JP4286338B2 - Nuclear medicine diagnostic equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In the present invention, radiation such as gamma (γ) rays emitted by a radioisotope (radioisotope, RI) administered to a subject such as a patient is detected one-dimensionally or two-dimensionally. The present invention relates to a nuclear medicine diagnostic apparatus for obtaining an RI distribution.
[0002]
[Prior art]
A radioisotope (RI) is injected into a subject such as a patient, and radiation such as gamma rays (γ) emitted from the body is detected by a one-dimensional or two-dimensional detector to obtain an RI distribution. It is equipped with a SPECT device using single photon emission computed tomography (SPECT) that displays functional distribution images such as lesions in the body, blood flow, and fatty acid metabolism, and a plurality of detectors. There is known a PET apparatus using a simultaneous detection positron emission computed tomography (PECT) in which imaging is performed by simultaneously detecting gamma rays emitted in the direction of 180 ° when annihilating by combining with electrons (electrons). Recently, SPECT apparatuses including a plurality of detectors for performing SPECT and simultaneous detection type PET have been known. These devices in general are collectively referred to as nuclear medicine diagnostic devices.
[0003]
[Problems to be solved by the invention]
In the conventional SPECT apparatus, an anger-type detector that detects gamma rays by arranging a plurality of scintillators and photomultiplier tubes (PMTs) in close proximity occupies the mainstream. Due to limitations in resolution, counting characteristics, etc., we could not expect a dramatic improvement in performance over the current level.
[0004]
On the other hand, in the simultaneous detection type PET apparatus, a method of performing imaging by simultaneously detecting the timing at which gamma rays are emitted in the 180 ° direction by a combination of a bismuth germanium oxide (BGO) detector, a photomultiplier tube and a photodiode is mainstream. It is.
[0005]
Furthermore, recently, a nuclear medicine diagnostic apparatus that can realize an coincidence type PET by mode switching using an Anger type detector having a plurality of detectors has emerged and is becoming mainstream.
[0006]
However, in any nuclear medicine diagnostic apparatus, a detector for detecting gamma rays is mainly composed of a scintillator, and the gamma rays incident on the detector are once converted into weak light by the scintillator, and this weak light is converted into photoelectrons. It is necessary to convert it into an electrical signal using a multiplier tube or a photodiode. Therefore, the nuclear medicine diagnostic apparatus has become large and has limited performance.
[0007]
In view of this, semiconductor detectors made of semiconductor cells such as cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been attracting attention. Since this semiconductor detector directly converts gamma rays into electrical signals (so-called direct conversion type), the efficiency of conversion into electrical signals is high, and gamma rays can be individually detected in the semiconductor cell. Therefore, by arranging a plurality of such semiconductor cells in one or two dimensions to form a one or two-dimensional detector, the energy resolution and counting characteristics (time resolution) can be improved, and the nuclear medicine diagnostic apparatus can be greatly improved. Small size and weight reduction is expected.
[0008]
By the way, in such a semiconductor detector, a voltage application electrode and a signal extraction electrode are formed in a semiconductor cell, and a predetermined voltage is applied to both ends thereof. When gamma rays are incident on the semiconductor detector, when the gamma rays are absorbed by the semiconductor cell, a predetermined amount of charge generated according to the amount of energy is induced to the signal extraction electrode. The induced charge is charged up by a charge amplifier, and appropriate signal processing is performed through a waveform shaping circuit that converts the peak value into a signal that reflects the energy value of the gamma ray, thereby reconstructing an RI image for nuclear medicine diagnosis.
[0009]
However, the time resolution for measuring the energy resolution of gamma rays and the generation time of positrons changes according to the voltage applied to the semiconductor cell via the voltage application electrode, but there is a trade-off between this energy resolution and time resolution. Since it is common to have a relationship, the performance of either energy resolution or time resolution had to be sacrificed when it was desired to use both SPECT and coincidence PET.
[0010]
The present invention has been made in view of the above circumstances, and an object of the present invention is to apply to a semiconductor cell based on RI nuclides administered to a subject or energy of gamma rays incident on a semiconductor cell of a semiconductor detector. It is an object of the present invention to provide a nuclear medicine diagnostic apparatus capable of improving the energy resolution or the counting characteristic (time resolution) according to the object to be collected and adjusting the voltage to be reduced and reducing the size and weight.
[0012]
[Means for Solving the Problems]
  In order to solve the above problems, the claims1In the nuclear medicine diagnostic apparatus comprising a radiation semiconductor detector for detecting radiation emitted from a subject, the invention described in (2), voltage applying means for applying a predetermined voltage to a semiconductor cell in the radiation semiconductor detector, When performing collection for single photons, the operation of the voltage applying means is controlled so as to apply a first voltage to the semiconductor cells, and when collecting for positrons, And a control means for controlling the operation of the voltage application means so as to apply the second voltage.
[0013]
  Claim1In the nuclear medicine diagnostic apparatus according to claim 1,2The invention described in item 1 is characterized in that the first voltage is lower than the second voltage.
[0014]
  In order to solve the above problems, the claims3In the nuclear medicine diagnostic apparatus comprising a radiation semiconductor detector for detecting radiation emitted from a subject, the invention described in (2), voltage applying means for applying a predetermined voltage to a semiconductor cell in the radiation semiconductor detector, Adjusting means for adjusting a predetermined voltage applied by the voltage applying means based on an incident count rate of radiation.The adjusting means reduces the voltage applied to the semiconductor cell by the voltage application means when the radiation incidence count rate is low, and the semiconductor device by the voltage application means when the radiation incidence count rate is high. The voltage applied to the cell is increased.
[0016]
  From claim 13In the nuclear medicine diagnostic apparatus according to the invention described above,4The invention described in item 1 is characterized in that the semiconductor cell is made of CdTe or CdZnTe.
[0017]
  From claim 13In the nuclear medicine diagnostic apparatus according to the invention described above,5The semiconductor cell described in the above item is characterized in that the semiconductor cell has a PIN structure.
[0018]
  From claim 13In the nuclear medicine diagnostic apparatus according to the invention described above,6The voltage application means applies a negative voltage within a range of -400V to -1500V to the semiconductor cell.
[0019]
  From claim 13In the nuclear medicine diagnostic apparatus according to the invention described above,7The invention described in 1 is characterized in that the electrodes formed in the semiconductor cell are arranged in a horizontal direction with respect to the incident direction of radiation.
[0020]
  From claim 13In the nuclear medicine diagnostic apparatus according to the invention described above,8The invention described in 1 is characterized in that the electrodes formed in the semiconductor cell are arranged in a direction perpendicular to the incident direction of radiation.
[0021]
  From claim 13In the nuclear medicine diagnostic apparatus according to the invention described above,9According to the invention described in item 3, the predetermined voltage applied to the semiconductor cell by the voltage applying unit is adjusted by increasing or decreasing stepwise within a predetermined time.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0023]
1 and 2 are block diagrams showing the configuration of the nuclear medicine diagnostic apparatus according to the embodiment of the present invention. 1 and 2, the nuclear medicine diagnosis apparatus according to the embodiment of the present invention is arranged in one or two dimensions for detecting radiation such as gamma (γ) rays emitted from a subject such as a patient. .., 1n and voltage application electrodes (cathodes) 30a, 30b,..., 30n through the semiconductor cells 1a, 1b,. , 1n through the high voltage unit 2 for applying the negative applied voltage (−HV) and the signal extraction electrodes (anodes) 31a, 31b,. 3n and a plurality of low-speed waveform shaping circuits 4a, 4b,... 3n that shape the output of the charge amplifiers 3a, 3b,.・4n and a plurality of high-speed waveform shaping circuits 5a, 5b,..., 5n, and low-speed waveform shaping circuits 4a, 4b,. , 6n, and high-speed waveform shaping circuits 5a, 5b,..., 5n, which detect and store the peak values of the output waveform of 4n, and the high-speed waveform shaping circuits 5a, 5b,. , 7n and the outputs of peak hold (P / H) circuits 6a, 6b,..., 6n are selected. .., 7n based on the output of the selector 8, the timing control circuit 9 for outputting the address signal and the trigger output A signal, and the energy signal output from the selector 8 as A / D A / (Analog / Digital) A correction circuit 11 that performs gain adjustment and offset adjustment of energy information output from the A / D converter 10 based on the D converter 10, the address signal output from the timing control circuit 9, and the trigger output A; Timing of a pulse height analyzer 12 dedicated to nuclear medicine that performs energy discrimination processing on the output of the circuit 11 and another circuit system having the same configuration as the circuit system described above in the simultaneous detection type PET (positron emission computed tomography) Simultaneously generated based on the timing analyzer 13 for confirming the generation timing of the trigger output B signal output from the control circuit (not shown) and the trigger output A signal output from the timing control circuit 9 and the output of the timing analyzer 13 A coincidence counting judgment circuit 14 for judging whether or not a pulse height An image calculation unit 15 that performs image calculation based on the output of the analyzer 12, an image memory 16 that stores the calculation result obtained by the image calculation unit 15, and a CPU (central processing unit) that controls the whole nuclear medicine diagnosis apparatus ) 17, a collection control unit 18 that performs collection control in SPECT (Single Photon Emission Computed Tomography) and simultaneous detection type PET, a memory 19, and collection instruction information on SPECT and coincidence type PET collection instructions by an operator, Input from a radioisotope (radioisotope, RI) nuclide to be administered to a specimen, nuclide / energy information regarding energy of gamma rays emitted from the subject, a monitor 21, and a keyboard 20. RI nuclide depending on the nuclide / energy information The nuclide / energy identification circuit 22 that identifies gamma ray energy and outputs voltage information indicating an applied voltage to the semiconductor cells 1a, 1b,..., 1n to the high voltage unit 2 based on the identification result. And is composed of.
[0024]
In the simultaneous detection type PET or the like, since it is necessary to place two semiconductor detectors each composed of a plurality of semiconductor cells arranged one-dimensionally or two-dimensionally across the subject, the above-described gamma rays are used. Two circuit systems for detection / signal processing are provided. Thereby, both SPECT and simultaneous detection type PET can be optimally executed.
[0025]
Here, a semiconductor detector used in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention will be described.
[0026]
In general, a semiconductor cell used for a semiconductor detector is made of a semiconductor such as cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe, CZT). When such a semiconductor cell is applied to a detector for a nuclear medicine diagnostic apparatus, (1) as shown in FIG. 3A, in the incident direction of gamma rays emitted from the RI injected into the subject. On the other hand, the voltage application electrode and the signal extraction electrode (both electrodes are made of, for example, platinum (Pt)) are arranged in a one-dimensional or two-dimensional manner with a CZT crystal semiconductor cell interposed therebetween, or (2 As shown in FIG. 3B, the voltage application electrode (for example, composed of Pt) and the signal extraction electrode (for example, composed of indium (In)) are set in the horizontal direction with respect to the incident direction of the gamma rays. It can be arranged in one or two dimensions with a crystal semiconductor cell in between.
[0027]
  FIG. 4 is a diagram showing the output progress of the charge amplifier connected to the semiconductor cell shown in FIG. 3 used in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention. FIG. 4A shows an output process of a charge amplifier in which a voltage application electrode and a signal extraction electrode are charged up from a semiconductor cell in which the voltage application electrode and the signal extraction electrode are arranged in a direction perpendicular to the incident direction of the gamma ray as shown in FIG. And FIG.b) Shows the output progress of the charge amplifier that charges up the charge from the semiconductor cell in which the voltage application electrode and the signal extraction electrode are arranged in the horizontal direction with respect to the incident direction of the gamma rays as shown in FIG. 3B. . 4A and 4B, the vertical axis indicates the output of the charge amplifier, and the horizontal axis indicates the elapsed time from the time when the gamma rays are incident on the semiconductor cell (at the time of absorption).
[0028]
In the configuration shown in FIG. 3A, the electric field in the semiconductor cell is distorted by the arrangement of the voltage application electrode and the signal extraction electrode, and the movement of the holes is cancelled, as shown in FIG. 4A. Only the time determines the charge amplifier charge-up time. Therefore, this configuration is not suitable for accurately measuring the incident timing of gamma rays into the semiconductor cell.
[0029]
On the other hand, in the configuration shown in FIG. 3B, since holes and electrons are all induced as charges under a high voltage, the initial rise of the output waveform of the charge amplifier is delayed as shown in FIG. 4B. . When gamma rays are absorbed directly under the cathode, the initial rise time (slope) is determined by the moving speed of electrons, and when gamma rays are absorbed directly under the anode, the initial rise time is approximately Although it depends on the moving speed of the hole, the time resolution can be made 1 nsec or less. Therefore, such a configuration is also suitable for accurately measuring the incidence timing of gamma rays to the semiconductor cell.
[0030]
FIG. 5 is a diagram showing an energy band structure of a semiconductor cell in which a voltage application electrode and a signal extraction electrode are arranged as shown in FIG. 3 in the semiconductor detector used in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention. 5A shows the energy band structure of the semiconductor cell having the configuration shown in FIG. 3A, and FIG. 5B shows the energy band structure of the semiconductor cell having the configuration shown in FIG. 3B. Yes. Compared to the energy band structure shown in FIG. 5 (a), the energy band structure shown in FIG. 5 (b) has a large energy gap (1.1 to 1. vs 0.3 eV). 2eV), the noise of the hole is reduced, and the dark current (leakage current) from the semiconductor cell is reduced.
[0031]
Although the present invention is effective for both of the semiconductor detectors having the configurations shown in FIGS. 3A and 3B, as described above, for example, a semiconductor cell made of a CdTe crystal is used as a PIN. When the semiconductor detector has an energy band structure as shown in FIG. 5B, which has a structure, the cathode side electrode is Pt, the anode side electrode is In, and the dark current from the semiconductor cell is greatly reduced. It becomes effective. This is because the dark current is reduced by using a CdTe crystal semiconductor cell as a PIN structure, so that a voltage in the range of −400 V to −1500 V, which was not applied in the conventional CdTe crystal semiconductor cell, is reduced to 0. This is because it can be applied to a semiconductor cell having a thickness in the range of about 5 mm to 1.5 mm. As a result, information on holes and electrons generated by the absorption of gamma rays in the semiconductor cell is guided to the signal extraction electrode as charges without disappearing on the way, so that energy resolution is improved and induced charges in the charge amplifier are improved. The charge-up rate increases significantly reflecting the absorption time of gamma rays in the semiconductor cell.
[0032]
The relationship between the applied voltage applied to the semiconductor cell of the semiconductor detector and the dark current generated in the semiconductor cell is as follows. That is, when the semiconductor cell is composed of a CdTe crystal and has a PIN structure, when the voltage applied to the semiconductor cell is increased, the dark current in the semiconductor cell is increased, and as a result, the energy resolution is degraded. However, in this case, since the time for which the charge from the semiconductor cell is induced in the charge amplifier is shortened, the time resolution for measuring the time when the positron is generated is improved. From these, it can be seen that the energy resolution and the time resolution are in an inversely proportional relationship.
[0033]
In the nuclear medicine diagnosis apparatus according to the embodiment of the present invention shown in FIG. 1 and FIG. 2, the nuclide / energy identification circuit 22 includes a nuclide / RI nuclide administered to a subject and a nuclide / energy related to gamma-ray energy emitted from the subject. A table 22a that stores energy information and voltage information indicating an applied voltage in association with each other is stored. The table 22a is referred to based on nuclide / energy information keyed from the keyboard 20 by a doctor, an operator, or the like. Voltage information indicating an applied voltage applied to the semiconductor cells 1a, 1b,..., 1n is output to the high voltage unit 2.
[0034]
The high voltage unit 2 includes a voltage control unit 2a that adjusts a negative applied voltage applied to the semiconductor cells 1a, 1b,..., 1n, and is based on the voltage information output from the nuclide / energy identification circuit 22. Then, the applied voltage is adjusted by the voltage controller 2a, and the applied voltage is applied to the semiconductor cells 1a, 1b,.
[0035]
Next, the operation of the nuclear medicine diagnostic apparatus according to the embodiment of the present invention will be described.
[0036]
First, a predetermined RI is administered to a subject, and a semiconductor detector including CdTe crystal semiconductor cells 1a, 1b,..., 1n arranged in one or two dimensions is placed close to the subject. Thereafter, collection instruction information related to the collection instruction of SPECT and coincidence type PET, RI nuclides to be administered to the subject, and nuclide / energy information about the energy of gamma rays emitted from the subject are obtained from the keyboard 20 by a doctor or an operator. When key input is performed, the nuclide / energy information is input to the nuclide / energy identification circuit 22 via the CPU 17. Further, the CPU 17 that has received the collection instruction information gives an operation instruction to each part of the nuclear medicine diagnosis apparatus according to the embodiment of the present invention.
[0037]
In the nuclide / energy identification circuit 22, voltage information indicating the applied voltage corresponding to the nuclide / energy information input from the keyboard 20 is read with reference to the table 22 a, and the voltage information is stored in the high voltage unit 2. It is output to the voltage controller 2a.
[0038]
In the voltage control unit 2a of the high voltage unit 2, the negative applied voltage is adjusted based on the voltage information output from the nuclide / energy identifying circuit 22, and the adjusted negative applied voltage (−HV) is used as the voltage applied electrode. Applied to the semiconductor cells 1a, 1b,..., 1n through 30a, 30b,.
[0039]
When the gamma rays emitted from the subject are incident on the semiconductor cells 1a, 1b,..., 1n, the incident gamma rays are applied in the semiconductor cells 1a, 1b,. A predetermined amount of electric charge generated according to the amount of energy when absorbed is induced to the signal extraction electrodes 31a, 31b, ..., 31n. The induced charges are charged up by the charge amplifiers 3a, 3b,... 3n.
[0040]
The output of the charge amplifiers 3a, 3b,... 3n is lost by collecting all the information related to holes and electrons generated by the incident gamma rays being absorbed in the semiconductor cells 1a, 1b,. And a relatively low-speed waveform shaping circuit 4a, 4b,... 4n for obtaining sufficient energy resolution, and the time when gamma rays are absorbed in the semiconductor cells 1a, 1b,. Input to relatively high-speed waveform shaping circuits 5a, 5b,..., 5n for measurement.
[0041]
In the low speed waveform shaping circuits 4a, 4b,... 4n, the outputs of the charge amplifiers 3a, 3b,... 3n are waveform shaped at a low speed, and the peak value is converted into a signal reflecting the energy value of gamma rays.
[0042]
The peak hold (P / H) circuits 6a, 6b,..., 6n detect and store the peak values of the output waveforms of the low speed waveform shaping circuits 4a, 4b,. This peak value is information reflecting the energy value of gamma rays.
[0043]
On the other hand, in the high-speed waveform shaping circuits 5a, 5b,..., 5n, the outputs of the charge amplifiers 3a, 3b,. The
[0044]
FIG. 6 is a diagram showing output waveforms of the low-speed waveform shaping circuit and the high-speed waveform circuit when the applied voltage applied to the semiconductor cell constituting the semiconductor detector used in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention is changed. is there. In FIG. 6, the vertical axis represents the output voltage of the low-speed waveform shaping circuit and the high-speed waveform circuit, and the horizontal axis represents the elapsed time from the time when gamma rays are incident on the semiconductor cell (at the time of absorption). From FIG. 6, it can be seen that the output signal appears at an earlier time when the applied voltage applied to the semiconductor cell is higher than when the applied voltage applied to the semiconductor cell is low.
[0045]
In the comparators 7a, 7b,..., 7n, the outputs of the high speed waveform shaping circuits 5a, 5b,..., 5n are compared with a preset DC voltage (threshold level), and based on the comparison result. Thus, a timing signal reflecting the absorption time of the gamma ray in the semiconductor cell is output. This DC voltage is generally set to a level slightly higher than the level reflecting dark current in the semiconductor cell and the noise component of the subsequent circuit system, but the level of the noise component is applied to the semiconductor cell. When the applied voltage is low, it becomes low.
[0046]
FIG. 7 is a diagram showing output waveforms of the high-speed waveform shaping circuit and the comparator when the applied voltage applied to the semiconductor cell constituting the semiconductor detector used in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention is changed. . In FIG. 7, the vertical axis of the graph A shown above indicates the output voltage of the high-speed waveform shaping circuit, the vertical axis of the graph B shown below indicates the output voltage of the comparator, and the horizontal axes of the graphs A and B indicate the gamma rays. The elapsed time from the time of absorption in the semiconductor cell is shown.
[0047]
As can be seen from FIG. 7, if the applied voltage applied to the semiconductor cell is increased, the rise of the pulse signal output from the high-speed waveform shaping circuit is accelerated, and when the output voltage becomes larger than the DC voltage, the comparator A timing signal is output. Thereby, when it is desired to accurately measure the time during which the gamma rays are absorbed by the semiconductor cell, the accuracy of the measurement time is improved by increasing the applied voltage applied to the semiconductor cell.
[0048]
In this measurement time, there is a delay time slightly longer than the time when gamma rays are actually absorbed by the semiconductor cell. However, the presence of this delay time is not very important in the case of simultaneous detection PET. . Rather, it is more important that the pulse signal is output from the high-speed waveform shaping circuit after a certain delay time has elapsed since the time when the gamma rays were actually absorbed by the semiconductor cell. A shorter width and higher speed are more advantageous.
[0049]
In the present invention, the applied voltage applied to the semiconductor cells 1a, 1b,... 1n is adjusted according to the nuclide of RI and the energy of gamma rays, so that the low-speed waveform shaping circuits 4a, 4b,. The time constants of the peak hold circuits 6a, 6b,... 6n are set so that the energy resolution is sufficiently improved even for the signal that appears the latest.
[0050]
The outputs of the peak hold circuits 6a, 6b,..., 6n are input to a selector 8 constituted by an analog switch or the like. The selector 8 repeatedly operates in synchronization with the external clock signal, and sequentially outputs the outputs of the peak hold circuits 6a, 6b,..., 6n to the A / D converter 10 sequentially as energy signals.
[0051]
The outputs of the comparators 7a, 7b,..., 7n are input to the timing control circuit 9. The timing control circuit 9 includes an address signal indicating the position (channel) of the semiconductor cells 1a, 1b,..., 1n in which the gamma rays are absorbed according to the output status of the comparators 7a, 7b,. A trigger output A signal indicating that the gamma rays are absorbed by the semiconductor cell is output. For example, when gamma rays are incident on multiple channels at the same time and outputs are simultaneously generated from a plurality of comparators, one of the channels is set as a channel on which gamma rays are incident based on preset conditions. The address signal for that channel is output.
[0052]
The energy signal reflecting the energy value of the gamma ray in each channel output from the selector 8 is A / D converted by the A / D converter 10 in synchronization with the external clock signal, and then generated at any time in the timing control circuit 9. Based on the trigger output A signal and the address signal, it is input to the correction circuit 11 as energy information.
[0053]
The basic time constant of the timing control circuit 9 can be adjusted to be optimal under the control of the CPU 17 in accordance with the applied voltage applied to the semiconductor cells 1a, 1b,. However, it can be fixed.
[0054]
The correction circuit 11 has a correction table (not shown) for gain adjustment and offset adjustment. By referring to this correction table, the energy information output from the A / D converter 10 is real-time. Perform gain adjustment and offset adjustment.
[0055]
The output of the correction circuit 11 is input to a pulse height analyzer 12 dedicated to nuclear medicine, and energy discrimination processing is executed in the pulse height analyzer 12. Note that the window level necessary for this energy discrimination processing is converted into a DC level digital value by the CPU 17 in accordance with information on the RI nuclide, gamma ray energy, and collected window value input from the keyboard 20 by a doctor or operator. Input to the pulse height analyzer 12. The pulse height analyzer 12 outputs only the energy information of the gamma rays in the window of interest corresponding to the window level to the image calculation unit 15.
[0056]
In the image calculation unit 15, image calculation processing such as reduction / enlargement processing, smoothing processing, rotation processing, reconstruction processing, and the like is performed on the energy information output from the pulse height analyzer 12. Image data and the like obtained by these processes are stored in the image memory 16.
[0057]
In the case of coincidence type PET that needs to detect the generation timing of positrons, the following processing is performed.
[0058]
First, it has the same configuration as the circuit system described above connected to a semiconductor detector composed of a plurality of semiconductor cells different from the semiconductor detector composed of semiconductor cells 1a, 1b,. When the trigger output B signal output from the timing control circuit of another circuit system and the trigger output A signal output from the timing control circuit 9 are input to the timing analyzer 13, the timing analyzer 13 The generation timing of the trigger output B signal is confirmed.
[0059]
Timing information indicating the generation timing of the trigger output A signal and the trigger output B signal confirmed by the timing analyzer 13 is input to the coincidence counting determination circuit 14. The coincidence determination circuit 14 determines the pulse height only when it is determined that the trigger output A signal and the trigger output B signal are generated at the same time within a predetermined time window (usually within a range of several hundred psec to 15 psec). A permission signal for permitting the analyzer 12 to execute the energy discrimination process is output.
[0060]
In the pulse height analyzer 12, when the permission signal is received from the coincidence counting determination circuit 14, energy information of gamma rays obtained by executing the energy discrimination processing is output to the image calculation unit 15. As a result, various image calculation processes are performed by the image calculation unit 15, and the processing results are stored in the image memory 16 as image information related to the simultaneous detection type PET.
[0061]
By the way, in the nuclear medicine diagnosis apparatus according to the embodiment of the present invention configured as described above, what kind of collection is performed by a doctor, an operator, or the like is set in an operator console including the keyboard 20, the monitor 21, and the like. In general, centralized management is performed by the CPU 17. Therefore, the distinction between RI nuclides administered to a subject, energy of gamma rays incident on a semiconductor cell, collection of single photons by SPECT or collection of positrons (positrons) by simultaneous detection type PET, etc. For operators and operators, it can be recognized in advance.
[0062]
Therefore, as in the prior art, in addition to using information related to the above-described condition setting for the above-described gamma ray detection / processing circuit system, as in the present invention, based on the information related to them, single photons by SPECT are targeted. In the case of the collection, the high voltage unit 2 is instructed to set the applied voltage applied to the semiconductor cell to be relatively low. As a result, the dark current in the semiconductor cell is reduced and the energy resolution is the best.
[0063]
However, when collecting positrons by coincidence type PET with a relatively low applied voltage applied to the semiconductor cell as described above, the time until all charges are induced in the charge amplifier is obtained. It takes too much. Therefore, a high count characteristic (high time resolution) for detecting only a few (about 1%) information on true simultaneous detection from among information on simultaneous detection of a large number of random gamma rays cannot be obtained. From the above, the simultaneous detection type under the condition that the dark current in the semiconductor cell increases and the energy resolution deteriorates by increasing the applied voltage applied to the semiconductor cell only when collecting by the simultaneous detection type PET. Collection efficiency in PET can be improved.
[0064]
Further, in the present invention, a nuclear medicine diagnostic apparatus that only collects single photons by SPECT has a high count rate characteristic (incidence count rate), similar to the variable sampling method devised in the Anger-type gamma camera. In some cases, the applied voltage applied to the semiconductor cell is increased to increase the signal processing speed. When the count rate characteristic (incidence count rate) is low, the applied voltage is decreased to improve the energy resolution as much as possible. Can be prioritized. This makes it possible to automatically adjust the optimum applied voltage to the semiconductor cell based on the count rate characteristic under the monitoring of the CPU.
[0065]
Furthermore, in general, charge amplifiers are often destroyed by overcurrent via stray capacitance in semiconductor cells caused by switching of high applied voltage, and when a high applied voltage is continuously applied to semiconductor cells for a long time The output gain changes due to the charge-up phenomenon. In order to prevent this, under the control of the CPU, the applied voltage is turned on / off at any time before or after collection by SPECT or PET, and sometimes between collections, as shown in FIG. Is gradually performed so that the charge amplifier is not destroyed, and for example, a sequence is performed in which the applied voltage is switched from collection by SPECT to collection by PET.
[0066]
By applying the thus configured nuclear medicine diagnostic apparatus to a SPECT / PET system or a SPECT system, it is possible to easily realize optimum collection according to each collection condition at a relatively low cost.
[0067]
Further, in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention, by providing a temperature control mechanism that lowers the temperature of the semiconductor detector from room temperature, the semiconductor cell can be applied even when a high applied voltage is applied to the semiconductor cell. The increase in dark current in the apparatus can be suppressed, and the performance of the nuclear medicine diagnostic apparatus according to the embodiment of the present invention can be improved to the maximum.
[0068]
【The invention's effect】
As mentioned above, according to this invention, the following advantages are acquired by adjusting the applied voltage applied to the semiconductor cell of the semiconductor detector used for a nuclear medicine diagnostic apparatus as needed.
[0069]
(1) In collecting single photons such as SPECT, the optimum energy resolution and sensitivity according to the count rate characteristic can be realized simply and inexpensively.
[0070]
(2) In a nuclear medicine diagnostic apparatus capable of realizing SPECT and simultaneous detection type PET, the performance of both can be optimized by simple switching.
[0071]
(3) The charge amplifier can be prevented from being destroyed when the applied voltage applied to the semiconductor cell is raised or lowered.
[0072]
(4) It is possible to dramatically improve the collection by SPECT and simultaneous detection type PET implemented in the current Anger type gamma camera.
[0073]
In the present invention, for example, the energy resolution is 5% or less at 99m-Tc (conventionally about 10%), the maximum arrival count rate is 10 Mcps or more (conventionally about 2 Mcps), and the time resolution of the simultaneous detection type PET is 1 nsec or less (conventional) Is about 15 nsec). As a result, it is possible to improve the collection sensitivity several times, improve the quantitativeness of the image, improve the collection accuracy of the multi-nuclide, and dramatically reduce the noise of the image obtained in the simultaneous detection type PET. Furthermore, by improving the performance of the nuclear medicine diagnostic apparatus, it is possible to estimate the positron generation position to some extent based on the TOF (Time of Fight) method.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a nuclear medicine diagnosis apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a nuclear medicine diagnostic apparatus according to an embodiment of the present invention.
FIG. 3 is a diagram showing a configuration of a semiconductor detector used in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention.
4 is a diagram showing an output progress of a charge amplifier connected to the semiconductor detector shown in FIG. 3 used in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention.
5 is a diagram showing an energy band structure of a semiconductor cell in which a voltage application electrode and a signal extraction electrode are arranged as shown in FIG. 3 in the semiconductor detector used in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention. .
FIG. 6 is a diagram showing output waveforms of the low-speed waveform shaping circuit and the high-speed waveform circuit when the applied voltage applied to the semiconductor cell constituting the semiconductor detector used in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention is changed. It is.
FIG. 7 is a diagram showing output waveforms of a high-speed waveform shaping circuit and a comparator when an applied voltage applied to a semiconductor cell constituting a semiconductor detector used in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention is changed. is there.
FIG. 8 is a diagram for explaining a sequence of applied voltages applied to a semiconductor cell constituting a semiconductor detector used in the nuclear medicine diagnostic apparatus according to the embodiment of the present invention.
[Explanation of symbols]
1a, 1b, 1n semiconductor cell
2 High voltage unit
2a Voltage controller
3a, 3b, 3n charge amplifier
4a, 4b, 4n Low-speed waveform shaping circuit
5a, 5b, 5n High-speed waveform shaping circuit
6a, 6b, 6n Peak hold circuit
7a, 7b, 7n comparator
8 Selector
9 Timing control circuit
10 A / D converter
11 Correction circuit
12 Pulse height analyzer
13 Timing analyzer
14 Simultaneous counting judgment circuit
15 Image operation unit
16 Image memory
17 CPU
18 Collection control unit
20 keyboard
22 nuclide / energy identification circuit
22a table
30a, 30b, 30n Voltage application electrode
31a, 31b, 31n Signal extraction electrode

Claims (9)

In a nuclear medicine diagnostic apparatus comprising a radiation semiconductor detector for detecting radiation emitted from a subject, voltage applying means for applying a predetermined voltage to a semiconductor cell in the radiation semiconductor detector;
When performing collection for single photons, the operation of the voltage applying means is controlled so as to apply a first voltage to the semiconductor cells, and when collecting for positrons, A nuclear medicine diagnosis apparatus comprising: control means for controlling the operation of the voltage application means so as to apply a second voltage. The nuclear medicine diagnosis apparatus according to claim 1 , wherein the first voltage is lower than the second voltage. In a nuclear medicine diagnostic apparatus equipped with a radiation semiconductor detector for detecting radiation emitted from a subject,
Voltage application means for applying a predetermined voltage to the semiconductor cell in the radiation semiconductor detector;
Adjusting means for adjusting a predetermined voltage applied by the voltage application means based on the incidence count rate of radiation, and the adjustment means, when the incidence count rate of radiation is low, by the voltage application means A nuclear medicine diagnostic apparatus characterized in that the voltage applied to the semiconductor cell is decreased, and when the incidence count rate of radiation is high, the voltage applied to the semiconductor cell is increased by the voltage applying means. The nuclear medicine diagnostic apparatus according to any one of claims 1 to 3, wherein the semiconductor cell is made of CdTe or CdZnTe. The nuclear medicine diagnostic apparatus according to any one of claims 1 to 3, wherein the semiconductor cell has a PIN structure. The nuclear medicine diagnosis apparatus according to any one of claims 1 to 3, wherein the voltage application unit applies a negative voltage within a range of -400V to -1500V to the semiconductor cell. The nuclear medicine diagnosis apparatus according to any one of claims 1 to 3, wherein the electrode formed in the semiconductor cell is arranged in a horizontal direction with respect to a radiation incident direction. The nuclear medicine diagnosis apparatus according to any one of claims 1 to 3, wherein the electrode formed in the semiconductor cell is arranged in a direction perpendicular to a radiation incident direction. Predetermined voltage applied to the semiconductor cell by said voltage applying means according to claim 1, characterized in that it is adjusted by increases or decreases stepwise within a predetermined time up to 3 Nuclear medicine diagnostic equipment.

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