JPS63153049A - X-ray ct 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 [Field of Application of the Invention] The present invention relates to an XmCT equipment, and particularly to an X-ray detector suitable for obtaining good images.

[Background of the invention]

FIG. 2 shows a block diagram of the main parts of the scanning system of the CT apparatus.

An X-ray irradiation slit 2 that makes the X-ray beam emitted from the X-ray tube 1 into a fan-shaped beam. Both the X-ray detector 3 and the rotary plate 4
It constitutes a scanning mechanism for rotating and scanning around the subject 5 to obtain X-ray attenuation data and reconstructing a CT image using a computer. Inside the detector 3, a large number of radiation detection elements 6 are arranged as shown by broken lines.

The X-ray detector 3 houses a phosphor element and a photoelectric conversion element, and its structure is shown in FIG.

The phosphor element 11 generates visible fluorescence when irradiated with X1s. When the photoelectric conversion element 12 is coupled in contact with this, the fluorescence is converted into an electrical signal, and the lead, 11113.1
4 and then output. Inside the detector 3, a large number (500 to 600) of such X-ray detection elements are housed.

The phosphor element 11 is made by solidifying phosphor powder with a binder, and a light guide is sandwiched between this and the photoelectric conversion element 12. Fluorescent elements are subject to variations in manufacturing conditions (variations in composition, non-uniformity of components).

Due to non-uniform cut dimensions, non-uniform cut surface conditions, etc.), it is difficult to achieve uniform properties.

Figure 4 (A) shows how the non-uniformity of characteristics is expressed.
The radiation detection element shown in FIG. 4(B) is the phosphor element 11 described above. It has a shape in which a transparent material called a light guide 15 is sandwiched between photoelectric conversion elements 12. The light guide 15 allows only visible light to pass through, causing the rise and fall of xm. In addition to working as a filter, it also works to diffuse the light from the phosphor element 11 and make its characteristics uniform.

The graph in FIG. 4(A) is an example of the local sensitivity distribution on the detection element as a function of position.

This can be obtained by measuring the output of the photoelectric conversion element 12 when the phosphor element 11 is irradiated with a narrow X-ray beam of constant intensity.

The shape of the graph will be similar to a trapezoid. The near-horizontal part in the center indicates that the sensitivity is uniformly distributed, and the slope toward the left and right edges indicates that the sensitivity is decreasing, where the phosphor still exists. The reason why the sensitivity has already decreased is that there is a loss in the amount of light reflected at the ends of the phosphor element 11 and the ends of the light guide 15. In addition, the amount of loss tends to vary from element to element.6 For CT detector elements, uniformity of the sensitivity distribution is extremely important. The required uniformity is 1% or less of the average value near the peak in FIG. 4(A). The allowable range is schematically shown in FIG. 4(A) as a hatched band-shaped region.

The solid-state X-ray detection element of the present invention has higher xm utilization efficiency than conventionally used gas ionization chamber detectors,
Therefore, it has been found that unless the requirement for uniformity of the sensitivity distribution is made even higher than in the past, ring-shaped artifacts (false images) will occur in CT images.

As a result, the hatching bandwidth shown in Fig. 4 becomes narrower, and due to variations in the manufacturing conditions of the elements, the sensitivity distribution curve becomes 5th.
As some examples are shown in Figures (a), (b), (c), and (d), they take on a variety of shapes, making it difficult to control them so that they are uniform.

[Purpose of the invention]

An object of the present invention is to improve the uniformity of the sensitivity distribution of an XM detection element and to improve the image quality of a CT apparatus using this x#I detection element.

[Summary of the invention]

As mentioned above, the uniformity of the sensitivity distribution of the X-ray detection element depends on the uniformity of the phosphor element and the uniformity of the photoconduction path until the fluorescence reaches the photoelectric conversion element. Regarding the latter, in the present invention, This is intended to improve uniformity by not using a sensitivity-decreasing portion near the end of the phosphor element, where uniformity is likely to be impaired.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a sectional view of the detector, showing a portion corresponding to 3°6 in FIG. 2(B), and 21 is the detector case.

22 is a cross section of a circuit board that supports the X-ray detection element 23, and the structure of the detection element 23 is as shown in FIG.

The upper part of the detector case 21 forms a part of the detector case, and also contains a material with high density (e.g. lead, tungsten, etc.)
two thick members 24 are arranged at intervals,
Only the XM that enters this gap (slit) 25 enters the detection element 23.

However, at this time, it is assumed that the Xi beam indicated by 26 is narrowed down by the Xa irradiation slit 2 over a wider range than the width of the slit 25.

At this time, since the length of the phosphor cord 11 is greater than the width of the slit 25, the X-rays are incident only on the part 28 directly below the slit, which is close to the end where the sensitivity decreases in Fig. 4. Portion 27 is not used because xi is blocked.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to easily suppress variations in the sensitivity distribution that tend to occur between detection elements to 1% or less, so that a CT apparatus with good image quality can be realized.

[Brief explanation of the drawing]

Figure 1 is a sectional view of the xm detector, Figure 2 is an explanatory diagram of the main parts of the CT scanning device, and Figure 3 is the Xi! Figure 4 is a perspective view showing the structure of the detector. Figure 4 is a diagram showing the sensitivity distribution and structure of the X-ray detector. Figure 5 is a diagram showing the sensitivity distribution and structure of the X-ray detector.
The figure is a diagram illustrating an example of variations in sensitivity distribution curves. 1...X-ray tube, 2...xi irradiation slit, 3...
Detector, 4... Rotating plate, 5... Subject, 6... X
Line detection element, 11... Fluorescent element, 12... Photoelectric conversion element, 13° 14... Electrode, 15... Light guide,
21...Detector cover, 22...Circuit board, 23.
...XM detection element, 24...Detector side slit shielding material.

Claims (1)

[Claims] 1. An X-ray source and an X-ray detector are arranged facing each other, an X-ray irradiation slit is provided between them, and a detector is provided on the entrance surface of the X-ray detector to limit the width of the X-ray entrance aperture. An X-ray CT device that obtains a tomographic image of the subject from the measured X-ray absorption rate by rotating and scanning the subject placed in the X-ray beam from the X-ray source from multiple directions. In, the above X
The detector slit opening width in the direction orthogonal to the tomographic plane scanned by the ray beam is configured to be smaller than the sensitive width in the same direction of the X-ray detection element constituting the X-ray detector. X-ray CT device.