JPH02242189A - Gumma camera apparatus - Google Patents

Abstract

PURPOSE:To make the tone of an image uniform by detecting scintillation light which is generated in a scintillator with a photomultiplier which is divided into a plurality of groups, and computing the incident position of radiation. CONSTITUTION:An electric signal is outputted from the output terminal of a photomultiplier 16 of a detector 12 in correspondence with the incident position of a gumma ray. The signal is converted into a digital signal in an A/D converter 30. The signals are divided in a comparator 31 based on the magnitudes of the signal values. The signals are outputted as the position signals for the specified coordinates for every group comprising an X axis and a Y axis at the final stage in an encoder 32. To which group the output signal belongs is distinguished based on the signal from a group selecting circuit 27. When the distinguished signal and the position signals of specified coordinates are supplied into an absolute-coordinate-position computing circuit 28, the absolute- coordinate-position signals X and Y of the incident gamma ray are outputted from said circuit. Thus, the position coordinates of a plurality of incident radiations which are inputted at the same time can be computed accurately, and the density of an image can be made uniform.

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 suitable for high count rate RI diagnosis.

(Prior Art) Figure 6 shows the internal structure of a scintillation camera. In the figure, 1 is a scintillator that emits scintillation light when radiation (gamma rays) emitted from a subject to which a radioisotope has been administered is incident, and 2 is optically coupled to scintillator 1 and converts the scintillation light into an electrical signal. It consists of multiple photomultiplier tubes. The scintillator 1 and photomultiplier tube 2 described above constitute a detector 9 together with a collimator, a light guide, etc. (not shown). The output signal from the detector 9 passes through each preamplifier 3 and is then supplied to the X, Y position calculation circuit 4, where the position information of the scintillation light is calculated. That is, the position calculation circuit 4 is constituted by a weighting circuit using a resistance matrix, for example, and obtains information of X+, 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 pulse height value information is calculated. Based on the calculated position information and wave height information, the display system 8 displays an RI distribution image within the subject.

(Problem to be Solved by the Invention) The incident time interval of gamma rays emitted from the subject's body and incident on the detector 9 is determined by the incident time interval t (seconds), where the average incident rate is γ (count 7 seconds). probability density function f
(t) is as shown in the following equation.

f (t)-γ·e-'rt That is, since f (t) takes the maximum value when it is 1-0, the probability that gamma rays will be incident is highest when the incident time interval t is O. Further, as the average incidence rate γ increases, the probability density function f(1) becomes a sharper function.

In this way, especially when the average incidence rate is high, the probability that a plurality of gamma rays will be incident on the scintillator 1 at the same time increases. In this case, the position of incidence of these incident gamma rays on the scintillator 1 is calculated as the center position, that is, the middle of the plurality of positions of incidence, since the weighting using the resistance matrix is calculated by the position calculation circuit 4 composed of a circuit. It was getting worse. In other words, it was calculated incorrectly. Such miscalculations occur most often in the center of the detector 9, so in the case of RI diagnosis with a high count rate, the center of the detector becomes a profile that rises, resulting in uneven image density. was there.

This invention was made in view of the above-mentioned problems, and its purpose is to avoid miscalculation even when multiple radiations are incident on the detector at the same time, and to adjust the positions of each of the multiple simultaneously incident radiations. It is an object of the present invention to provide a gamma camera device that can accurately calculate coordinates and thereby make image density uniform even in the case of RI diagnosis with a high count rate.

[Structure of the Invention (Means for Solving the Problems)] In order to achieve the above object, the present invention is directed to a system that uses only radiation in a predetermined direction among the radiation emitted from a radioisotope (RI) administered into a subject. A collimator that allows radiation to pass through, a scintillator that receives radiation that has passed through this collimator and generates scintillation light with an amount of light proportional to the physical quantity of the radiation, and a scintillator that receives the scintillation light generated by this scintillator and generates an electrical signal that is proportional to the amount of light. A plurality of output photomultiplier tubes and these photomultiplier tubes are divided into a plurality of groups, a specific coordinate position signal is calculated for each of these groups, and based on each of these specific coordinate position signals, the A position calculator that calculates the position signal of incident radiation, and energy discrimination based on the summed signal of output electric signals from the plurality of photomultiplier tubes, and outputs an unblank signal only when radiation in a desired energy range is incident. and means for creating an RI distribution image within the subject based on an unblank signal from the energy discriminator and an absolute coordinate system position signal from the position calculator. It is something to do.

(Function) 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, scintillation light with an amount proportional to the physical amount of incident radiation is generated and supplied to a plurality of photomultiplier tubes. These photomultiplier tubes are divided into a plurality of groups, and each group outputs an electric signal corresponding to the incident radiation, that is, a specific coordinate position signal. A position calculator calculates a position signal of the incident radiation in an absolute coordinate system based on these signals. On the other hand, the energy discriminator compares the sum of the outputs of the plurality of photomultiplier tubes with a set reference value, and outputs an unblank signal only when the conditions are satisfied, that is, when the radiation has the desired energy. An Rr distribution image within the subject is created based on the absolute coordinate system position signal and unblank signal obtained in this way.

As described above, according to the device of this invention, the scintillation light generated by the scintillator is detected by the photomultiplier tubes divided into multiple groups, and the incident position of the radiation is calculated, so even if multiple radiation It is possible to accurately calculate the position coordinates of multiple simultaneous incident radiations without causing miscalculations even if they are incident at the same time.
Therefore, even in the case of RI diagnosis with a high count rate, the image density can be made uniform.

(Embodiment) The configuration of an embodiment of the present invention will be described with reference to FIGS. 1 to 4. 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.

For example, as shown in FIG. 2, these plural photomultiplier tubes 16 are arranged such that 61 photomultiplier tubes form a hexagonal light-receiving plane. Although the details will be described later, when collecting output signals, for example, the X axis (Xi, X2,
−, Xn) and the Y axis (Yl.

Y2. ..., Yn).

Each output terminal of each photomultiplier tube 16 is connected via a preamplifier 17 to a position calculator 19, which will be described in detail later.

In addition, each output terminal of each preamplifier 17 is connected to an adder 2.
0 and is configured to supply this summed output signal to the pulse height analyzer 21. This pulse height analyzer compares the supplied added output signal with a set reference value and outputs an unblank signal UNB only when the added output signal value exceeds the set reference value.

A collection memory 22 is provided to which the final output from the position calculator 19, the X, Y position signal in absolute coordinates, and the unblank signal UNB from the wave height analyzer 21 are supplied.

This collection memory has an X, Y two-dimensional memory area of the absolute coordinate system, and when the position calculator 19 gives the Xi, Y1 position signals, and the wave height analyzer 21 supplies the UNB signal, the memory becomes XIYI. 1 is added to the data stored in the section. Such an operation is performed every time the output is supplied from the position calculator 19 and the wave height analyzer 21, and after collecting sufficient data, the data is stored in the collection memory 22.
RI distribution image data within the subject is stored. This R.I.
In order to supply the distribution image data as a display image, a display memory 23 is provided, data is once transferred thereto, and the transferred data is supplied to a display 25 via a D/A converter 24.

As shown in FIG. 3, the position calculator 19 is composed of a specific coordinate position detection circuit 26, a group selection circuit 27, and an absolute coordinate system position calculation circuit 28. Specific coordinate position detection circuit 2
6 detects the output signal of the photomultiplier tubes 16 having a magnitude greater than a set value for each group with respect to the photomultiplier tubes 16 grouped on the X axis and Y axis as shown in FIG. It is output as a specific coordinate position signal. The group selection circuit 27 is a circuit that performs selection control of each group in grouping the photomultiplier tubes 16. The absolute coordinate system position calculation circuit 28 calculates an absolute coordinate system position signal based on the specific coordinate position signal for each group outputted from the specific coordinate position detection circuit 26 and the group selection signal outputted from the group selection circuit 27. Calculate and output.

As shown in FIG. 4, the specific coordinate position detection circuit 26 has an independent circuit configuration for each group.

Both groups have the same circuit configuration, so to explain only the X-axis group, each output of the photomultiplier tube is connected to the OR circuit 29, and this output terminal is connected to the A/D converter 30.
Connect to. As a result, the A/D converted output signal is outputted as a specific coordinate position signal by the comparator 31 and encoder 32.

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 electric signals from each photomultiplier tube 16 are amplified by each preamplifier 17 and then supplied to a position calculator 19.

In the position calculator 19, the data is taken into a specific coordinate position detection circuit 26 shown in FIG. These signals are collected by OR circuit 29 and converted into digital signals by A/D converter 30. These digital signals are sent to comparator 3
1, and are finally outputted by the encoder 32 as specific coordinate position signals for each group of X-axis and Y-axis. The group to which this output signal belongs is identified by a signal from the group selection circuit 27. This identification signal and the specific coordinate position signal are supplied to the absolute coordinate system position calculation circuit 28, so that the absolute coordinate position signal X of the incident gamma ray is transmitted from this circuit.
, Y are output.

-4, the output signals from each preamplifier 17 are added by an adder 20 and supplied to a pulse height analyzer 21.

This pulse height analyzer receives the added value signal and outputs an unblank signal UNB when this value is higher than the set reference value.

The absolute coordinate position signals X, Y from the position calculator 19 and the UNB signal from the wave height analyzer 21 are supplied to a collection memory 22, and one count data is added to the memory data at the memory position designated by X, Y.

By repeating this operation, the collection memory 2
2, RI distribution data within the subject is collected and stored. This collected data is temporarily transferred to the display memory 23, and the D/A
After converting into an analog signal with the converter 24, the display 25
An RI distribution image within the subject is displayed.

According to the device having the above configuration, it is not only possible to calculate the incident positions of radiation (gamma rays) that are incident one by one at time intervals, but also to divide the photomultiplier tubes 16 into a plurality of groups and Since the output signal is processed, it is also possible to calculate the incident position of each of a plurality of gamma rays incident at the same time.

Furthermore, 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, the grouping of photomultiplier tubes is shown on the L axis (LL, L2.=
-, Ln), M-axis (ML, N2.---, Mn), and N-axis (Nl, N2°--., Nn).

Furthermore, in the embodiment shown in FIG. 1, the energy discrimination of incident gamma rays is performed in an analog manner by the adder 20 and the pulse height analyzer 21, but by using the digital signal in the position calculator 19, It is also possible to implement it digitally. Furthermore, the added outputs of the photomultiplier tubes do not necessarily have to be the entire outputs, and a countable part of the outputs is sufficient.

[Effects of the Invention] As described above, according to the gamma camera device of the present invention, scintillation light generated by a scintillator is detected by photomultiplier tubes divided into a plurality of groups, and the incident position of radiation is calculated. Therefore, even if multiple radiations are incident at the same time, there will be no miscalculations.
It is possible to accurately calculate the positional coordinates of each of a plurality of simultaneously incident radiations, thereby making it possible to make the image density uniform even in the case of RI diagnosis with a high count rate.

[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 mode of grouping of photomultiplier tubes in the same embodiment, FIG. 3 is a block diagram showing the configuration of the position calculator in the device shown in FIG. 1, and FIG. FIG. 5 is an explanatory diagram showing the mode of grouping of photomultiplier tubes in another embodiment of the present invention, and FIG. FIG. 2 is a block diagram showing the configuration of a conventional device. 12...detector, 16...photomultiplier tube. 19...Position calculator, 20...Adder. 21... Wave height analyzer, 22... Collection memory. 23...Display memory, 24...D/A converter. 25...Display device, 26...Specific coordinate position detection circuit. 27...Group selection circuit. 28...Absolute coordinate system position calculation circuit agent Patent attorney Noriyuki Kensuke Patent attorney Takeshi Kondo

Claims (3)

[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 scintillation of the amount of light proportional to the physical quantity of the radiation that has passed through this collimator. A scintillator that generates light, a plurality of photomultiplier tubes that receive the scintillation light generated by the scintillator and output an electric signal proportional to the amount of light, and these photomultiplier tubes are divided into a plurality of groups, a position calculator that calculates a specific coordinate position signal for each of these groups and calculates a position signal of incident radiation in an absolute coordinate system based on each of these specific coordinate position signals; and outputs from the plurality of photomultiplier tubes. An energy discriminator that performs energy discrimination based on the summed signal of electrical signals and outputs an unblank signal only when radiation in a desired energy range is incident, and an unblank signal from this energy discriminator and an absolute A gamma camera device comprising means for creating an RI distribution image within the subject based on a coordinate system position signal. (2) The gamma camera device according to claim 1, wherein the photomultiplier tubes in the position calculator are divided into two groups. (3) The gamma camera device according to claim 1, wherein the photomultiplier tubes in the position calculator are divided into three groups.