JPH0452416B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an adjustment device for a positron CT apparatus.

Positron CT equipment reconstructs the distribution image of RI (radioisotope) of positron-emitting nuclides. In other words, when a positron disappears, it emits two gamma rays in a 180 degree direction.
Therefore, a large number of radiation detectors are arranged in a ring shape, and the direction of the positron is determined by detecting when gamma rays are simultaneously incident on a pair of detectors. The data thus accumulated is then subjected to image reconstruction processing by a computer to obtain an RI distribution image. In order to detect simultaneous incidence in this way, it is necessary to completely match the time delays of the large number of detectors used and the amplifiers and the like that constitute the output signal system of each detector.

In this case, all combinations of two of the large number of detectors must be matched, but conventionally, delay time adjustment has been performed for each of the large number of combinations. However, since the number of combinations is enormous, the problem is that adjustment takes a long time.

In view of the above, an object of the present invention is to provide an adjustment device for a positron CT apparatus that can adjust the time delays of all detectors in a short time.

An embodiment of the present invention will be described below with reference to the drawings. In the figure, a large number of detectors 11, 12, . . . 1n for detecting gamma rays are arranged in a ring shape. These detectors 11,1
Each of 2,... consists of a combination of a scintillator and a photomultiplier tube, and each output is sent to a delay circuit 2.
1, 22, and then sent to group circuits 31, 32, and so on, respectively. The delay circuits 21, 22, . . . are of a type in which the delay time can be varied; they latch a command regarding the delay time from the CPU 80, and the delay time is determined in accordance with the latched command. Group circuits 31, 32
... is a kind of OR circuit, each of which is connected to several adjacent detectors, and the outputs of the group circuits 31, 32... are sent to a coincidence detection circuit (not shown), and the group circuits 31, 32... Co-occurrence of signals is detected between each output of... Several detectors connected to one group circuit can be considered as adjacent detectors arranged almost linearly, and it is impossible for gamma rays to be incident on them at the same time. This is because it is sufficient to detect simultaneous incidence with the detector connected to the detector. Therefore, the coincidence detection circuit first detects which group circuit's output and which group circuit's output occur simultaneously, and after identifying the combination of group circuits, it is possible to identify the combination of group circuits connected to that group circuit. It is arranged to detect which output of the detector is sent through the group circuit.

Each output of the group circuits 31, 32, . The output from the reference detector 60 is sent to the time-to-wave height converter 50 as a stop signal, and an output with a wave height corresponding to the time from the start signal to the stop signal is generated, and this output is used for AD conversion. It is sent to the container 70.

The reference detector 60 is housed within a cylindrical lead shield 61 and detects gamma rays from a reference radiation source 62. As the reference radiation source 62, for example, ⁶⁸ Ga,
Use radioactive isotopes such as ⁶⁸ Ge and ²² Na, which are positron-emitting nuclides of 100μCi or less. The reference detector 60 is composed of detectors 11, 12, etc., which are also a combination of a scintillator and a photomultiplier tube, and the scintillators include a plastic scintillator, NaI,
Any device such as BGO may be used, but in order to improve measurement accuracy, it is preferable to use something that can extract a fast timing signal, such as a plastic scintillator.

This lead shield 61 is attached to the output rotating shaft 64 of the rotary drive device 63, and in this state is placed inside the ring-shaped array of the detectors 11, 12, . . . during adjustment. Then, the rotation shaft 64 is positioned at the center of the ring-shaped arrangement so that the reference radiation source 62 sequentially faces each detector as it rotates. In this case, a lead shield 6 is used to prevent gamma rays from the reference radiation source 62 from entering any detector other than the one intended
1 is necessary for sufficient collimation. The reference detector 60 is then positioned in a direction 180 degrees different from the detector facing the reference radiation source 62. Note that during actual object measurement other than during adjustment, the reference detector 60, rotation drive device 63, etc. are removed, and the object is placed inside the ring-shaped detector arrangement.

In this configuration, first, the reference radiation source 62 is made to face one detector, for example, the detector 11. When two gamma rays are emitted from the reference ray source 62 in a direction of 180 degrees, one of the two gamma rays enters the detector 11 and the other enters the reference detector 60 at the same time. The signal output from the detector 11 is sent to the delay circuit 2.
1 and the group circuit 31 to the switching circuit 40. Since the rotation drive device 63 is controlled by the CPU 80, the reference radiation source 6 is
2 is facing the detector 11.
This is determined by the CPU 80, and under the control of the CPU 80, the switching circuit 40 is switched to the group circuit 31 to which the detector 11 is connected. the result,
The time-to-wave height converter 50 generates an analog voltage value output with a wave height corresponding to the time difference between the output of the reference detector 60 and the output that has passed through the delay circuit 21 of the detector 11 . The AD converter 70 digitizes this analog voltage value so that it can be taken into the CPU 80. In this way, the time difference data is input to the CPU 80 and stored.

Next, the rotary drive device 63 operates and the lead shield 6
1 is rotated and the reference source 62 is moved to the next detector 1.
2, the time difference with respect to the output of the reference detector 60 is similarly measured, and the obtained time difference data is stored in the CPU 80.

In this way, time difference data based on the output generation time of the reference detector 60 is obtained for each of the detectors 11, 12, ... arranged in a ring shape, and each detection is performed based on this time difference data. Vessel 1
The delay circuits 21, 22, . . . are controlled by the CPU 80 so that the time difference between the output generation times of 1, 12, . . . becomes zero. In this way, the delay amount is automatically adjusted using the output generation time of the reference detector 60 as a medium.

Note that the CPU 80 does not automatically adjust the delay amount, but simply prints out the time difference data for each of the detectors 11, 12, etc., and manually adjusts the delay circuits 21, 2 according to this printed value.
2,... may be adjusted, and AD
By connecting a multi-channel analyzer that analyzes the output wave height of the time-to-wave height converter 50 in multiple stages instead of the converter 70 and the CPU 80, the time difference can be measured manually, and the amount of delay can be adjusted manually based on this measurement result. In any case, the reference detector 60
Since the time difference between each detector 11, 12, etc. is measured sequentially, errors do not accumulate and accurate measurements are possible.
1, 12, . . . , which is extremely small compared to the conventional method, and the adjustment time can be greatly reduced.

In the above embodiment, the group circuits 31, 32,...
This method is often used in this type of positron CT device because it can reduce the number of detection combinations for simultaneous incidence.
As in the above embodiment, this group circuit 31, 3
This group circuit 31, 32,
If the outputs of... are connected to the switching circuit 40, the number of wiring lines can be reduced. However, it will be obvious that the present invention can be similarly applied to a positron CT apparatus in which such a group circuit is not used, by directing the outputs of the delay circuits 21, 22, . . . to the switching circuit 40.

As described above with respect to the embodiments, according to the present invention, the time difference between each detector is measured via the reference detector, so the time difference can be measured accurately, and the time difference can be measured according to the measurement result. By adjusting the amount of delay, the time difference between the detectors can be made substantially zero, and since the number of measurements required is only the number of detectors, the adjustment time can be significantly shortened.

[Brief explanation of drawings]

The figure is a block diagram of one embodiment of the present invention. 11, 12,...1n...detector, 21,22...
...Delay circuit, 31, 32...Group circuit, 40
...Switching circuit, 50...Time pulse height converter, 60...
...Reference detector, 61...Lead shield, 62...Reference radiation source, 63...Rotary drive device, 70...AD converter, 80...CPU.

Claims (1)

[Claims] 1 Equipped with a large number of detectors arranged in a ring shape and a delay circuit with a variable delay time that delays the output of each detector, and detects the simultaneous occurrence of each detector output delayed by each delay circuit. In the positron CT device, the data obtained by the above-mentioned detectors is processed for image reconstruction to reconstruct the distribution image of the radioisotope of the positron-emitting nuclide within the object placed inside the ring-shaped array of the above-mentioned detectors. The center of rotation of the radioisotope of the positron-emitting nuclide arranged inside the ring-shaped array of the detector is the center of the ring-shaped array of the detectors, so that the radioisotope faces each of the detectors in turn. a mechanism for rotating the radioisotope such that the radioisotope is substantially aligned with the reference detector; 1. An adjustment device for a positron CT device, comprising a circuit for detecting a time difference between a detector output and the reference detector output.