JPS5977836A - Computer tomographic apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Rotate-Rotate computed tomography apparatus.

As schematically shown in FIG. 1, the Rotate-Rotate computed tomography apparatus uses a radiation source 1, such as an X-ray tube, and a radiation detector array 2, such as a combination of a scintillator and a photomultiplier, as an object. The radiation beam irradiated from the radiation source 1 spreads in a fan shape, passes through the subject 3, and enters each radiation detector in the radiation detector row 2. The radiation source 1 and the radiation detector row 2 are rotated together around the rotation center axis 4 in the subject 3, and information regarding the transmitted radiation intensity is collected from each radiation detector, and this information is convolved and packed. Processing is performed using an image reconstruction algorithm such as froshection, and the two-dimensional distribution of radiation absorption rate in the tomographic plane of the subject 3 is reconstructed as a tomographic image.

By the way, conventionally, as shown in the first factor, the distance between the detectors in the central part of the radiation detector row 2 is finely set (this distance is d) to form the high-density part 5, and the distance in the peripheral part is narrowed. 2d to form the low-density portion 6 (see, for example, Japanese Patent Laid-Open No. 161039/1983).

This is because by increasing the resolution of the image of the subject 3 toward the center, a high-resolution image of the patient's head and spinal cord can be obtained with good cost performance.

Furthermore, in each case where the rotational position of the radiation source 1 and the radiation detector array 2 is 00° and 180°, the second
As shown in the figure, the radiation detector row 2 is shifted by d/4 with respect to the rotation center axis 4 so that the sampling points in the high-density area 5 are located exactly in the middle of each other. 1q ■ Attempt to cancel streaking artifacts that appear from the ends of bones in the composition image.

However, in the past, since the detector spacing ratio between the high-density part 5 and the low-density part 6 is an even ratio such as 1:2, the sampling point in the low-density part 6 is equal to the rotation angle of Oe'.
At a rotation angle of 80 degrees, as shown in FIG. 2, there is a relationship that is not intermediate between them, and as a result, the above-mentioned artifacts that appear in the reconstructed image are unavoidable.

An object of the present invention is to provide a computed tomography apparatus that improves image quality by reducing artifacts such as those described in "-".

According to this invention, the detector spacing ratio between the high-density part and the low-density part of the radiation detector row is set to an odd ratio, and the position of the radiation detector row is set to the high-density Ir! By shifting the distance by a distance equal to 1/4 of the detector spacing in the L section multiplied by the above-mentioned number of tones, even in the low-density section, the sampling points can be set in the middle of each other at a rotation angle of 00' and a rotation angle of 180'. It is characterized in that it is set to 1 so that

An embodiment of the present invention will be described below with reference to the drawings. In the WS3 diagram, in the high-density part 5 of the radiation detector row 2, the radiation detectors are arranged finely at intervals of d, and in the low-density part 6, the radiation detectors are arranged coarsely at intervals of 3d, which is an odd number times, in this example, 3 times as large. ing. The position of this radiation detector array 2 is shifted from the rotation center axis 4 by a distance three times d/4.

Therefore, as shown in FIG. 4, when the rotation angle between the radiation source 1 and the radiation detector array 2 is 00° and 180°, the sampling points are different from each other in both the high-density area 5 and the low-density area 6. It is exactly in the middle position. Therefore, image artifacts and other moiré (interference patterns) are reduced in both the high-density area 5 and the low-density area 6.

In the above embodiment, the arrangement interval ratio of the radiation detectors 1411a in the radiation detector row 2 was set to 1:3;
The ratio is not limited to this, and may be set to 1:5, for example.

As described in Embodiment 1-1, according to the present invention, the sampling point in each case where the rotation angle between the radiation source and the radiation detector array is 0° and 180° is at any point in the radiation detector array. Since the parts are located exactly in the middle of each other, artifacts and moiré from the bone ends that appear in the reconstructed image are reduced, and the image quality is improved. Therefore, if the resolution of the central part of the image is to be maintained at the same level, the total number of radiation detectors in the radiation detector array can be reduced, contributing to cost reduction; If they are the same, the resolution of the central part of the image can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional example, FIG. 2 is a schematic diagram for explaining the sampling points in FIG. 1, FIG. 3 is a schematic diagram of an embodiment of the present invention, and FIG. FIG. 3 is a schematic diagram for explaining sampling points. l...Radiation source 2...Radiation detector row 3...Subject 4...Rotation center axis

Claims (1)

[Claims] (1) A radiation source and a row of radiation detectors are arranged facing each other with the subject in between, and the radiation beam emitted from the radiation source spreads in a fan shape and passes through the subject, and each row of radiation detectors detects a single line. In this state, ff1
The radiation source and the radiation detector row are rotated around the subject at j, information about the intensity of transmitted radiation is collected from each radiation detector, this information is processed for image reconstruction, and the tomographic plane of the subject is The two-dimensional radiation absorption rate in 41
In a computed tomography apparatus that reconstructs a tomographic image as a tomographic image, a high-density area in which radiation detectors are arranged at fine intervals is provided in the center of the radiation detector row, and a coarse area that is a common number times the said interval is provided in the peripheral area. A low-density part is provided in which radiation detectors are arranged at intervals, and the position of the radiation detector array is set at a distance equal to the odd number times 1/4 of the distance between the radiation detectors in the high-density part with respect to the rotation center axis. A computerized tomography apparatus characterized by being shifted.