JP2729276B2 - Scintillation camera - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scintillation camera, and more particularly, to a scintillation camera which is hardly affected by noise.

2. Description of the Related Art As shown in FIG. 1, a conventional scintillation camera has a collimator 1 that passes only gamma rays that are incident on a detector surface in a direction perpendicular to the gamma rays emitted from a radioisotope in a subject. A scintillator 2 that emits light by a gamma ray incident through the collimator 1, and a light guide 3 that transmits an optical signal of the scintillator 2.
A photomultiplier tube (hereinafter abbreviated as “PMT”) 4 which is optically coupled to the scintillator 2 via the light guide 3, converts the light into an electric signal, amplifies and outputs the electric signal, and the PMT 4 An A / D conversion circuit 5 for converting an output signal of the A / D into a digital signal, an integration circuit 6 for repeatedly adding and integrating the signals output from the A / D conversion circuit 5,
A position calculating circuit 7 for calculating the position of the gamma ray incident on the scintillator 2 based on the signal intensity of the output signal of the integrating circuit 6, and accumulating and storing data of the position of the gamma ray obtained by the position calculating circuit 7; A memory circuit 8 for storing an image and a scintigram;
A display position 9 for displaying the scintigram stored in the
In order to control the A / D conversion circuit 5 and the integration circuit 6, an addition circuit 11 for adding the signal from the PMT 4 and a gamma ray is incident on the scintillator 2 with the addition signal of all the PMTs 4 from the addition circuit 11. And a timing circuit for producing a control signal for making the integration circuit 6 perform integration for a predetermined time.
12 and oscillates in a sufficiently short time as compared with the integration time of the integration circuit 6, and the A / D conversion circuit 5, the integration circuit 6, the timing circuit 12
And an oscillation circuit 13 for controlling the time.

In such a conventional scintillation camera,
In order to obtain the position of the gamma ray incident on the scintillator 2 with high accuracy, it is necessary to convert the light emitted from the scintillator 2 by the incidence of the gamma ray into an electric signal with less noise and to amplify the light. In addition, since the scintillator 2 emits light for about 1 μs after the incidence of the gamma ray, the integrating circuit 6 integrates over the above time after the gamma ray enters the scintillator 2 and a signal is output from the A / D conversion circuit 5. There is a need.

FIG. 3 shows details of the A / D conversion circuit 5, the integration circuit 6, and the timing circuit 12.

The A / D conversion circuit 5 includes an A / D converter 21, and performs A / D conversion of an output signal of the PMT 4 in synchronization with a clock signal output from the oscillation circuit 13. The integrating circuit 6 includes an adder 23 and a latch 24.
The output signal of the A / D conversion circuit 5 is sequentially accumulated by an adder to perform an integrating operation. The timing circuit 12 is an addition circuit 11
The comparator 25 determines whether or not a signal has been input, and if a signal has been input, flips a flip-flop (hereinafter abbreviated as “F / F”) 26 to turn the counter 27 on.
Release the clear. The counter 27 counts the clock signal from the oscillating circuit 13, obtains a certain time, sends a clear signal to the F / F 26 and the latch 24 in the integrating circuit 6, returns the F / F 26 and prepares for the next gamma ray incidence. At the same time, the latch 24 is cleared and the integrated value is returned to zero. When the F / F 26 returns to its original state, it clears the counter 27, releases the latch 24, and integrates until the next gamma ray is incident.

[Problems to be solved by the invention]

However, in such a conventional scintillation camera, the adder 23 performs the integration operation for a certain period of time after the gamma ray incidence in the integration circuit 6. However, the integration operation is continuously performed after the processing by the previous gamma ray incidence. , The noise generated by PMT4 between the incidence of gamma rays, and A /
Since the noise generated by the D conversion circuit 5 is also integrated,
Noise other than the incident signal due to the gamma ray is included, and the position calculation accuracy in the position calculation circuit 7 is reduced. After the timing circuit 12 determines the incidence of gamma rays, the integrating circuit 6
When the integration operation is started with, the output signal of PMT4 is added to the addition circuit.
Since it is determined by the comparator 25 after the addition in 11, a delay occurs as compared with the case where the output signal of the PMT 4 directly enters the A / D converter 21,
The initial portion having a large amount of information is lost in the signal obtained by the incidence of the gamma ray, and the output signal integrated by the integrator 6 is reduced and the signal-to-noise ratio (hereinafter abbreviated as "S / N ratio") is reduced. It deteriorates, and the position calculation accuracy in the position calculation circuit 7 decreases. This is shown in FIG. FIG. 4A shows an output signal of the PMT 4, and FIG. 4B shows an output process of the integration circuit 6. In particular, the solid line shows the case where the initial part of the signal is lost, and the broken line shows the case where the initial part of the signal is not lost.

As described above, in the conventional scintillation camera, noise is introduced during the signal integration operation, and the position calculation accuracy is reduced.

Therefore, an object of the present invention is to provide a scintillation camera capable of solving such a problem.

[Means for solving the problem]

Means of the present invention for solving the above problems include a scintillator that emits light by incident radiation, a PMT that is optically coupled to the scintillator and converts the light into an electric signal, and converts an output signal of the PMT into a digital signal A / D conversion circuit, an integration circuit for cumulatively adding the output signals of the A / D conversion circuit, an addition circuit for adding all the electrical signals of the PMT, and an accumulation circuit for the integration circuit using the output signal of the addition circuit. A timing circuit for controlling start / stop of addition, an oscillation circuit for outputting a reference signal for synchronizing the timing circuit and the A / D conversion circuit and the integration circuit, and a digital signal output from the integration circuit are used. Calculation circuit for calculating the incident radiation position of the scintillator, a memory circuit for storing the position signal output from the position calculation circuit, and a scintigram stored in the memory circuit In the scintillation camera having a display device for displaying, the integration circuit shifts an output signal of the A / D conversion circuit to a subsequent stage in synchronization with a reference signal output by the oscillation circuit, thereby increasing a time delay. This is achieved by a scintillation camera characterized by comprising a shifter to be produced, an adder for accumulatively adding signals delayed by the shifter, and a latch circuit.

[Action]

In the scintillation camera thus configured, since a time delay is created by the shifter of the integration circuit, even if the detection of the radiation incidence in the timing circuit is delayed from the A / D conversion of the signal by the A / D conversion circuit, the accumulation is performed. In this case, a delay can be eliminated, and all signals necessary for position calculation can be cumulatively added. Further, unnecessary signals are not cumulatively added. As a result, noise contamination can be reduced, the S / N ratio can be improved, and the position calculation accuracy in the position calculation circuit can be increased.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. 1 and FIG.

FIG. 1 is a block diagram showing an embodiment of a scintillation camera according to the present invention. In FIG. 1, this embodiment shows a scintillator 2 which emits light by incident radiation, a PMT 4 which is optically coupled to the scintillator 2 and converts the light into an electric signal, and an A which converts an output signal of the PMT 4 into a digital signal. / D conversion circuit 5, an integration circuit 6 for accumulatively adding the output signals of the A / D conversion circuit 5, an addition circuit 11 for adding all the electric signals of the PMT 4, and an integration circuit for the output signal of the addition circuit 11. A timing circuit 12 for controlling the start / stop of the cumulative addition of the circuit 6;
An oscillation circuit 13 for outputting a reference signal for synchronizing the D conversion circuit 5 and the integration circuit 6; a position calculation circuit 7 for calculating the incident radiation position of the scintillator 2 using the digital signal output from the integration circuit 6; A memory circuit 8 for storing the position signal output from the position calculation circuit 7, and a display device 9 for displaying the scintigram stored in the memory circuit 8.
Consists of

In the above configuration, the integration circuit and the timing circuit are different from the conventional device in this portion.

FIG. 2 is a block diagram showing the internal configuration of the laminated circuit 6 and the timing circuit 12 according to the present invention. The integration circuit 6 includes a shifter 22, an adder 23, and a latch 24, and the timing circuit 12 includes a comparator 25, an F / F 26, and a counter 27.

From the start time at which the A / D converter 21 performs A / D conversion of the signal of the PMT 4, the shifter 22 detects the incidence of radiation and the F / F 2
Oscillation circuit 1 determines the time until 6 clears latch 24.
The output signal of the A / D conversion circuit 5 is sequentially shifted to the subsequent stage by the number divided by the cycle of the reference signal output from 3, that is, the number of clocks required for releasing the clearing of the latch 24, thereby creating a time delay. The output signal of the shifter 22 is added to the value held by the latch 24 in the adder 23. The output signal of the adder 23 is newly held by the latch 24, and the value of the latch 24 is the result of adding the value held up to the previous time and the output signal of the shifter 22. As a result, the output signals of the shifter 22 are sequentially added and
The holding is repeated and the cumulative addition is performed to integrate the digital signal. The latch 24 continues to be cleared as long as there is no gamma ray incident, and does not accumulate noise.

The timing circuit 12 compares the output signal of the addition circuit 11 with a comparator.
At 25, the voltage is compared with the voltage when gamma rays are not incident.
When gamma rays are incident, the output of the adder circuit 11 increases, and the F / F 26 is triggered by detecting the incidence of a gamma ray that produces a difference from the voltage when the gamma ray is not incident. The F / F 26 is triggered by the detection of the incidence of the gamma ray, and releases the clear of the latch 24 and the counter 27. At this time, a signal due to gamma ray incidence, which is A / D converted by the A / D conversion circuit 5 and given a time delay by the shifter 22, is input to the adder 23. Therefore, the signal due to the gamma ray incidence is cumulatively added by the adder 23 and the latch 24. The counter 27 counts the reference signal and measures the number of times of cumulative addition of the signal, that is, the integration time. When the count of the counter 27 reaches a predetermined value, a clear signal is output to the F / F 26 to stop the operation by the trigger of the F / F 26 to clear the latch 24 and the counter 27. As a result, the latch 24 clears the cumulative addition result output to the position calculation circuit 7 and waits until the next gamma ray incidence without performing the cumulative addition.

〔The invention's effect〕

Since the present invention is configured as described above, it is not necessary to repeat the cumulative addition until the next gamma ray is incident after the end of the cumulative addition in the integrating circuit 6 due to the incidence of the gamma ray. As a result, the noise due to the PMT 4 and the noise due to the A / D conversion circuit 5 are not cumulatively added between the incidences of the gamma rays, so that the mixing of the noises can be suppressed low.

Further, even if the accumulation circuit is started by the integration circuit after detecting the incidence of the gamma ray by the timing circuit 12, the initial portion of the gamma ray signal is not damaged and the S / N ratio does not decrease.

From this, the integration circuit 6 can be configured so that noise is not mixed and the signal is not damaged, so that the S / N ratio can be improved, and the position calculation accuracy in the position calculation circuit 7 can be improved. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of a scintillation camera of the present invention and a conventional example, FIG. 2 is a block diagram showing the internal configuration of an integrating circuit and a timing circuit according to the present invention, and FIG. FIG. 4 is a block diagram showing the internal configuration of the circuit and the timing circuit, and FIG. 4 shows output waveforms of the photomultiplier and the integrating circuit. 2 ... Collimator, 4 ... Photomultiplier tube (PMT), 5 ... A / D conversion circuit, 6 ... Integration circuit, 7 ... Position calculation circuit, 8 ... Memory circuit, 9 ... Display device, 11 ... Addition circuit, 12 ... Timing circuit, 13 oscillation circuit, 21 A / D converter, 22 shifter, 23
Adder, 24 latch, 25 comparator, 26 F / F, 27 counter.

Claims (1)

(57) [Claims] 1. A scintillator which emits light by incident radiation, a photomultiplier optically coupled to the scintillator and converts the light into an electric signal, and an A which converts an output signal of the photomultiplier into a digital signal. / D conversion circuit, an integration circuit for accumulatively adding the output signals of the A / D conversion circuit, an addition circuit for adding the electric signals of all the photomultiplier tubes, and an output signal of the addition circuit. A timing circuit for controlling start / stop of the cumulative addition;
An oscillation circuit that outputs a reference signal for synchronizing the A / D conversion circuit and the integration circuit; a position calculation circuit that calculates an incident radiation position of the scintillator using a digital signal output by the integration circuit; A scintillation camera comprising: a memory circuit that stores a position signal output from a calculation circuit; and a display device that displays a scintigram stored in the memory circuit.
In synchronization with the conversion of the A / D conversion circuit, the signal is sequentially transferred to the subsequent stage, and the A / D conversion circuit starts the A / D conversion of the incident radiation signal, and then the timing circuit starts the cumulative addition of the integration circuit. A shifter for creating a time delay until a signal is output, an adder for cumulatively adding the signal of the shifter, and a latch for holding the signal of the adder, assisting the cumulative addition and outputting the signal to the position calculating circuit. A scintillation camera.