JP2550540B2 - Positron ECT device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a positron ECT apparatus which administers a positron-emitting radioisotope into the body of a subject, collects coincidence counting data of radiation emitted from the body, and processes the data to compute an image.

[Prior art]

In the positron ECT apparatus, the coincidence circuit detects that radiation is simultaneously incident on two detectors and detection signals are simultaneously generated from the two detectors, and collects coincidence count data (count) for each combination of detectors. The signal processing time is a dead time and is not counted even if the next radiation enters. Therefore, as the count rate increases, the number of radiations that are overlapped and incident within the processing time relatively increases, and counting due to dead time increases. Therefore, this dead time correction has been conventionally performed. The conventional dead time correction is performed after the data collection is completed as follows. FIG. 2 shows a cross section of the head of the subject who collects data, and it is assumed that the change in the count data for the region A in this cross section is as shown in FIG. At this time, when the time from the start to the end is divided into n times, it is assumed that the count data in each time division is f1, f2, ..., Fn. At the end of the data collection, the data obtained by adding all of these, f1 + f2 + ... fn, is obtained, so this is multiplied by the correction count C and the calculation of C {f1 + f2 + ... fn} ... (1) is performed. The dead time is corrected. By the way, originally, the dead time correction coefficients c1, c2, ..., Cn corresponding to the count rate in each time segment are obtained, and these are multiplied by the data for each time segment to obtain f1 · c1 + f2 · c2 +… fn · Correct dead time can be corrected by calculating cn (2). Therefore, it is necessary to obtain the value of C such that C {f1 + f2 + ... fn} = f1.c1 + f2.c2 + ... fn.cn and perform the dead time correction of the above equation (1).

[Problems to be Solved by the Invention]

However, since the value of C differs depending on the area, it cannot be commonly used for all areas of the screen. For the sake of clarity, consider two regions, R and L, as shown in FIG. 4, and assume that the change in the count data in each region is as shown in FIG. There are 3 time divisions and 2 in order in the R area.
Count data of 0, 30, and 100 are obtained, and in the region of L, 50, 5
Suppose that it was constant at 0 and 50. In this case, both R and L are 150 after the data collection is completed and all the data are added. Therefore, in the conventional correction of the formula (1), the data of R and L are equal even after the correction, no matter what value of the correction coefficient C is used. On the other hand, when the dead time is corrected by the equation (2), the dead time correction coefficient in each time segment is 1.1, 1.2,
If it is 2.0, R: 20 × 1.1 + 30 × 1.2 + 100 × 2.0 = 258 L: 50 × 1.1 + 50 × 1.2 + 50 × 2.0 = 215, which is the correct data after correction, and different values for regions R and L. Becomes Therefore, if the correction is performed by the formula (1) as in the conventional case, the correct correction cannot be performed unless the correction coefficient C is calculated for each of all the areas in the entire screen.
However, it must be said that it is actually impossible to obtain the correction coefficient C for all areas in this way. After all,
Correct correction results cannot be obtained by performing dead time correction after the end of data collection as in the past. An object of the present invention is to provide a positron ECT device capable of accurately performing dead time correction.

[Means for solving problems]

In the positron ECT device according to the present invention, a large number of radiation detectors arranged in a ring shape, a coincidence circuit that detects that a detection signal is simultaneously generated for each combination of two detectors, and a coin coincidence circuit A buffer memory that receives the output and collects the coincidence count data for each combination of detectors for each unit time, and the coincidence count data for each combination of the detectors that is read from the buffer memory for each unit time, A dead time correction circuit that corrects by applying a dead time correction coefficient corresponding to the count rate for each unit time, and the simultaneous count data for each detector combination corrected for each unit time for each detector combination A data acquisition memory for summing and a plane on which the ring array of detectors that process the collected data are located. It is the distinctive feature that takes and an image reconstruction device for reconstructing a tomographic image.

[Action]

A buffer memory is provided to collect coincidence count data for each combination of detectors for each unit time. Then, the dead-time correction circuit causes the dead-time correction count corresponding to the count rate for each unit time to act on the coincidence count data for each combination of detectors read out from the buffer memory for each unit time. The dead time is corrected by. Therefore, the dead time correction according to the equation (2) is performed on the coincidence count data for each detector combination. In this way, the coincidence count data for each combination of detectors is collected in the data collection memory while the dead time is corrected in real time for each unit time. Since the dead time correction is performed on the coincidence counting data for each combination of the detectors, more accurate correction can be performed.

【Example】

In FIG. 1, a large number of radiation detectors 11 are arranged in a ring shape around a subject 10 to form a detector system 1. The radiation detector 11 is composed of, for example, a combination of a scintillator and a photomultiplier tube. Subject 11
A positron-releasing radioisotope of the species is administered into the body, and when the positron disappears, it emits two γ rays in the 180 ° direction. The two γ-rays are respectively incident on and detected by different detectors 11, and the detection signals thereof are simultaneously sent to the coincidence circuit 2 and simultaneously counted. The coincidence circuit 2 outputs a coincidence counting signal for a combination of the two detectors 11 when the detection signals are simultaneously input from the two detectors 11. Therefore, the coincidence counting signal is output for each combination of the detectors 11. There are a considerable number of combinations of the detectors 11. The coincidence counting signal is temporarily stored in the buffer memory 3 for each combination. After accumulating the unit time, the coincidence count data for each combination of the detectors 11 is read from the buffer memory 3. The addressing memory 5 generates addressing signals corresponding to each of the detector 11 combinations.
In the data collection memory 6, the coincidence count data for each combination of the detectors 11 read out from the buffer memory 3 every unit time is added every unit time at the address designated by this address designation signal. Here, the data collection memory 6 is
Obtaining coincidence count data (count of coincidence count signals) for each combination of detectors 11 means obtaining a count for each position signal. That is, the fact that the detection signals were simultaneously generated from a certain two detectors 11 means that the positron disappeared on the line connecting the two detectors 11. The line connecting the two detectors 11 is for each combination of a large number of detectors 11 arranged in a ring shape, and they indicate the position of the positron. Therefore, a count can be obtained for each position signal of the positron. In the buffer memory 3, data (count of simultaneous counting signals) for each unit time is collected for each position signal of the positron. A correction coefficient is applied to the output of the buffer memory 3 corresponding to the count rate per unit time output from the dead time correction circuit 4. That is, in the dead time correction circuit 4, the dead time correction count corresponding to the count rate in the unit time is obtained, and this correction coefficient is multiplied by the data collected every unit time. This is performed in real time for each unit time, and after correction, each data is collected at the corresponding address of the data collection memory 6 and added, so the calculation of the above formula (2) is performed for each position signal. It will be. Although the data collected in the data collection memory 6 has been subjected to dead time correction, this data is sent to the image reconstruction device 7 and processed according to an image reconstruction algorithm such as the back projection method. Be seen. That is, the data (count) is projected on the line determined by the position signal. As a result, the detector of the subject 10
A tomographic image in the plane where the 11 ring-shaped arrays are located is reconstructed. This tomographic image is displayed on the display device 8.

【The invention's effect】

According to the positron ECT device of the present invention, the dead time correction is performed by correcting the coincidence count data for each combination of detectors in real time with the correction count corresponding to the count rate of the unit time. More accurate dead time correction can be performed without being affected by the difference in the count rate depending on the position on the tomographic plane and the temporal change in the count rate at each position.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIGS. 2 to 5 are for explaining the inconvenience of the conventional dead time correction, and FIGS. 2 and 4 are tomographic images. , FIG. 3 and FIG. 5 are graphs showing the time change of the count data. 1 ... Detector system, 2 ... Coincidence circuit, 3 ... Buffer memory, 4 ... Dead time correction circuit, 5 ... Addressing memory, 6 ... Data collection memory, 7 ...
Image reconstruction device, 8 ... Display device, 10 ... Subject, 11 ... Detector.

Claims (1)

(57) [Claims] 1. A large number of radiation detectors arranged in a ring shape, and a coincidence circuit for detecting that a detection signal is simultaneously generated for each combination of two detectors.
An output of the coincidence circuit is input, and a buffer memory that collects coincidence counting data for each combination of detectors for each unit time, and a coincidence counting data for each combination of detectors that is read from the buffer memory for each unit time On the other hand, a dead time correction circuit that applies and corrects a dead time correction coefficient corresponding to the count rate for each unit time, and the simultaneous coefficient data for each combination of detectors that is corrected for each unit time is detected by the detector. A data collection memory that adds the data for each combination, and an image reconstruction device that processes the collected data and reconstructs a tomographic image on a plane in which the ring-shaped array of the detectors is located. Positron ECT device.