JPS62167493A - Gamma camera - Google Patents

Abstract

PURPOSE:To avoid pileup and to enhance a counting rate, by dividing a total visual field into several fields and providing a change-over means for sending the output of the photoelectric converter means of one region to a position and energy operation means when the incident of radioactive rays to said one region is confirmed. CONSTITUTION:A gamma camera uses 19 PMTs (photomultiplier tubes)1 and the total visual field thereof is divided into seven regions A-G. The output of each PMT1 is sent to the presum amplifier 2 of each region and the output of PMT1 at every region is added. When one radioactive rays are incident to the visual field, output is generated from neighboring PMT1 to confirm the region having generated output by a comparator 3 and a control signal is generated from a control circuit 6 and only the analogue switch 5 of the judged region is closed and only an addition signal obtained by adding the output of PMT1 of said region is sent to a sum amplifier 7 and an added energy signal is outputted from the amplifier 7. At the same time, a control signal is outputted to an analogue switch 9 from the circuit 6 and the output of PMT1 of a selected specific region is sent to a sum amplifier 10 and subjected to weighing addition to output a position signal.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a one-angle type gamma camera.

In the conventional one-gauge gamma camera, a large number of PMTs (photomultiplier tubes) are lined up on the back of the scintillator, and each PMT (photomultiplier tube) is
By weighting and adding the MT outputs according to their positions, the light emitting position within the scintillator caused by the radiation that has entered the field of view is determined, and the energy signal is obtained by adding all the PMT outputs.

Problems to be Solved by the Invention However, since signal processing is performed by one position calculation circuit and one energy calculation circuit for the entire field of view, there is a drawback that the counting rate cannot be increased due to the pile amplifier problem. In other words, if the radiation incident events are separated in time, each signal is separated and can be processed separately, as shown in Figure 2 (a), but if the events occur close in time, Then, the signals overlap as shown in FIG. 2(b), making it impossible to perform position calculation and energy calculation. Pile-up problems occur when events approach each other in this way, and in such a case, normal signal processing cannot be performed, so event processing has to be stopped in both cases, making it impossible to improve the counting rate. .

An object of the present invention is to provide a gamma camera that improves the counting rate by improving the prevention of pile-up.

Means for Solving the Problems The gamma camera according to the present invention divides the entire field of view into a plurality of regions so as to overlap each other, and includes an adding means for obtaining the sum of the outputs of the photoelectric conversion means entering each region, and the adding means. and a switching means for sending only the output of the photoelectric conversion means in the area where it is determined that the light emission has occurred to the position calculation means and the energy calculation means.

The switching means divides the entire field of view into a plurality of regions, and when it is determined that radiation is incident on one of the regions, the output of the photoelectric conversion means belonging to that region is sent to the position calculation means and the energy calculation means. Therefore, if radiation subsequently occurs in another area, the signal of that event cannot pass through this switching means. Therefore,
Pile-ups can be avoided and the counting rate can be improved.

Embodiment In the embodiment shown in FIG. 1, 19 PMTl's are used and arranged within the field of view as shown. A, B, C, D, E, F, G as indicated by the dotted lines in the whole field of view.
divided into two areas. These regions have mutually overlapping parts, each covering 7 PMTIs, and region A
is in the center, area B is in the upper left, area C is in the left, area is in the lower left, area E is in the lower right, area F is in the right, and area G is in the upper right.

The output of each of these PMTIs is sent to the presum amplifier 2 provided for each region, and the PMTl of each region is
The outputs of are added. When one radiation enters the field of view and a scintillator (not shown) emits light, an output is generated from the PMTI near the light emitting position. Therefore, from the magnitude of the added signal for each region, the comparator 3
Accordingly, it is possible to determine in which region light emission has occurred. When it is determined in which region the light emission has occurred, the control circuit 6 generates a control signal based on the result and closes only the analog switch 5 in the region where it has been determined that the light emission has occurred.

Therefore, PM that succumbs to the area determined to have generated light emission
Only the sum signal obtained by adding the outputs of Tl is sent to the sum amplifier 7 via the delay circuit 4. Therefore, from this sum amplifier 7, the PMT that succumbs to the area where it is determined that light emission has occurred
An energy signal obtained by adding only the outputs of I is output.

The other analog switches 5 are kept open until the output of the energy signal from the sum amplifier 7 is finished, so that even if a radiation incident event occurs in another region, the sum signal of that region is sent to the sum amplifier 7. There isn't. Therefore, pile-ups are eliminated and the counting rate is improved.

Note that the delay circuit 4 is for compensating for time delays in the comparator 3 and the control circuit 6.

At the same time, a control signal is output from the control circuit 6 to the analog switch 9 of the position signal calculation system. For the same reason, the outputs of all the PMTIs are sent to this analog switch 9 via the delay circuit 8, and only the outputs of the PMTIs that fall within the region where it has been determined that light emission has occurred are selected by the control signal. P of the specific area selected in this way
The output of the MTI is sent to the sum amplifier 10, and each PM
A weighted addition is performed according to the digit II\ of T1, and a digit δ signal is obtained. In this position signal calculation system as well, the output of PMTI in other areas is stopped by the analog switch 9 until the sum amplifier IO generates a position signal, so that pile-up can be eliminated.

The above mode is particularly effective when the counting rate is high, but in the case of a normal low counting rate/high resolution mode, the control circuit 6 closes all analog switches 5.9.

Then, the output of PMT1 in the entire field of view is not selected for each region, and is used for energy calculation and position calculation in the same way as usual.

Effects of the Invention According to the gamma camera of the present invention, pile-up can be reduced and the counting rate can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a waveform diagram. 1...PMT 2...Presum amplifier 3...Comparator 4.8...Delay circuit 5.9...Analog switch 6...Control circuit 7.10...Sum amplifier

Claims (1)

[Claims] (1) A scintillator, a large number of photoelectric conversion means arranged on the back side of the scintillator, and light emission inside the scintillator caused by radiation that enters the field of view by weighting and adding the outputs of the photoelectric conversion means according to their positions. In a gamma camera having a position calculation means for calculating a position and an energy calculation means for obtaining an energy signal by adding all the outputs of the photoelectric conversion means, the entire field of view is divided into a plurality of regions so that each region overlaps, and each region is Adding means for obtaining the sum of the outputs of the input photoelectric conversion means, means for determining in which region light emission has occurred based on the output of the addition means, and means for calculating only the output of the photoelectric conversion means of the region where it is determined that light emission has occurred. A gamma camera characterized in that it has a position calculation means and a switching means for sending data to the energy calculation means.