JPS5876785A - Scintillation camera - Google Patents

Abstract

PURPOSE:To attain pictures with good linearity by a camera wherein output from each photoelectric converter disposed in rear of a scintillator is divided by the total output to be normalized, and locational arithmetic operation is performed after conversion from non-linear characteristic to linear characteristic. CONSTITUTION:Fluorescence generated by radiation incident upon a scientillator 1 enters PMT 31-3n, which outputs are fed via preamplifiers 41-4n to an adder 5 where they are totally added. When an added signal (a) exceeds a given value in a trigger circuit 6, a trigger signal (b) is applied to integration circuits 80-8n and also fed to a timing generating circuit 7 to issue a signal (c). The signal (a) and the output from each preamplifier are respectively integrated in a period from the signal (b) to (c) by the circuit 80 and the circuits 81-8n. In division circuits 101-10n, outputs from the circuits 81-8n are divided by the output of the circuit 80 and then stored in memories 131-13n, respectively. These data signals are applied via D/A converters 141-14n to X- and Y-direction positional arithmetic circuits 15, 17 of weighed addition type. A picture 21 with good linearity can be attained from outputs of these circuits 15, 17.

Description

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

In an anchor-type scintillation camera, a large number of photomultiplier tubes (hereinafter abbreviated as PM'l') are arranged on the back of a scintillator that emits light in response to incident radiation, and each PMT
From the output, the position of the light emitting point is calculated by a position calculation circuit, which is usually a resistance matrix weighted addition circuit or the like. 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.

Especially in the case of normal anchor-type scintillation cameras,
In order to improve spatial resolution, attempts are being made to make scintillators, light guides, etc. thinner, and to use threshold preamplifiers, but this tends to degrade spatial nonlinearity, and images are generally i
' Distorted towards the center.

In view of the above, an object of the present invention is to provide an improved scintillation camera that can obtain images with good spatial linearity.

An embodiment of the present invention will be described below with reference to the drawings. In Figure 1, γ incident on scintillator l
Rays, etc. are absorbed and emit light.

A portion of that light passes through the light guide 2 to each PMT.
31 to 311, the signal is converted into a current signal, and further converted into a voltage signal by each preamplifier 41 to 4n. The outputs of each of these preamplifiers 41 to 4n are added by an adder circuit 5 to obtain a 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 is generated. are sent to each of them. In the timing generating circuit 7, when the trigger signal S is inputted, a signal C is outputted, and when a signal d, which will be described later, is inputted to the timing generating circuit 7, the signals 0 to D are sequentially generated at appropriate timings.

The signal a from the adding circuit 5 is sent to the integrating circuit 80,
In addition, each output of the preamplifiers 41 to 4n is connected to an integrator circuit 81 to 8.
Integration is started by the above signal S, integration is ended by signal C, and signals V, , V, ~V are sent to each of n.
n are obtained respectively, and sample and hold times bY 90 are obtained by the signal e.

91 to 9n, and divided into division circuits 101 to 10.
n through the signal V,/V, ~Vn/V. Ask each of r. These signals are operated by the signal f - the lean pull bold circuit l1l-1In and the AD converter 121''-12n operated by the signal V'g. , 2 Note these signals v, ~v-if non a II l :(1
~13n, and each of the signals w1~W* is read out from each by the signal 111]2, and after these are converted into analog signals by each of the DA converters 141''=14n, normal weighting is performed. The signals WX and yY are inputted to the X-direction position calculation circuit 15 and Y-direction position calculation circuit 17 of the additional stop method, and the signals WX and yY are obtained.
6.18, it is made into an X signal as a position signal and an X signal, and sent to the display device H21.

On the other hand, the signal V is sent to the pulse height analysis circuit 2o, and if it is within the set energy window, the signal d is output as a blank signal.

Further, the signals v and ゛ from the sample and hold circuit 90 are taken in by the sample and hold circuit 19 operated by the signal I, and are sent to the display device 2 as an energy signal (Z signal).
Sent to 1. Therefore, in the display device 21, the X signal and
A bright spot is displayed at the position indicated by the signal.

Looking at one PMT here, the dependence of the integrated output (■) on the light emitting position (hereinafter referred to as response characteristics) mainly depends on the solid angle from the light emitting position of the PMT, and P M
If the distance r from the T center axis to the light emitting position is drawn, it becomes a bell-shaped non-linear type as shown in FIG. Well, the response characteristics depend not only on the solid angle but also on the total amount of light emitted. Therefore, in the above configuration, the division circuits 101 to 10n first output a signal V, which is approximately proportional to the total light emission amount, v (V'1 to
A signal V/V that is normalized by dividing each signal of Vn) and is purely proportional to the solid angle.

After converting to V/V, this normalized signal is converted to V/V.

is converted into, for example, a trapezoidal response characteristic W using the nonlinear memo 'J 131''-13n as shown in FIG. The conversion characteristic from V/V to W is as shown in Fig. 4, and this conversion characteristic is a nonlinear memo 'J l 31=
l 3 n are stored in advance. Each of the non-linear memos 31 to 13n is composed of a semiconductor memory such as I)-B, OM, or the like. In addition, Figures 2 and 3
The figure was drawn assuming that the energy linearity of the PMT and preamplifier is sufficiently good (that is, the dependence of V/V is independent of V).

In this way, the PMT output V + "□ V n is divided by the signal ■ proportional to the total light emission amount, and after normalization, it is converted to the response characteristic W that improves the non-direction Mi property, so the total It is possible to perform conversion to improve nonlinearity without depending on the amount of light emitted, and there is no need to standardize the signal obtained by position calculation by dividing it by the Z signal etc.
Since the output of each PMT can be changed by changing the storage contents of each of l 31 = 13 n, 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, sample and hold circuits 90.91-9
It is also possible to first perform AD conversion on each output of n, and then use a memory to digitally divide the outputs to obtain y and -y. It's Sword, Division Circuit 101"
-10n, the outputs of the preamplifiers 41-4n to be input to each of the integrating circuits 81-8n are delayed, and the integration time of the integrating circuits 81-8 is controlled according to the signal V. It is also possible to construct a configuration in which the calculation is performed and substantially divided. Historically, the output of nonlinear memory 131=13n w
1 to W and - are converted into analog signal parts -Wn, and then the positions are calculated by the position calculation circuit 15. It is also possible to digitally calculate the position using the signals W, ~W, 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, scintillator, light guide or P
Conventional methods in which the response characteristics of the PMT output to the light emitting position are changed only by the arrangement of the optical system such as the MT or by means such as masking generally reduce the light receiving area and sacrifice the energy resolution. In this case, there is no reduction in energy resolution.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
A graph showing the response characteristics of T, Figure 3 is a graph showing the response characteristics of M T and a trapezoidal response characteristic, and Figure 4 is a graph representing the response characteristics of PMT and a trapezoidal response characteristic. 1 is a graph showing conversion characteristics between . l...Scintillator 2...Light guide 31~3n...
- Photomultiplier tube 5...Addition circuit 6...Trigger circuit 7...Timing generation circuit 80.81-8n...Integrator circuit tot-to port...Division circuit 131-13n...Nonlinear memory 15...Y Direction position calculation circuit 17... Y direction position calculation circuit 20... Wave height analysis circuit 21... Display device applicant Takasugi Seisakusho Co., Ltd. (9) -48:

Claims (1)

[Claims] (1) In a scintillation camera that has a scintillator that emits light in response to incident radiation and a number of photoelectric converters arranged on the back of this scintillator, and the position of the light emitting point is calculated from the output of each photoelectric converter. , after normalizing each output of the photoelectric converter by dividing it by the sum of all photoelectric converter outputs, converting each normalized output using a nonlinear relationship determined in advance for each photoelectric converter, and calculating this conversion. A scintillation camera characterized in that a position calculation is performed using the output.