JPS5960380A - Scintillation camera - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] This invention relates to a scintillation camera.

A scintillation camera is equipped with a flat scintillator and a number of photoelectric converters optically coupled to the back surface of the scintillator via light kites. The principle is to output a noculus and calculate the radiation incident position based on the magnitude of the peak value of the output pulse of each photoelectric converter. Therefore, if two or more radiations are incident at the same time, the outputs and lass will overlap, making it impossible to accurately calculate the position. Conventionally, we detect when two or more radiation incidences overlap in time and issue an illumination signal.
A pile-up removal circuit is provided to remove the position calculation result by receiving the signal from the pile amplifier. Therefore, there is a problem that the counting rate cannot be increased. Specifically, since the output pulse is approximately 1 g5ec, for example, 500 ns is applied to two points 12 and 13 within the field of view 11 in Fig. 1 (approximately corresponding to the 41-plane shape of the 'P plate-shaped scintillator).
When radiation is incident at intervals of ec, the output pulses 21 and 22 overlap as shown in FIG. 2, so calculations for both positions are eliminated by the pile-up signal. Therefore, what is the maximum counting rate? The speed is about 200 km/sec.

In view of the above, the present invention is configured such that even if a plurality of radiations are incident consecutively in time, if the incident positions are far apart, a plurality of position calculation circuits independently calculate the position. By doing so, it is an object of the present invention to provide a scintillation camera whose counting rate characteristics are improved so as to count things that were conventionally omitted.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, the output pulses of each of the photomultipliers v31, which are a number of photoelectric converters, are sent via a preamplifier 32 to a switching circuit 33, in which each output pulse is divided into two positions. The calculation circuits 34 and 35 are configured to sequentially allocate each incident radiation. Individual radiation incidences are detected as follows. Each output pulse from each of the preamplifiers 32 is sent through each resistor 41 to an adder 42, where they are summed to obtain a summation signal of the output pulses. After this summation signal is differentiated by a differentiating circuit 43 consisting of a capacitor and a resistor,
It is compared with the reference voltage v2 by the comparator 44, and this comparator 44
A pulse corresponding to each incident radiation is outputted from. This pulse is sent to the flip-flop 45, and this pulse is sent to the flip-flop 45.
Pflo and P45 repeat inversion every time radiation is incident.

The switching circuit 33 includes a delay circuit 51 and an analog switch 5.
2.53, comparator 54, AND circuit 55.56,
e) i-stable circuit 57.58. The comparator 54 compares each output pulse of the photomultiplier @31 that has passed through the preamplifier 32 with the reference voltage v2, and sends the output to an AND circuit 55, 56 if each output pulse is greater than a predetermined value. At this time, one of the two AND circuits 55, 56 is always supplied with flj from the flip-flop 45, and an output is generated from the AND circuit to which ll'lj is supplied, and the monostable circuit 57, 58 Through one of the analog switches 52, 53 is closed. Next, when radiation is incident, the flip-flop 45 is reversed and the other AN
Since the D circuit now produces an output, the other analog switch 52, 53 is closed.

In this way, each output pulse is sequentially distributed to each of the two digit l calculation circuits 34, 35 each time the radiation is incident.

Here, the monostable circuits 57 and 58 are analog switches 52 and 58.
It determines the time when 53 will be closed.

This time is usually set to 17 isec or less. The delay circuit 51 delays the output pulse in accordance with the timing delay when the analog switches 52 and 53 are closed.

Due to the function of the comparator 54, only output pulses of a predetermined value or higher are used for the position 3+ calculation. Therefore, for example, point 1 in Figure 4
When radiation is incident on the photomultiplier 2, a large output pulse from the photomultiplier tube 31 located in the area surrounded by the dotted line 14 is sent to the position calculation circuit 34, for example. Suppose that radiation is subsequently incident at a distant point 13,
This time, the output pulse from the photomultiplier tube 31 within the dotted line 15 in the vicinity is sent to the other position calculation circuit 35.

Therefore, these output pulses 2 as shown in FIG.
1.22 is sent to each position calculation circuit independently and does not overlap. As a result, even if these two radiation incidences overlap in time, they will be counted by 31 at each position, improving the count rate characteristics.

In addition, 2 output from the two position calculation circuits 34 and 35
A sample and hold circuit is used to create one position signal from two position signals. The two position signals may be sent to a display device on the prefectural side and combined on one display screen.

By the way, in the example described in -, radiation is incident again at point 12 at the third point 1. In such cases, the output pulses sent to the same position calculation circuit may be in the opposite direction, and in such a case, it is not possible to obtain reliable position information from the position calculation circuit. Therefore, the previous calculation circuit 34.35
A pile-up removal circuit similar to the conventional one is provided inside each of them.

Although two position calculation circuits are used in the embodiment 1-, it goes without saying that three or more may be used.

As explained in Embodiment 11 below, according to the present invention, it is now possible to calculate the position of incident radiation and count it to 111 even though it was not counted by 51 due to pileup in the past. In comparison, the count rate characteristics can be improved. 5.Furthermore, since only the large output pulses of the photoelectric converter are used for position calculation, small output pulses containing more noise can be removed from position calculation, which improves the spatial resolution of images. can be achieved at the same time.

[Brief explanation of drawings]

ffr, Figure 1 is a schematic diagram showing the radiation incident point for explaining the conventional example, and Figure 2 is an illustration for explaining the conventional example.
; Figure 3 is a waveform diagram showing an embodiment of the present invention;
FIG. 4 is a schematic diagram showing a radiation incident point for explaining the operation of the same embodiment, and FIG. 2185 is a reliable waveform diagram for explaining the operation of the same embodiment. 11・・・・・・・・・・・・Field of view12.13・
・・・・・・Radiation incident point 31・・・・・・・・・・・・Photoelectric f-multiplier tube 3
2・・・・・・・・・・・・Preamplifier 33...
・・・・・・・・・・・・Switching circuit 34.35...
...Position 51 Arithmetic circuit 42...
・・Adder 43・・・・・・・・・・・・・Differential circuit 44.54・・Comparator 45・・・・・・・・・・・・・・・Flip Frump 51・・・・・・・・・・・・Delay circuit 52.5
3...Analog switch 55.56...
・AND circuit 57.58... Monostable circuit

Claims (1)

[Claims] (+) scintillator and a number of photoelectric converters optically coupled to the back surface of the scintillator, each photoelectric converter outputs a pulse in response to scintillation light generated when radiation enters the scintillator, and each photoelectric converter outputs a pulse. In a scintillation camera that calculates the radiation incident position by the magnitude of each peak value of the output pulse of the converter, at least two position calculation circuits and a sum signal of the output pulses of each photoelectric converter are used to calculate the individual positions. a radiation incidence detection circuit that detects radiation incidence; and a radiation incidence detection circuit that is controlled by the radiation incidence detection circuit and sequentially distributes the output pulses of each of the photoelectric converters to each of the at least two position calculation circuits for each radiation incidence. a switching circuit, the switching circuit including a comparator for detecting that the output pulse of each of the photoelectric converters is greater than a predetermined value, and configured to transmit only the output pulse that is greater than or equal to the predetermined value. A scintillation camera characterized by: