JPH0368890A - Gamma camera apparatus - Google Patents

Abstract

PURPOSE:To obtain an RI distribution image having no strain by removing the output of a photomultiplier tube outputted by a noise component when the effect of the noise component is estimated to recalculate an gamma ray incident position. CONSTITUTION:The gamma ray incident position signals X, Y calculated by the second position calculator 19 are next sent to a re-calculator 20 and the effect as the noise due to the adjacent photomultiplier is checked. When the calculation result enters an L1-region, the output of the photomultiplier E adjacent to the right is received as noise and, therefore, the output of the photomultiplier E is cut and the recalculation of a gamma incident position is executed only by photomultipliers C, D to obtain an output signal at this point of time. In the same way, the output of the photomultiplier C is cut even with respect to a region L2 to perform recalculation to obtain the output signal at this point of time. By this method, an RI distribution image having no strain can be obtained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a gamma camera device that creates RI distribution data within a subject administered with a radioisotope (RI), and particularly relates to The present invention relates to a gamma camera device with improved means for calculating the incident position of radiation.

(Prior Art) A general configuration of a scintillation camera is shown in FIG. 12. 1 is a scintillator that generates scintillation light when radiation (gamma rays) emitted from a subject to which a radioactive isotope has been administered is incident, and 2 is a plurality of scintillators that are optically coupled to scintillator 1 and convert the scintillation light into electrical signals. This is a photomultiplier tube. The scintillation and photomultiplier tube 2 described above constitutes a detector 9 together with a collimator, a light guide, etc. (not shown). The output signal from this detector 9 passes through each preamplifier 3, and then
The information is supplied to the Y position calculation circuit 4, where the scintillation light generation position information is calculated. That is, the position calculation circuit 4 is composed of a weighting circuit using, for example, a resistance matrix, and has an origin of X,
Position information of X'', X-, Y'', and Y in the Y orthogonal coordinate system is obtained. The output signal of the detector 9 is also supplied to a pulse height analysis circuit 7 via a variable resistor 5 and a summing amplifier 6, where energy value information of the incident radiation is obtained. An RI distribution image within the subject can be displayed on the display system 8 based on the position information and energy value information.

Here, to explain in detail the means for calculating the sold-out position of the scintillator 1 when radiation is incident, for example, as shown in FIG. are arranged so that they are placed in Now, assuming that the value of "weighting by position" given to each photomultiplier tube 2 is given as shown in FIG.・The calculation method for calculating the j position is shown in the same figure.The method in this figure deals with only the X-axis direction and is calculated as +0.5.Although not shown, the calculation method for the Y-axis direction is also It is calculated in exactly the same way.

However, as described above, since the photomultiplier tube 2 has a finite number of 61 pieces arranged in a hexagonal shape, the symmetry of the X, Y position coordinate system has been deteriorated. In other words, ideally there would be no problem if the number of photomultiplier tubes could be increased to infinity, but as a practical matter, it is impossible to dramatically increase the number of photomultiplier tubes used due to economic and performance reasons. Therefore, the checkered pattern along the arrangement direction of the photomultiplier tubes is emphasized and superimposed on the RI distribution image.

Therefore, in order to eliminate as much as possible the checkered pattern superimposed on the RI portion Vli image, the following means have already been devised. That is, of the radiation emitted from the RI administered into the subject, only the radiation that has passed through the collimator is incident on the scintillator. Here, a scintillation light beam proportional to the energy value of the incident radiation is generated and supplied to a plurality of photomultiplier tubes. Each of these photomultiplier tubes outputs an electrical signal proportional to the supplied light. The first position calculator calculates the approximate position of incidence of the incident radiation based on the electrical signals.

The approximate incident position information of the incident radiation 11 thus calculated is supplied to the second position calculator. This allows the second position calculator to calculate the calculated approximate person 1. ), select a group of a predetermined number of photomultiplier tubes surrounding the photomultiplier tube located at position 2), and select a group of photomultiplier tubes of a predetermined number surrounding the photomultiplier tube located at position 2. Calculate more accurate radiation incident position information.

More accurate incident position information calculated in this way is achieved, and RI distribution data within the subject is finally created using this information.

According to this means, it is possible to obtain an RI distribution image in which superimposition of the checkered pattern is suppressed as much as possible.

(Problems to be Solved by the Invention) However, even with the above-mentioned means, there is still room for further improvement. That is, the seven photomultiplier tubes targeted by the second position calculator are shown in FIG. 15, and the symbols A-G are attached to each, and the relationship between the coordinate axes, M, and N is as shown in the figure. do. The problem here is the actual light emission position (radiation incidence position) with respect to the photomultiplier tube.
is far from its center 0 to a certain extent, combined with the fact that the number of photomultiplier tubes used for position calculation is limited, it is not possible to accurately calculate the emission position by simple weighted addition. .

The reason for this will be explained with reference to FIG. In order to simplify the explanation, this figure shows three photomultiplier tubes C, C, and C on the M axis.
Only D and E are shown. Now, assuming that light is emitted at a position P near the left peripheral part of the photomultiplier tube in the center of the diagram, the output values from photomultiplier tubes C and D will be relatively large and almost equal, and - the tip of the sword. The output of the electron multiplier E has a small value compared to the others. As a result, the output of the photomultiplier tube E acts as a noise component, and shifts the calculated light emission position from the actual light emission position to the right in the figure, that is, toward the photomultiplier tube E.

This deterioration of the light emission position calculation accuracy ultimately results in distortion of the RI distribution image.

This invention has been made in view of the above-mentioned problems, and its purpose is to provide a method in which the emission position of incident radiation is located at a position apart from the center position of the photomultiplier tube located at the center position of the selected group. Another object of the present invention is to provide a gamma camera device that can calculate the light receiving position with high precision and thereby obtain an RI distribution image from which distortion has been removed.

[Structure of the Invention (Means for Solving the Problems)] In order to achieve the above object, the present invention has a method of transmitting only radiation in a predetermined direction among the radiation emitted from a radioisotope (RI) administered into a subject. a scintillator that receives the Group 1, 1 line that has passed through the collimator and generates scintillation light with an amount of light proportional to its energy value; and a scintillator that receives the scintillation light from this scintillator and generates an electrical signal that is proportional to the amount of light. A plurality of output photomultiplier tubes, a first position calculator that calculates the approximate incident position of the incident radiation based on each output signal from these photomultiplier tubes, and the first position calculator A group consisting of a predetermined number of photomultiplier tubes surrounding the photomultiplier tube located at the calculated approximate incident position of the incident radiation is selected, and the photomultiplier of the thus selected group is a second position calculator that calculates a more accurate incident position of the incident radiation based on each output of the tube; and a photoelectron whose radiation incident position calculated by the second position calculator is located at the center of the group. If the photomultiplier tube is significantly separated from the center point of the multiplier tube, a means for recalculating the corresponding radiation incident position by excluding the photomultiplier tube emitting noise output, and a method corrected by the recalculation means. R in the subject based on the light emission position signal.
The present invention is characterized in that it comprises means for creating I distribution data.

(Effect) Hougetsu-1, which is produced by RI administered into the subject.
Of the radiation, only the radiation that has passed through the collimator is incident on the scintillator. Here, scintillation light with an amount proportional to the energy value of the incident radiation is generated and supplied to a plurality of photomultiplier tubes. Each of these photomultiplier tubes outputs an electrical signal proportional to the supplied light. The first position calculator calculates the approximate position of incidence of the incident radiation based on the electrical signals. The approximate incident position information of the incident radiation thus calculated is supplied to the second position:1 calculator. As a result, the second position calculator selects a group of a predetermined number of photomultiplier tubes surrounding the photomultiplier tube located at the calculated approximate incident position, and More accurate incidence (orientation information) of the incident radiation is calculated based on the output signal of the photomultiplier tube.

Here, if the radiation incidence position calculated by the second position calculator is located significantly away from the center point of the photomultiplier tube occupying the center of the group, suddenly exclude the photomultiplier tube that emits a noise output. Then, recalculate the incident position of the corresponding Group 1/1 line. Based on the radiation incident position information recalculated in this manner, RI distribution data within the subject is created.

(Embodiment) The configuration of an embodiment of the present invention will be described with reference to FIGS. 1 to 11. In FIG. 1 showing the overall configuration of this embodiment, a detector 12 is provided to detect radiation (gamma rays) emitted from a subject 11 to which RIIO has been administered.

This detector 12 includes a collimator 13 that allows only gamma rays in a predetermined direction to pass through, a scintillator 14 that converts the gamma rays that have passed through this collimator into scintillation light, a light guide 15 that guides the scintillation light generated by this scintillator, and a light guide 15 that guides the scintillation light generated by this scintillator. It is composed of a plurality of photomultiplier tubes 16 that receive scintillation light from a scintillator 14.

Further, as shown in FIG. 2, for example, the plurality of photomultiplier tubes 16 include 61 photomultiplier tubes arranged so as to form a hexagonal light-receiving plane.

Each output terminal of each photomultiplier tube 16 is connected via a preamplifier 17 to a first position calculator 18 for calculating the approximate incident position of incident gamma rays, which will be described in detail later.

The output signals Xo and Yo of the position calculator 18 are also supplied to a second position calculator 19 for calculating a more accurate position of incidence of the incident radiation, which will be described in detail later. At the output side of this second position calculator 19, a recalculator 20 is provided for correcting miscalculations that occur in specific cases, which will be described in detail later.

A collection memory 21 is provided to which the radiation incident position signals Xs, Ys whose miscalculations have been corrected by the recalculator 20 are supplied. This acquisition memory is designated by the X, Y position signals.
For example, when a position signal of Xi, Yl, which is provided with a dimensional memory area and is corrected by the recalculator 20, is given, Xi,
1 is added to the data stored in the memory section designated by Yl. Such an operation is performed each time a correction signal is supplied from the recalculator 20, and after sufficient data collection has been performed, the RI distribution image data within the subject is stored in the collection memory 21. In order to use this RI distribution image data as a display image, a display memory 22 is provided to temporarily transfer the data thereto, and the transferred data is supplied to a display 24 via a D/A converter 23.

As shown in FIG. 3, the first position calculator 18 is composed of a specific coordinate system position calculation circuit 25, a group selection circuit 26, and an absolute coordinate system position calculation circuit 27. The specific coordinate system position calculation circuit 25 calculates, as shown in FIG.
The output signal of the photomultiplier tube 16 having a magnitude greater than a set value for each group is detected and output as a specific coordinate system position signal. The group selection circuit 26 is a circuit that performs selection control of each group in grouping the photomultiplier tubes 16. The absolute coordinate system position calculation circuit 27 calculates the absolute coordinate system position based on the specific coordinate system position signal for each group outputted from the specific coordinate system position calculation circuit 25 and the group selection signal outputted from the group selection circuit 26. Signal Xo.

Calculate and output Yo.

As shown in FIG. 4, the specific coordinate system position calculation circuit 25 has an independent circuit configuration for each group of photomultiplier tubes. Here, the photomultiplier tube 16 has an L axis (Ll, L2°-, Ln), an N axis (Ml,
M2. -, Mn), 3 of the N axis (Nl, N2.-, Nn)
are grouped into. Each group has the same circuit configuration, so to explain only the L-axis group, each output of the photomultiplier tube is connected to the OR circuit 28,
This output terminal is connected to an A/D converter 29. As a result, the A/D converted output signal is outputted as a specific coordinate system position signal by the comparator 30 and encoder 31.

The position calculator 19 of 3fI2 is constructed as shown in FIG. That is, the approximate incident position signal Xo of the incident gamma ray input from the first position calculator 18.

A decoding circuit 32 to which Yo is supplied is provided. This decoding circuit receives the signals Xo and Yo, and
Seven analog switches 33 transmit signals for selecting a group of a total of seven photomultiplier tubes 16 surrounding the photomultiplier tube 16 in a hexagonal shape with the photomultiplier tube 16 present at the center in the center.
supply to. FIG. 2 shows how the photomultiplier tubes 16 are divided into groups. For example, when the photomultiplier tube with serial number 14 is selected by the first position calculator 18, the surrounding serial numbers 7.8, 13°, 14.15
, 21.22 photomultiplier tube groups are selected.

Other items will be selected in the same manner as above. An arithmetic unit 34 is provided which receives each output of the seven analog switches 33, that is, each output of the photomultiplier tube 16 selected by the decoding circuit 32. This calculation unit generates a more accurate gamma ray entry position signal X based on all received signals.

Y is calculated, and the energy value of the incident gamma ray is determined from the total value of all received signals, and when this value is within a set range, it is output as the incident position signals X and Y of the incident gamma ray.

This calculation section 34 is constructed as shown in FIG.

The output signals of each analog switch 33 are connected to the L-axis, M-axis, and N-axis (shifted by 60 degrees from each other) as shown in FIG.
A specific coordinate system position calculation circuit 35 for allocating coordinates is provided. Since this circuit is completely the same as the circuit configuration shown in FIG. 4 already described, the explanation here will be omitted. The respective output signals from this circuit 35 are separately supplied in parallel to a numerator weighting section 36 and a denominator weighting section 37 for position calculation, and then to adders 38 and 39.

A dividing unit 40 is provided which separately performs calculations on the output signals of the adding units 38 and 39 for each coordinate. Each of these parts is operated according to the arithmetic expression shown in FIG. Further, a coordinate conversion unit 41 is provided which calculates a more accurate incident position of the incident gamma ray by receiving the coordinate position signals calculated by the division unit 40 or the coordinate position signals of the M and N axes.

Next, the operation of the embodiment having the above configuration will be explained.

In FIG. 1, a detector 12 detects gamma rays emitted from a subject 11 to which RIIO has been administered. At this time, an electrical signal is output from the output terminal of the photomultiplier tube 16 of the detector 12 according to the incident position of the gamma ray. These output electric signals have a higher signal peak value in the photomultiplier tube 16 located near the gamma ray incident position. The output electrical signals from each of the photomultiplier tubes 16 are amplified by each preamplifier 17 and then supplied to a first position calculator 18 .

In the first position calculator 18, the data is input into a specific coordinate system position calculation circuit 25 shown in FIG. These signals are collected by an OR circuit 28 and converted into digital signals by an A/D converter 29.

These digital signals are sorted by the comparator 30 according to the magnitude of the signal value, and finally outputted by the encoder 31 as specific coordinate system position signals for each group of L-axis, M-axis, and N-axis. The group to which this output signal belongs is identified by a signal from the group selection circuit 26. By supplying this identification signal and the specific coordinate system position signal to the absolute coordinate system position calculation circuit 27,
From this circuit, the absolute coordinate system position signal Xo of the incident gamma ray,
Yo is output.

The signals Xo, Yo output from the first position calculator 18 in this manner are supplied to the second position calculator 19. In this second position calculator, a decoder circuit 32 receives the signals Xo and Yo, and generates a total of seven photomultipliers surrounding the photomultiplier tube located at these coordinate positions Xo and Yo in a hexagonal shape. A group of doubler tubes is selected by operating and controlling each analog switch 33. The entire output of the photomultiplier tube 16 selected in this way is supplied to the calculation section 34.

The output signals supplied to this calculation section are first shifted by 60 degrees from each other by a specific coordinate system position detection circuit 35.
It is divided into three axis coordinates: M and H.

Next, each signal for each coordinate is sent in parallel to the numerator weighting section 36 and the denominator weighting section 37, and then sent to the elimination section 40 via the addition sections 38 and 39. By dividing in this division section, the positions of M and N on each coordinate axis for the input 1 and 1 gamma rays are calculated as shown in Figure 8 (a).
11m as shown in ).

It is calculated as n points. The coordinate transformation unit 41 converts each of those points 1. Perpendicular lines are drawn from m and n, and their intersection C is output as the more accurate incident positions X and Y of the incident gamma rays. If the three perpendicular lines do not intersect correctly as described above, the center of gravity of the triangle formed by the three perpendicular lines can be used instead, as shown in FIG. 8(b). FIG. 9 shows a flowchart of the coordinate converter 41.

The gamma ray incident position signals X, Y calculated by the second position calculator 19 are then sent to a recalculator 20, where t[, which is noise due to an adjacent photomultiplier tube, is checked. That is, this procedure will be explained with reference to FIGS. 10 and 11.

The T510 diagram extracts and shows three photomultiplier tubes C, D, and E arranged along the M axis in the selected block.

On the light-receiving surface of the photomultiplier tube in the center of the figure, the center point is term 4, and the threshold points Ql and Q2 are on the left and right, respectively.
Set. These threshold chain points divide the photomultiplier tube into a region Lo including the center thereof and the surrounding region, and regions Ll and L2 on the left and right outside of this region.

If the calculation result by the second position calculator 19 falls within the Lo region, that is, the vicinity including the center point of the photomultiplier tube,
Since no noise influence from the adjacent photomultiplier tube output is expected, the calculation result is used as is as the gamma ray incident position at that point. On the other hand, the calculation result is Ll
When entering the region, the output of the photomultiplier tube E on the right is received as noise, so the output of this multiplier tube E is cut and the gamma ray incident position is recalculated using only photomultiplier tubes C and D. This is the output signal at this point. Similarly, regarding region L2, in this case, the output of the photomultiplier tube C on the left affects as noise, so the output of this multiplier tube C is cut and recalculated to obtain the output at this point. .

(The flowchart is shown in FIG. 11.) As mentioned above, each data corrected by the recalculator 20 is supplied to the collection memory 21, where it is stored as X and Y two-dimensional RI density distribution data. . Next, this accumulated data is supplied to a display 23 via a display memory 21 and a D/A converter 22, whereby an RI distribution image within the subject 11 is displayed.

Note that this invention is not limited to the above-described embodiments, and design changes can be made as appropriate without changing the gist of the invention. For example, instead of using a first position calculator 18 for calculating the approximate position of incidence of the incident gamma rays, as shown in FIGS. It is also possible to use a resistor matrix that is generally used in the past.

[Effects of the Invention] As described above, according to the gamma camera device of the present invention, when a noise component is expected to have an influence on the calculation result by the position and il-calculator, the noise component is outputted. Since the gamma ray incident position is recalculated by excluding the output of the photomultiplier tube, it is possible to provide an RI distribution image without distortion.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing the arrangement of photomultiplier tubes in the same embodiment, FIG. 3 is a block diagram showing the configuration of the first position calculator in the apparatus shown in FIG. 1, and FIG. 3 is a block diagram showing the configuration of a specific coordinate position detection circuit in the first position calculator, FIG. 5 is a block diagram showing the configuration of the second position calculator in the device shown in FIG. 6 is a block diagram showing the configuration of the calculation section shown in FIG. 5, FIGS. 7 and 8 are diagrams for explaining the operation of the calculation section, respectively, and FIG. 9 is a block diagram showing the configuration of the calculation section shown in FIG. 6. FIG. 1O is a flowchart showing the operation of the recalculator in FIG. 1, FIG. 11 is a flowchart showing the operation procedure of the recalculator, and FIG. The block diagram showing the configuration and FIGS. 13 to 16 are diagrams for explaining the operation of the conventional device, respectively. 12...Detector 16...Photoelectron 1-magnifier 18...First position calculator 19...Second position calculator 2 0...Recalculator 1...Collection memory 22 ...Display memory 3...D/A converter 4...Display device

Claims (2)

[Claims] (1) A collimator that allows only the radiation in a predetermined direction to pass among the radiation emitted from the radioisotope (RI) administered into the subject, and a collimator that receives the radiation that has passed through this collimator and emits a light amount proportional to its energy value. A scintillator that generates scintillation light, a plurality of photomultiplier tubes that receive the scintillation light from this scintillator and output electric signals proportional to the amount of light, and an input signal based on each output signal from these photomultiplier tubes. a first position calculator for calculating the approximate incident position of the radiation; and a predetermined position surrounding the photomultiplier tube located at the approximate incident position of the incident radiation calculated by the first position calculator. a second position calculator that selects a group consisting of a number of photomultiplier tubes and calculates a more accurate incident position of the incident radiation based on each output of the photomultiplier tubes in the thus selected group; and if the radiation incidence position calculated by this second position calculator is significantly separated from the center point of the photomultiplier tube located at the center of the group, the photomultiplier tube emitting noise output is means for excluding and recalculating the corresponding radiation incident position;
and means for creating RI distribution data within the subject based on the light emission position signal corrected by the recalculation means. (2) the recalculation means sets a threshold value for dividing the light-receiving surface of the photomultiplier tube located at the approximate incident position of the incident radiation into a central region and a peripheral region;
If the calculation result by the second position calculator falls within the central area, the calculation result is output as it is as a radiation incident position signal, and if it falls into the peripheral area, the calculation result is output as a radiation incident position signal, and if it falls into the peripheral area, the photoelectron increaser is 2. The gamma camera device according to claim 1, wherein the gamma camera device performs the recalculation excluding the output of the multiplier, and outputs the result of the recalculation as a radiation incident position signal.