JPH1114757A - Gamma camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably process a photoelectric multiplying tube(PMT) output signal and prevent the deterioration of a camera image by outputting an electric signal obtained by photoelectrically converting a scintillation light as a digital signal. SOLUTION: The scintillation light emitted from a scintillator 29 by γ-ray is incident on a plurality of digital PTM 31. The PTM 31 photoelectrically converts this light, and A/D converts and outputs its analog electric signal after it is subjected to a processing such as integration, sample/hold or the like by a signal processing circuit 31a. This digital signal is inputted to an electronic circuit board 33 through a cable 32. In the circuit board 33, the sensitivity of the PMT 31 is regularly made constant by a deterioration-with-age correcting circuit, and the deterioration of a camera image is suppressed. The output characteristic of the PMT 31 is corrected by a nonlinear correcting circuit. This signal is transmitted to a processing device through a frame 2 and a cable, and the processing device forms a gamma camera image, or the distribution image of a radioactive isotope within a subject, and indicates it on a display.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a gamma camera provided with a two-dimensional detector including a scintillator and a photomultiplier tube (PMT).

[0002]

2. Description of the Related Art A gamma camera of this type, which is conventionally known, is classified as a kind of so-called nuclear medicine diagnostic equipment. Nuclear medicine diagnostic devices use the property that when a radiopharmaceutical labeled with a radioisotope (RI) is administered into a subject, it is absorbed and concentrated in a specific organ or tissue determined by the properties of the drug. This device detects gamma rays emitted from RI from outside the body and images the dose distribution. One particular RI is
It has an affinity for a specific organ and is deeply related to the function or tissue of the organ. For this reason, it is said to be useful for diagnosing the shape and function (metabolism function, etc.) of an organ and for diagnosing the presence or absence of a lesion.

[0003] The history of nuclear medicine diagnostic equipment began around 1951, when it was called a scintillation scanner that collects images by scanning one scintillation detector two-dimensionally. In 1956, a system called anger camera with a relatively large NaI single crystal and a two-dimensional detector having a plurality of PMTs was developed by Anger of the United States, which is a gamma camera (called a scintillation camera). Is widely used clinically today.

The above conventional gamma camera operates as follows. That is, an output signal from each PMT is transmitted to an electronic circuit board via a cable. In the electronic circuit board, the transmitted signal is integrated by an integrating circuit including a capacitor and a resistor, thereby forming a waveform. Done. Then, processing such as position calculation is performed based on the waveform-shaped PMT output signal, and a gamma camera image is created.

[0005]

The above conventional gamma camera has the following disadvantages. That is, the output signal from the PMT is an analog signal, and is likely to be affected by noise or the like when transmitted over a relatively long distance by the cable. In addition, due to individual variations such as errors in the capacitance of the above cable or capacitor, each PMT
Change occurs in the output waveform, and this causes an undershoot. Therefore, there is a disadvantage that the gamma camera image is deteriorated due to these causes. Further, the electronic circuit board that processes the output signal from the PMT has a relatively large size and generates a large amount of heat because it is an analog circuit. Therefore, there is a disadvantage that signal drift or the like occurs and the signal becomes unstable.

The present invention provides a gamma camera capable of stably processing an output signal of a PMT without being affected by noise or drift when transmitting a cable, thereby preventing deterioration of a gamma camera image. The purpose is to do.

[0007]

In order to solve the above problems and achieve the object, the present invention uses the following means. (1) The gamma camera of the present invention includes a digital photomultiplier tube device provided to photoelectrically convert scintillation light and to output an electric signal obtained by the photoelectric conversion as a digital signal. (2) The gamma camera according to the present invention is the gamma camera described in (1) above, wherein the digital photomultiplier is optically coupled to a scintillator that emits scintillation light, and the scintillation light is A photomultiplier tube that converts the photoelectric signal into an electric signal, outputs an electric signal, an integration circuit that integrates the electric signal output from the photomultiplier tube, and converts the electric signal integrated by the integration circuit into an A signal. And an A / D converter for converting the digital signal into a digital signal. (3) The gamma camera according to the present invention is the gamma camera according to the above (1) or (2), and further includes a time-dependent change correcting means for correcting a time-dependent change in the output of the digital photomultiplier tube device. Have. (4) The gamma camera of the present invention provides the gamma camera according to (1) or (2) above.
Or the gamma camera according to (3), further comprising a non-linear circuit for correcting output characteristics of the digital photomultiplier tube.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is an external view of a gamma camera according to a first embodiment of the present invention. As shown in FIG. 1, the gamma camera includes a detector 1, a gantry 2, a top 3, a display 4, a processing device 5, and a cable 6. The detector 1 is supported by a gantry 2 so that it can rotate and move in a predetermined direction. That is, the detector 1 can rotate in the direction indicated by the arrow CCW or CW in the drawing (the direction around the top 3), and the detection surface of the detector 1 can move in the arrow OPEN direction in the drawing. I have. A subject (not shown) is placed on the top 3. The display 4 is connected to the processing device 5 and displays a gamma camera image created by the processing device 5. The processing device 5 is connected to the gantry 2 via a cable 6.

FIG. 2 is a sectional view showing the structure of the detector 1. As shown in FIG. 2, the detector 1 has a collimator 20, a lead shield 21, an iron frame 22, a lead plate 23, an iron plate 24, and an iron lid 25. The γ-ray emitted from the RI administered into the subject enters the scintillator 29. The collimator 20 has an opening of a predetermined size, and limits the direction of the γ-ray reaching the scintillator 29 and defines the size of the field of view.

The lead shield 21 is provided so as to cover the aluminum plate 28, the scintillator 29, the glass plate 30, the digital PMT 31, the flange 27, and the support rod 26. The lead shield 21 and the lead plate 23 are used as shield materials for preventing radiation (γ-rays) from leaking to the outside.

A flange 27 is attached to the iron frame 22 via a support bar 26. An aluminum plate 28, a scintillator 29, and a glass plate 30 as a light guide are attached to the flange 27. This glass plate 3
0 is a multiple digital photomultiplier tube (PMT)
31 are attached.

The digital PMT 31 is a scintillator 29
Are optically coupled to each other via a glass plate 30.
Scintillation light (fluorescence) emitted from the scintillator 29 by the incidence of γ-rays enters the digital PMT 31 via the glass plate 30.

Each of the digital PMTs 31 photoelectrically converts scintillation light emitted from the scintillator 29 and outputs an analog electric signal.
T) and a signal processing circuit 31a for processing the analog electric signal output from the PMT. The signal processing circuit 31a includes an amplifier, a waveform shaping circuit, a BLR circuit, an S / H circuit, and an A / D circuit.

The waveform shaping circuit comprises an integrating circuit for integrating an analog electric signal output from the PMT by a capacitor and a resistor. BLR (Baseline Lister:
The BaseLine Restorer circuit adjusts a base portion of a signal (integrated signal) output from the waveform shaping circuit to a predetermined value. The S / H circuit samples / holds a signal output from the BLR circuit. The A / D circuit A / D converts the signal sampled and held by the S / H circuit and outputs the signal as a digital signal. In the PMT, correction processing such as energy correction and direct ray correction is performed. These energy correction and direct ray correction are known technologies.

The output terminal (A) of each digital PMT 31
The output terminal of the / D converter is connected to an electronic circuit board 33 via a cable 32. The electronic circuit board 33 is provided on the iron plate 24, and performs various signal processing on a digital PMT output signal output from the digital PMT 31. That is, it includes a temporal change correction circuit for correcting a temporal change in the output of the photomultiplier, a non-linear correction circuit for correcting the output characteristics of the photomultiplier, and a position / energy calculating circuit.

The time-dependent change correction circuit measures the output change of the photomultiplier tube over time from the time when the correction data for the energy correction and the direct ray correction is collected, and calculates the correction amount based on the output change. The calculated value is multiplied (for example, 1.5 times) by the multiplier to the output of the A / D circuit. Thereby, the sensitivity of the photomultiplier can be always kept constant, and deterioration of the gamma camera image can be suppressed. Further, the output characteristics of the photomultiplier tube are also corrected by the nonlinear correction circuit.

The position / energy calculation circuit includes a process for obtaining the gamma ray incident position information (X, Y) and the gamma ray energy information Z from the corrected signals. The output end of the electronic circuit board 33 is connected to the gantry 2 via a cable 34.

As shown in FIG. 4, the signal processing circuit 3
1a may be configured by an amplifier, an S / H circuit, and an A / D circuit, and the waveform forming circuit and the BLR may be arranged in a stage preceding the temporal correction circuit of the electronic circuit board 33.

FIG. 5 is a graph showing the output characteristics of the PMT before and after the nonlinear correction. The output of the PMT before correction has a characteristic that changes as the point source is moved away from the center of the PMT as shown in FIG. If an image is created with such characteristics, an image corresponding to the area corresponding to the central part of the PMT is raised. Thus, the nonlinear correction circuit applies a correction to the output of the A / D converter to reduce the output at the center of the PMT as shown in FIG. As a result, an image in a preferable mode can be obtained without obtaining the image as described above.

The output digital signal (PMT output signal) is sent to an electronic circuit board 33 via a cable 32. The digital PMT output signal is supplied to the electronic circuit board 33.
Is transmitted to the processing device 5 via the cable 34, the gantry 2, and the cable 6.

Returning to FIG. The processing device 5 creates a gamma camera image, that is, a distribution image of radioisotopes in the subject, based on signals output from the electronic circuit board 33 and transmitted via the gantry 2 and the cable 6. The created gamma camera image is displayed on the display 4.

According to the present embodiment described above, since the digital PMT 31 outputs a digital signal, it is possible to reduce the influence of noise when transmitting on the cables 32 and 34. Also, undershoot due to a change in the output waveform does not occur. Therefore, deterioration of the gamma camera image due to these causes can be prevented. Further, the problem of heat generation in the electronic circuit board 33 for processing the output signal from the digital PMT 31 is improved. Therefore, it is possible to stabilize the signal without causing a signal drift or the like.

(Modification) The gamma camera shown in the first embodiment includes the following modifications. The time-dependent change correction circuit has a D / A converter and an analog multiplier circuit, and converts the digital signal integrated and shaped by the integration circuit into an analog signal by the D / A converter. An A / D converter which multiplies the temporal change correction amount by an analog multiplier and then performs A / D conversion again. The one in which the aging change correction circuit is provided in the processing device 5.

[0024]

According to the present invention, it is possible to reduce the influence of noise or drift when transmitting a cable.
It is possible to provide a gamma camera capable of stably processing the output signal of the MT, thereby preventing the deterioration of the gamma camera image.

[Brief description of the drawings]

FIG. 1 is an external view of a gamma camera according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a structure of a detector 1 included in the gamma camera according to the embodiment.

FIG. 3 is a block diagram showing a configuration example of a detector 1 included in the gamma camera according to the embodiment.

FIG. 4 is a block diagram showing another configuration example of the detector 1 included in the gamma camera according to the embodiment.

FIG. 5 is a graph showing PMT output characteristics before and after nonlinear correction by a nonlinear correction circuit included in the gamma camera according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Detector 2 ... Stand 3 ... Top plate 4 ... Display 5 ... Processing device 20 ... Collimator 21 ... Lead shield 22 ... Iron frame 23 ... Lead plate 24 ... Iron plate 25 ... Iron lid 26 ... Support rod 27 ... Flange 28 ... Aluminum Plate 29 ... Scintillator 30 ... Glass plate 31 ... Digital PMT 32 ... Cable 33 ... Electronic circuit board 34 ... Cable

Claims (3)

[Claims] 1. A means for converting radiation emitted from a radioisotope in a subject into light, a plurality of photomultipliers for converting the light into analog electric signals, and a plurality of photomultipliers near the photomultiplier. A signal processing unit that is provided and outputs a digital signal based on the analog signal; an image processing unit that obtains a distribution image of a radioisotope in a subject based on an output of the signal processing unit; Display means for displaying an image based on an output of the means. 2. The gamma camera according to claim 1, further comprising a temporal change correcting unit that corrects a temporal change of an output of the signal processing unit. 3. The gamma camera according to claim 1, further comprising a non-linear circuit for correcting an output characteristic of the signal processing unit.