JPS60260874A - Scintillation camera - Google Patents

Abstract

PURPOSE:To improve the accuracy of position detection of a scintillation camera by providing a dividing circuit between a matrix adding circuit and a position calculating circuit, and dividing a matrix signal by an energy signal. CONSTITUTION:An incident gamma ray is converted to light by a scintillator 1, and converted to an electric signal 101 by a photoelectric multiplier 2. The electric signal is added by a matrix adding circuit 3 for each matrix and becomes a matrix signal 102, and all of them are added by an adding circuit 8 and become an energy signal 106. Dividing circuits 20 of X9 channel and Y5 channel output a matrix signal 102'' obtained by dividing the matrix signal 102 by the energy signal 106. As the matrix signal 102'' is divided by the energy signal 106 by the dividing circuit 20, the magnitude as a whole becomes constant regardless of energy of incident gamma rays, statistical fluctuation in the scintillator 1 and photoelectric multiplier, and spread in magnitude of signals caused by unstable factors of the circuit.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a scintillation camera.

[Background of the invention]

A scintillation camera is a device that detects r-rays emitted by a radiopharmaceutical administered to a patient to obtain an image of the distribution of the radiopharmaceutical in the body, and is widely used because it is effective in diagnosing the function of organs.

Figure 1 shows the configuration of this scintillation camera.
Explain the operation. In Figure 1, 1 is a scintillator that generates a flash of light corresponding to the energy of R-rays when it is incident, and 2 is a photoelectron that is optically coupled to scintillator 1 and converts the incident light into an electrical signal 101. It is a multiplier tube.

FIG. 2 shows an example in which 19 photomultiplier tubes 2 are arranged in a scintillation pattern. Each photomultiplier tube 2 is arranged in 9 columns in the x direction and 5 rows in the y direction. For example, the photomultiplier tube 2 in the center is in the X5 row.

He will be assigned to line 73. In FIG. 1, reference numeral 3 denotes a matrix addition circuit consisting of adders for 9 channels in the X direction and 5 channels in the Y direction, and each output signal 10 of the photomultiplier tube 2 is
1 is added to each matrix determined by the allocation method, and a matrix signal 102 is output.

4 is a 14-channel voltage divider amplifier circuit that switches the voltage division ratio with respect to the energy of the incident R-ray to suppress changes in signal magnitude due to the energy level within a certain range; 5 is a line from the voltage divider circuit 4; , X in which column signals 102' are arranged in time series
", X-, Y", a delay line mixing circuit that produces the Y-signal 103;
", Y-4 channel waveform shaping circuit, 7 detects zero crossing of bipolar pulse signal 104", X-, Y+
.

This is a Y″44 channel low cross detection circuit.

On the other hand, in FIG. 1, 8 is an addition circuit that adds all the output signals 10f- of the photomultiplier tube 2 to generate an energy signal 106 corresponding to the energy of the incident r-ray, and 9 is the magnitude of the energy signal 106. a pulse height analysis circuit 1 for determining whether or not the r-ray incident from the source has the desired energy;
10 is a control circuit that outputs the brightness modulation signal UN8108 and the position calculation control signal 109 according to the determination signal 107 from the wave height analysis circuit; 11 is a control circuit that outputs the position calculation control signal 109 and the zero crossing signal 105 from the zero cross detection circuit 7; 1'2 is a time-voltage conversion circuit 1 with x'', x-, y'', and Y-4 channels that converts the time difference into voltage.
The position signal X is obtained by subtracting X- from X+ and Y- from Y+ for the
This is a subtraction circuit that creates 111 and Y112.

In the conventional scintillation camera described above, the reason why the voltage dividing amplifier circuit 4 is placed between the matrix addition circuit 3 and the delay line mixing circuit 5 is that the zero cross detection circuit 7 is In order to prevent the zero crossing detection accuracy from changing, a signal 102' having a constant range of magnitude is input from time to time to the position calculation circuit system after the delay line mixing circuit 5, regardless of the magnitude of the energy of the incoming r-line. This is to prevent the position detection accuracy (resolution) from deteriorating due to noise in the position calculation circuit system. The latter reason is important when the energy of the incident r-rays is small, and small matrix signals 10 that are susceptible to noise
The influence of noise is minimized by making 2 equal to the signal size when the energy is large. However, for the former reason, the conventional voltage dividing amplifier circuit 4 is insufficient. That is, although the voltage division amplifier circuit 4 has a voltage division ratio that divides the range of incident r-ray energy used into several stages, it is usually about 4 to 10 stages, and the magnitude of the matrix signal 102' cannot be made completely constant. . In addition, the amount of light emitted by the scintillator 1 and the photomultiplier tube 2 for a constant r-ray energy
The magnitude of the output signal 101 has a spread of about 10 to 15 factors due to statistical variations and circuit instability factors, but the conventional voltage dividing amplifier circuit 4 could not correct this spread. .

[Purpose of the invention]

The purpose of the present invention is to supply a matrix signal of a constant size to the position calculation circuit system in the subsequent stage, regardless of the magnitude of the energy of incident R-rays or the spread of the signal magnitude due to the scintillator and photomultiplier tube. An object of the present invention is to provide a scintillation camera with excellent position detection accuracy.

[Summary of the invention]

In the present invention, instead of the partial voltage amplifier circuit inserted between the matrix addition circuit □ and the position calculation circuit system in the conventional scintillation camera, a division circuit that divides the matrix signal by the energy signal is inserted, which solves the above problems. This is to solve the problem.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. 1st
The same parts as in the conventional example in the figure are given the same reference numerals and detailed explanations will be omitted.

In FIG. 3, an incident r-ray is converted into light by a scintillator 1, and converted into an electric signal 101 by a photomultiplier tube 2. The electric signals 101 are added matrix by matrix in the matrix addition circuit 3 to become a matrix signal 102, and all are added in the addition circuit 8 to become an energy signal 106. The division circuits 20 of the X9 channel and the X5 channel convert the matrix signal 102 into the energy signal 1.
The matrix signal 102'' divided by Y112 and brightness modulation signal UN
Output B 108.

Since the matrix signal 102'' is divided by the energy signal 106 by the division circuit 20, the energy of the incident R-ray, the statistical fluctuations in the scintillator 1 and the photomultiplier tube, and the signal caused by instability factors of the circuit are calculated. The overall size remains constant regardless of the size spread.The matrix signals 102'' in the X9 column and Y5 row only change in mutual size depending on the incident position of the r-ray. It will have only information. As a result, the position detection accuracy (resolution) in the subsequent position calculation circuit system can be significantly improved.

Furthermore, this method of dividing the matrix signal by the energy signal is also effective for scintillation cameras using high-speed digital position calculation circuits, which are being studied in recent years. In a scintillation camera using a digital position calculation method, the matrix signal 1
02 is converted into a digital signal by an AD conversion circuit, and the position is determined by a high-speed digital position calculation circuit. In this case, by inserting a division circuit before the AD conversion circuit, the digitization precision (number of bits) of the AD conversion circuit and the amount of circuitry of the high-speed digital position calculation circuit can be significantly reduced. Furthermore, in this digital position calculation type scintillation camera, the AD conversion circuit can be provided with a division function. Generally, commercially available AD converters have one analog signal terminal, a plurality of digital signal terminals, and a reference voltage input terminal. Even for types that have an internal reference voltage source, many have a reference voltage output terminal that is not connected internally and is connected via external wiring, increasing the degree of freedom in circuit design. The AD converter converts an analog signal into a digital signal using the voltage at this reference voltage input terminal as a reference.Then, the energy signal 106 is input to the reference voltage input terminal, and the analog input signal is converted using this as a reference. By digitizing the matrix signal 102 input to the terminal, you can essentially obtain the same effect as dividing the matrix signal 102 by the energy signal 106 and then AD converting it.One channel of this AD conversion circuit is shown in Fig. 4. In Fig. 4, 21 is an AD converter;
One of the matrix signals 102 is input to the analog input terminal, and an energy signal 106 is input to the reference voltage input terminal. The digital matrix signal 102'' of the AD converter 21 becomes a signal having only position information that is not affected by incident r-ray energy, etc., and is manually input to a high-speed digital position calculation circuit at the subsequent stage.

[Effects of the Invention] According to the present invention, the matrix signal input to the position calculation circuit system is controlled by the energy of incident r-rays, statistical fluctuations in the scintillator and photomultiplier tube, and signal instability caused by circuit instability factors. It can be kept constant regardless of the size spread, and has the effect of improving the position detection accuracy of the scintillation camera.

[Brief explanation of drawings]

FIG. 1 is an example of the configuration of a conventional scintillation camera, and FIG. 2 is an arrangement diagram of a photomultiplier tube 2 on a scintillator 1.
FIG. 3 is a block diagram of a scintillation camera according to an embodiment of the present invention, and FIG. 4 is a partially detailed diagram of an AD conversion circuit in a digital 9-position calculation type scintillation camera. 1...Scintillator, 2...Photomultiplier tube, 3...
- Matrix addition circuit, 4... Voltage amplification circuit, 5... Delay line mixing circuit, 6... Waveform shaping circuit, 7... Zero cross detection circuit, 8... Addition circuit, 9... Wave height analysis circuit, 10... Control circuit, 11... Time-voltage conversion circuit, 12... Subtraction circuit, 20... Division circuit, 2
1...AD converter. Agent Patent Attorney Akio Takahashi

Claims (1)

[Claims] 1. A scintillator, a plurality of photomultiplier tubes regularly arranged on the scintillator, an adding circuit that adds the outputs of all the photomultiplier tubes to create an energy signal, and a The rff is determined from the difference in the relative magnitude of the matrix signals of multiple matrix adder circuits that collectively add the outputs for each row and column to which they are assigned, and the matrix signals of these matrix adder circuits.
A scintillation camera comprising a position calculation circuit that generates an iJ incident position signal, characterized in that a division circuit is provided between the matrix addition circuit and the position calculation circuit, and divides the matrix signal by the energy signal. scintillation camera.