JPH0447792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to scintillation cameras, and particularly to techniques that are effective when applied to scintillation cameras that obtain scintillograms when the counting rate is high.

Background Art A scintillation camera uses a scintillator to convert gamma rays (hereinafter referred to as γ-rays) emitted from a radioisotope (hereinafter referred to as RI) into light using a scintillator, and determines the emission position of this light. The distribution of RI is displayed by electrically calculating .

The light output from the scintillator is converted into an electrical signal by a photomultiplier and amplified. The signal amplified by the photomultiplier has a waveform as shown in FIG. If the amount of light emitted by the scintillator is small, quantum noise will occur and the image quality will deteriorate as shown in Figure 2, so the output signal of this photomultiplier is integrated as shown in Figure 3. Measures are being taken to reduce noise.

Further, regarding the relationship between the light emitting position of the scintillator and the output of the photomultiplier, the closer the photomul is to the light emitting position, the larger the output becomes.

Further, position calculation is performed by combining a plurality of photomultiply outputs on the X and Y axes of orthogonal coordinates, calculating the position where the signal is maximum, and finding the light emitting point, that is, the point of incidence of the γ-ray.

In addition, the time interval between gamma rays incident on the scintillator becomes shorter if the specific radioactivity of the RI administered into the subject is high, and there is insufficient time to calculate the position and integrate the actual gamma rays. The incident position can no longer be determined, and an artifact occurs that displays the image at a different position.

In order to eliminate this artifact, out of the gamma rays that incident close to each other in time, the latter should be integrated until the position calculation of the gamma ray that incident first is completed, or the latter should be integrated for a certain period of time and saved. A method has been proposed for starting the position calculation of .

However, as shown in Figure 4, with this method, as the time interval between the incidences of gamma rays becomes shorter, the gamma rays that are incident earlier among the gamma rays that are incident in close proximity to each other are integrated. During this time, as shown in FIG. 4, the latter is incident, and the signal before the position calculation (see FIG. 5) causes an artifact.

Other methods have also been proposed in which the integration time is shortened when the amount of incident gamma rays is large, but this method has the drawback that the shorter the integration time, the greater the influence of quantum noise.

OBJECTS OF THE INVENTION An object of the present invention is to provide a scintillation camera that can obtain good scintigrams without artifacts.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

Outline of the Invention Among the inventions disclosed in this application, an overview of typical inventions is as follows.

In other words, in a scintillation camera,
When γ-rays that are close in time are incident, one γ-ray
If the next gamma ray is incident continuously during the line integration,
When the next γ-ray is incident during the integration of one γ-ray,
The integration of the first γ-ray is stopped, and the position calculation of this γ-ray is not performed. Further, by not performing integration and position calculation for the next γ-ray, a good scintigram can be obtained.

Configuration of the Invention The configuration of the present invention will be explained together with examples.

FIG. 6 is a block diagram showing an embodiment of the present invention.

In Figure 6, 1 was administered into the subject.
This is a radiation detector (hereinafter simply referred to as a detector) for detecting gamma rays emitted from RI, and is made up of multiple photomuls. 2A to 2N are integration circuits that integrate the output from the photomultiplier of the detector 1, and the integration time thereof is kept constant. Reference numeral 3 denotes a position calculating circuit for calculating the position of the γ-ray based on the outputs from the integrating circuits 2A to 2N. Reference numeral 4 designates an adder circuit for adding the outputs of each photomultiply group of the detector 1, and 5 designates a rising edge detection circuit for the output signal from the adder circuit 4. Reference numeral 6 denotes a control circuit, which includes an integral control section 6A for controlling the integral circuits 2A to 2N and a position calculation control section 6B for controlling the position calculation circuit 3. 7 is an AND gate circuit for generating an integral clear signal.

Next, the operation of this embodiment will be explained. In FIG. 6, when a signal corresponding to the incident γ-ray is output from the photomultiplier of the detector 1, this output signal is input to the integrating circuits 2A to 2N. At the same time, it is also output to the adder circuit 4. The output signal of the adder circuit 4 is input to the rising edge detecting circuit 5, and when the rising edge of this signal is detected, the rising edge detecting circuit 5 outputs γ.
A signal that detects that the wire is incident is output. This detection signal is input to the control circuit 6 and the AND gate circuit 7, an integration start signal is output, and each of the integration circuits 2A to 2N starts integration.
After a certain period of time, the integrated value is sent to the position calculation circuit 3, and the position is calculated. Here, during the integration of the γ rays, the output of the integration control section 6A of the control circuit 6 is input to one input terminal of the AND gate circuit 7. When the next γ-ray is incident during the integration of the γ-ray, the rise detection circuit 5
, it detects it and generates an output signal, and this output signal is input to the other input terminal of the AND gate circuit 7, so the AND gate circuit 7 is established and outputs an integral clear signal, and the control circuit 6 to clear the integral signal. At this time, the integral clear signal also prevents the position calculation start signal from being output.

In the above embodiment, the integration time was set constant, but the integration or storage is performed until the previous position calculation is completed, thereby minimizing the influence of dead time (time during which other processing cannot be performed) by the position calculation circuit 3. It is also possible to use a combination of a circuit that terminates the above-mentioned integration after doing so.

Further, although the maximum number of γ-rays in a certain period of time in the scintillation camera according to the embodiment described above is reduced, most of the γ-rays that are not counted become artifacts even when the position is calculated. Furthermore, even if no artifacts occur, the integration time becomes shorter and the position calculation accuracy is lowered due to quantum noise. Therefore, compared to the conventional method, accuracy and image quality are improved by the amount of artifacts removed.

Effects As explained above, according to the new technical means disclosed in the present application, artifacts caused by gamma rays incident temporally close to each other are removed, so there is no need to reduce the accuracy of position calculation. It is possible to obtain a scintigram with high accuracy and no artifacts.

[Brief explanation of the drawing]

Figures 1 to 5 are diagrams for explaining the problems of conventional scintillation cameras, and Figure 6 is
1 is a block diagram showing the configuration of an embodiment of the present invention; FIG. DESCRIPTION OF SYMBOLS 1...Detector, 2A to 2N...Integrator circuit, 3...Position calculation circuit, 4...Addition circuit, 5...Rise detection circuit, 6...Control circuit, 6A...Integral control section, 6B...Position calculation control section, 7...And gate circuit.

Claims (1)

[Claims] 1. In a scintillation camera that generates an electrical signal corresponding to gamma rays incident on a scintillator and integrates this electrical signal to reduce noise when converting the gamma ray to an electrical signal, during the electrical signal integration, A scintillation camera characterized by comprising means for stopping the integration of the electrical signal being integrated when the next electrical signal is input.