JPH0572990B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a scintillation camera that detects radiation (gamma rays) emitted from a radioisotope administered into the body of a subject and displays its distribution image, and in particular, The present invention relates to a scintillation camera that can improve count rate characteristics in a state where the incident count rate of radiation is high.

BACKGROUND TECHNOLOGY A conventional scintillation camera disclosed, for example, in Japanese Patent Application Laid-open No. 59-97071, uses γ emitted from the body of a subject 1, as shown in FIG.
A detector 2 that enters radiation such as a line and converts it into an electrical signal, an integrating circuit 3 that integrates the output signal of this detector 2 over a certain period of time to generate an energy signal, and an energy signal from this integrating circuit 3. a window circuit 4 that determines whether it is within a predetermined level; a position calculation circuit 5 that calculates the position of the incident radiation based on the output signal of the detector 2 and the determination of the window circuit 4; the integration circuit 3 and the position calculation circuit 5; It comprises a control circuit 6 that controls the arithmetic operation of the circuit 5, and a display circuit 7 that displays the radiation incident position calculated by the position calculation circuit 5. Note that the detector 2 is formed by combining a scintillator 2a and a photomultiplier tube 2b. Further, in FIG. 4, reference numeral 8 represents a memory circuit, and reference numeral 9 represents a pulse height analysis circuit.

Next, its operation will be explained. First, gamma rays emitted from the subject 1 are converted into light by the scintillator 2a of the detector 2, and this light is converted into an electrical signal by the photomultiplier tube 2b and output. The output signal from the detector 2 is input to a position calculation circuit 5, where the incident position of the γ-ray is calculated and a position signal _S1 is output. Further, the electric signals from each photomultiplier tube 2b of the detector 2 are added together by an adder 10, and inputted to an integrating circuit 3 and a control circuit 6. This control circuit 6 detects the input of the output signal from the detector 2 and sends an integration start signal S ₂ to the integration circuit 3, and also sends a position calculation start signal S ₃ to the position calculation circuit 5. . The energy signal S ₄ integrated by the integrating circuit 3 is input to the window circuit 4 . This window circuit 4 is
Because the sensitivity of the scintillator 2a to gamma rays differs depending on the location, or the sensitivity of the photomultiplier tube 2b differs among individuals, even if gamma rays of the same energy are incident, the energy from the integrating circuit 3 will vary depending on the location. Since the signal S ₄ changes, preliminary energy analysis is performed in consideration of the amount of correction for this change, and it is determined whether the energy signal S ₄ is within a predetermined energy level range. Then, the window circuit 4 inputs the determination signal _S5 output from the control circuit 6 after a certain integration time, and determines whether the energy signal _S4 is within the upper and lower limits of a predetermined level, If it is within that range, a window signal _S6 is sent to the control circuit 6. When the control circuit 6 receives the in-window signal _S6 , it instructs the position calculation circuit 5 to continue calculating the position. On the other hand, the energy signal S ₄ from the integration circuit 3 is also input to the pulse height analysis circuit 9 . When the position calculation in the position calculation circuit 5 is completed, the wave height analysis circuit 9 reads the correction amount from the memory circuit 8 that stores the correction data, and superimposes it on the input energy signal S ₄ to a predetermined value. Analyze whether you are at the energy level of The wave height analysis circuit 9 analyzes the wave height, and when it is determined that the target gamma ray is incident at a predetermined energy level, a recording signal _S7 is output. In this state, the display circuit 7 emits a bright spot from the position signal S ₁ and the recording signal S ₇ to display a scintigram.

Here, the internal configuration of the window circuit 4 is as follows:
As shown in FIG. 5, it consists of a lower limit comparator 11, an upper limit comparator 12, a first gate circuit 13, and a second gate circuit 14. The lower limit comparator 11 is set with a lower limit signal L that determines whether the level of the energy signal S ₄ is higher than the lower limit, and the upper limit comparator 12 is set with a lower limit signal L that determines whether the level of the energy signal S ₄ exceeds the upper limit. The upper limit signal U to be judged is set. When the energy signal _S4 outputted from the integrating circuit 3 is larger than the lower limit and does not exceed the upper limit, as shown by the solid line in FIG. 6, the lower limit comparator 11 is inverted, but the upper limit comparator 12
is not inverted, and a signal is output from the first gate circuit 13 from these operations. When the determination signal _S5 is input from the control circuit 6 in this state, the second gate circuit 14 performs an AND operation on both signals and outputs an in-window signal _S6 . Also,
As shown by the chain line in FIG. 6, when the energy signal S ₄ ' exceeds the upper limit, the in-window signal S ₆ is not output and the position calculation in the position calculation circuit 5 is stopped. Therefore, there is no need to calculate the position of part A (the shaded part in Figure 6), which exceeds the upper limit of the energy level and does not need to be displayed, so it is not necessary to calculate the position of part A (the shaded part in Fig. Also, the number of displayed bright spots did not saturate quickly, and as a result, the maximum counting rate could be increased.

Problems to be Solved by the Invention However, in such a scintillation camera, the integration circuit 3 integrates the output signal of the detector 2 for a certain period of time (integration time T ₁ in FIG. 6), so the integration is The window circuit 4 was unable to determine the energy level until the end (when the determination signal _S5 was output). In other words, the determination time T ₂ required to determine the energy level
is equal to the above integration time _T1 . Here, as shown by the solid line in FIG. 6, the regular energy signal S ₄
In this case, there is no problem because the energy level cannot be determined unless it is integrated over the entire integration time _T1 . However, especially when the incident count rate of gamma rays is high or two or more gamma rays are incident in a short period of time, the sixth
When the energy signal S ₄ ' becomes excessive as shown by the chain line in the figure, the part A that exceeds the upper limit level is unnecessary, so we would like to judge the energy level at point B that exceeds the upper limit level. Since the device does not accept the next signal during time T ₁ , the subsequent time
_T3 is the dead time, and blank time occurs in the device. Therefore, the scintillation camera as a whole wastes time, and the dead time mentioned above is
During T ₃ , the next incident γ-ray could not be measured, which caused a limit to the count rate characteristics in a state where the incident count rate of γ-rays was high. Therefore, an object of the present invention is to solve such problems.

Means for Solving the Problems The means of the present invention for solving the above problems consists of a detector that receives radiation emitted from a subject and converts it into an electrical signal, and an output signal of this detector that is kept constant. an integration circuit that integrates time and generates an energy signal;
a window circuit that determines whether the energy signal from the integration circuit is within a predetermined level; a position calculation circuit that calculates the position of the incident radiation based on the output signal of the detector and the determination result of the window circuit; In a scintillation camera having a control circuit that controls the operation of the circuit and the position calculation circuit, and a display circuit that displays the radiation incident position calculated by the position calculation circuit, the window circuit is connected to the energy signal from the integration circuit. exceeds the upper limit of determination within the above-mentioned fixed time range, this is detected and a detection signal is sent to the control circuit, which causes the control circuit to stop the calculation operations of the above-mentioned integration circuit and position calculation circuit. It is done by making it happen.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a scintillation camera according to the present invention. This scintillation camera detects radiation such as gamma rays emitted from a radioisotope administered into the body of the subject 1 and displays its distribution.
, an integrating circuit 3, a window 4', a position calculation circuit 5, a control circuit 6', and a display circuit 7. The detector 2 is made up of a combination of a scintillator 2a that converts gamma rays emitted from the subject 1 into light, and a photomultiplier tube 2b that converts this light into an electrical signal. The integrating circuit 3 converts electrical signals from each photomultiplier tube 2b of the detector 2 into an adder 10.
The energy signal _S4 is generated by inputting the sum of the sums and performing integration over a certain period of time. Further, the window circuit 4' is connected to the integration circuit 3.
The integrated energy signal _S4 is input and it is determined whether the energy level is within a predetermined range. This is the γ of the scintillator 2a.
Because the sensitivity to radiation differs depending on the location, or the sensitivity of the photomultiplier tube 2b differs individually,
This is because even if γ-rays of the same energy are incident, the energy signal S ₄ from the integrating circuit 3 changes depending on the location, so preliminary energy analysis is performed in consideration of the amount of correction for this. Further, the position calculation circuit 5 inputs the output signal of the detector 2, calculates the incident position of the γ-ray, and sends out a position signal _S1.It is determined whether or not to continue the position calculation. It is influenced by the determination result of the window circuit 4'.
Further, the control circuit 6' controls the calculation operations of the integration circuit 3 and the position calculation circuit 5, and detects the input of the output signal from the detector 2 and sends an integration start signal S to the integration circuit 3. ₂ and at the same time sends a position calculation start signal _S3 to the position calculation circuit 5, and stops the calculation according to the determination result of the window circuit 4'. The display circuit 7 displays the incident position of the γ-ray calculated by the position calculation circuit 5. In FIG. 1, reference numeral 8 is a memory circuit that stores correction data, and reference numeral 9 reads out the correction amount from the memory circuit 8 and superimposes it on the energy signal _S4 output from the integration circuit 3 to obtain a predetermined value. This is a wave height analysis circuit that analyzes whether the energy level is at the current level.

Here, in the present invention, the window circuit 4' detects and controls when the energy signal _S4 from the integrating circuit 3 exceeds the upper limit for determining the energy level within a certain integration time range. The detection signal is sent to the circuit 6'. Further, the control circuit 6' is configured to stop the calculation operations of the integration circuit 3 and the position calculation circuit 5 by receiving the detection signal. The window circuit 4' includes a lower limit comparator 11, an upper limit comparator 12, a first gate circuit 13, a second gate circuit 14, and a third gate circuit 15, as shown in FIG. . The lower limit comparator 11 is set with a lower limit signal L that determines whether the level of the energy signal _S4 is higher than the lower limit of a predetermined range, and the upper limit comparator 12 is set with a lower limit signal L that determines whether the level of the energy signal _S4 is higher than the lower limit of a predetermined range. An upper limit signal U is set to determine whether the upper limit has been exceeded. If the energy signal S ₄ output from the integrating circuit 3 is greater than the lower limit (L) and does not exceed the upper limit (U), the lower limit comparator 11 is inverted, but the upper limit comparator 12 is inverted.
is not inverted, and a signal is output from the first gate circuit 13 using both of them, and when the judgment signal _S5 is input from the control circuit 6', the signal is output from the second gate circuit 14.
is the in-window signal S ₆ by ANDing both signals.
Output. Further, when the energy signal S ₄ exceeds the upper limit, the upper limit comparator 12 is inverted, and only this inverted signal causes the third gate circuit 15 to output an over signal S ₈ as a detection signal. Note that this over signal _S8 is a judgment signal from the control circuit 6'.
Output regardless of _S5 .

Next, the operation of the scintillation camera of the present invention configured as described above will be explained.
The same operations as in the conventional example shown in the figure will be omitted, and the operations of the window circuit 4' and the control circuit 6' will be mainly explained. First, the energy signal _S4 from the integrating circuit 3 is input to the window circuit 4'.
This window circuit 4' receives the judgment signal _S5 output from the control circuit 6' after a certain integration time _T1 , and judges whether the energy signal _S4 is within the upper and lower limits of a predetermined level. do. Now, as shown by the solid line in FIG. 3, if the energy signal _S4 is normal and larger than the lower limit and does not exceed the upper limit, it is transmitted through the second gate circuit 14 shown in FIG. 2 as described above. and outputs the in-window signal _S6 . This in-window signal _S6 is input to the control circuit 6', and the control circuit 6' instructs the position calculation circuit 5 to continue calculating the position. The integration time of the energy signal _S4 in the integrating circuit 3 at this time is a constant time _T1 . Next, especially when the incident count rate of γ-rays is high, or when two or more γ-rays are incident in a short period of time, the energy signal S ₄ ' is maintained at a constant integration time T ₁ as shown by the broken line in FIG. If the upper limit is exceeded before , the over signal S ₈ is outputted via the third gate circuit 15 shown in FIG. 2 as described above. The over signal _S8 is input to the control circuit 6'. In this state, the control circuit 6' has not yet outputted the judgment signal _S5 to the window circuit 4'.
When the over signal _S8 is input, a calculation stop signal is immediately sent to the position calculation circuit 5 and the integration circuit 3. Therefore, the processing is stopped after point B where the energy signal S ₄ ' exceeds the upper limit level.
The energy signal S ₄ ' results in a curve shown by a dashed line in FIG. That is, the actual integration time at this time is T ₁ ′ (T ₁ ′<T ₁ ), and the energy level determination time is T ₂ ′ (T ₂ ′<T ₂ ). From this, it is possible to detect that the energy level has exceeded the upper limit without waiting for the end of the regular integration time _T1 , and the dead time _T3 of the conventional example shown in Fig. 6 can be detected.
can be removed.

Effects of the Invention As explained above, the present invention operates the window circuit 4' to detect the energy level when the energy signal _S4 from the integrating circuit 3 exceeds the upper limit within a certain integration time _T1 . The over signal _S8 is detected and sent to the control circuit 6', and the control circuit 6' thereby stops the arithmetic operations of the integration circuit 3 and position calculation circuit 5, as shown in FIG. Excessive energy signal as shown in
Processing is stopped after point B where S ₄ ' exceeds the upper limit level, and the actual integration time T ₁ ' and determination time T ₂ ' can be shortened. Therefore, the dead time _T3 of the conventional example shown in FIG. 6 can be removed, thereby eliminating blank time in the apparatus. From this, the scintillation camera as a whole can abort the processing of high-level energy signals midway through and measure the next γ-ray incident, and the count rate characteristics when the γ-ray incident count rate is high. can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the scintillation camera according to the present invention, FIG. 2 is a block diagram showing the internal configuration of the window circuit, FIG. 3 is a graph explaining the operation of the window circuit, and FIG. 4 5 is a block diagram showing a conventional scintillation camera, FIG. 5 is a block diagram showing the internal structure of the window circuit, and FIG. 6 is a graph explaining the operation of the conventional window circuit. 1... Subject, 2... Detector, 3... Integrating circuit, 4'... Window circuit, 5... Position calculation circuit, 6'... Control circuit, 7... Display circuit, 8...
Memory circuit, 9... Wave height analysis circuit, 11... Lower limit comparator, 12... Upper limit comparator, 13... First gate circuit, 14... Second gate circuit, 15...
Third gate circuit, S ₄ ... energy signal, S ₅ ...
Judgment signal, _S6 ...In-window signal, _S8 ...Over signal (detection signal).

Claims (1)

[Claims] 1. A detector that receives radiation emitted from a subject and converts it into an electrical signal, an integrating circuit that integrates the output signal of this detector over a certain period of time to create an energy signal, and an energy signal from this integrating circuit. a window circuit that determines whether or not is within a predetermined level; a position calculation circuit that calculates the position of the incident radiation based on the output signal of the detector and the determination result of the window circuit; and operations of the integration circuit and the position calculation circuit. In a scintillation camera that has a control circuit that controls the operation and a display circuit that displays the radiation incident position calculated by the position calculation circuit, the window circuit is controlled by the energy signal from the integrating circuit within the certain time range. When the upper limit of determination is exceeded, this is detected and a detection signal is sent to the control circuit, which causes the control circuit to stop the calculation operations of the integration circuit and the position calculation circuit. scintillation camera.