JPH0227633B2 - SHINCHIREESHONKAMERA - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in scintillation cameras commonly referred to as Anger type cameras.

In an Anger-type scintillation camera, a large number of photomultiplier tubes (hereinafter referred to as PMTs) are arranged on the back of a scintillator that emits light in response to incident radiation. The position of the light emitting point is calculated by a position calculation circuit. By the way, in general, the PMT output with respect to the scintillator light emission position is bell-shaped nonlinear. (See Figure 2).
Because of this nonlinearity, the resulting image generally contains nonlinearity.

In particular, in the case of ordinary Anger-type scintillation cameras, in order to improve spatial resolution, the scintillator, light guide, etc. are made thinner, and threshold preamplifiers are used. tends to deteriorate, and the image is generally distorted toward the center of each PMT.

In view of the above, an object of the present invention is to provide a scintillation camera that is improved so as to be able to obtain lines with good spatial linearity.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, gamma rays and the like that are incident on the scintillator are absorbed and emit light. A portion of that light passes through light guide 2 to each PMT.
31 to 3n, the signal is converted into a current signal, and further converted into a voltage signal by each preamplifier 41 to 4n. The output of each of these preamplifiers 41 to 4n is output from an adder circuit 5.
are added to obtain signal a. This signal a is input to the trigger circuit 6, and when the signal a is larger than a predetermined threshold value, a trigger signal b is generated. sent to each.
In the timing generation circuit 7, when the trigger signal b is inputted, the signal c is outputted, and when the later-described signal d is further inputted, the signals e to i are sequentially generated at appropriate timings.

Signal a from the adder circuit 5 is sent to an integrating circuit 80, and each output of the preamplifiers 41 to 4n is sent to each of the integrating circuits 81 to 8n. Integration is started by the above signal b, and by signal c. After the integration is completed, the signals V ₀ and V ₁ to Vn are obtained, and the signal e
The signal is taken into each of the sample and hold circuits 90, 91 to 9n, and passes through the division circuits 101 to 10n to obtain each of the signals _V1 / _V0 to Vn/ _V0 . These signals are operated by the sample and hold circuits 111 to 11n operated by the signal f and by the signal g.
The signals are converted into digital signals v _{1 -vo} through AD converters 121 - 12n, respectively. These signals v ₁ ~
v _o is input to each of the nonlinear memories 131 to 13n, and each of the signals w ₁ to w _o is read out from each of the nonlinear memories 131 to 13n by the signal h, and these are input to the DA converters 141 to 13n.
After being converted into analog signals by each of the signals W _X , W
Get W _{Y. These} signals _W
are converted into X and Y signals as position signals and sent to the display device 21.

On the other hand, the signal V ₀ is further sent to a pulse height analysis circuit 20, and if it falls within the set energy window, a signal d and an unblank signal are output from this pulse height analysis circuit 20. Further, the signal V' ₀ from the sample-and-hold circuit 90 is taken in by the sample-and-hold circuit 19 operated by the signal i, and sent to the display device 21 as an energy signal (Z signal). Therefore, on the display device 21, a bright spot is displayed at the position indicated by the X signal and the Y signal.

Looking at one PMT here, the dependence of the integrated output V on the light emission position (hereinafter referred to as response characteristics) mainly depends on the solid angle from the light emission position of the PMT, and the light emission position from the PMT central axis. When drawn with respect to the distance r, it becomes a bell-shaped non-linear type as shown in FIG. Furthermore, the response characteristics depend not only on the solid angle but also on the total amount of light emission. Therefore, in the above configuration, the output V (signals V 1 to Vn) is first normalized by dividing the output V (signals V ₁ to Vn) by the signal V ₀ that is approximately proportional to the total light emission amount in the division circuits 101 to 10n, and the output V is made to be purely proportional to the solid angle. After converting the normalized signal V/V ₀ to the signal V/V ₀ , the nonlinear memory 1
31 to 13n, the response characteristic W is converted into a trapezoidal response characteristic W, for example, as shown in FIG. This trapezoid-shaped response characteristic W was determined to improve the nonlinearity and spatial resolution that occur when performing position calculations, and the conversion characteristic from V/V ₀ to W is shown in Figure 4. This conversion characteristic is stored in advance in each of the nonlinear memories 131 to 13n. These nonlinear memories 131 to 13n each have P-
It is composed of semiconductor memory such as ROM. In addition, in Figures 2 and 3, the energy linearity of the PMT and preamplifier is sufficiently good (i.e., V/
The drawing is based on the assumption that the r dependence of V ₀ does not depend on V ₀ .

In this way, the PMT outputs V ₁ to Vn are standardized by dividing them by the signal V ₀ that is proportional to the total light emission amount, and then converted to a response characteristic W that improves nonlinearity, so the total light emission amount Conversion for improving nonlinearity can be performed without dependence, and there is no need to standardize the signal obtained by position calculation by dividing it by a Z signal or the like later. Furthermore, since the output of each PMT can be changed by changing the storage contents of each of the nonlinear memories 131 to 13n, variations in response to the light emitting position of the individual PMTs used can also be corrected.

Note that the configuration of the above embodiment can be modified in various ways. For example, it is also possible to first perform AD conversion on the outputs of the sample and hold circuits 90, 91 to 9n, and then digitally divide the outputs using a memory to obtain v ₁ to v _o . Also, instead of using the division circuits 101 to 10n, the outputs of the preamplifiers 41 to 4n that should be input to each of the integration circuits 81 to 8n are delayed, and the signal
It is also possible to configure the integration time of the integration circuits 81 to 8n to be controlled according to V ₀ so as to substantially perform division. Furthermore, nonlinear memories 131 to 13
The outputs w ₁ to _{w o} of n are once converted into analog signals W ₁ to Wn and then position calculations are performed by the position calculation circuits 15 and 17. If , it is also possible to calculate the position digitally using the digital signals w ₁ to w _o as they are.

As described above with respect to the embodiments, according to the present invention, an image with excellent spatial linearity can be obtained. Furthermore, energy correction using a more accurate position signal is possible. Furthermore, with the conventional method of changing the response characteristics of the PMT output to the light emitting position only by the arrangement of optical systems such as scintillators, light guides, or PMTs, or by means such as masking, the amount of received light generally decreases and the energy resolution is sacrificed. However, according to the present invention, there is no reduction in energy resolution.

[Brief explanation of drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
The figure is a graph showing the response characteristics of PMT, Figure 3 is a graph showing the response characteristics of PMT normalized by the total luminescence amount and the trapezoidal response characteristics, and Figure 4 is the graph showing the response characteristics of PMT and the trapezoidal response characteristics. It is a graph showing the conversion characteristics between. 1...Scintillator, 2...Light guide, 3
1 to 3n...Photomultiplier tube, 5...Addition circuit, 6
...Trigger circuit, 7...Timing generation circuit, 8
0,81~8n...Integrator circuit, 101~10n...
...Division circuit, 131-13n...Nonlinear memory,
15... X direction position calculation circuit, 17... Y direction position calculation circuit, 20... Wave height analysis circuit, 21... Display device.

Claims (1)

[Claims] 1. A scintillation camera that includes a scintillator that emits light in response to incident radiation, a large number of photoelectric converters arranged on the back side of this scintillator, and a position calculation circuit that calculates the position of a light emitting point from the output of each photoelectric converter, a circuit that substantially divides and normalizes each output of the photoelectric converter by the sum of all photoelectric converter outputs, and each of the standardized outputs is inputted;
A scintillation camera characterized by comprising an input/output converter that converts each photoelectric converter according to a nonlinear relationship determined in advance and outputs the converted signal to the position calculation circuit.