JPH0552472B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application This invention relates to an ECT device (emission type computerized tomography device), and particularly relates to an ECT device (emission type computerized tomography device), and particularly to a method for measuring the total amount of radioisotope (hereinafter abbreviated as RI) administered to a subject. This invention relates to an ECT device that has been improved to reduce image artifacts caused by temporal fluctuations.

(B) Prior Art In an ECT device, RI is administered to a subject, and radiation emitted from the RI within the subject is detected by a number of detectors placed outside the subject. and,
An image regarding the distribution of RI within the subject is reconstructed by processing data obtained from each detector regarding the number of radiation particles incident on each detector using an image reconstruction algorithm. Usually, the data sampling position or direction (the position of the detector or the direction of incidence of the radiation detected by the detector) is sequentially changed,
For each of them, data sampling operations are performed at fixed time intervals one after another. Therefore, if the time of each sampling period is different and the total amount of RI administered to the subject varies over time,
As a result, artifacts occur in the reconstructed image.

For example, C ¹⁵ O ₂ gas is continuously inhaled by a patient, replaced by H ₂ ¹⁵ O in the lungs, and this amount of H ₂ ¹⁵ O is kept constant in the head while this amount is inhaled around the head. When reconstructing images by detecting radiation from H ₂ ¹⁵ O, if the amount of H ₂ ¹⁵ O in the head fluctuates rapidly due to the patient's breathing style or instability of the gas controller, a ring-shaped arch may appear in the image. The problem of tay act occurring is often experienced. In particular, when positrons are used as radionuclides and the number of sampling positions is increased by mechanical scanning that combines fobbling and rotation, if the amount of H ₂ ¹⁵ O varies greatly at each scanning position, concentric artefacts may occur. act is observed.

This problem can similarly occur in the case of ECT devices that use a single photon as the radionuclide. In this case, data sampling is performed for a fixed period of time by sequentially changing the direction of radiation incidence on each detector, so if there is a change in the total amount of RI between each sampling period, the obtained data will be affected. This is because

(c) Purpose It is an object of the present invention to provide an ECT device that is improved so that artifacts do not occur even if the total amount of RI within the subject changes over time.

(D) Configuration In the ECT device according to the present invention, the total amount of radiation incident on a large number of detectors is counted for each sampling period in which the data sampling position and direction are changed, and the average value of these is calculated. The data obtained in each sampling period is corrected according to the deviation of the total amount for each sampling period from this average value.

(E) Embodiment FIG. 1 shows an embodiment in which the present invention is applied to a positron ECT device. In this figure, a large number of radiation detectors 1, 2,..., n are arranged in a ring shape around a subject 10. The output of each detector is sent to the coincidence circuit 11. For positron, 180°
Since it emits two γ-rays in the same direction, if it is detected that it is incident on two detectors at the same time, it can be determined that a positron exists on the line connecting the two detectors. If the gamma rays from the object 10 in Figure 1 are incident on detectors 1 and k at the same time, it can be seen that the positron is on the straight line connecting detector 1 and k that passes through the center 0. be. Therefore, the coincidence circuit 11 detects coincidence (simultaneous incidence).
By detecting this, it is detected which straight line the positron hit among the many straight lines connecting each detector, and the contents of the data collection memory 12 are added by 1 for each straight line. Count values related to straight lines can be obtained. Each count value is stored in the storage device 14 via the CPU 13, and later, only the count values related to straight lines in the same direction are arranged according to the position of the straight line to obtain projection data in a large number of directions. By back projecting this multidirectional projection data, the original image, that is, object 1
A concentration distribution image of positrons in 0 is reconstructed.

In order to make the sampling points in each projection data denser (increase the points from which each count value constituting one projection data is obtained, that is, the position of the straight line from which the count value is obtained, and narrow the interval between them), Usually, scanning by wobbling (FIG. 2) or scanning by rotation (FIG. 3) is performed. The wobbling scan is shown in Figure 2.
The ring of detectors 1, 2..., n is moved as a whole on a small circumference centered on center 0, and sampling operations are normally performed at each point W1 to W5, which divides this circumference into five equal parts. It is done. That is,
Among the projection data in the direction of the line connecting detectors 1 and k, the data obtained by detectors 1 and k is at point W.
1 to W5 for each of the lines S1 to S5, and the sampling points are increased five times. In addition, as shown in Fig. 3, rotation scanning is performed by moving the rings of detectors 1, 2, ..., n as a whole by θ/2.
(the angle between adjacent detectors is θ), and each detector is positioned between the adjacent detectors before rotation. By performing a sampling operation at this position, data for a new straight line SP can be obtained, for example, as shown in the figure.
The sampling points can be doubled for one projection data. Therefore, by performing such wobbling and rotation in combination, nine new sampling positions can be added within each sampling interval that would otherwise be available.

However, since the sampling operation at each sampling position differs in time, if the total amount of RI in the subject 10 itself is different, projection data such as that shown in FIG. 4A would be obtained if there were no such difference. As a result, projection data as shown in FIG. 4B is obtained. In other words, a data sampling operation is performed at point W1 of the wobbling scan within a certain time at a certain time, a data sampling operation is performed at point W3 for a certain time at a later time, and a data sampling operation for a certain time is performed at point W4 at a later time. When a data sampling operation is performed, if the amount of RI increases rapidly only during the data sampling period at point W4, and then returns to the same as before, then only the data obtained at this point W4 will be used at other points. The result will be larger than the obtained data. Since this is true for all data obtained during the sampling period of point W4, all projection data will be as shown in FIG. 4B. Therefore, if such projection data is used as is to reconstruct an image, a ring-shaped artifact will occur on the radius corresponding to the position (distance from the center 0) of this large data.

Therefore, a counting circuit 15 is provided as shown in FIG. 1, and all of the coincidences detected by the coincidence circuit 11 are counted online (without adding the contents of the memory 12) for each sampling period. Then, the average value of the total count for each sampling period is calculated by the CPU 13, and further,
The deviation of each value of the total count for each sampling period from this average value is determined, and each data obtained during that sampling period is corrected according to this deviation. That is, correction is performed by multiplying each data by a coefficient that eliminates the deviation. As a result, the total number of coincidences in each sampling period corresponds to the total amount of RI at that time. converted into wax data values. That is, when data such as that shown in FIG. 4B is obtained, the data is corrected to data such as that shown in FIG. 4A by the above correction. Therefore, by using the corrected data, an image free of artifacts can be reconstructed.

Note that although the data correction is performed online in the above example, it is also possible to perform the correction processing offline later.

In addition, although the example applied to a positron ECT device has been described above, it is also
The same applies to ECT devices.

(f) Effects According to the present invention, fluctuations in the total amount of RI in the subject are detected, and based on this fluctuation, data affected by this fluctuation is corrected.
It becomes possible to reduce image artifacts caused by fluctuations in the total amount. Therefore, for example, in an examination using C ¹⁵ O ² gas, even if the amount of RI in the body changes due to the patient's breathing or the condition of the gas supply device, ring-shaped artifacts do not occur, allowing stable imaging. Can be executed. Furthermore, since almost real-time processing is possible, there is no problem of extended processing time.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a schematic diagram for explaining fobbling scanning, Fig. 3 is a schematic diagram for explaining rotation scanning, and Fig. 4 A and B are projections. It is a graph showing data. 1 to n... Radiation detector, 10... Subject, 1
1... Coincidence circuit, 12... Data collection memory, 13... CPU, 14... Storage device, 1
5... Counting circuit.

Claims (1)

[Claims] 1. Radiation emitted from a radioactive isotope administered into the subject is made to enter a large number of radiation detectors placed outside the subject, and data on the number of incident radiation detectors during a certain sampling period are collected, and the detection By changing the detection position or direction of radiation by the instrument, the above sampling operation is performed sequentially for a fixed sampling period for each different detection position or direction, and the data obtained by these is used to detect the radioactive isotopes in the subject. In an ECT device that reconstructs an image related to the distribution of An ECT device comprising: means for correcting data obtained in each sampling period according to a deviation in each total number.