JPS5934181A - Scintillation camera - Google Patents

Abstract

PURPOSE:To change optionally input/output characteristics of a photoelectric multiplier (PMT), and to improve the uniformity of space resolution, by applying a nonlinear amplifying signal of a final diode output of each PMT to each anode output. CONSTITUTION:A scintillator 1 generates scintillation light is accordance with incidence of radiant rays such as gamma-rays, and this light is led to a PMT3. The PMT3 consists of many diodes D1-Dn and an anode A. A signal which is fetched from the final diode Dn and is passed through a diode signal generating circuit 5 is inputted to a preamplifier 4. All outputs Vi from each diode signal generating circuit 5 are added in an adding circuit 7, and an energy signal Z is obtained. An input current of each preamplifier 4 is subjected to voltage conversion, its output voltage is inputted to a position calculating circuit 6 consisting of a resistance matrix weighting adding circuit, a dividing circuit, etc., and position signals X, Y are obtained.

Description

[Detailed description of the invention] This invention relates to improvements in scintillation cameras.

Generally, a scintillation camera uses an array of many photomultiplier tubes (hereinafter abbreviated as PM'l').
A method of improving spatial resolution by imparting nonlinear characteristics to each preamplifier itself that converts the anode output of each PMT into current and voltage, or to the signal transmission system between each preamplifier and the position calculation circuit (Special Publication No. 51 -2983
9) or a method for improving uniformity (see Japanese Patent Publication No. 56-51312).

This invention changes the input/output characteristics of P M 'I' in a total sense by adding a nonlinear amplified signal of the final dynode output of each PMT to each anode output, thereby improving the spatial resolution. The object of the present invention is to provide a scintillation camera that is improved in both the performance and uniformity.

An embodiment of this invention will be described below with reference to the drawings. In FIG. 1, a scintillator 1 causes scintillation in response to incidence of radiation such as R-rays.
For example, it is made of NaI (Tn) crystal. On the back side of this scintillator 1, a large number of PMTs 3 are connected via a sheet guide 2.
are arranged, and the 7-nteletion light generated within the scintillator 1 is guided to each PMT 3 by the light guide 2. As shown in FIG. 2, each PMT 3 repeats photoelectrons emitted from a photocathode K by each of a large number (usually 8 to 14 stages) of dynodes D1 to D made of a material with high secondary electron emissivity. Is it configured so that the electrons are emitted and multiplied and then collected at the anode A?Along with the output from the anode A, the signal taken out from the final dynode J9 and passed through the dynode signal generation circuit 5 is sent to the preamplifier 4. I am trying to input it into .

This dynode signal generation circuit 5 has a final dynode Dn
The emitter follower circuit 51 and the nonlinear amplifier 52 are AC-coupled. The output taken from the final dynode Dn is linearly amplified by the emitter follower circuit 51 and output V1 is sent to the adder circuit 7 and the nonlinear amplifier 52.The adder circuit 7 generates each dynode signal. All the outputs Vi from the circuit 5 are added together to obtain the energy signal Z.The nonlinear amplifier 52 has a nonlinear characteristic of output current 0 with respect to input signal iK as shown in FIG. , (4) The voltages VPI and VF6 are changed by the reference signal VR. This reference signal R is obtained from the reference signal generation circuit 9 and is proportional to the energy signal Z. The output current ■0 of the 52 is applied to the input terminal of the preamplifier 4 together with the output current of the anode A, but since electrons are collected at the anode A and an output is generated from the anode A, this output current is in the direction in which the anode AK current flows. Therefore, in the end, the output current ■0 of the nonlinear amplifier 52 is subtracted from the output current of the anode A, and the input/output characteristics of the PMT 3 in a total sense, that is, the input signal of the preamplifier 4 with respect to the amount of incident light. The characteristics are shown in Figure 4.

The input current given to each preamplifier 4 is converted into current and voltage, and the output voltage is inputted into a position calculation circuit consisting of an adder circuit, a divider circuit, etc. with resistance matrix weighting.
Obtain position signals X and Y. The energy signal Z is also input to a wave height analyzer 8 in which the width and level (center level) of the shield are determined by the energy window setting device 10.
When the energy signal Z is within this window, the brightness signal UNBLANK and the timing signal are generated.

According to the above configuration, the input/output characteristics of each PMT 3 end up as shown in FIG. 4, so light emission occurs in the scintillator 1 at a distance e from the central axis of the PMT 3 When (fJ), the characteristics of the input signal to the preamplifier 40, that is, the response characteristics of PMT3, are as shown by the solid line a in Figure 8I!5.

The response characteristics of the PMT in a normal synnarration camera are as shown by the dotted line, but compared to this, the input signal of the preamplifier 4 near the center axis is suppressed, and non-uniformity due to spatial distortion is suppressed. I know it will be improved. 1
However, with the characteristic of this solid line a, very weak signals from far away are removed. The light from the light emitting point far from PMT3 is weak and contains many noise components, so if a weak signal is used for position calculation, the error will increase and the spatial resolution of the image will deteriorate accordingly. By not using such weak signals for position calculation, this can be prevented and the spatial resolution can be improved.

Furthermore, since the nonlinearity of the nonlinear amplifier 52 in the dynode signal generation circuit 5 is ultimately controlled according to the energy signal Z for each event of radiation incidence, multiple spectra can be generated when there are several peaks of the energy spectrum of the incident radiation. Measurement and multinuclear f:! It can also be used for ii measurements.

Note that the nonlinearity of the nonlinear amplifier 52 is controlled by the energy window setter 10 as shown by the dotted line in FIG. It may be uniformly controlled by. In this case, a compromise is necessary between low energy peaks and high energy peaks in the case of multispectral measurements.

Further, in the above embodiment, the sum of the final dynode outputs of each PMT 3 is used as the energy signal Z input to the pulse height analyzer 8, but it is also possible to use the sum of each output of the preamplifier 4. In this case, since the output of each preamplifier 4 has been corrected to improve uniformity, non-uniformity due to the position dependence of the energy signal Z is also improved.

Furthermore, it goes without saying that the nonlinearity of the nonlinear amplifier 52 may be other than that shown in FIG.

As described above with respect to the embodiments, according to the present invention, it is possible to improve the spatial resolution of a scintillation camera and to improve the non-uniformity caused by spatial distortion.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram showing in detail the dynode signal generating circuit 5 of FIG. Figure 4 is PMT3O input/output characteristic diagram, Figure 5 &iP
It is a MT3 (7) response characteristic diagram. 1...Scintillator 2...Light guide 3...
・PMT 4...Preamplifier 5...Dynode signal generation circuit 51...Emitter follower circuit 52...Nonlinear amplifier 6...Position calculation circuit 7...
・Addition circuit 8... Wave height analyzer 9... Reference signal generation circuit 10... Energy wind setting device Applicant: Shimadzu Corporation 1st round recruitment 3 drawing book q sub

Claims (3)

[Claims] (1) A scintillator that generates scintillation in response to incident radiation, a large number of photomultiplier tubes arranged on the back of this scintillator to which light from the scintillator is guided, and anode outputs of each class of photomultiplier tubes that are connected to current and voltage. In a scintillation camera having a plurality of preamplifiers for converting and a position calculation circuit for calculating a scintillation position based on the output of each of the preamplifiers, the output of the cylindrical amplifier is converted from the final dynode of each of the photomultiplier tubes to the anode output. The scintillation camera is characterized in that each input is input to a corresponding preamplifier. (2) Equipped with a summing circuit that obtains an energy signal by summing the final dynode outputs of each photomultiplier, each of the incident radiation! 2. The syntelevision camera according to claim 1, wherein the nonlinear characteristics of said nonlinear amplifier are controlled based on an energy signal obtained for each image. (3) The nonlinear characteristic of the nonlinear amplifier is controlled in accordance with the level of an energy window applied to a pulse height analyzer for analyzing the pulse height of the upper pulse signal. scintillation camera.