 has seven grooves as an example.

  Each portion of the CdTe element divided by the groove corresponds to one pixel (pixel) that detects the radiation 6. Thereby, one CdTe element has a plurality of pixels. When one radiation detector 5 includes eight CdTe elements 50 and one CdTe element 50 includes eight pixels, one radiation detector 5 has a resolution of 64 pixels. By increasing or decreasing the number of grooves, the number of pixels of one CdTe element 50 can be increased or decreased.

  Further, the substrate 51 has a first end side width on which each of the plurality of CdTe elements 50 is mounted, and a width of the second end opposite to the first end side on which the plurality of CdTe elements 50 are mounted. It is formed wider than the part side. The substrate 51 is supported by the card holder 53 and the card holder 54 on the second end side. Further, a card edge portion 60 provided with a plurality of patterns 60a capable of electrically connecting the radiation detector 5 and an external control circuit is provided on the second end side. Further, between the element connection part (not shown) formed on the substrate 51 that is electrically connected to the CdTe element 50 and the card edge part 60, each of the plurality of CdTe elements 50 and the element connection part are interposed. A plurality of electronic component mounting portions 61 for mounting electronic components such as resistors and capacitors to be electrically connected are provided. The electronic component mounting unit 61 is mounted with an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and the like which will be described later.

  As an example, the substrate 51 is formed to have a length of about 40 mm in the wide direction, that is, the longitudinal direction. The substrate 51 has a short direction from the end of the wide portion to the end of the narrowed portion, that is, from the end of the portion where the element connecting portion is provided to the end of the card edge portion 60. In FIG. 2, the length is about 20 mm.

In this embodiment, the compound semiconductor constituting the semiconductor device, for example, was used CdTe not limited to, radiation detection is CdZnTe (CZT) element γ rays, a compound semiconductor such as HgI ₂ elements An element can also be used.

(Circuit configuration of the nuclear medicine diagnostic apparatus 1)
FIG. 4 is a block diagram showing an outline of a circuit configuration of the nuclear medicine diagnosis apparatus according to the first embodiment.

  As shown in FIG. 4, the radiation detection apparatus 2 of the nuclear medicine diagnosis apparatus 1 includes, for example, n detector heads and one bias power source 23 connected to the n detector heads. I have. In FIG. 4, the first detector head 3a to the nth detector head 3z are illustrated as an example. The first detector head 3 a to the n-th detector head 3 z have the same configuration as the detector head 3.

  As shown in FIG. 4, the control device 8 is schematically configured to include a control unit 80 having a time management unit 800 and a refresh control unit 81.

  The control unit 80 is configured using, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like.

  The time management unit 800 manages the start time of the refresh process. The control unit 80 generates a refresh control signal based on the instruction from the time management unit 800 or the instruction input to the input unit 90.

  The control unit 80 is connected to the input unit 90 and the display unit 91. The input unit 90 is an input device such as a keyboard, for example, and generates an operation signal corresponding to an operation and outputs the operation signal to the control unit 80. The display unit 91 is a liquid crystal monitor, for example, and displays a reconstructed image based on a display control signal output from the control unit 80. The controller 80 outputs a bed control signal for driving the bed 22 to the bed 22. The controller 80 outputs a data control signal and a collection control signal to each detector head. The data control signal is a signal such as information on a frame imaged by the detector head. The collection control signal is a signal that controls collection of electric charges generated by the incidence of radiation.

  Further, the control unit 80 is connected to the refresh control unit 81. Based on the refresh control signal output from the control unit 80, the refresh control unit 81 sets a later-described refresh circuit to an on state as a first state or an off state as a second state at a predetermined cycle. For this purpose, a SW on signal as a first signal and a SW off signal as a second signal are generated. Below, the refresh process of the detector head 3 is demonstrated.

(Refresh processing)
FIG. 5 is a block diagram of a radiation detection circuit mounted on the radiation detector according to the first embodiment and its peripheral circuits.

  When the radiation 6 enters the CdTe element 50 and interacts with it (photoelectric effect, Compton scattering, or electron pair generation), atoms in the CdTe element 50 are ionized, and a pair of electrons and holes is generated. . Since the number of pairs is proportional to the energy of the incident radiation 6, it is possible to obtain excellent energy determination accuracy (energy resolution) by accurately reading out the energy.

  When electrons and holes generated in the CdTe element 50 are merely incident on the CdTe element 50, they recombine and disappear. Therefore, by applying a high voltage (for example, 600 V) bias voltage between the positive electrode and the negative electrode of the CdTe element 50 to generate an electric field between the electrodes, electrons move toward the positive electrode, and holes are Move towards the negative electrode. The radiation detection circuit 500 of the radiation detector 5 is a circuit that reads out and outputs this movement as a signal.

  The radiation detection circuit 500 is schematically configured to include, for example, a CdTe element 50, an ASIC 501, an FPGA 502, a bypass circuit 503, and a refresh circuit 504 as a refresh unit.

  The ASIC 501 is a circuit for generating a digital signal by processing an analog signal (radiation detection signal) output from the CdTe element 50, for example, a charge amplifier, a waveform shaping circuit, a peak hold circuit, and an A / D conversion circuit. Etc.

  The FPGA 502 generates an event signal including information such as the incident time and the incident position (pixel) of the radiation 6 by, for example, correction processing for correcting the wave height of the digital signal output from the ASIC 501, and controls the control device 8. To the unit 80.

  For example, the bypass circuit 503 has a function of bypassing a refresh current flowing through a bias resistor of the CdTe element 50 during the refresh process. With this bypass function, the refresh process is performed within a short time. Usually, the time required for the refresh process is the magnitude of the current and bias voltage from the bias power supply and the capacitance of the coupling capacitor for electrically separating the input portion of the charge amplifier from the bias voltage applied to the CdTe element 50. And the product of the bias resistance. Since a high resistance is usually selected as the bias resistor, the time required for the refresh process becomes longer accordingly. Therefore, in order to complete the refresh process within a short time, a bypass function constituted by a circuit element having a low bias resistance component is used in the refresh process instead of the high resistance bias resistor. In response to the SW ON signal, the refresh circuit 504 is turned on, which is a state in which the bias voltage is not supplied, so that the bias voltage accumulated in the coupling capacitor or the like is discharged at high speed via the bypass circuit 503. Further, the bias voltage is charged to the coupling capacitor or the like via the bypass circuit 503 at high speed when the refresh circuit 504 is turned off in response to the SW off signal. Yes.

  For example, the refresh circuit 504 is turned on by a SW on signal output from the refresh control unit 81 and turned off by a SW off signal. The refresh circuit 504 is a circuit for eliminating the polarization of the CdTe element 50, for example.

  Polarization is a phenomenon in which the charge collection efficiency decreases with time. In semiconductor elements, lattice defects, residual impurities, etc. are inherent in the crystal. Due to these defects, deep levels are formed in the semiconductor element, and carriers in the crystal are captured or emitted. That is, when radiation is incident on the semiconductor element, the generated carriers are trapped or emitted by traps in the crystal. Accordingly, in the semiconductor element, for example, electrons as carriers stay in the crystal and become a scattering center in the crystal or generate a space charge, thereby preventing the movement of carriers, so that the charge collection efficiency is long. The energy resolution decreases with the decrease. Further, the polarization proceeds faster as the temperature of the semiconductor element increases. Polarization also depends on the applied bias voltage, and progresses faster as the bias voltage is lower. However, the polarization can be eliminated by stopping the bias voltage applied to the semiconductor element. That is, the refresh process is a process for temporarily stopping the bias voltage applied to the semiconductor element, for example.

  In addition, the refresh control unit 81 outputs, for example, a SW on signal for performing a refresh process to each of a plurality of radiation detector groups described later to each refresh circuit 504 in accordance with a predetermined period.

(About detector groups)
FIG. 6 is a block diagram relating to a group of detectors according to the first embodiment. The nuclear medicine diagnosis apparatus 1 according to the present embodiment has a schematic configuration in which a plurality of radiation detectors 5 mounted on one detector head are divided into one or more groups, and each group has a refresh circuit. Has been. Further, the nuclear medicine diagnostic apparatus 1 has one bias power source 23 for a plurality of detector heads.

  When the plurality of detector heads 3 mounted on the gantry 20 are described as the first detector head 3a to the nth detector head 3z, the plurality of radiation detectors 5 constituting the first detector head 3a are as follows. For example, the first detector group 5a to the m-th detector group 5z can be grouped. The first detector head 3a has a refresh circuit for each group of detectors, the first refresh circuit 504a is connected to the first detector group 5a, and the second refresh circuit 504b is the second refresh circuit 504b. The mth refresh circuit 504z is connected to the mth detector group 5z.

  As for the other detector heads, for example, the radiation detector 5 is divided into m groups in the same manner as the first detector head 3a. The grouping of the radiation detectors 5 may be different within each detector head 3.

  The bias power supply 23 has a rated current Is, and supplies the bias current Ib and the refresh current Ir to the first detector head 3a. The rated current Is is a current that satisfies the relationship of Is >> Ir >> Ib. Normally, the rated current Is of the bias power source is selected so that a current having a certain margin can be supplied to the refresh current Ir, but is selected to be as low as possible so that the rated current value is as close to the refresh current Ir as possible. When the first detector group 5a is the target of the refresh process, the SW on signal is input to the first refresh circuit 504a, the first refresh circuit 504a is turned on, and the first detector group A refresh current Ir flows in the first refresh circuit 504a connected to 5a. On the other hand, the second refresh circuit 504b to the m-th refresh circuit 504z connected to each of the other second detector group 5b to m-th detector group 5z are in the OFF state, and the second detector A bias current Ib flows through each of the group 5b to the m-th detector group 5z. Below, operation | movement of the nuclear medicine diagnostic apparatus 1 which concerns on 1st Embodiment is demonstrated.

(Operation of the first embodiment)
FIG. 7A is a schematic diagram relating to the first refresh processing according to the first embodiment, FIG. 7B is a schematic diagram relating to the second refresh processing, and FIG. It is the schematic regarding a refresh process. The horizontal axis in FIGS. 7A to 7C is time t.

  The time management unit 800 of the control device 8 measures, for example, the operation time of the nuclear medicine diagnosis apparatus 1 and outputs a trigger signal to the control unit 80 when the operation time exceeds a predetermined threshold value. . The control unit 80 generates a refresh control signal based on the input trigger signal. This refresh signal includes information on in which order the refresh processing of the detector group is performed. The trigger signal may be generated based on an instruction in the operation of the input unit 90.

Refresh controller 81 generates an SW ON signal based on the input refresh control signal, at time t ₁ shown in FIG. 7 (a), the first detector head 3a for performing a first refresh process first 1 to the refresh circuit 504a. The other refresh circuits remain in the off state and are in a state where a bias voltage is applied, and the radiation 6 is subsequently detected.

  For example, as shown in FIG. 6, the SW ON signal is input to the first refresh circuit 504a of the first detector head 3a. The first refresh circuit 504a to which the SW on signal is input is turned on, and the refresh current Ir flows.

  The radiation measurement stop period due to the refresh process is the discharge time required from when the bias voltage is cut off until it reaches zero potential, the fixed time for maintaining the zero potential, and the charge time required for charging from the start of bias voltage supply. And a waiting time when the bias voltage is stable and radiation can be detected.

The refresh control unit 81 generates a SW off signal for stopping the first refresh process and outputs the SW off signal to the first refresh circuit 504a. First refresh circuit 504a is the input of the SW off signal, at time t _2, it turned off, the supply of the bias voltage from the bias power supply 23 for the first detector group 5a is started, the first refresh process Ends.

Next, the refresh controller 81, as shown in FIG. 7 (b), the SW ON signal for the first refresh process starts the second refresh processing time t ₃ after the period T from the end Generated and output to the second refresh circuit 504b of the first detector head 3a that performs the refresh process.

  For example, as shown in FIG. 6, the SW ON signal is input to the second refresh circuit 504b of the first detector head 3a. The second refresh circuit 504b to which the SW on signal is input is turned on, and the refresh current Ir flows.

The refresh control unit 81 generates a SW off signal for stopping the second refresh process, and outputs the SW off signal to the second refresh circuit 504b. The second refresh circuit 504b is the input of the SW off signal, at time t _4, turned off, the supply of the bias voltage from the bias power source 23 to the second detector group 5b is started, the second refresh process Ends. Then, the nuclear medicine diagnostic apparatus 1 performs after period T, during the time t _{5 ~} time t ₆ shown in FIG. 7 (c), a third refresh process for the third detector group.

  The nuclear medicine diagnosis apparatus 1 repeats the above processing at the cycle T, and when the m-th refresh processing is completed, subsequently, performs the refresh processing of the first detector group of the second detector head to detect all detections. The refresh process is continued until the refresh process for all detector groups in the detector head is completed.

(Effects of the first embodiment)
According to the nuclear medicine diagnostic apparatus 1 according to the first embodiment, the plurality of radiation detectors 5 of the plurality of detector heads mounted on the gantry 20 are divided into several groups, and refresh processing is performed for each group. As a result, the current capacity required for the bias power supply is reduced as compared with the case where the refresh process is performed at one time. Since the current capacity is small, the bias power source becomes small, and the nuclear medicine diagnostic apparatus 1 can be miniaturized.

[Second Embodiment]
The second embodiment is different from the first embodiment in that the nuclear medicine diagnostic apparatus has a bias power source for each detector head. In the following embodiments, portions having the same functions and configurations as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and description thereof is omitted.

(Circuit configuration of the nuclear medicine diagnostic apparatus 1)
FIG. 8 is a block diagram showing an outline of a circuit configuration of the nuclear medicine diagnosis apparatus according to the second embodiment. FIG. 9 is a block diagram relating to a group of detectors according to the second embodiment.

  As shown in FIG. 8, the radiation detection apparatus 2 of the nuclear medicine diagnosis apparatus 1 includes, for example, n detector heads and n bias power sources connected to the respective detector heads in the gantry 20. ing. In FIG. 8, as an example, the first detector head 3a to the nth detector head 3z and the first bias power source 23a to the nth bias power source 23z are illustrated.

  As shown in FIG. 9, the first bias power supply 23a has a rated current Is, and supplies the bias current Ib and the refresh current Ir to the first detector head 3a. The second bias power supply supplies a bias voltage to the second detector head, and the mth bias power supply 23z supplies a bias voltage to the nth detector head 3z. The rated current Is is a current that satisfies the relationship of Is >> Ir >> Ib. Below, operation | movement of the nuclear medicine diagnostic apparatus 1 which concerns on 2nd Embodiment is demonstrated.

(Operation of Second Embodiment)
The time management unit 800 of the control device 8 measures, for example, the operation time of the nuclear medicine diagnosis apparatus 1 and outputs a trigger signal to the control unit 80 when the operation time exceeds a predetermined threshold value. . The control unit 80 generates a refresh control signal based on the input trigger signal.

  The refresh control unit 81 generates a SW on signal based on the input refresh control signal, and outputs it to the first refresh circuit 504a of the first detector head 3a that performs the first refresh process. The other refresh circuits remain in the off state and are in a state where a bias voltage is applied, and the radiation 6 is subsequently detected.

  For example, as shown in FIG. 9, the SW ON signal is input to the first refresh circuit 504a of the first detector head 3a. The first refresh circuit 504a to which the SW on signal is input is turned on, and the refresh current Ir flows.

  The refresh control unit 81 generates a SW off signal for stopping the first refresh process and outputs the SW off signal to the first refresh circuit 504a. The first refresh circuit 504a is turned off by the input of the SW off signal, the supply of the bias voltage from the first bias power supply 23a to the first detector group 5a is started, and the first refresh process is ended. To do.

  Next, the refresh control unit 81 generates a SW on signal to start the second refresh process after a period T from the end of the first refresh process, and the first detector head 3a that performs the refresh process. The data is output to the second refresh circuit 504b.

  For example, as shown in FIG. 9, the SW ON signal is input to the second refresh circuit 504b of the first detector head 3a. The second refresh circuit 504b to which the SW on signal is input is turned on, and the refresh current Ir flows.

The refresh control unit 81 generates a SW off signal for stopping the second refresh process, and outputs the SW off signal to the second refresh circuit 504b. The second refresh circuit 504b is the input of the SW off signal, at time t _4, turned off, the supply of the bias voltage from the first bias power supply 23a to the second detector group 5b is started, the second The refresh process ends.

  The nuclear medicine diagnosis apparatus 1 repeats the above processing at the cycle T, and when the m-th refresh processing is completed, subsequently, performs the refresh processing of the first detector group of the second detector head to detect all detections. The refresh process is continued until the refresh process for all detector groups in the detector head is completed.

(Effect of the second embodiment)
According to the nuclear medicine diagnostic apparatus 1 according to the second embodiment, each detector head mounted on the gantry 20 has a bias power source. Supply of voltage is performed stably.

[Third Embodiment]
The third embodiment is different from the above-described embodiment in that a dummy event signal is generated.

(Configuration of nuclear medicine diagnostic apparatus 1)
FIG. 10 is a block diagram of a radiation detection circuit and its peripheral circuits mounted on the radiation detector according to the third embodiment.

  The refresh control unit 81 is configured to generate a refresh signal in addition to the SW on signal and the SW off signal. The refresh signal is output to the FPGA 502 of the radiation detection circuit 500. This refresh signal is a trigger signal that causes the FPGA 502 to generate a dummy event signal.

  When the refresh signal is input, the FPGA 502 generates a dummy event signal, and adds time stamp information in the same manner as the normal event signal, thereby generating a refresh marker signal. The refresh marker signal is output to the control unit 80. The time stamp information added to the refresh marker signal indicates the time when the data measurement is stopped by the refresh process. The FPGA 502 may further generate a dummy event signal indicating the end time of the refresh process from the refresh signal, but since the refresh process cycle T is a predetermined value, it can be calculated. It is assumed that a dummy event signal indicating the end time is not generated.

  The FPGA 502 is assumed to receive an external trigger signal such as an electrocardiogram synchronization signal.

  In the nuclear medicine diagnosis apparatus 1, a bias voltage is supplied to the CdTe element 50 via the bias power supply 23, the refresh circuit 504, and the bypass circuit 503. When the refresh control unit 81 does not generate a dummy event signal indicating the time of the refresh process, the start of the refresh process is recognized by recognizing the measurement stop period by the refresh process, that is, the presence of the dead time, from the interval of the event signal. You may do it.

  That is, in a normal operation situation, the arrival of the event signal is much narrower than the measurement stop period by the refresh process, and the measurement stop period by the refresh process can be recognized from the time information of the event signal by the list mode. By generating this dummy event signal at the front end, it is possible to avoid influences such as errors in the time information of the list data by the back end circuit system. Below, the modification which concerns on this Embodiment is shown.

(Modification 1)
FIG. 11 is a schematic diagram regarding dynamic scan data collection according to the first modification. FIG. 11 illustrates data collection from the first frame to the nth frame. Here, list mode collection is assumed.

  Dynamic scan data collection refers to collecting a state in which a radiopharmaceutical administered to a subject is taken into a tissue in the subject as a temporal image, that is, as data from which a dynamic image is obtained.

  List mode collection means that time information is added to the incidental information (semiconductor element position information, radiation energy information, and other information) of the detected event (time stamp information), and time series without any histogramming. This mode collects data. After the data collection is completed, the time series data is re-edited into desired frame data, and the image of each frame is reconstructed.

FIG. 11 shows a case where a plurality of refresh processes are performed within the data collection period. T _ref shown in FIG. 11 indicates a cycle of the refresh process, and T _rest indicates a data measurement stop period by the refresh process.

  In the data measurement stop period, the event signal indicating the incidence of the radiation 6 is not originally input to the control device 8. However, in the present embodiment, the refresh control unit 81 generates a refresh signal as the refresh process starts, so that the control unit 80 of the control device 8 has a refresh marker generated by the FPGA 502 to which the refresh signal is input. The signal is input as a dummy event signal.

  When editing the desired frame data from the collected list mode data, the control device 8 can read the refresh marker signal and check the data measurement stop period by the refresh process from the list mode data. Frame data excluding the data measurement stop period can be created. In addition, when editing the frame data including the period during which the refresh process is performed, the control device 8 replays an image from each frame data in consideration of the count rate per collection time excluding the period during which the refresh process is performed. Configure.

(Modification 2)
FIG. 12 is a schematic diagram regarding static scan data collection according to the second modification. Static scan data collection refers to collecting data from which a static image of a subject can be obtained.

  FIG. 12 shows that one refresh process was performed at a certain time during data collection. In this case, as in the case of the dynamic scan data collection described above, when the control device 8 edits the frame data including the period during which the refresh process has been performed, An image is reconstructed from each frame data in consideration of the counting rate.

(Modification 3)
FIG. 13 is a schematic diagram regarding data collection in the ECG gate measurement mode according to the third modification. The ECG gate measurement mode is also referred to as an electrocardiogram-synchronized measurement multi-gate mode, and is a mode in which data is collected in synchronization with an R wave of an electrocardiogram pulse input to the FPGA 502 as an external trigger signal.

In FIG. 13, it is assumed that the RR wave interval (T _r−r ) is divided into n fractions.

  When the refresh process is performed, the refresh marker is collected in the control device 8 corresponding to the time when the refresh process is started. When editing the list mode data to the desired time phase data, the control device 8 reads this refresh marker, confirms the data measurement stop period by the refresh process, selects RR wave interval data without data loss, The fractional data of the simultaneous phase is added to create an image of each time phase data.

(Modification 4)
FIG. 14 is a schematic diagram regarding data collection by SPECT (Single Photon Emission Computed Tomography) scanning according to the fourth modification. The upper diagram in FIG. 14 shows the first to m-th SPECT scans that are multiple sets of steps, and the middle diagram in FIG. 14 is an enlargement of the second SPECT scan as a set of steps. FIG. 14 is a diagram showing the time when the refresh process is performed. In step & shoot scan data collection, data is collected by rotating the detector head continuously or discontinuously around the subject.

In FIG. 14, the number of steps is n, and the number of SPECT scans is m. In this modification, it is assumed that one set of projection data necessary for SPECT imaging is obtained with n steps. The collection time _Tacq per step is about 30 s, and the number of steps is about 60.

In the present modification, the refresh processing cycle T _ref is approximately the same as the collection time T _acq per step, and the measurement stop period T _rest is T _acq >> T _rest .

In the present modification, when the number of refresh processes that occur during data measurement at each step is different, the control device 8 obtains the total measurement stop period (sum of T _rest ) at each step from the acquired refresh marker. In the step, the image is reconstructed in consideration of the count rate per collection time excluding the measurement stop period. Note that m SPECT scan data are added as necessary to reconstruct an image.

(Modification 5)
FIG. 15 is a schematic diagram regarding data collection in the high-speed fanning scan mode by the SPECT scan according to the fifth modification. In FIG. 15, the number of steps is n and the number of SPECT scans is 5.

  In the high-speed fanning scan mode, the time per SPECT scan is about 120 s, and the acquisition time per step is as short as about 2 s. In this modification, even if the list mode collection is performed, it is difficult to repair data loss in the refresh process.

Therefore, in the case of the high-speed fanning scan mode, when the predetermined data collection protocol is T _acq << T _ref , the refresh process is started before the measurement is performed, and immediately after the collection at each step, that is, to the next step. The refresh process is terminated within the movement time T _{rest ′} .

  The control device 8 outputs a collection control signal that satisfies the above condition to the refresh control unit 81 based on the designated data collection protocol. The FPGA 502 and the refresh circuit 504 receive the optimized refresh signal, SW on signal, and SW off signal.

Here, as another modification example, in the SPECT scan mode, when the sum of the measurement stop period T _{rest ′} including the number of steps and the movement time to each step and the collection time T _acq is shorter than the refresh cycle T _ref , In a SPECT apparatus that presupposes a high-speed fanning scan, it is affected by the refresh process every certain step.

  In the above case, the refresh process may be repeated a plurality of times in the same step. For this reason, when executing the refresh process, it is preferable to change the refresh process cycle for each SPECT scan.

Similarly, in the dynamic mode, the following settings can be selected. Top frame subsequent continuous or time _{T acq} the measurement of discontinuous n frames _ends, when the _n, the refresh controller _{81, T acq,} a n satisfying _n ≦ _{T ref} The refresh circuit 504 performs the refresh process immediately after the n + 1th measurement is started after the nth frame is measured. Similarly, as the head frame (n + 1) th frame, the refresh controller 81 selects the n that satisfies the following _{T acq, n} ≦ _{T ref,} the refresh circuit 504, the n-th frame after the measurement, n + 1 th A refresh process is performed immediately before the start of measurement. The control device 8 sequentially performs this process for all the set frames. When n satisfying the above condition does not exist, the refresh process is performed at an arbitrary time within the frame period being measured.

  Furthermore, when a radiation detector generating noise is detected by the control device 8 due to polarization or some trouble, the detector group or semiconductor element group to which the radiation detector belongs is selectively refreshed. Process.

  Note that the control device 8 sets the k-th detector group from the first detector group to the detector system consisting of k detector groups sequentially or in any order at the time of measurement start. When the refresh process is performed without overlapping each other, data collection may be started from the time when the refresh process for all the detector groups is completed in the frame mode collection.

In the frame mode, the control device 8 may perform the refresh process according to the designated data collection mode. In this case, the control device 8 sets a predetermined measurement start delay time (T _delay = T _rest ) for each detector group, and performs a refresh process for each individual detector group or semiconductor element group. The measurement start delay time T _delay of each detector group is kT _{ref for} the first detector group and T _ref for the kth detector group. Here, k = 1, 2, 3,...

Accordingly, each detector group has a different measurement start delay time T _delay , and the first detector group has the maximum measurement start delay time T _delay . That is, the actual measurement may be started after kT _delay = kT _rest time as a whole.

When T _acq <T _{ref in} the static mode or the dynamic mode based on the frame mode acquisition, the control device 8 performs the actual measurement after performing the refresh process for all the detector groups according to the above-described delay time before starting the measurement. And each detector group should not be refreshed within the T _acq period.

Similarly, in the static mode based on the frame mode collection, the control device 8 may _execute the refresh process subsequent to the refresh process at the start of the collection during the collection period when T _acq > T _ref .

As described above, two types can be selected: when refresh processing is terminated for all detector groups, and when actual measurement is started after a common measurement start delay time T _delay for each detector group. And

  In the latter case, the measurement collection time differs for each detector group.

In the dynamic mode based on the frame mode acquisition, when T _acq > T _ref , after performing the refresh process for all the detector groups according to the delay time described before the start of measurement, the actual measurement is started, continuous following the frame, or, _{T acq} the measurement end time discrete n-th _frame, when the _{n, T acq,} select the n satisfying _n ≦ _{T ref,} finished measurement of the n-th frame Thereafter, the next refresh process is performed, and after the measurement start delay time T _delay predetermined for each detector group elapses, the (n + 1) th measurement is started.

Similarly, the n + 1-th frame is set as the top frame _{, n} that satisfies the next T _{acq, n} ≦ T _ref is selected, and after the measurement of the n-th frame is completed, the refresh process is performed and the n + 1-th measurement is started. The control device 8 sequentially performs this process.

As described above, two cases can be selected: the case where the refresh process is terminated for all detector groups, and the case where actual measurement is started after a common measurement start delay time T _delay for each detector group. Shall. In the latter case, the measurement collection time differs for each detector group. When n satisfying the above condition does not exist, the control device 8 performs the refresh process at an arbitrary time within the frame period being measured.

  Specifically, the refresh circuit 504 is an electronic circuit including a switching element, for example. A circuit configuration (on state) for supplying a bias voltage from a bias power source to the CdTe element 50 by switching on and off of the switching element, a bias voltage from the bias power source being disconnected from the CdTe element 50, and a coupling capacitor or the like A circuit configuration (off state) for discharging the accumulated bias voltage can be obtained.

  Although the embodiments of the present invention have been described above, the embodiments and modifications described above do not limit the invention according to the claims. In addition, it should be noted that not all the combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

DESCRIPTION OF SYMBOLS 1 ... Nuclear medicine diagnostic apparatus 2 ... Radiation detection apparatus 3 ... Detector head 3a ... 1st detector head 3z ... nth detector head 4 ... Collimator 5 ... Radiation detector 5a ... 1st detector group 5b ... Second detector group 5z ... mth detector group 6 ... radiation 7 ... communication cable 8 ... control device 20 ... gantry 21 ... opening 22 ... bed 23 ... bias power supply 23a ... first bias power supply 23z ... nth Bias power supply 30 ... Base 31 ... Support 32 ... Connector 50 ... CdTe element 51 ... Substrate 52 ... Flexible substrate 53 ... Card holder 54 ... Card holder 55 ... Elastic member mounting part 56 ... Elastic member 57 ... Projection part 58 ... With groove Hole 59 ... Protruding part 60 ... Card edge part 60a ... Pattern 61 ... Electronic component mounting part 80 ... Control part 81 ... Refresh control part 90 ... Input part 91 ... Display part 300 The radiation detector stand 310 ... wall portion 311 ... groove 312 ... recess 313 ... flat surface 500 ... radiation detection circuit 501 ... ASIC
502 ... FPGA
503 ... Bypass circuit 504 ... Refresh circuit 504a ... First refresh circuit 504b ... Second refresh circuit 504z ... Mth refresh circuits 510-513 ... Substrate terminals 520-523 ... Connection unit 800 ... Time management unit

Claims (10)

A plurality of radiation detector groups having semiconductor elements for detecting radiation;
A bias power supply for supplying a bias voltage to each of the plurality of radiation detector groups;
Provided between the bias power supply and each of the plurality of radiation detector groups, the bias voltage is not supplied by the input first signal, and the bias voltage is set by the input second signal. A plurality of refresh units in which a refresh process of a target radiation detector group is performed by becoming a second state that is a supply state;
A refresh control unit that controls the plurality of refresh units by outputting the first signal or the second signal to the plurality of refresh units;
A radiation imaging apparatus comprising: A plurality of detector heads having at least one of the plurality of radiation detector groups;
The radiation imaging apparatus according to claim 1, wherein the number of the bias power supplies is the same as the number of the plurality of detector heads.   The refresh control unit outputs the first signal for performing the refresh process to each of the plurality of radiation detector groups to each of the refresh units according to a predetermined period. The radiation imaging apparatus described.   The radiation imaging apparatus according to claim 3, wherein the refresh control unit outputs the first signal and the second signal according to the cycle of the refresh process.   The radiation imaging apparatus according to claim 4, wherein the refresh control unit generates a dummy event signal.   The radiation imaging apparatus according to claim 5, wherein the refresh control unit adds time stamp information indicating a time when the first signal or the second signal is generated to the dummy event signal.   The radiation imaging apparatus according to claim 6, wherein the refresh control unit outputs the first signal and the second signal to the refresh unit based on the acquired control signal.   The radiation imaging apparatus according to claim 7, wherein when the data collection time is shorter than the time required for the refresh process, the refresh process is performed before the start of data collection or after the end of data collection.   The radiation imaging apparatus according to claim 8, wherein when the sum of the data collection time and the time required for the refresh process is shorter than the period, the period of the refresh process changes for each frame. When the time when the measurement of the n frames following the first frame is shorter than the cycle, the refresh control unit satisfies that the time when the measurement of the n frames is shorter than the cycle. Select
The radiation imaging apparatus according to claim 9, wherein the refresh unit performs the refresh process before the start of the (n + 1) th measurement after the end of the measurement of the nth frame.

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