JPS5814072A - Simultaneous counting circuit of positron lateral tomogram device - Google Patents

Abstract

PURPOSE:To reduce the number of signal combinations to detect simultaneous counting by making logic sum of a plurality of detectors across more than two detection layers and using the sum as input signal for a simultaneous counting circuit. CONSTITUTION:Detectors 11-13 are positioned at respective layers of an annularly arranged three-layer detector at the same position on their circumferences. Outputs of i-th detectors 20A-20C and outputs of j-th detectors 20D- 20F are respectively logically processed by OR circuits 40A and 40B and applied to a corresponding simultaneous counting circuit 30. Accordingly the number of signal combinations to detect simultaneous counting is smaller by one in comparison with the five combinations in the case in which each layer and each detector layer are separated to be independent of other each layer of the three- layer detector. If, in the same way, the number of combinations of detection signals after logical processing through the OR circuit is determined, the constitution with simultaneous counting circuits of a suitable small number becomes sinultaneous counting circuits of a positron tomogram device that have counting rate characteristic practically satisfactory.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a positron transverse tomography device, particularly a device for depicting the biodistribution of a plurality of positron-emitting nuclides as images. FIG. 1 is a schematic diagram of the configuration of a positron transverse tomography device. In the figure, 1 is for detection (scintillator)
, 2 is a photomultiplier tube, 3 is a storage part for electronic circuits such as a preamplifier, 4 is a subject, 5 is a coincidence circuit, 6 is a data acquisition circuit, 7 is a data processing device, and 8 is an image display It is a device.

With this device, if we detect the lag that occurs when positrons emitted from positron-emitting nuclides within the subject are annihilated by combining with electrons in the substance near the emission position 9,
It can be seen that the positron-emitting nucleus was present on the straight line 10 connecting the detectors. The coincidence circuit 5 is used to confirm that two annihilation gamma rays have been detected simultaneously.

In FIG. 1, a scintillator for detecting gamma rays, such as a sodium oxide crystal, is used as the detector 1. The annihilation gamma rays generated by the annihilation of positrons are converted into scintillation (light) by the detector 1, and this scintillation light is transmitted to the photomultiplier tube 2 at a known time interval (for example, 10 nS).
) are detected by an AND circuit, and information representing the combination of detectors that generated these two signals (for example, a bug is detected in circuit 6, and a count value is recorded in the memory corresponding to the pair of detectors). After data collection is completed, the data processing device 7 performs image reconstruction and displays the result on the image display device 8.The data processing device 7 and the image display device 8
This is the same as that used in X-ray transverse tomography devices that are currently widely used in clinical examinations.

Up to now, single-layer devices with a single fault plane have been manufactured as positron transverse fault devices;
Recently, multi-section devices that can simultaneously collect data on multiple transverse sections have been proposed and manufactured. FIG. 2 shows the sample layer of the detection section of this multi-section positron transverse tomography device. In this configuration example, the results of coincidence detection by multi-layered detector-detector pairs are also used to reconstruct and display images of tomographic planes located between adjacent detector layers.

Generally, the same circuit as the coincidence circuit in the detector layer can be used for coincidence counting between the detector layers. For example, the signal generated within the subject 4 in FIG. 2 is shown in FIG. 3 as an example of a coincidence circuit configuration based on the above concept. 11, 1
2 and 13 are No. 1 shown in FIG. Second. A third detector layer is shown, and 21-26 indicate detectors. The symbol (i-n) within each detector indicates the detector number. We assume that the number of detectors in one detector layer is
In the figure, only one of them is shown and the others are omitted.

The coincidence circuits 31, 33, 35 are the first . Second. Third
The coincidence circuit 32 corresponds to the detector pair in the detector layer of
, 34 have the same circuit configuration as the number circuit 32, 34 has the same circuit configuration as the coincidence circuit 31, etc.

The configuration example of the coincidence circuit shown in FIG. 3 shows the basic concept of creating combinations of input signals. It is assumed that one coincidence circuit is provided for every combination of detectors that take coincidence counts.

At this time, when the output of the AND circuit in the coincidence circuit occurs, it means that two input signals are generated at the same time.
The identification signal of the coincidence circuit (for example, a method commonly used in detection path technology as shown in FIG. 3) may be applied to the data acquisition circuit, and a description thereof will be omitted.

Now, in the configuration example of the coincidence circuit shown in FIG. 3, since the coincidence circuits within each detector layer and between each detector layer are separated and independent, it is possible to easily deal with increases and decreases in the number of detector layers.
It is also convenient for circuit maintenance work. Further, the counting rate at the input of each coincidence counting circuit is equal to the counting rate of each detector, and therefore is suppressed to a relatively low value, and there are few omissions in coincidence counting, and good counting rate characteristics can be expected. However, if a large number of coincidence circuits are installed, there is a method of reducing the combination of signals for detecting coincidence, especially by handling them all together. However, in order to cope with the increase in the number of coincidence circuits installed due to stratification, the structure was constructed with an appropriate number of coincidence circuits, and the outputs of multiple detectors were logically summed. By using at least one input signal as the input signal, the number of combinations of signals for detecting coincidence can be reduced. Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 4 is a configuration diagram of the coincidence counting circuit of the present invention when the detector layer is three layers. In this example, the outputs of the detectors with the same number in each detector layer (detectors located at the same position on the circumference when the detectors are arranged in a ring) are combined using an OR circuit and collectively It is characterized by the fact that it is handled as such. Fourth
In the figure, the inputs to the OR circuits 20A to 40B are j at each layer.
These are the outputs of the first detectors 20B, 20D, and 20F.

When the counting rate at the output of the detector is assumed to be equal and is set to n, the inputs of the coincidence circuit each have a counting rate of 3n. (both are n). Therefore, the fourth
Although not shown in the embodiment shown in the figure, the output signals of each detector layer are input to the OR circuits 40A and 40B, and are also input to the encoder at the same time, and the identification signal of the detector combination, which is the output signal of the coincidence circuit, is input to the OR circuits 40A and 40B. , a detector layer or a detection dense layer combination clock counting circuit is installed. Therefore, in the case of the detector layer 3r@, since there are two layers between the detector layers, the number of coincidence circuits is V7 compared to the configuration shown in FIG. The structural feature of FIG. 5 is that one of them is υ, and the other is the logical sum of the detector outputs of two adjacent detector layers.

Let's be specific. Detectors belonging to the first detector layer 11 (
The output of number 1) 20A is directly input to the coincidence counting circuit 30A. Furthermore, the output of the detector (number j) 20B in the first detector layer 11 and the output of the detector (number j) 20G in the second detector layer 12 are logically summed by an OR circuit 40C, and then are simultaneously output. It is input to the counting circuit 30A. As a result, the coincidence of the detector pair tj can be detected in the first detector layer 11, and the coincidence circuit 30B processes the pair. The coincidence circuit 30C processes kl detector pairs.

The input counting rate with this configuration is n and 2n when the output counting rate of one detector is n. Therefore, compared to the configuration shown in FIG. 3, the number of coincidence counts is 2.5 times greater. In this way, although a coincidence circuit is not provided between the detector layers, relatively good count rate characteristics can be expected, and this embodiment has wider applicability than the embodiment shown in FIG. In this embodiment, it is sufficient to output the signal of layer 2 (signal of detector number j).

In the above description, a method is generally adopted in which the output of the detector is handled directly or as multiple signals. To apply the present invention in this manner,

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the overall configuration of the positron transverse tomography device.
FIG. 2 is a block diagram of a detector system, FIG. 8 is a diagram of a conventional coincidence circuit, FIG. 4 is a diagram of an embodiment of the coincidence circuit of the present invention, and FIG. 5 is another embodiment. H, 12, 13--detector layer, 30.3OA, 30B
, 30C...coincidence circuit, 40A, 40B,
40C, 40D...OR circuit. Patent applicant: National Institute of Radiological Sciences, Science and Technology Agency, Intangible J
L, Fig. 1 3 Fig. 2

Claims (1)

[Claims] 1. In a coincidence circuit that has multiple detector layers and detects the coincidence of annihilation gamma rays by detector pairs within a detector layer and between adjacent detector layers, the detector layer belongs to two or more detector layers. Coincidence counting 3 of a positron transverse tomography device in which at least one input signal is a logical sum signal of outputs of a detector or a group of detectors, and a signal of an output of a detector or a group of detectors belonging to one detector layer and this Detector layer and this detector