JPH0640129B2 - Ring type ECT device correction method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for correcting the sensitivity of an ECT device (emission CT device) in which detectors are arranged in a ring shape.

2. Description of the Related Art There are four known methods for correcting the sensitivity of a conventional ring-type positron ECT device, as shown in FIGS. Both of them serve as a reference in the ring-shaped array of the detector 1.
A radiation source such as ⁶⁸ Ge- ⁶⁸ Ga is arranged, data is collected, correction data is created from this data, and it is applied to the measurement data when an actual subject is measured to correct the sensitivity. However, as a reference radiation source for collecting the correction data, the ring radiation source 4 is used in FIG. 3A and the ring radiation source 4 is used in FIG.
In FIG. 3C, the rod-shaped radiation source 5 is used, and in FIG.
In FIG. D, the cylindrical phantom 7 is used. In the case of FIGS. 3A and 3D, data is collected from each detector 1 with the ring-shaped radiation source 4 and the cylindrical phantom 7 kept stationary. On the other hand, in the case of FIG. 3B, the rod-shaped radiation source 5 is rotated at a constant radius to collect data. In the case of FIG. 3C, the flat-plate radiation source 6 is rotated intermittently, and the distribution data of the simultaneous counting in the direction perpendicular to the plane of the flat-plate radiation source 6 is obtained for each angle. collect.

Problems to be Solved by the Invention A fundamental problem with these conventional correction methods is that the sensitivity at the center of the visual field and the sensitivity at the peripheral portion of the visual field are different.
For example, in the case of FIGS. 3A and 3B, data representative of the sensitivity in the peripheral portion of the visual field can be obtained, but data representative of the sensitivity in the central portion cannot be obtained. Conversely, FIG. 3C
In the case of 1, the data representative of the sensitivity of the central portion can be obtained, but the data representative of the sensitivity of the peripheral portion cannot be obtained.

On the other hand, in the case of FIG. 3D, the most accurate data can be collected which is representative of the sensitivities of both the central part and the peripheral part of the visual field, but another problem occurs. That is, radiation absorption occurs in the columnar phantom 7 itself, and this absorption is large and is affected by the scattering coincidence count, so that the collected data loses accuracy. In addition, if the diameter of the cylindrical phantom 7 is 20 cm or more, the weight becomes very heavy and it is difficult to set it easily. Therefore, the measurement for collecting the correction data is simplified. There is the inconvenience of not being able to do it.

The present invention can collect data representative of both the sensitivity in the central part of the visual field and the sensitivity in the peripheral part, and can obtain accurate correction data without being affected by absorption and scattering, and is easy to handle. Therefore, it is an object of the present invention to provide a correction method for a ring-type ECT device that can easily perform measurement for collecting correction data.

Means for Solving the Problems A correction method for a ring-type ECT device according to the present invention is to continuously rotate a plate-shaped radiation source in a ring-shaped arrangement of detectors, and to change the rotation angle during the continuous rotation. It is characterized in that data is collected regardless of the data, correction data is created from this data, and this correction data is applied to the actual measurement data of the subject to correct the sensitivity.

Function Since the flat-plate radiation source is continuously rotated and data is collected during the continuous rotation regardless of the rotation angle, it is possible to collect data on the radiation source equivalent to the cylindrical phantom. Moreover, since it is actually a flat plate-shaped radiation source, it hardly absorbs or scatters itself unlike a cylindrical phantom. Therefore, while obtaining the same data as the data collected using the cylindrical phantom, the problem of absorption and scattering when using the cylindrical phantom can be avoided, and highly accurate data can be obtained.

Make correction data from the data collected in this way,
If sensitivity is corrected, it can be corrected accurately at the center of the field of view and at the periphery.

Embodiment FIG. 1A is a schematic view from the front when carrying out a correction method of a ring type positron ECT apparatus according to an embodiment of the present invention, and FIG. 1B is a side sectional view. As shown in these drawings, a flat plate-shaped radiation source 2 is inserted into the center of a ring-shaped array of a detector 1 of a ring-type positron ECT device, and this is continuously rotated by a driving device such as a motor 3. The plate-shaped radiation source 2 is composed of a very thin plate-shaped container made of a resin such as acryl and containing a positron-emitting nuclide such as ⁶⁸ Ge- ⁶⁸ Ga. Then, during this continuous rotation, data is collected for a certain period of time. That is, regardless of the rotation angle of the flat-plate radiation source 2, all coincidence count data obtained during a certain time during the rotation are collected.

In this way, when the plate-shaped radiation source 2 is continuously rotating, it is not seen instantaneously, but when viewed from the entire time of continuous rotation, a circle with a solid interior as shown in FIG. 2A. It can be virtualized as a columnar phantom 2 '. Therefore, similar to the cylindrical phantom 7 of FIG. 3D, data representative of the sensitivity of the central portion of the visual field and data representative of the sensitivity of the peripheral portion can be obtained.

However, since the plate-shaped radiation source 2 rotates to form the virtual cylindrical phantom 2 ', the cylindrical phantom 7
It is necessary to treat it differently from. That is, since the plate-shaped radiation source 2 rotates to form the virtual columnar phantom 2 ', it has a geometrical property that the density is high at the central portion but becomes lower toward the peripheral portion. It has to be corrected. Therefore, when the coincidence count data in a certain direction is collected from the collected data and its distribution is taken, since it has a sharp peak in the central portion as shown in FIG. 2B, geometric correction is added to this. Then, it is converted into the distribution data as shown in FIG. 2C.

The distribution data shown in FIG. 2C is the data affected by the sensitivity fluctuation, so the reciprocal of this data is obtained,
By multiplying it by each projection data obtained by the actual measurement of the subject, it is possible to perform the sensitivity correction by eliminating the influence of the sensitivity variation included in the actual measurement data of the subject. That is, the reciprocal of the distribution data in FIG. 2C is the correction data.

The sensitivity correction data is created from data collected by rotating the flat plate radiation source 2. Since the flat plate radiation source 2 itself is thin and has a short radiation transmission path, the data is absorbed or scattered by itself. Is much less likely to occur. Therefore, it is possible to avoid the problem of absorption and scattering, which is a problem when using the cylindrical phantom, and it is possible to obtain highly accurate correction data.

Although the ring-type positron ECT device using a positron-emitting nuclide as the radioisotope has been described above, it can be applied to sensitivity correction of a single photon ECT device using a single-photon emitting nuclide.

EFFECTS OF THE INVENTION According to the correction method of the ring type ECT device according to the present invention, the plate-shaped radiation source is continuously rotated to virtually form a cylindrical phantom with very small absorption and scattering of the radiation source itself. Therefore, highly accurate sensitivity correction data can be obtained. Further, since it is only necessary to continuously rotate the plate-shaped radiation source, the weight is light, the handling is easy, and the correction data can be easily collected.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1A is a schematic view from the front, FIG. 1B is a sectional view from the side, and FIG.
FIG. A is a schematic diagram showing a state in which a plate-shaped radiation source is continuously rotated to form a virtual cylindrical phantom, FIG. 2B is a diagram showing projection data in one direction, and FIG. 2C is a geometrical diagram. FIGS. 3A, 3B, 3C, 3D and 3D are schematic diagrams from the front showing the conventional example, respectively. DESCRIPTION OF SYMBOLS 1 ... Detector, 2 ... Plate-shaped radiation source 2 '... Virtual cylindrical phantom, 3 ... Motor 4 ... Ring-shaped radiation source, 5 ... Rod-shaped radiation source 6 ... Plate-shaped radiation source, 7 ... Cylindrical phantom

Claims (1)

[Claims] 1. A flat line source is continuously rotated in a ring-shaped array of detectors, data is collected regardless of the rotation angle during the continuous rotation, and correction data is created from this data. A method for correcting a ring type ECT device, characterized in that the correction data is applied to actual measurement data of an object to correct the sensitivity.