JPH0616097B2 - Uniformity correction method for ECT device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting sensitivity unevenness and sensitivity change of a detector of an ECT apparatus (emission type computed tomography apparatus).

2. Description of the Related Art The ECT apparatus creates a concentration distribution image of a radioisotope administered to a patient by an image reconstruction method using a computer, but the detector for detecting radiation such as γ-rays has uneven sensitivity. Can cause non-uniformity in the reconstructed image. For example, in the case of a ring type ECT device in which a rectangular NaI scintillator is used as a detector and a large number of the detectors are arranged in a ring shape, the uniformity of the reconstructed image deteriorates due to the variation in the sensitivity of each detector.

Therefore, it is necessary to obtain the correction coefficient in advance in order to improve the uniformity by compensating for the sensitivity unevenness and sensitivity change of the detector, but in the past, a cylindrical radiation source containing a radioisotope was made beforehand. , Put this in the shooting area,
Data of this cylindrical radiation source is collected, and an image is reconstructed from this data to obtain a correction coefficient.

The problem to be solved by the invention However, if a cylindrical radiation source is used to reconstruct the image as in the conventional case, data must be collected through a collimator, and a correction coefficient with few statistical fluctuations can be obtained. It takes a long time to collect data in order to obtain it.

Since the sensitivity change in each detector occurs over time or due to temperature change, it is necessary to calibrate the correction coefficient frequently, so it may take time to collect the correction data as described above. It's actually a big problem.

In addition, the cylindrical radiation source is troublesome to handle, and it takes a long time to collect the correction data, and there is a concern that radioisotope contamination may spread.

The present invention provides a uniformity correction method for an ECT device that can collect correction data in a short time, can use a point source that is easy to handle, and has little radioisotope contamination. To aim.

According to the uniformity correction method of the ECT apparatus of the present invention, first, the data of the cylindrical radiation source is collected through the collimator to obtain the correction coefficient, and at the same time, the collimator is not used. Collect the data of the point source in the state, and from the next time, collect the data of the point source without going through the collimator,
The correction coefficient is calibrated by comparing the data without the collimator.

It is considered that the variation in working sensitivity depends on the variation in efficiency of the collimator and the variation in detection efficiency of the detector system. Among them, the variation in the efficiency of the collimator occurs during manufacturing, and does not change thereafter with the passage of time or changes in temperature. On the other hand, variations in the detection efficiency of the detector system change with the passage of time and changes in temperature. Therefore, if the variation in the efficiency of the collimator is measured only once at the beginning, it is not necessary to perform the measurement thereafter, and the calibration to be performed regularly or whenever the temperature changes may be performed only on the detector system. Become.

Therefore, it is necessary to collect the data including the collimator only once at the beginning to obtain the correction coefficient including the collimator. At this time, collect the data of only the detector system excluding the collimator. From the second time onward, if data is collected for the detector system with the collimator removed, and the data obtained without this collimator are compared, and the correction coefficient obtained first is corrected, the change over time Alternatively, the correction coefficient initially obtained can be calibrated according to a temperature change or the like.

By doing so, the point source can be used after the second time, and data can be collected in a short time because data is collected with the collimator removed.

Embodiment FIG. 1 schematically shows an example of a ring type ECT device. The ring type ECT device is configured by arranging a large number of detectors 1 in a ring shape as shown in FIG. 1 so that the direction of radiation incident on each detector 1 can be changed by a collimator such as a turbofan collimator 2. Has become. In the case of the turbofan collimator 2, the turbofan collimator 2 is rotated in the directions of a and b so that the incident direction on each detector 1 is changed so as to scan the entire imaging region.

First, the cylindrical radiation source 3 is placed in this imaging region. The cylindrical radiation source 3 is a water tank filled with water containing a radioisotope in a cylindrical container. Then, the turbofan collimator 2 rotates to collect data. In this way, the data for each position of the collimator 2 for each detector 1 is collected. When the number of the detector 1 is set in the horizontal direction and the collimator address indicating the position of the collimator 2 is set in the vertical direction, matrix-shaped data as shown in FIG. 2 is collected. This data is stored in the data collection memory in the ECT device.

When the data of the cylindrical radiation source 3 is collected in this way, assuming that there is no sensitivity variation in the collimator 2 and the detector 1, what kind of data will be obtained can be calculated. it can. Therefore, if this ideal value is compared with the data actually collected as described above, it is necessary to correct the variation in the detector 1 and the collimator 2 that actually exist to achieve the uniformity. It is possible to obtain the matrix distribution of the correction coefficients Ai, j as shown in FIG.

Immediately after this, as shown in FIG. 3, the turbofan collimator 2 is removed and the point source 4 is placed instead of the cylindrical source 3. The point source 4 is a radioisotope sealed in a small container and is easy to handle. Then, data is collected in this state. Then, data is obtained for each of the detectors 1 and, as shown in FIG. 4, a one-dimensional distribution of the data Bi that is one-dimensionally distributed in the address direction of the detector 1 is obtained. This data Bi
Represents the variation in the sensitivity of the system of the detector 1. That is,
The variation of the detection efficiency of the turbofan collimator 2 is Cj
Then, the correction coefficient Ai, j has a relationship between Bi and Cj. That is, it can be expressed as Ai, j = f (Bi, Cj).

The second correction data collection is performed at an appropriate time after a certain period of time has passed or a temperature change has occurred.
This is done by using a point radiation source 4 as shown in FIG.
The data Bi showing the variation in the sensitivity of the system of the detector 1 is collected. Here, if the obtained data Bi is Bi + ΔBi due to the influence of a change over time or a temperature change, according to the change of Bi → Bi + ΔBi, Ai, j + ΔAi, j = f (Bi + ΔBi, Cj) after calibration The correction coefficient Ai, j + ΔAi, j can be obtained. Specifically, for example, the correction coefficient can be calibrated by calculating Ai, j + ΔAi, j = Ai, j × {(Bi + ΔBi).

In this way, after the second time, the data can be collected with the collimator 2 removed, so that the data can be collected with high sensitivity, and the data collection can be completed in an extremely short time of about 1 to 2 minutes. Further, since the point radiation source 4 can be used, it is easy to handle, and it is possible to prevent radioisotope contamination and reduce the exposure dose.

EFFECTS OF THE INVENTION According to the present invention, it is possible to collect data for correction from the second time onward in an extremely short time, and it is possible to perform it as part of the daily performance inspection work of the apparatus. Moreover, there is less concern about radioisotope contamination, and the dose of radiation can be reduced.

[Brief description of drawings]

1 and 3 are schematic diagrams for explaining one embodiment of the present invention, FIG. 2 is a data distribution diagram obtained in FIG. 1,
FIG. 4 is a data distribution chart obtained in FIG. 1 ... Detector 2 ... Turbofan collimator 3 ... Cylindrical radiation source 4 ... Point radiation source

Claims (1)

[Claims] 1. The first time, data of a cylindrical radiation source is collected through a collimator to obtain a correction coefficient, and at this time, a point radiation source is used in place of the cylindrical radiation source and no collimator is used. Data is also collected, data is collected from the second time using a point radiation source without passing through the collimator, and the data in the state without the first collimator and the data after the second time are collected. A uniformity correction method for an ECT apparatus, characterized in that the correction coefficient is calibrated by comparing with data obtained without a collimator.