JPH0619436B2 - Positron CT system - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a positron CT apparatus that captures an RI distribution image in a subject using a positron-emitting radionuclide as RI (radioisotope).

[Prior art]

In the positron CT device, 180 when the positron disappears
The data is collected based on the detection by the coincidence counting circuit that two gamma rays emitted in the .degree. Direction are simultaneously incident on the two radiation detection records. However, since the time delay of the signal in the signal channel from each radiation detector to the coincidence counting circuit is different in each channel, the delay time in each channel is adjusted so that the timing to reach the coincidence counting circuit is matched. There is a need. In the past, this timing adjustment was usually done manually.

[Problems to be Solved by the Invention]

However, manually adjusting the timing in this way requires a great deal of time and labor, and
There is a problem that it is practically difficult to raise the accuracy to a certain degree or higher. Therefore, conventionally, the time width of simultaneous counting (time window) has to be widened to some extent to measure. When the time window is widened in this way to perform coincidence counting, the ratio of random coincidence counting increases, and the room of the reconstructed image deteriorates, and
There is a problem that other performances such as count rate characteristics are also deteriorated. An object of the present invention is to provide a positron CT device capable of automatically performing highly accurate timing adjustment.

[Means for Solving the Problems]

In order to achieve the above object, the positron C according to the present invention
In the T apparatus, a large number of radiation detecting means arranged in a ring shape, a delay adjusting means capable of externally controlling a delay amount of a radiation incident timing signal from each of the detecting means, and each of the delay adjusting means The coincidence counting means to which the timing signal is input, the means for measuring the sensitivity of each detecting means by the output data from the coincidence counting means when a predetermined radiation source is placed, and the delay amount set in the delay adjusting means are described. Means for detecting a delay amount for obtaining the maximum sensitivity from the respective sensitivities measured when the delay amount is changed and setting the delay amount in various delay adjusting means are provided.

[Work]

A predetermined radiation source such as a correction radiation source is placed, and radiation from this is made incident on each of a large number of radiation detection means arranged in a ring shape, and each timing signal is input to the coincidence counting means via the delay adjustment means. . Then, the delay amount set in the delay adjusting means is changed, and the sensitivity is measured from the output data of the coincidence counting means in each case. When the amount of delay changes, the sensitivity also changes, and the delay amount with the highest sensitivity can be detected from the distribution of sensitivity with respect to the delay amount. Therefore, the delay amount having the highest sensitivity thus obtained is set in each delay adjusting means. Then, the delay time of the signal in each channel is corrected, and the radiation is simultaneously incident on each detection means. Therefore, if there is, the timing signals input to the coincidence counting means are secured with high accuracy. To be done.

【Example】

Next, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, a scintillator 1 and a photomultiplier tube 2 optically coupled to the scintillator 1 form a radiation detector, and the radiation detectors are arranged in multiple rings.
Photomultiplier tube 2 according to radiation incident on scintillator 1
The signal output from is input to the timing signal generation circuit 3, and a signal representing the radiation incidence timing is generated. This timing signal is sent to the coincidence counting circuit 5 after its delay amount is adjusted through the delay adjusting circuit 4. Such a signal system is provided for each channel of a large number of radiation detectors, and the respective timing signals are input to the coincidence counting circuit 5 after adjusting the delay amount. In a normal photographing operation, the coincidence counting output from the operation counting circuit 5 is sent to the CPU 6 to be counted for each channel combination, and the data thus collected is sent to the image reconstructing device 7 for image reconstruction. It The resulting image is displayed as a tomographic image on the display device 8. In this embodiment, the CPU 6 performs the following sensitivity measurement and delay amount detection / setting operations in addition to the above-mentioned operations. That is, this operation is performed when an appropriate radiation source such as a correction radiation source is placed in the ring-shaped array of radiation detectors.
As shown in FIG. 2, the CPU 6 first controls the delay adjustment circuit 4 so that the delay amount is minimized. In this state, the CPU 6 counts the output of the coincidence counting circuit 5 and measures the sensitivity for each channel. After that, the delay amount is slightly increased, sensitivity measurement is similarly performed, and this is repeated until the delay amount becomes maximum. It is desirable to carry out such a measurement one by one or several detectors. When the delay amount reaches the maximum, the delay amount that gives the highest sensitivity is detected for each channel. That is, the distribution of the sensitivity (count) with respect to the delay amount is obtained as shown in FIG. 3, and the delay amount having the maximum sensitivity is obtained from such a graph. In this way, the maximum sensitivity is obtained for each channel, and each delay amount is written and set in each delay adjustment circuit 4. Then, the timing adjustment in each channel is automatically performed with high precision, and an image with excellent image quality can be obtained when performing normal shooting as described above. It is desirable to make such timing adjustments periodically according to the secular change of the feed time on each channel, and at the time of the periodic adjustment, the optimum delay amount for each channel is set as described above. If it can be obtained, it is made into a file and saved in the storage device of the CPU 6, and when the power of the positron CT device is turned off, turned on again, and started up, it is read from the storage device and written again in each delay adjustment circuit 4. It is preferable to do so. Further, here, the CPU 6 measures the sensitivity, detects the delay amount,
Although it is assumed that the setting operation is performed, it is of course possible to configure the dedicated hardware. The algorithm is not limited to the above even when a computer is used. It is also possible to adopt a configuration that can be used together with manual adjustment.

【The invention's effect】

According to the positron CT apparatus of the present invention, it is possible to automatically and extremely accurately adjust the timing of each channel. Therefore, the time and labor required for manual adjustment can be significantly reduced. In addition, because the timing can be adjusted with high precision in this way,
It is also possible to improve the sensitivity. Further, since the time window of the coincidence counting circuit can be narrowed, the image quality of the reconstructed image can be improved by reducing the random coincidence counting, and at the same time, other performances such as the counting rate characteristic can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a flow chart showing an operation procedure in the CPU of FIG. 1, and FIG.
The figure is a graph showing the distribution of sensitivity with respect to the delay amount. 1 ... Scintillator, 2 ... Photomultiplier tube, 3 ... Timing signal generation circuit, 4 ... Delay adjustment circuit, 5 ... Simultaneous counting circuit, 6 ... CPU, 7 ... Image reconstruction device, 8 ...
... display device.

Claims (1)

[Claims] 1. A large number of radiation detecting means arranged in a ring shape, a delay adjusting means capable of externally controlling a delay amount of a radiation incident timing signal from each of the detecting means, and each of the delay adjusting means. The coincidence counting means to which the timing signal is input, the means for measuring the sensitivity of each detecting means by the output data from the coincidence counting means when a predetermined radiation source is placed, and the delay amount set in the delay adjusting means are described. A positron CT apparatus, comprising means for detecting a delay amount for obtaining the maximum sensitivity from the respective sensitivities measured when changed and setting the delay amount in each delay adjusting means.