JPH0385481A - Gamma camera - Google Patents

Abstract

PURPOSE:To reduce calculation quantity and to simplify algorithm by using a part of the outputs of a plurality of PMTs in contact with the outer periphery of a central photomultiplier tube (PMT) corresponding to an approximate position to calculate each axis. CONSTITUTION:The radiation detected by a scintillator 1 is photoelectrically converted by a PMT 2 and the approximate position of the center of light emission is detected on the basis of the output of the PMT 2. The specific PMT 2 the center of a light emitting position and a block consisting of six PMTs around said PMT 2 are selected by a selection circuit 4 and three axes L1-N1 whose crossing angles are mutually 60 deg. with respect thereto are set. For example, with respect to an L1-axis, predetermined weighting and addition are performed corresponding to a light emitting position by the predetermined weighting part 11 and adding parts 13, 14 in an L-axis weighting/adding part 10. In the same way, weighting and addition are performed even with respect to an M1-axis and an N1-axis by an M-axis weighting/adding part 20 and an N-axis weighting/adding part 30 and, when the outputs thereof are divided by 3 being the number of PMTs of respective axes by a dividing part 31, the max. light emitting positions on three axes L1 - N1 are calculated and the triangular center of gravity G obtained by drawing a perpendicular to the axes L1 - N1 from the positions becomes the light emitting position of SC 1. Therefore, calculation quantity can be reduced to a large extent and a calculation method can be simplified.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention includes a large number of photomultiplier tubes that are installed on the back side of a scintillator and performs photoelectric conversion, and determines the light emission position from the output of the photomultiplier tubes. Regarding gamma cameras seeking.

(Prior Art) A conventional gamma camera, for example, a gamma camera that employs an angle type, has a scintillator that inputs radiation, and a large number of photomultiplier tubes (hereinafter referred to as PMTs) that are attached to the back of this scintillator and that perform photoelectric conversion. It is equipped with

FIG. 5 is a schematic block diagram showing a PMT of this type of gamma camera, and FIG. 6 is a schematic block diagram showing weighted addition for each coordinate axis of the PMT. -For example, the PMT group is N0
Consisting of 61 PMTs from No. 01 to No. 61, the light emitting position within the scintillator due to radiation (not shown) that has entered the field of view is determined by setting each PMT output for each axis (axis for calculation) to that position. It is obtained by performing weighted addition accordingly.

For example, as shown in Figure 6, radiation input from a scintillator to multiple PMTs via glass and a light guide is
5 PMTs (Le No. 1 to No. 0.5 shown in Figure 5)
PMT) and undergoes photoelectric conversion. and each PMT
The outputs are Wl--2, W2--1. W3-0
．． A predetermined weighting of W4-+1°W5-+2 is performed and these outputs are added. As a result, No, 1 to N
025, that is, the maximum light emission positions of the plurality of PMTs with respect to the X axis are determined, and further the maximum light emission positions with respect to the Y axis (not shown) are determined.

In this way, in the coordinate system used to calculate the position of light emission, the X axis,
Cartesian coordinates consisting of two axes, the Y-axis, were used.

Recently, a method using three wheels (crossing angle of 60°) has also been proposed in order to improve the accuracy of the light emitting position.

(Problems to be Solved by the Invention) However, conventional gamma cameras have the following problems. In other words, in the gamma camera described above,
In calculating the light emitting position using the three-axis method, it was necessary to perform weighting, addition, etc. three times. For this reason, there is a problem in that the calculation of the light emitting position takes more time than necessary.

Furthermore, since calculations are performed on three axes, there is a problem in that the circuit configuration becomes complicated.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a gamma camera that can shorten the calculation time of the light emitting position, has a simple configuration, and can improve reliability.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems and achieve the objects, the present invention takes the following measures. That is, the present invention includes a plurality of conversion means installed on the back side of a scintillator for photoelectric conversion, a detection means for detecting the approximate position of light emission based on the output of the conversion means, and a plurality of conversion means for detecting the approximate position of light emission based on the output of the conversion means, and the above-mentioned conversion means corresponding to the approximate position detected by the detection means. A selection means for selecting a plurality of transformation means centered around the transformation means and in contact with the outer periphery of this transformation means, and a part of the output of the plurality of transformation means selected by this selection means, for each axis of the three-axis coordinates. and calculating means for performing weighted addition according to the position of the converting means, converting the three-axis coordinates into two-axis coordinates, and determining the light emitting position within the scintillator.

(Effects) By taking such measures, the following effects will be exhibited. By using only a part of the output of the conversion means selected by the selection means, the number of conversion means used for weighting and addition for each axis is reduced, so the amount of calculation for the light emission position is reduced.

This reduces the calculation time for the light emitting position, and also simplifies the algorithm, which simplifies the circuit configuration.
Furthermore, the reliability of the device can be improved.

(Example) Fig. 1 is a schematic block diagram showing a gamma camera according to the present invention, Fig. 2 is a schematic diagram for explaining the PMT block of the gamma camera, and Fig. 3 is a schematic diagram of the three axes set in the PMT block. FIG. 4 is a schematic diagram showing the case where three PMTs are used for each axis. FIG. 4 is a schematic diagram showing the case where five PMTs are used for each of the three axes set in the PMT block.

In FIG. 1, the gamma camera includes a photomultiplier tube 2 (PMT) which is attached to the back of a scintillator 1 and serves as a plurality of conversion means for photoelectric conversion, and a detection means which detects the approximate position of the emission center based on the output of the PMT 2. A hexagonal block consisting of a plurality of PMTs 2 centered on one of the PMTs 2 corresponding to the approximate position detected by the position detection circuit 3 and touching the outer periphery of the PMT 2 shown in FIG. It has a selection circuit 4 as selection means for selecting.

Further, the gamma camera selects the PM selected by the selection circuit 4.
Calculation as a calculation means to calculate the light emitting position in the scintillator by weighting and adding each axis of the three-axis coordinate according to the position of the PMT2 and converting the coordinate from the three-axis coordinate to the two-axis coordinate using a part of the output of T2. circuit 5, an energy calculation circuit 6 that adds all the outputs of the PMT 2 and obtains an energy signal;
It is equipped with

The calculation circuit 5 inputs the output of the PMT 2 and has an L-axis weighting/adding unit 101 consisting of three axes;
0. N-axis weighting/addition unit 30. A division unit 31 that divides these weighting/addition outputs by the number of PMTs on each axis. Based on the three-axis output from this dividing unit 31, the X-coordinate position is output as two-axis output.

It is composed of a coordinate conversion section 32 that performs coordinate conversion to a Y coordinate position.

The axis weighting/adding section 10 includes a numerator weighting section 11. which weights the PMT output. It is composed of a denominator weighting section 121 that weights PMT outputs, and addition sections 13 and 14 that add weighted outputs by the number of PMTs on each axis. Also M
The axis weighting/adding section 20 and the N-axis weighting/adding section 30 also have the same configuration as the axis weighting/adding section 10 described above.

Next, the present embodiment will be described with reference to the drawings. First, as shown in FIG. 1, radiation is photoelectrically converted by a plurality of PMTs 2 provided on the back surface of a scintillator 1, and the approximate position of the emission center is detected by a position detection circuit 3 based on the output of the PMTs 2. Then, as shown in FIG. 2, the selection circuit 4 selects a PMT block consisting of a specific PMT 2 at the center of the light emitting position and six PMTs 2 around this specific PMT 2. For example, No, 7.8.13, 14°15.21
．． This is a PMT block BK consisting of 22 blocks.

Here, as shown in FIG. 3(a), the PMT block B
Three coordinate axes having mutually intersecting angles of 60 degrees with respect to K, namely, the L1 axis, the N1 axis, and the N axis are set. That is, three PMT outputs are used for each axis. For example, Figure 3 (
As shown in b), for the M axis, the PMTs of C, D, and E are
Use output.

(1) And these three L1 axes and J axes.

For each axis of the N1 axis, an L-axis weighting/adding section 10° and an M-axis weighting/adding section 20. The numerator weighting unit 1 denominator weighting unit (the numerator weighting unit 111 and the denominator weighting unit 12 in the L-axis weighting/adding unit 10) provided in the N-axis weighting/adding unit 30 calculate the light emission position as shown in FIG. 6, for example. A predetermined weighting is performed according to. Furthermore, addition units provided in each section (addition units 13 and 14 in the L-axis weighting/addition unit 10) perform addition, and the output of this addition is sent to the division unit 31.
By dividing by the number of PMTs on each axis (3), the maximum light emitting position (the dot position shown in the figure) on all three axes can be obtained.

Further, perpendicular lines are drawn to the axes from the determined maximum light emitting positions on each axis, and the center of gravity G1 of the triangle obtained by these three perpendicular lines is determined, which becomes the light emitting position of the scintillator.

Since the number of PMT2 used for weighting and addition is reduced to three for each axis in determining the light emission position in this way, the amount of calculation is significantly reduced compared to the conventional calculation using seven PMT2. As a result, the time required for calculation can be significantly shortened, and the algorithm can be simplified, so that the reliability of the device can be improved. Furthermore, since the algorithm is simplified, the circuit configuration can be simplified.

(2) Next, weighted addition on each axis is performed using five PMTs.
The case of carrying out 2 will be explained.

As shown in FIG. 4(a), the coordinate system consists of the L2, N2, and N2 axes, which are shifted by 30 degrees from the coordinate system shown in FIG. 3 and consisting of the axes 2M1 and N1. For example, Figure 4 (
As shown in b), for the N2 axis, five PMTs of BCDEF are subject to calculation. Even when calculating the light emission position using these five PMTs 2, it can be performed in the same manner as described above.

In other words, by drawing perpendicular lines to the axes from the maximum light emission position on each axis determined as shown in Figure 4 (a), and finding the center of gravity G2 of the triangle obtained by these three perpendicular lines, this is the light emission of the scintillator. position.

Since the number of PMT2 used for weighting and addition is reduced to five for each axis in determining the light emitting position in this way, the amount of calculation is relatively reduced compared to the conventional calculation using seven PMT2. This reduces the time required for calculation and simplifies the algorithm, thereby improving the reliability of the device. Furthermore, since the algorithm is simplified, the circuit configuration can be simplified.

Note that the present invention is not limited to the embodiments described above. In the embodiment described above, three or five PMT2 are selected, but any other number of PMT2 may be selected as long as the number does not exceed the conventional seven PMT2. Of course, various modifications can be made without departing from the spirit of the invention.

[Effects of the Invention] According to the present invention, by using only a part of the output of the conversion means selected by the selection means, weighting and
Since the number of conversion means used for addition is reduced, the amount of calculation for the light emitting position is reduced.

This reduces the calculation time for the light emitting position, and also simplifies the algorithm, which simplifies the circuit configuration.
Furthermore, it is possible to provide a gamma camera that can improve the reliability of the device.

[Brief explanation of drawings]

Fig. 1 is a schematic block diagram showing a gamma camera according to the present invention, Fig. 2 is a schematic diagram for explaining the PMT block of the gamma camera, and Fig. 3 is a schematic diagram for explaining the PMT block of the gamma camera. A schematic diagram showing the case where three PMTs are used, FIG. 4 is a schematic diagram showing the case where five PMTs are used for each of the three axes set in the PMT block, and FIG. 5 is a schematic diagram showing the conventional PMT. FIG. 6 is a schematic diagram showing calculation of the light emission position of PMT. DESCRIPTION OF SYMBOLS 1...Scintillator, 2...PMT, 3...Position detection circuit, 4...Selection circuit, 5...Calculation circuit, 6...
...Energy calculation circuit, 10...L-axis weighting/addition section, 20...M-axis weighting/addition section, 30...N
Axis weighting/addition section, 31... Division section, 32... Coordinate transformation section, 11... Numerator weighting section, 12... Denominator weighting section, 13.14... Addition section, PMT... Photomultiplier tube, L+, Mr, N+, L2, M2
, N2...each axis.

Claims (1)

[Claims] The system mainly includes a plurality of conversion means installed on the back side of the scintillator for photoelectric conversion, a detection means for detecting the approximate position of light emission based on the output of the conversion means, and the conversion means corresponding to the approximate position detected by the detection means. A selection means for selecting a plurality of transformation means in contact with the outer periphery of the transformation means, and a part of the outputs of the plurality of transformation means selected by this selection means are used to position the transformation means with respect to each axis of the three-axis coordinate. 1. A gamma camera comprising calculation means for converting the three-axis coordinates into two-axis coordinates by performing weighted addition according to the above, and determining the light emitting position within the scintillator.