JPS60260875A - Scintillation camera - Google Patents

Abstract

PURPOSE:To simplify the configuration of a circuit by obtaining energy calibrated digital signals of each row and column by adding an energy signal to an AD convertor as a reference voltage signal. CONSTITUTION:The AD convertor 5 is provided with a reference voltage input terminal, and outputs a digital signal corresponding to the ratio of magnitude of inputted analog signal to the reference voltage signal. An analog matrix signal 103 is inputted as an input analog signal of the AD convertor 5, and an energy signal 102 is inputted as the reference voltage signal. As the ratio of magnitude of the analog matrix signal 103 to energy signal 102 is constant even when the magnitude of the energy signal changes provided that the position of incidence of gamma rays is fixed, a digital matrix signal 105 becomes one calibrated for energy. Thus, AD conversion and correction for energy of the matrix signal become possible only by the AD converting circuit 5, and the circuit configuration can be simplified.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is a scintillation method that digitizes row and column addition signals and digitally processes the magnitudes of the row and column signals to determine the r-ray entry pair position. It's about cameras.

[Background of the invention]

With the recent development of electronics, high-speed and high-precision AD converters and digital elements have become easily available. In response to this, position calculation methods using digital circuits, which can more easily realize ideal weight calculations than position calculations using analog circuits, are being put into practical use.

The position calculation method using this digital circuit is basically the same as the position calculation using an analog circuit, and the outputs of the photomultiplier tubes arranged regularly on the scintillator are summarized for each row and column to which the photomultiplier tubes belong. In this method, the matrix signal is converted into a digital signal by an AD converter (the digital matrix signal obtained by converting the matrix signal is subjected to weighting calculation processing to obtain a position signal. If the matrix signal is weighted as is, there is a problem that the position resolution will decrease due to the height of the incident gamma ray energy and the spread of the photoelectric peak, so it is necessary to normalize the digital matrix signal by dividing it by the energy signal. This division is necessary for each matrix; for example, in a scintillation camera with 61 photomultiplier tubes, the number of matrices is 26, so 2
As many as 6 channels of division circuits are required. therefore,
Conventional position calculation methods using digital circuits have the problem of requiring a large number of division circuits, making the multiple circuits complex.

[Purpose of the invention]

An object of the present invention is to provide a digital position calculation type scintillation camera with a simplified circuit configuration.

[Summary of the invention]

The present invention simplifies the circuit configuration by adding an energy signal as a reference voltage signal of the AD converter and performing AD conversion and normalization only by the AD converter.

[Embodiments of the invention]

An embodiment of the present invention will be explained below with reference to FIG. 1st
- In the figure, when a γ-ray enters a scintillator 1, light proportional to its energy is generated, which is converted into an electrical signal by a photomultiplier tube 2 optically coupled to the scintillator 1. The output signal 101 of the photomultiplier tube 2 is larger as the photomultiplier tube is closer to the light emitting point on the scintillator 1, and the sum of all output signals 101 is proportional to the incident γ-ray energy.

Adder circuit 3 adds all output signals 101 to produce energy signal 102 .

FIG. 2 shows an example in which 19 photomultiplier tubes are arranged in a hexagonal dense arrangement. In this case, the number of rows and columns in the X direction and Y direction is 9, respectively.
It becomes 5. In this case, the matrix addition circuit 4 is composed of a 14-channel addition circuit, and outputs 14 matrix signals 103.

The AD conversion circuit 5 also includes 14 channels of AD converters, and each AD converter outputs a digital matrix signal 105. The arrangement of photomultiplier tubes is not limited to the hexagonal close-packed arrangement shown in this example, and any regularity is sufficient. Further, the matrix may be set not only in the XY orthogonal coordinates but also in the oblique coordinates, and the number of photomultiplier tubes is not limited to 19.

On the other hand, the energy signal 102 also becomes a digital signal 104 in the AD conversion circuit 6. This digital energy signal 1
04 is judged by the energy discrimination circuit 8 whether or not it is a gamma ray of the target energy, and if it is a gamma ray of the target energy, it outputs a collection signal U108.

FIG. 3 shows details of one channel of the AD conversion circuit 5. The AD converter 51 has a reference voltage input terminal, and outputs a digital signal corresponding to the magnitude ratio of the input analog signal to the reference voltage signal. For example, in a 10-bit AD converter, the reference voltage signal is 1 volt, and the input analog signal is 0, 5 F? If it is default, the digital output signal will be 210X(0,5/1)-512.

In this embodiment, an analog matrix signal 103 is input as an input analog signal to the AD converter 51, and an energy signal 102 is input as a reference voltage signal. If the incident position of the γ-ray is constant, the ratio of the magnitude of the analog matrix signal 103 to the energy signal 102 is constant even if the magnitude of the energy signal changes, so the digital matrix signal 105 is It becomes calibrated. Since this digital matrix signal 105 does not change depending on the magnitude of the incident gamma ray energy, the digital position calculation circuit 7 calculates the magnitude of each digital matrix signal to determine the gamma ray incident position, and calculates the magnitude of the incident gamma ray energy. Output Y2O2. child·
position signal X106. Y2O2 is the collected signal U108
At the same time, the data are collected by a data collection unit not shown in FIG. 1 to form an R1 biodistribution image.

Note that the analog matrix signal 103 is the sum of only each matrix, so all the photomultiplier tube outputs 10
Since it is smaller than the energy signal 102 obtained by adding 1, a certain gain may be added to the analog matrix signal 103 as long as it does not become larger than the energy signal 102.

〔Effect of the invention〕

According to the present invention, only the AD conversion circuit can perform AD conversion of matrix signals.
Calibration for conversion and energy becomes possible, and the circuit configuration can be simplified.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of digital position calculation according to the present invention, Fig. 2 is a diagram of matrix settings for the photomultiplier tube arrangement, and Fig. 3 is a block diagram of one channel of the AD conversion circuit of Fig. 1. This is a block diagram showing details of the AD converter. 1...Scintillator, 2...Photomultiplier tube, 3...
・Addition circuit, 4...Matrix addition circuit, 5, 6...AD
Conversion circuit, 7... Digital position calculation circuit, 8... Energy discrimination circuit, 51... AD converter, 103...
・Analog matrix signal, 102...Energy signal, 1
05...Digital matrix signal. Agent Patent Attorney Akio Takahashi 4 ( (1-; ) 1 Giant 1 (x)

Claims (1)

[Claims] 1. A scintillator, a plurality of photomultiplier tubes arranged regularly on the scintillator, an adding circuit that adds the outputs of all the photomultiplier tubes to create an energy signal, and these photomultipliers. A plurality of matrix adders that collectively add the outputs of the tubes for each row and column to which the photomultiplier tubes belong, and analog addition signals for each row and column of these matrix adders are made to correspond to the ratio of the reference voltage signal. a plurality of AD converters for converting into digital signals; and a digital position calculation for determining the incident position of the γ-rays incident on the scintillator by calculating the magnitude of the digital signals of each time and column from these AD converters. 1. A scintillation camera comprising a circuit, characterized in that the energy signal is added to the AD converter as a reference voltage signal to obtain energy-calibrated digital signals for each row and column.