JPH0511056A - Ect apparatus - Google Patents

Abstract

PURPOSE:To achieve the absorbing correction for the approximation of the outer shape of a body to be detected, the improvement of the quantitative property of an image and the shortening of processing time by obtaining a correcting based on the similar circle of the profile, which is obtained from the sinogram of the intended cross section of the body to be tested, and making the correction coefficient act on each profile data. CONSTITUTION:The image data from a rotating gun camera 1 are collected with a data collecting device 12 and stored into an image memory 4 through a CPU 3. A sinogram of the intended cross section of a body to be detected, which is formed by sinogram forming device 5 is used, and a circle similar to profile is obtained. A correcting coefficient is computed with a correcting-coefficient computing device 6 based on the circle. Absorbing correction for all profile data constituting the sinogram is performed with a correcting device 7 by using the correcting coefficient. The data after the absorbing correction are processed with an image reconstituting device 8, and the reconstituted image is displayed on a display device 9. Since not the profile itself but the circle similar to the profile is obtained based on the sinogram. much time is not required for processing, the excessive correction is not performed and the quantitative property of the image can be enhanced by the adequate absorbing correction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ECT (emission computer tomography) apparatus of a type in which a gamma camera is rotated or a type in which radiation detectors are arranged in a ring shape.

[0002]

2. Description of the Related Art An ECT apparatus obtains a concentration distribution of radioactive substances accumulated in a subject (patient's body) as a tomographic image. Radiation radiated around the subject (γ-ray)
Is detected by a radiation detector outside the subject to obtain profile data in each direction (view) for a desired cross section and processed by an algorithm such as backprojection,
An image of the cross section, that is, a concentration distribution image of the radioactive substance in the cross section is reconstructed.

In order to detect radiation and obtain profile data for each view, a gamma camera is rotated around the subject, or radiation detectors are arranged in a ring around the subject. ..

In such an ECT apparatus, when radiation is emitted from a radioactive substance inside a subject and is emitted to the outside, it is absorbed by the tissue inside the subject, so it is necessary to correct this. Conventionally, this absorption correction is based on the assumption that the head is a cylinder with a diameter of 20 cm when the subject is a head in a ring-type ECT device, and the radiation passes through the cylinder and is emitted to the outside. The profile data of each view is weighted according to the passing distance, and the decrease due to the absorption is compensated.

In addition, such absorption correction is not usually performed in the ECT device by the rotation of the gamma camera.

[0006]

However, if absorption correction is not performed, a problem arises in the quantitativeness of the obtained image. Also, when performing absorption correction assuming that the subject is a cylinder with a constant diameter, when the external shape of the actual fault plane is smaller than that, such as when the fault plane is near the top of the head, Correction is performed on the reconstructed image, resulting in a high count as if a large amount of radioactive material is accumulated on the crown of the reconstructed image.

It is conceivable that the contour of the subject is obtained from the sinogram and absorption correction is performed accordingly, without assuming that the subject is a cylinder having a constant diameter, but it is very difficult to obtain the contour from the sinogram. It is time consuming and not practical.

In view of the above, the present invention makes it possible to improve the quantitativeness of an image, because the processing does not take time, and the absorption correction corresponding to the outer shape of the desired cross section of the subject can be performed.
An object is to provide an ECT device.

[0009]

In order to achieve the above object, in the ECT apparatus according to the present invention, a circle approximate to the contour is obtained from a sinogram in a desired cross section of the subject, and a correction coefficient is calculated from this circle, It is characterized in that the correction coefficient is applied to each profile data forming the sinogram to correct the profile data, and then the image reconstruction processing is performed. Since the contour itself is not calculated from the sinogram, but a circle that is close to the contour is calculated and the correction coefficient is calculated from this circle and correction is performed, processing does not take time. Further, since the circle is close to the actual contour of the desired cross section of the subject, no inconvenience due to excessive correction will occur. Therefore, the quantitativeness of the image can be improved by appropriate absorption correction.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. This embodiment is applied to an ECT device of a type in which a gamma camera is rotated. As shown in FIG. 1, image data from the gamma camera 1 is collected by a data collecting device 2 and stored in an image memory 4 via a CPU 3. Store. The gamma camera 1 is rotated around the head of the subject 10 as shown in FIG. 2, and angular directions (views) # 1, # 2, ..., #m, #n ,.
The image data from each of the above is obtained as shown in FIG. 3, and these are stored in the image memory 4 together with the angle information.

Here, when a tomographic image is to be reconstructed at a cross section corresponding to the i-th line in these image data, the sinogram creation device 5 uses the data arranged on this i-th line as the image data of each view. Come out of. The data arranged in each line extracted for each view is profile data, and by arranging the profile data in the order of views, a sinogram as shown in FIG. 4 is created.

Next, all the data (count numbers) forming the sinogram thus created are added to obtain the average count number. An appropriate threshold value is determined based on this average value. Then, as shown in FIG. 5, the profile data for each view is compared with this threshold value to obtain the distance r of the portion corresponding to the contour. Since this distance r is obtained for each profile of each view, for example, the maximum value is searched from among the many distances r. The maximum distance r is treated as the diameter of a circle that approximates the contour of the head of the subject 10 in the cross section. Therefore, as shown in FIG. 6, the distance across the approximate circle P is projected in one direction to obtain the correction coefficient Q. The calculation for obtaining the correction coefficient Q is performed by the correction coefficient calculation circuit 6.

This correction coefficient is used in the correction device 7 to perform absorption correction of the profile data of each view. In this correction device 7, first, by approximating the sinogram of FIG. 4 (the locus of the center point of each profile data thereof) by a sine function, the center of the head in the above cross section with respect to the rotation center axis of the gamma camera 1 is calculated. Find the position. Each profile data is multiplied by the correction coefficient so that the center of the head thus obtained coincides with the center of the correction coefficient. In this way, the correction device 7 performs absorption correction on all profile data forming the sinogram.

The profile data after this absorption correction is
The tomographic image in the cross section corresponding to the i-th line is reconstructed by being processed by the image reconstructing device 8. The reconstructed image is displayed by the display device 9.

Although the above embodiment is applied to the ECT device of the type in which the gamma camera is rotated, it is also applicable to the ECT device of the type in which the radiation detectors are arranged in the ring type. In that case, since profile data of a desired cross section is directly collected to create a sinogram, it is sufficient to perform an operation of obtaining an average value of all data forming the sinogram, and the structure can be simplified. Further, in the above, the sinogram creation, the correction coefficient calculation, and the correction processing are configured to be performed by dedicated hardware, but the CPU 3 may be configured to perform the processing by software.

[0016]

As described in the above embodiments, according to the ECT apparatus of the present invention, absorption correction can be performed by approximating the actual contour of the subject under a desired cross section, and the quantitativeness of the image is enhanced. At the same time, since the contour of the outer shape of the subject itself is not obtained, the processing does not take time.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the movement of the gamma camera of the embodiment with respect to the subject.

FIG. 3 is a diagram showing an image obtained in each view.

FIG. 4 is a diagram showing a sinogram.

FIG. 5 is a diagram showing profile data.

FIG. 6 is a diagram for explaining obtaining a correction coefficient from an approximate circle.

[Explanation of symbols]

 1 gamma camera 2 data acquisition device 3 CPU 4 image memory 5 sinogram creation device 6 correction coefficient calculation device 7 correction device 8 image reconstruction device 9 display device 10 subject

Claims (1)

Claim: What is claimed is: 1. A means for obtaining a circle that approximates a contour from a sinogram of a desired cross section of a subject, and calculating a correction coefficient from this circle, and the correction data for each profile data forming the sinogram. E is provided with a correction unit for performing correction on the image data and an image reconstruction unit for performing image reconstruction processing using the corrected profile data.
CT device.