JP4545628B2 - Radiation detection circuit, radiation detector and radiation inspection apparatus - Google Patents

Description

  The present invention relates to a radiation detection circuit, a radiation detector, and a radiation inspection apparatus, and more particularly to a radiation detection circuit, a radiation detector, and a radiation inspection apparatus that detect gamma rays from a radioisotope in a subject.

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

  Since the radiation of the two gamma rays emitted from the positron nuclide in the direction of about 180 degrees to each other is omnidirectional, the gamma ray detector surrounds the subject 360 degrees in order to improve the detection efficiency and shorten the examination time. Be placed.

  Further, since the position where the positron in the subject disappears is specified based on the incident position of the gamma ray to the gamma ray detector, it is desirable that the incident position can be accurately detected. In order to accurately detect the incident position, it is only necessary to downsize a gamma ray detection element such as a cell of a scintillator and a photomultiplier or a semiconductor detection element. In addition, a large number of gamma ray detection elements are required in accordance with miniaturization (for example, see Patent Document 1).

Each of the gamma ray detection elements includes a preamplifier that amplifies the detection signal from the gamma ray detection element, a waveform shaping circuit, and a detection circuit that includes a time pickoff circuit for determining the incident time of the gamma ray from the amplified detection signal. Connected.
JP 11-344568 A

  By the way, a preamplifier, a subsequent waveform shaping circuit, and the like are required according to the number of gamma ray detection elements. Therefore, as the number of gamma ray detection elements is increased, it is necessary to increase the number of preamplifiers and subsequent waveform shaping circuits. As a result, the circuit configuration of the IC chip on which the detection circuit is mounted becomes complicated, and the cost of the IC chip increases. As a result, the cost of the PET apparatus increases. In particular, when the subject is a human body, there is a problem that the number of gamma ray detection elements is enormous and the cost of the PET apparatus is greatly increased.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a low-cost radiation detector and radiation inspection apparatus.

  According to one aspect of the present invention, there is provided a radiation detection circuit to which a detection element for detecting gamma rays is connected, wherein the two detection elements are electrically connected, and a differential of a detection signal supplied from each of the detection elements. A differential amplifier that outputs an amplified signal; and a detection data generation unit that identifies a detection element on which the gamma ray is incident and measures an incident time of the gamma ray based on a signal component of each polarity of the differential amplified signal. A radiation detection circuit is provided.

  According to the present invention, two detection elements are connected to one differential amplifier that is an input unit of the radiation detection circuit, and detection signals supplied from each of the two detection elements are processed. Based on the signal components of the polarities of the differential amplification signals, the detection element on which the gamma rays are incident is identified, and the incident time at which the gamma rays are incident is measured. Therefore, according to the present invention, the number of amplifiers can be halved compared to a conventional radiation detection circuit in which an amplifier is provided for each detection element. As a result, a low-cost radiation detection circuit can be realized. Moreover, the number of circuit elements of the detection circuit per detection element can be reduced, and the complexity of the circuit is reduced when a large number of detection circuits are provided. The incident time of the gamma ray measured by the detection data generation unit may be a time obtained by adding a predetermined time to the time when the gamma ray is actually incident on the detection element, or may be the time when the actual incident time of the gamma ray is estimated. Good.

  The detection data generation unit detects a polarity of the differential amplification signal, outputs a polarity discrimination signal indicating the polarity, and a gamma ray incident event from the signal component of each polarity of the differential amplification signal And a detection data generation circuit for identifying a detection element by the polarity discrimination signal and determining a gamma ray incident time by the detection pulse. . With such a configuration of the radiation detection circuit, it is possible to identify which of the two detection elements the gamma ray is incident on, and to output information on the detection element and information on the time of incidence of the gamma ray. it can.

  According to another aspect of the present invention, the radiation detector includes a detection element that detects gamma rays and any one of the radiation detection circuits described above, and the two detection elements are arranged apart from each other. A radiation detector is provided.

  According to the present invention, the radiation detector has the same effect as the above-described radiation detection circuit. Furthermore, in the radiation detector of the present invention, since two detection elements arranged apart from each other are connected to one differential amplifier of the radiation detection circuit, one gamma ray is incident on these two detection elements simultaneously. There is nothing to do. Therefore, since the radiation detector of the present invention can avoid that the detection signals supplied from the two detection elements cancel each other, it can reliably detect the incident gamma rays.

  According to another aspect of the present invention, the radiation detector includes a detection element that detects gamma rays and one of the radiation detection circuits described above, wherein the two detection elements do not interfere with each other. A radiation detector is provided.

  According to the present invention, the radiation detector has the same effect as the above-described radiation detection circuit. Furthermore, in the radiation detector of the present invention, two detection elements that do not interfere with each other are connected to one differential amplifier of the radiation detection circuit, so that the detection signals supplied from the two detection elements cancel each other. Can be avoided. Therefore, the radiation detector of the present invention can reliably detect incident gamma rays. Note that “two detection elements that do not interfere with each other” refers to two detection elements in a state in which a detection signal is not simultaneously induced in each of the two detection elements by the incidence of one gamma ray. As such two detection elements, two detection elements that are arranged apart from each other, or two signal extraction electrodes that are not adjacent to each other as in the following cases are connected to one differential amplifier. The case of a detection element is also included.

  The detection element has a plate-like semiconductor crystal having one end face as an incident surface on which gamma rays are incident, and each of the first main surface and the second main surface orthogonal to the thickness direction of the semiconductor crystal. A first electrode portion to which a bias voltage is applied, and a second electrode portion, wherein the first electrode portion is made of a metal film that substantially covers the first surface, and the second electrode portion is The second surface may include a plurality of detection signal extraction electrodes arranged at substantially equal intervals along the incident surface, and the detection signal extraction electrodes may be electrically connected to the differential amplifier. With such a configuration, the number of amplifiers is reduced, and the number of circuit elements of the radiation detection circuit is reduced, so that the radiation detection circuit can be provided in the vicinity of the detection element. As a result, since the semiconductor detection elements can be arranged closely, the detection efficiency and spatial resolution of the radiation detector can be improved. Furthermore, the radiation detector can be miniaturized.

  The second electrode section includes n detection signal extraction electrodes, and two detection signal extraction electrodes that are not adjacent to each other among the n detection signal extraction electrodes are electrically connected to one differential amplifier. It is good also as a structure connected to. However, n is an integer of 3 or more. In this way, by electrically connecting two detection signal extraction electrodes that are not adjacent to each other to one of the differential amplifiers, a gamma ray incident on an incident surface adjacent to one detection signal extraction electrode is extracted from the other detection signal extraction electrode. It is possible to avoid affecting the electrodes. According to another aspect of the present invention, any one of the above-described radiation detectors is disposed around a subject containing a radioisotope so as to surround the subject and detects gamma rays generated from the radioisotope. There is provided a radiological examination apparatus comprising: a detecting means having information processing means for acquiring distribution information of the radioisotope in a subject based on detection data acquired from the detecting means.

  According to the present invention, since the radiation detector is provided, a low-cost radiation inspection apparatus can be realized. Furthermore, a high-performance radiation inspection apparatus that is excellent in detection efficiency and spatial resolution of the radiation detector can be realized.

  According to the present invention, the number of preamplifiers can be reduced by connecting two detection elements to a differential amplifier, and further, other circuit elements constituting the detection circuit can be reduced. Therefore, a low-cost radiation detection circuit, radiation detector, and radiation inspection apparatus can be provided.

  Embodiments will be described below with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram of a radiation detection circuit according to the first embodiment of the present invention. FIG. 1 also shows the detection elements.

Referring to FIG. 1, a radiation detection circuit 10 according to a first embodiment includes a differential amplifier 11 having two detection elements D ₁ and D ₂ connected thereto, a waveform shaping circuit 12, and a constant fraction disk. It comprises a limiter 13 (hereinafter referred to as “CFD”), a polarity discriminator 14, a detection data generation circuit 15, and the like.

In the radiation detection circuit 10, two detection elements D ₁ and D ₂ are electrically connected, and a detection signal resulting from the incidence of gamma rays is supplied from each of the _two detection elements D ₁ and D ₂ . The two detection elements D ₁ and D ₂ are preferably arranged so as not to interfere with each other. As described above, “does not interfere with each other” means that the detection signals are not simultaneously induced in each of the two detection elements by the incidence of one gamma ray. In such a case, two detection elements D ₁ and D ₂ are arranged apart from each other, or two detection signal extraction electrodes that are not adjacent to each other in the semiconductor detection element shown in FIG. This is the case when connected to the electrode. This specific aspect will be described in detail in the second embodiment.

The detection elements D ₁ and D ₂ may be a combination of a scintillator and a photomultiplier, or may be a semiconductor detection element.

Differential amplifier 11 has a non-inverting input one detection element D ₁ to the terminal is connected, the other detection element D ₂ is connected to the inverting input terminal. The output side of the differential amplifier 11 is connected to each of the non-inverting input terminal and the inverting input terminal via a resistor and a capacitor connected in parallel. The differential amplifier 11 amplifies the detection signal from _one detection element D ₁ while maintaining the polarity, and amplifies the detection signal from the other detection element D ₂ by inverting the polarity. The case where the detection signals from the detection elements D ₁ and D ₂ are close in time and overlap each other will be described with reference to FIG.

  The waveform shaping circuit 12 shapes the detection signal received from the differential amplifier 11 into a waveform that can be easily processed. The waveform shaping circuit 12 includes, for example, a passive filter composed of a resistor and a capacitor, and an active filter in which an operational amplifier is added thereto. The configuration of the waveform shaping circuit 12 is not particularly limited, and includes a high-pass filter, a low-pass filter, or a combination of a high-pass filter and a low-pass filter. The orders of the high-pass filter and the low-pass filter are appropriately selected, but are preferably set in the first to fifth order in terms of easy circuit manufacture.

  The CFD 13 outputs a detection pulse after a predetermined time from the incident time of the gamma rays based on the detection signal from the waveform shaping circuit 12.

FIG. 2 is a block diagram illustrating an example of a CFD. Referring to FIG. 2 together with FIG. 1, the CFD 13 includes resistors R ₁ and R ₂ that divide the output signal of the waveform shaping circuit 12 and a delay circuit 21 that delays the output signal of the waveform shaping circuit 12 by a predetermined time. And a differential amplifier 22, a zero-cross detection circuit 23, and the like.

  The CFD 13 divides the output signal of the waveform shaping circuit 12 and supplies a signal having a reduced peak value (for example, a peak value that is 1/5 of the original peak value) to the inverting input terminal of the differential amplifier 22. On the other hand, the CFD 13 delays the output signal of the waveform shaping circuit 12 by a predetermined time and supplies it to the non-inverting input terminal of the differential amplifier 22. The differential amplifier 22 has a zero-cross point at a predetermined time (time from the start of rising) whose output signal hardly depends on the peak value of the rising edge of the output signal of the waveform shaping circuit 12. The zero cross point is detected by the zero cross detection circuit 23 and a detection pulse is output to the detection data generation circuit 15 in accordance with the detected timing.

Instead of the CFD 13, a known time pick-off circuit (a circuit that detects the timing of an event in which gamma rays are incident on the detection elements D ₁ and D ₂ ) may be used. Examples of the time pick-off circuit include a constant fraction circuit and a leading edge timing circuit that detects the rising start time of the output signal of the waveform shaping circuit 12.

  Returning to FIG. 1, the polarity discriminator 14 detects the polarity of the output signal of the waveform shaping circuit 12 and outputs a polarity discrimination signal indicating the polarity. The polarity discriminator 14 outputs, for example, a polarity discrimination signal of “High” when the polarity of the output signal of the waveform shaping circuit 12 is positive and “Low” when the polarity is negative.

  The detection data generation circuit 15 measures the time when the detection pulse from the CFD 13 is received and sets it as incident time data. Specifically, the detection data generation circuit 15 includes a clock circuit, a counter circuit, a latch circuit, and the like, although not illustrated. The counter circuit receives a clock signal having a predetermined frequency from the clock circuit, and generates time data based on the clock signal. The counter circuit records the time data at the time of receiving the detection pulse in the latch circuit. The time data is not particularly limited in the number of bits, but is 48 bits, for example, and is set so that the least significant bit corresponds to a time width of, for example, about 30 n to 100 n seconds.

Further, the detection data generation circuit 15 identifies which detection element D ₁ , D ₂ is irradiated with gamma rays by the polarity discrimination signal “High” or “Low”, and detects each of the detection elements D ₁ , D _2. The detection element number assigned to is recorded. Then, the detection data generation circuit 15 outputs the detection element number and the incident time data as detection data to the information processing unit. The information processing unit performs a coincidence process, a process of regenerating image data at the position of the positron nuclide RI, and the like. The information processing unit will be described in the second embodiment.

  3A to 3F are diagrams for explaining the operation of the radiation detection circuit shown in FIG. The operation of the radiation detection circuit will be described with reference to FIGS. 3A to 3F together with FIGS.

As shown in FIG. 3A, it is assumed that gamma rays γ ₁ and γ ₂ are incident on the two detection elements D ₁ and D ₂ at different times. Incident gamma rays generate detection signals in the detection elements D ₁ and D ₂ by photoelectric conversion. Here, it is assumed that the detection signal is positive.

As shown in FIG. 3B, the output of the differential amplifier has a positive detection signal from the detection element D ₁ and a negative detection signal from the detection element D _{2 as} indicated by a solid line. Further, as shown by the broken line for reference, the tail portion of the detection signal from the detection device D ₁ are overlapped with the detection signal from the next detection element D _2. In particular, when CdTe is used as the detection element, the tail portion of the detection signal from each of the detection elements D ₁ and D ₂ is slowly attenuated. Therefore, when two gamma rays are incident on one detection element D ₁ , A so-called pile-up phenomenon occurs in which two detection signals having the same polarity overlap each other. The differential amplifier 11 is easily saturated when a pile-up phenomenon occurs, and a zero cross point cannot be obtained in the CFD 13 from the detection signal. That is, it becomes impossible to determine the incident time of gamma rays.

However, in the radiation detection circuit 10, when the gamma ray γ ₁ is incident on _one detection element D ₁ and subsequently the gamma ray γ ₂ is incident on the other detection element D ₂ , the differential amplifier 12 generates a detection signal having a reverse polarity. Since they are added together, the pile-up phenomenon can be suppressed. Then, the incident time of gamma rays can be determined based on each detection signal.

  As shown in FIG. 3C, the output of the waveform shaping circuit 12, for example, each of two peaks is sharp, that is, the peak width is narrow. That is, the two peaks are separated from each other.

As shown in FIG. 3D, the output of the CFD 13 outputs a detection pulse corresponding to each peak of the waveform shaping circuit 12. Incidentally, two detection pulses tend to incident time of the gamma ray detection pulse derived from the detection element D ₂ that enters subsequently is shifted in time backwards. However, the time width of the time data for determining the time of the detection pulse is about 30 nsec to 100 nsec, and since this shift time is smaller than the time width of the time data, there is no problem.

Further, as shown in FIG. 3E, the output of the polarity discriminator 14 is detected from the detection element D _{1 in accordance} with the polarity of the peak value of the output of the waveform shaping circuit 12 shown in FIG. The time corresponding to the signal is “High”, and the time corresponding to the detection signal from the detection element D ₂ is “Low”.

As shown in FIG. 3 (F), the output of the detection data generation circuit 15 includes the detection element number corresponding to the polarity of the output of the polarity discriminator 14 in FIG. 3 (E) and the CFD 13 shown in FIG. 3 (D). Detection data consisting of incident time data corresponding to the output signal is sequentially output. In this manner, the radiation detection circuit 10 associates the incident time data of the gamma rays γ ₁ and γ ₂ incident on the _two detection elements D ₁ and D ₂ connected to one differential amplifier 11 with the detection elements. Output to the information processing unit.

According to the present embodiment, since the two detection elements D ₁ and D ₂ are connected to the differential amplifier 11 of one radiation detection circuit 10, radiation detection in which a preamplifier is provided for each conventional detection element. Compared to the circuit, the number of preamplifiers can be halved. Therefore, a low-cost radiation detection circuit can be realized.

Furthermore, according to the present embodiment, two detection signals from the two detection elements D ₁ and D ₂ are processed by the one waveform shaping circuit 12 and the CFD 13, so that radiation detection is performed for each conventional detection element. Compared with the case where a circuit is provided, the number of circuit elements of the radiation detection circuit required per detection element can be reduced. Therefore, an even lower cost radiation detection circuit can be realized.

  The radiation detection circuit 10 as a whole or most of the radiation detection circuit 10 is mounted on an IC chip (shown in FIG. 8 of the second embodiment), for example, an ASIC (Application Specific Integrated Circuit). In such an IC chip, an analog circuit such as the differential amplifier 11 and the waveform shaping circuit 12 and a digital circuit such as the detection data generation circuit 15 are mixedly mounted. For such a hybrid IC chip, it is relatively difficult to design an analog circuit because of a lack of design CAD. Analog circuits are vulnerable to noise, so special noise design is required. However, in the radiation detection circuit 10, since the number of amplifiers (differential amplifiers) per detection element is halved, the circuit design of the IC chip is facilitated. In addition, since a space for separating the analog circuit and the digital circuit on the IC chip can be secured, it is easy to take measures against noise.

(Second Embodiment)
FIG. 4 is a block diagram showing a configuration of a PET apparatus according to the second embodiment of the present invention. In the figure, portions corresponding to the portions described above are denoted by the same reference numerals, and description thereof is omitted.

Referring to FIG 4, PET device 30 processes are disposed around the subject S, the detector 31 ₁ to 31 ₄ for detecting the gamma rays, the detection data from the detector 31 ₁ to 31 _4, to give an information processing unit 35 to regenerate the image data of the position of the positron nuclide RI in the body of the subject S that is, a display unit 36 for such view the image data, movement of the object S and the detector 31 ₁ to 31 ₄ The control unit 37 controls the information processing unit 35 and the control unit 37. The input unit 38 includes a terminal that sends instructions to the control unit 37, a printer that outputs image data, and the like.

Detector 31 _{1-31 4} introduces a test agent labeled with a positron nuclide RI in advance subject S, gamma gamma _a emitted from the subject S, detects a gamma _b. Each of the detectors 31 _{1 to} 31 ₄ includes a plurality of detection substrates 34 provided with the semiconductor detection element 41 and the radiation detection circuit 10. The semiconductor detection element 41 is disposed so as to face the subject S, and detects two gamma rays γ _a and γ _b generated simultaneously when the positron from the positron nuclide RI disappears. Since the two gamma rays γ _a and γ _b are emitted at an angle of approximately 180 degrees, the two gamma rays γ _a and γ _b enter the semiconductor detection element 41 of the detector 31 facing each other with the subject S interposed therebetween. Each of the two semiconductor detection elements 41 on which the gamma rays γ _a and γ _b are incident transmits an electrical signal (detection signal) generated by photoelectric conversion of the gamma rays γ _a and γ _b to the radiation detection circuit 10.

As described in the first embodiment, the radiation detection circuit 10 identifies the electrode of the semiconductor detection element 41 on which the gamma rays γ _a and γ _b are incident from the detection signal and measures the incident time. Then, the radiation detection circuit 10 sends the incident time and the electrode number (and further the semiconductor detection element number) of the semiconductor detection element 41 that detected the gamma rays γ _a and γ _b to the information processing unit 35 as detection data. The radiation detection circuit 10 is configured in the same manner as the radiation detection circuit according to the first embodiment.

  The information processing unit 35 performs coincidence detection and image data regeneration by an image regeneration algorithm based on the detection data. In the coincidence detection, when there are two or more pieces of detection data whose incident times substantially coincide with each other, it is determined that these pieces of detection data are valid and used as coincidence information. In the coincidence detection, detection data whose gamma ray incident times do not match is determined to be invalid and discarded. Then, a predetermined image regeneration algorithm (for example, Expectation Maximization method) is obtained from the coincidence information, the electrode number and the semiconductor detection element number included in the coincidence information, and the position information of the semiconductor detection element 41 corresponding thereto. ) To regenerate the image data. The display unit 36 displays the image data regenerated in response to the request from the input / output unit 38.

  With the above configuration and operation, the PET apparatus 30 detects gamma rays from the positron nuclide RI selectively located in the body of the subject S, and regenerates image data of the distribution state of the positron nuclide RI. Next, a specific example of the semiconductor detection element will be described.

FIG. 5 is a perspective view of a semiconductor detection element of the first example constituting the detector. Referring to FIG. 5, the semiconductor detection element 41 of the first example includes a thin plate-like semiconductor crystal body 42 and electrodes 43, 44 ₁ to 44 ₁ formed on the surfaces orthogonal to the thickness direction (X-axis direction). 44 ₆ In the semiconductor detection element 41, one of the end faces (XZ plane) of the semiconductor crystal body 42 is a gamma ray incident surface 41a. It is assumed that gamma rays are incident substantially in the Y direction.

Examples of the material of the semiconductor crystal 42 include cadmium telluride (CdTe), Cd _1-x Zn _x Te (CZT), and thallium bromide (TlBr) that are sensitive to gamma rays having an energy of 511 keV. . CdTe may be doped with Cl (chlorine) in terms of reducing leakage current. For example, the semiconductor crystal body 42 has dimensions of about 0.5 mm in thickness (X-axis direction), about 10 mm in depth (Y-axis direction), and about 10 mm in width (Z-axis direction). The longer the semiconductor crystal 42 is, the more preferable it is because the area of the incident surface 21a for gamma rays is increased. However, it is preferable to set the semiconductor crystal 42 in the range of 5 mm to 30 mm for convenience of manufacturing such as manufacturability.

  The electrode 43 is made of a metal film that substantially covers one surface orthogonal to the thickness direction (X-axis direction) of the semiconductor crystal body 42. In the case where the semiconductor crystal 42 is made of CdTe and the setting is made to apply the positive bias voltage Vb, the electrode 43 is set to In. As a result, a Schottky junction is formed between the electrode 43 and CdTe. The bias voltage Vb is a direct-current voltage and is set to 60 V to 1000 V, for example.

The electrodes 44 _{1 to} 44 ₆ are provided on a surface facing the surface on which the electrode 43 is provided. The electrodes 44 _{1 to} 44 ₆ are striped, have a thickness (X-axis direction) of about 1 mm, and a depth (Y-axis direction) that is substantially the same length and width as the depth (Y-axis direction) of the semiconductor crystal 42. (Z-axis direction) has a width of about 0.3 mm. The distance L1 between the electrodes 44 _{1 to} 44 _{6 in} the Z-axis direction is set to about 0.5 mm. As the interval L1 and the width are smaller, the detection position accuracy of gamma rays is improved, and as a result, the spatial resolution of the detector is improved. However, the interval L1 is preferably set in the range of 0.25 mm to 1.5 mm.

Electrodes 44 _{1 to} 44 ₆ are electrodes for taking out detection signals generated by the incidence of gamma rays. Each of the electrodes 44 _{1 to} 44 ₆ is connected to a radiation detection circuit (described in detail in FIG. 6). Thus, by arranging the electrodes 44 _{1 to} 44 ₆ in the Z-axis direction, the position in the Z-axis direction of the gamma rays incident on the incident surface 41a of the semiconductor crystal body 42 is specified. That is, the gamma rays γ _b incident on the semiconductor crystal 42 form a number of electron-hole pairs (charges) corresponding to the energy by photoelectric conversion. A bias voltage Vb is applied to the semiconductor crystal body 42 so that the electrode 43 has a positive voltage with respect to the electrodes 44 _{1 to} 44 ₆ . Due to the electric field generated by the bias voltage Vb, electrons move to the electrode 43, and holes move to any of the electrodes 44 _{1 to} 44 ₆ closest to the incident position and are taken out as detection signals. For example, as shown in FIG. 3, when the gamma ray gamma _b is incident on the vicinity of the electrodes 44 _2, a detection signal is taken out from the electrode 44 _2. Detection signal is sent to the radiation detector, together with the incident time of the gamma ray gamma _b, the electrode 44 ₂ is detected, as the position information. Incidentally, gamma gamma _b is, for example, when incident on the incident surface 41a in the vicinity between the electrode 44 ₂ and the electrode 44 _3, the detection signal appears at both electrodes 44 ₂ and the electrode 44 _3. In this case, the information processing unit 35 shown in FIG. 4, those incident between the electrode 44 ₂ and the electrode 44 _3, or of the electrodes 44 ₂ and the electrode 44 _3, a detection signal output value higher Treated as incident on the electrode.

FIG. 6 is a block diagram of a detector of the PET apparatus according to the second embodiment. FIG. 6 shows one semiconductor detection element 41 and the radiation detection circuit 10. Although three radiation detection circuits 10 are connected to the _six electrodes 44 _{1 to} 44 ₆ provided in the semiconductor detection element 41, for convenience of explanation, they are connected to the differential amplifiers 11 ₂ and 11 _3. The radiation detection circuit 10 is omitted.

Referring to FIG. 6, the detector 31 includes a semiconductor detection element 41 and a radiation detection circuit 10. The semiconductor detection element 41 has the same configuration as the semiconductor detection element shown in FIG. 5, and has six electrodes 44 _{1 to} 44 ₆ for extracting detection signals. The radiation detection circuit 10 has the same configuration as the radiation detection circuit 10 shown in FIG.

The semiconductor detection element 41 and the radiation detection circuit 10 are connected as follows. That is, electrodes that are not adjacent to each other are connected to each of the non-inverting input terminal and the inverting input terminal of each of the differential amplifiers 11 _{1 to} 11 ₃ . For example, the electrode 44 ₁ of the semiconductor detection element 41 and the electrode 44 ₄ located between the electrode 44 ₂ and the electrode 44 ₃ are respectively connected to the non-inverting input terminal and the inverting input terminal of the differential amplifier 11 ₁ . Further, an electrode 44 _2, each electrode ₄₄₅ is a non-inverting input terminal of the differential amplifier 11 ₂ is connected to the inverting input terminal, and the electrode 44 _3, and the electrode 44 ₆ are each of the differential amplifier 11 ₃ Connected to non-inverting input terminal and inverting input terminal. In addition, the example of the combination of electrodes mentioned above is an example, and it cannot be overemphasized that the other combination of two electrodes which are not mutually adjacent | abutted may be sufficient.

By connecting the two electrodes 44 _{1 to} 44 ₆ that are not adjacent to each other to one differential amplifier 11 _{1 to} 11 ₃ in this way, the non-inverting input terminals of the differential amplifiers 11 _{1 to} 11 ₃ are caused by the incidence of one gamma ray. In addition, it is avoided that the detection signals are simultaneously input to the inverting input terminals and the detection signals are canceled by the differential amplifiers 11 _{1 to} 11 ₃ . Therefore, the detector 31 can reliably detect the incidence of gamma rays.

Furthermore, the connection between the differential amplifier of such electrodes 44 ₁ to 44 ₆ and the radiation detection circuit 10, not the electrodes 44 ₁ to 44 ₆ are only six, applicable in the case of n (n is an integer of 3 or more) it can.

Furthermore, the connection between the semiconductor detection element 41 and the differential amplifiers 11 _{1 to} 11 ₃ is not limited to the mode shown in FIG. 6. For example, one electrode of a different semiconductor detection element is connected to one differential amplifier. May be. Instead of the semiconductor detection element of the first example, a semiconductor detection element of the second example described below may be used.

  FIG. 7 is a perspective view of the semiconductor detection element of the second example. The semiconductor detection element of the second example is a case where a detection signal is taken out from the electrode side to which a positive voltage bias is applied. The relationship between the semiconductor detection element and the coordinate axis is set in the same manner as in FIG.

Referring to FIG. 7, the semiconductor detection element 46 of the second example includes a thin plate-like semiconductor crystal body 42 and electrodes 43 ₁ to 43 ₆ formed on each of the surfaces orthogonal to the thickness direction (X-axis direction). , 44. The semiconductor crystal 47 is made of the same material as the semiconductor crystal 42 shown in FIG.

The semiconductor crystal body 47 has recesses 47a formed on the surfaces of the electrodes 43 ₁ to 43 ₆ along the Y-axis direction. Electrodes 43 ₁ to 43 ₆ are formed on the surface of the semiconductor crystal body 47 (surfaces of the convex portions) between the adjacent concave portions 47a and the concave portions 47a. The distance L ₂ between the electrodes 43 ₁ to 43 _{6 in} the Z-axis direction is set to about 0.5 mm. The smaller the interval L ₂ is, the better the detection position accuracy of gamma rays is. As a result, the spatial resolution of the detector 31 is improved, but it is preferably set in the range of 0.25 mm to 1.5 mm.

  Further, the semiconductor crystal 47 has substantially the same size as the semiconductor crystal 42 shown in FIG. The thickness of the portion where the recess 47a is provided (the distance from the bottom surface of the recess 47a to the opposite surface) is preferably set in the range of 0.2 mm to 0.9 mm.

The electrodes 43 ₁ to 43 ₆ are made of In, and a positive bias voltage Vb is connected to the radiation detection circuit through a resistor.

  The electrode 44 is a metal film made of Pt, for example, provided so as to substantially cover one surface of the semiconductor crystal 42. The electrode 44 is grounded or connected to a negative voltage power source.

The semiconductor detection element 46 of the second example has the same function as the semiconductor detection element of the first example. Furthermore, the semiconductor detection element 46 of the second example is provided with a recess 47a between the electrodes 43 ₁ to 43 ₆ , so that electrons generated by the incidence of gamma rays are more than the holes of the semiconductor detection element of the first example. Can be concentrated on one electrode. Therefore, in the semiconductor detection element 46 of the second example, the detection signal has a larger charge amount or output voltage than in the case of the semiconductor detection element of the first example. Therefore, the S / N ratio of the detection signal is improved, and for example, the incident time can be determined more accurately.

  The semiconductor detection element 46 of the second example can achieve the same effect as the semiconductor detection element of the first example, that is, downsizing of one unit of the semiconductor detection element. Further, the semiconductor detection element 46 of the second example can improve the S / N ratio of the detection signal as compared with the semiconductor detection element of the first example.

Note that the electrodes 44 _{1 to} 44 ₆ shown in FIG. 5 and the electrodes 43 ₁ to 43 ₆ shown in FIG. 7 show the case where there are six electrodes, but the number is not limited to six, and two to five may be used. Alternatively, it may be 7 or more, for example, 10 or 20. At that time, electrodes that are not adjacent to each other are connected to the differential amplifier.

  FIG. 8 is a cross-sectional view of a principal part of the detector of the PET apparatus according to the second embodiment of the present invention. In the figure, portions corresponding to the portions described above are denoted by the same reference numerals, and description thereof is omitted.

  Referring to FIG. 8, the detector 31 is configured by stacking detection substrates 34 in the X-axis direction. The detection substrate 34 includes a semiconductor detection element 41, an IC chip 51, a wiring substrate 52, and the like. The semiconductor detection element 41 is the semiconductor detection element 41 of the first example shown in FIG.

  In the detection substrate 34, the semiconductor detection element 41 is provided on the front end portion 52 a of the wiring substrate 52. Further, the detection substrate 34 is provided with an IC chip 51 on the base side of the semiconductor detection element 41.

  The wiring substrate 52 is made of, for example, a single-plate ceramic substrate, a multilayer ceramic substrate, or a multilayer printed wiring board (for example, a glass cloth epoxy resin laminate or a glass cloth polyimide resin laminate). The wiring substrate 52 is provided with electrode pads 53 and 56 for bonding the semiconductor detection element 41 or wire bonding, electrode pads 58 for bonding the IC chip 51, and wiring (not shown).

In the semiconductor detection element 41, the electrodes 44 _{1 to} 44 ₆ are joined to the electrode pad 53 via the joining portion 54 and are electrically connected. The electrode 43 is electrically connected to the electrode pad 56 by a conductive wire 55.

Although the IC chip 51 is not shown, the detection circuit 31 shown in FIG. 6 is mounted. The IC chip 51 is bonded to the electrode pads 58 of the wiring board 51 by, for example, solder bumps. The IC chip 51 is electrically connected to the semiconductor detection element 41 via a wiring (not shown) of the wiring board 51. In this connection, the differential amplifiers 11 _{1 to} 11 ₃ shown in FIG. 6 and the electrodes 44 _{1 to} 44 _{6 of the} semiconductor detection element 41 are connected in the same manner as shown in FIG.

  As described above, the detection substrate 34 is configured by the semiconductor detection element 41 and the IC chip 51 on which the radiation detection circuit is mounted, thereby reducing the size of the detector 31 while maintaining the area of the incident surface 41a of the semiconductor detection element 41. Can be planned. Further, the height of the IC chip 51 may be substantially equal to or less than the height of the semiconductor detection element 41, and the thickness of the detection substrate 34 in the X-axis direction may be reduced. In this way, by further densely stacking the detection substrates 34 in the X-axis direction, it is possible to reduce the dead space between the detection substrates 34 and improve the detection efficiency of gamma rays. At the same time, the spatial resolution of the detector 31 can be improved.

Although detailed illustration is omitted, for example, the two IC chips shown in FIG. 8 are combined into one differential amplifier of the radiation detection circuit of the IC chip, and the semiconductor detection element 41 on one detection substrate 34. One of the electrodes 44 _{1 to} 44 ₆ may be connected to one of the electrodes 44 _{1 to} 44 ₆ of the semiconductor detection element 41 of the other detection substrate 34.

Further, the electrodes of the semiconductor detection element 41 connected to one differential amplifier are different from the detectors 31 _{1 to} 31 ₂ shown in FIG. 4, for example, the electrodes of the semiconductor detection element selected from the detector 31 ₁ and the detector 31 _2. You may connect. However, in this case, it is preferable to select the semiconductor detection element so that a virtual line connecting the incident surfaces of the two semiconductor detection elements does not cut the subject S. By doing so, it is avoided that each of the pair of gamma rays generated at the same time enters the two selected semiconductor detection elements at the same time, and the incident event of the gamma rays becomes undetectable.

Further, in FIG. 8, an example using the semiconductor detection element 41 of the first example is given, but the semiconductor detection element of the second example may be used instead of the semiconductor detection element of the first example. In this case, in the semiconductor detection element of the second example, it is preferable to join the electrodes 43 ₁ to 43 ₆ and the electrode pads 53 of the wiring board 52 shown in FIG. In FIG. 8, two detection boards 34 are shown, but the number of detection boards 34 provided in one detector is not particularly limited.

  According to the present embodiment, the radiation circuit 10 has the same effect (low cost) as the radiation detection circuit according to the first embodiment. Therefore, the cost of the detector 31 and the PET apparatus 30 can be reduced. Furthermore, by using the semiconductor detection elements 41 and 46 as the detection elements and mounting the radiation detection circuit on the IC chip 51, the detection substrate 34 can be thinned. Thereby, the detection substrates 34 can be densely stacked to improve the detection efficiency and spatial resolution of the detector 31, and the size can be reduced.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the present invention described in the claims. It can be changed. For example, in the above-described second embodiment, the PET apparatus has been described as an example, but the present invention can be applied to a SPECT (Single Photon Emission Computed Tomography) apparatus.

It is a block diagram of a radiation detection circuit concerning a 1st embodiment of the present invention. It is a block diagram of a constant fraction discriminator. (A)-(F) is a figure for demonstrating operation | movement of the radiation detection circuit shown in FIG. It is a figure which shows typically the structure of the PET apparatus which concerns on the 2nd Embodiment of this invention. It is a perspective view of the semiconductor detection element of the 1st example which constitutes the detector of the PET device concerning a 2nd embodiment. It is a block diagram of the detector of the PET apparatus which concerns on 2nd Embodiment. It is a perspective view of the semiconductor detection element of the 2nd example. It is principal part sectional drawing of a detector.

Explanation of symbols

10 Radiation Detection Circuit 11 Differential Amplifier 12 Waveform Shaping Circuit 13 Constant Fraction Discriminator (CFD)
14 polarity discriminator 15 detects the data generating circuit 21 a delay circuit 22 differential amplifier 23 zero-cross detection circuit 31, 31 ₁ to 31 ₄ detector 34 detects the substrate 35 information processing unit 36 display unit 37 control unit 38 input-output unit 41, 46 a semiconductor Detection element 42, 47 Semiconductor crystal body 43, 43 ₁ to 43 ₆ , 44, 44 _{1 to} 44 ₆ Electrode 51 IC chip 52 Wiring substrate 53, 56, 58 Electrode pad D ₁ , D ₂ Detection element

Claims (9)

A radiation detection circuit to which a detection element for detecting gamma rays is connected,
A differential amplifier in which two detection elements are electrically connected, and outputs a differential amplification signal of a detection signal supplied from each of the detection elements;
A radiation detection circuit comprising: a detection data generation unit that identifies a detection element on which a gamma ray is incident and measures an incident time of the gamma ray based on a signal component of each polarity of the differential amplification signal. The detection data generation unit
A polarity discriminator for detecting the polarity of the differential amplification signal and outputting a polarity discrimination signal indicating the polarity;
An incident timing detection circuit that detects an incident event of a gamma ray from a signal component of each polarity of the differential amplification signal and generates a detection pulse;
The radiation detection circuit according to claim 1, further comprising: a detection data generation circuit that identifies a detection element by the polarity discrimination signal and determines an incident time of gamma rays by the detection pulse. A radiation detector comprising a detection element for detecting gamma rays and the radiation detection circuit according to claim 1,
The radiation detector, wherein the two detection elements are spaced apart from each other. A radiation detector comprising a detection element for detecting gamma rays and the radiation detection circuit according to claim 1,
The radiation detector, wherein the two detection elements do not interfere with each other. The detection element is
A plate-like semiconductor crystal having one end face as an incident face on which gamma rays are incident;
A first electrode portion and a second electrode portion to which a bias voltage is applied to each of the first main surface and the second main surface orthogonal to the thickness direction of the semiconductor crystal body,
The first electrode portion is made of a metal film that substantially covers the first surface,
The second electrode portion includes a plurality of detection signal extraction electrodes arranged on the second surface at substantially equal intervals along the incident surface,
5. The radiation detector according to claim 3, wherein the detection signal extraction electrode is electrically connected to the differential amplifier.   The radiation detector according to claim 5, wherein the second electrode portion has a second surface that is substantially flat, and adjacent detection signal extraction electrodes are spaced apart from each other.   The second electrode portion has a plurality of concave portions with the second surface provided at substantially equal intervals along the incident surface, and a detection signal extraction electrode is provided between adjacent concave portions. The radiation detector according to claim 5. The second electrode portion has n detection signal extraction electrodes,
8. The n detection signal extraction electrodes, wherein two detection signal extraction electrodes that are not adjacent to each other are electrically connected to one of the differential amplifiers. The radiation detector according to one item (n is an integer of 3 or more). The radiation detector according to any one of claims 3 to 8, wherein the radiation detector is arranged around a subject containing a radioisotope so as to surround the subject and detects gamma rays generated from the radioisotope. Having detection means;
An information processing unit that acquires distribution information of the radioisotope in a subject based on detection data acquired from the detection unit.

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