JPS62167494A - Apparatus for correcting non-linearity of gamma camera - Google Patents

Abstract

PURPOSE:To enable the correction of a non-linear high frequency component, by preliminarily calculating correction coefficient in a small section and converting the same to coordinates in the small section when one positional signal was calculated to read the correction coefficient. CONSTITUTION:gamma-Rays from RI (radioactive isotope) administered to an exami nee 1 are quided to a large number of PMTs (photomuliplier tubes) 5 through a collimator 2, a scintillator 3 and a light guide 4 and the outputs thereof are subjected to positional operation by a positional operation circuit 6 to obtain position signal X, Y which are, in turn, converted to digital signals by A/D converters 7 and N-th PMT5 nearest to said position (X, Y) is detected by a PMT number detection circuit 8 and signals Xn, Yn showing the center posi tion of N-th PMT5 are generated from PMT position generating circuits 9. The signals Xn, Yn are subtracted from the signals X, Y by subtractors 10 and the position (X, Y) is converted to the position (x, y) of the coordinates of N-th PMT5. The address of a strain quantity memories 11 is indicated by the position signals DELTAx, DELTAy and preliminaily stored strain quantities DELTAx, DELTAy are read and subtracted from the signals X, Y by subtractors 12 to obtain a corrected true position (X', Y').

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a mounting for correcting non-linearities in the position calculation of a gamma camera.

A conventional gamma camera is a flat scintillator that, when radiation enters from the front side of the scintillator and emits light, transmits the light to a photomultiplier tube (hereinafter abbreviated as PMT) arranged on the back side of the flat scintillator. ), and calculate the position using the principle that the closer the PMT is to the light emitting point, the greater the output will be. This is to obtain a distribution image.

However, since perfect linearity is not guaranteed between the distance from the light emitting point to the PMT and the PMT output, non-uniformity may occur in the image due to this non-linearity. Inevitable.

Conventionally, in order to correct the nonlinearity of the 1'ho calculation,
By actually photographing a point source or a linear source whose position is known, measure the positional deviation at each position within the field of view, and calculate the amount of correction for each position to eliminate this deviation. It is a common practice to calculate this in advance, and when photographing an actual subject, each position found is corrected using the amount of correction for that position.

Problems to be Solved by the Invention However, in the past, the sampling points for actually measuring positional deviations were coarse, and the amount of correction between them was determined by linear interpolation, so non-linear high frequency components could not be fully corrected. When viewed in a micro area, the non-uniformity is not improved and there is a drawback that discontinuous and noticeable non-uniformity remains.

Of course, this drawback can be overcome by increasing the density of sampling points, but this is not practical because it not only takes time but also increases memory capacity and circuit complexity, increasing costs.

This invention enables detailed correction and eliminates distortion caused by nonlinear high-frequency components without requiring much time or cost.
An object of the present invention is to provide a nonlinearity correction device for a gamma camera.

Means for Solving the Problems A gamma camera nonlinearity correction device according to the present invention includes a scintillator, a plurality of PMTs arranged on the back surface of the scintillator, and a method for determining the position of radiation incident on the scintillator from the output of the PMTs. a position calculation circuit for calculating, a circuit for detecting the PMT closest to the radiation position determined by the device signal output from the position calculation circuit, and a circuit for detecting the PMT closest to the radiation position determined by the device signal output from the position calculation circuit; A circuit that converts into
a storage circuit in which the stl+ correction coefficient is stored;
It consists of a circuit that reads out this correction coefficient using a position signal in the above coordinate system and applies it to the position signal of the original position calculation circuit.

The PMTs arranged on the back side of the scintillator usually have the same shape, and the electrical system including the preamplifier that processes their output can be considered to have the same characteristics, so the nonlinearity pattern is different from each other. It appears the same regardless of PMT. Therefore, the correction coefficient in a small area directly under one PMT can be applied as is to other PMTs.

Therefore, the correction coefficients are determined and memorized in detail in advance in a small section corresponding to one PMT.
When one position signal is obtained, if we convert it to the coordinates of the above-mentioned small section and read out the correction coefficient, we can improve the density of sampling points without increasing the storage capacity, saving time and cost. Non-linear high frequency components can be corrected without this.

Embodiment In FIG. 1, gamma rays from RI administered to a subject 1 enter a scintillator 3 via a collimator 2 and emit light. This light is guided by the light kite 4 to a large number of PMTs 5, and its output is sent to the position calculation circuit 6. Weighting is performed using the principle that the closer the PMT 5 is to the light emitting point, the larger the output is. , Y is obtained.

These positions No. 43 X and Y represent the light emitting position of the scintillator 3 on the plane, but distortion (positional deviation from the true position) occurs due to the nonlinearity of the position calculation. In other words, if the obtained position (x, y) is as shown in Figure 2, it will be Δ from the true position (x', Y').
deviated by X and Δy. Therefore, this amount of distortion ΔX,
Δy is actually measured only in a small section corresponding to the area directly under one PMT 5, with the sampling point set at 57 degrees by −11 degrees. This can be done in advance using a point source or linear source whose digit n is known. Then, assuming that the relative coordinate system x, y in this section with the center of the PMT 5 as (0, 0) is at[/s], the distortion amounts ΔX, Δy are stored in the distortion amount memory 11.
Let me remember it.

When the position signals X and Y are obtained as described above in the actual photographing of the subject 1, these signals X and Y are first processed by the A/D
After being converted into a digital signal by the converter 7, it is sent to the PMT number detection circuit 8, and the PMT number closest to this position (X, Y) is
5 is detected. Here, if it is close to PMT5 of number N, the output of that number N will be generated, and the PM
The T position generating circuit 9 generates signals Xn and Yn representing the center position of the N-th PMT 5. And the subtractor lO is 43
Signals Xn and Yn are subtracted from signals X and Y, respectively. This 1. , the position FM (X, Y
) is converted to a partial coordinate position (x, y) with the center of PMT5 as (0°0). The address of the distortion amount memory 11 is specified by these position signals x, y, and the distortion amounts ΔX, Δy stored at that address are
is read and extracted. Therefore, the subtracter 12 subtracts the distortion amounts ΔX and Δy from the original position signals X and Y to produce a signal x.
', y'', the point (x
.

Y) is corrected for the positional deviation and becomes the true position (x', y'
) will be corrected.

Effects of the Invention According to the present invention, the correction coefficient is stored only in a small area directly below one PMT, and non-linearity patterns appear the same for other PMTs. This correction coefficient is used as is. Therefore, by determining the correction coefficients limited to this small area, the density of sampling points can be increased without increasing the storage capacity, and the time required to determine the correction coefficients can also be shortened. 5. Therefore, nonlinear high frequency components can be corrected at low cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing the positional relationship. 1... Subject 2... Collimator 3.
...Scintillator 4...Light guide 51. ,
PMT 6...Position calculation circuit 7...
・A/D converter 8...PMT number detection circuit 9...
・PMT stirrup generation circuit 10.12...Subtractor 11・
・・Distortion amount, memory

Claims (1)

[Claims] (1) A scintillator, a plurality of photomultiplier tubes arranged on the back side of the scintillator, a position calculation circuit that calculates the position of radiation incident on the scintillator from the output of the photomultiplier tube, and a position calculation circuit that calculates the position of radiation incident on the scintillator from the output of the photomultiplier tube. a circuit for detecting a photomultiplier tube closest to the radiation position determined by the output position signal; a circuit for converting the position signal into a position signal in a coordinate system of a small section regarding the photomultiplier tube; A storage circuit that stores correction coefficients measured in advance for each position in the coordinate system, and a storage circuit that reads out the correction coefficients using the position signals in the coordinate system and acts on the position signals of the original position calculation circuit. A gamma camera nonlinearity correction device consisting of a circuit that