JPS6338438A - X-ray ct apparatus - Google Patents

Abstract

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

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is directed to
The present invention relates to an X-ray CT apparatus having a scattered ray detector that detects X-rays other than X-rays.

(Prior Art) As a conventional X-ray CT apparatus, one having a configuration as shown in FIGS. 6 and 7 is known. FIG. 6 shows a front view, and FIG. 7 shows a side view, in which an X-ray main detector 4 consisting of a plurality of channels is arranged opposite to the X-ray tube 1, and
A scattered radiation detector 7 consisting of a single channel is disposed adjacent to at least one side of the main detector 4 in the length direction (rotational direction) Z. Both the main detector 4 and the scattered radiation detector 7 are constituted by scintillation detectors including, for example, a scintillator and a photodiode.

A 19 meter 2° object 3 is placed between the X-ray tube 1 and the main detector 4, and the X-ray tube 1. Collimator 2゜Main detector 4
and the scattered radiation detector 7 work together to scan the subject 2 by exposing it to X-rays while rotating around the subject 2 with the center @IIX as the rotation axis. .

X-rays emitted from the X-ray tube 1 and controlled by the collimator 2 into a beam having a desired slice thickness W and fan angle θ pass through the subject 3 and enter the main detector 4 or the scattered ray detector 7 . Here, the main detector 4 detects only the X-rays (main line) that have linearly passed through the subject 3 from the X-ray tube 1, and performs image Q processing based on the detected X-ray absorption coefficient data. is desirable.

However, in reality, the X-rays incident on the main detector 4 include, in addition to the above-mentioned main rays, those that have been scattered within the subject 3 and those that have arrived without passing through the subject 3 at all (hereinafter, these (referred to as scattered rays) are also included. Therefore, in order to perform accurate image processing, it is necessary to perform correction processing that takes these scattered rays into consideration, and for this purpose, a scattered ray detector 7 is disposed close to the detector 4. Since this scattered ray detector 7 is placed outside the path through which the beam of slice thickness W passes, the main rays do not enter, and only the scattered rays enter.

When performing the correction process using the scattered ray detector 7, the scattered rays detected by the scattered ray detector 7 are
The prerequisite is that it be detected in the same way. If there are scattered rays that are detected only by the scattered ray detector, an incorrect correction process will be performed and artifacts will occur in the captured image.

Incidentally, the positional relationship between the main detector 4 and the scattered radiation detector 7 provided in a conventional X-ray CT apparatus is not particularly determined to be a constant relationship. Therefore, in some cases, as shown in FIG. 7, the parts of the scattered rays S generated within the subject 3 that are incident on the main detector 3 and the scattered ray detector 7 do not show any correlation, resulting in incorrect correction processing. will be carried out.

As another example of a conventional X-ray CT apparatus, one having a configuration as shown in FIG. 8 is also known. A ring-shaped case 8 that accommodates the subject 3 is arranged inside the main detector 4 and the scattered radiation detector 7, and a portion corresponding to the passage path of the X-ray beam has an H
An n-port 9 is provided, and this opening 9 is covered by a cover 10 made of a material that hardly impedes the passage of the X-ray beam. The ring-shaped case 8 is the CT device main body 1
Like the X-ray tube 1 installed in 1! It is arranged to protect the subject 3 from the main body 11 and smoothly transfer the subject 3 into the apparatus main body 11, and is made of a thick member with relatively high X-ray absorption in order to maintain mechanical strength. ing.

The cover 10 covering the opening 9 is made of a thin member that sufficiently transmits X-rays (low X-ray absorption).

Incidentally, in the X-ray CT apparatus having such a configuration, the area of the opening 9 is determined to be the minimum serration necessary for the main line of the emitted X-rays to pass over the slice thickness W. Therefore, as shown in FIG. 8, the scattered rays S generated within the subject 3 can only enter the scattered ray detector 7 after passing through the ring-shaped case 8. On the other hand, most of the scattered radiation passes through the cover 10 and enters the main detector 4 through the opening 9.

Therefore, as in the previous example, the correlation between the scattered rays incident on both detectors 3.7 is disrupted, leading to incorrect correction processing.

(Problems to be Solved by the Invention) In this way, in the conventional X-ray CT apparatus, since there is no correlation between the scattered rays incident on the main detector and the scattered ray detector, it is necessary to correct the scattered rays. There is a problem that processing is not performed correctly.

The present invention has been made in response to such problems, and an object of the present invention is to provide an X-ray CT apparatus in which scattered radiation correction processing can be performed correctly.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention arranges a main detector on the slice surface of the object, and a scattered radiation detector on the slice surface. It is characterized by being arranged on an arc drawn perpendicular to the slice plane with the radius being the distance between an arbitrary point and the position of the main detector.

(Function) Since both the main detector and the scattered radiation detector are placed at the same distance from any point on the slice plane where scattered radiation is most likely to occur, there is a correlation between the scattered radiation doses incident on both detectors. can be set. Therefore, the scattering and gland correction processing can be performed correctly.

(Embodiment) FIG. 1 is a side view showing an X-ray CT apparatus according to a first embodiment of the present invention. It is arranged on an extension of the slice plane Y (the center plane of the slice thickness W) of the X-ray beam, which is controlled to have a width W. On the other hand, the scattered radiation detector 27 is placed at an arbitrary position on an arc drawn perpendicularly to the slice plane Y, with the radius being the distance R between the point C on the slice plane Y and the position of the main detector 24. be done. Point C on the slice plane Y is the intersection point 0 of the scanner rotation axis X and the slice plane Y.
It can be set at any point between OaT and the outside OaT of the assumed maximum diameter of the subject 23. At this time, if the direction of the scattered radiation detector 27 is on a plane formed by an arc as shown in Fig. 2 (a), the direction with the maximum sensitivity is the Moeki intersection O.
and the outer end T.

In addition, when cutting from a direction perpendicular to the slice plane Y, Fig. 2 <
b>, the X-ray tube 21 is arranged so that the direction having the maximum sensitivity faces between the intersection point O and the X-ray tube 21.

According to this embodiment, both the main detector 24 and the scattered ray detector 27 are located at the slice plane Y where scattered rays are most likely to occur.
Since they are arranged at equal distances from the arbitrary points above, approximately the same amount of scattered radiation will be incident on both detectors 24 and 27, and it is possible to have a correlation between the required scattered radiation doses. can. Therefore, the scattered radiation correction process can be performed correctly.

FIG. 3 shows a second embodiment of the present invention, which necessarily shows an example in which the position where the scattered radiation detector 27 is arranged is limited within a specific range. That is, let L be the distance between the outer end T of the object 23 and the position of the main detector 24, and the scattered radiation detector 27
is arranged at a position on a circular arc within a distance from the position of the main detector 24. Further, at this time, the vertical height positions of the scattered radiation detector 27 along the slice plane Y are set within a distance approximately 0.3 times the distance.

The second embodiment not only provides the same effects as the first embodiment, but also has the advantage of increasing the accuracy of scattered radiation correction.

FIG. 4 shows a third embodiment of the present invention, in which the main detector 2
4 and a scattered radiation detector 27, and a ring-shaped case 28 for accommodating a subject 23 is arranged. The ring-shaped case 28 has a straight line r1.
An opening 29 is provided with an area that sufficiently covers the area surrounded by r2. The ring-shaped case 28 is made of a thick member that has relatively high X-ray absorption.
A cover 30 that covers 9 is made of a thin member that sufficiently transmits X-rays.

According to this third embodiment, since the opening 29 is provided under the conditions described above, the scattered rays S generated within the subject 23 or the scattered rays generated on the inner surface of the ring-shaped case 28 can be detected by both. Since almost equal charges are injected into the vessels 24' and 27,
The same effects as in the first embodiment can be obtained.

FIG. 5 shows a fourth embodiment of the present invention, in which a circle or a columnar body is used as the subject 23 in the third embodiment, and the dimensions of each part are set as shown. In other words, if a cylindrical body with a radius of 180 aw is used, the ratio of about 60 m in the left and right directions from the slice plane Y is 1 [because it is assumed that scattered rays are generated from within the slicing area, the ratio is 60 m).
H Both points separated to the left and right, the main detector 24 and the scattered radiation detector 2
The ring-shaped case 28 is provided with two openings having an area that sufficiently covers the area surrounded by the straight line connecting the ring-shaped case 28 and the position 7.

This fourth embodiment also provides the same effect as the third embodiment.
can rise.

In each of the above embodiments, the scattered radiation detectors 27 are arranged on both sides of the main detector 24, but it is also possible to arrange them only on one side.

[Effects of the Invention] As described above, according to the present invention, since the main detector and the scattered radiation detector are arranged at approximately equal distances from the scattered radiation source, the amount of scattered radiation incident on the rain detector is reduced. A correlation can be established, and correct correction processing for scattered radiation can be performed.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an X-ray CT apparatus according to the first embodiment of the present invention, FIGS. 2(a) and (b) are schematic diagrams for explaining the first embodiment, and FIG. 4 is a side view showing the third embodiment of the invention, FIG. 5 is a side view showing the fourth embodiment of the invention, and FIGS. 6 and 7 are side views showing the second embodiment of the invention. The figures are a front view and a side view showing a conventional example, and Fig. 8 is a side view showing another conventional example. 21... X-ray tube, 23-... Subject, 24...
...Main detector, 27...Scattered radiation detector, 28 Ring-shaped case, 29...Opening, 30...Cover, X...Scanner rotation axis, Y...Slice, T...・
・Outer edge of the object, O...intersection of scanner rotation axis X and slice Y, C
... Any point between the intersection 0 and the outer end T,... The distance between the bottom of the outer end and the main detector 24, R... The distance between the point C and the scattered radiation detector 27, D ···arc. ,, 7/′. :1 i8 figure ε × b

Claims (4)

[Claims] (1) It has a main detector that detects X-rays that have linearly passed through the subject from the X-ray source, and a scattered ray detector that is placed close to this and detects other X-rays other than the above-mentioned X-rays. X
In a radiation CT system, the main detector is placed on the slice plane of the subject, and the scattered radiation detector is arranged perpendicularly to the slice plane with the distance between an arbitrary point on the slice plane and the position of the main detector as a radius. An X-ray CT apparatus characterized in that the X-ray CT apparatus is arranged on a circular arc drawn as shown in FIG. (2) A ring-shaped case that accommodates the subject is arranged inside the main detector and the scattered ray detector, and connects the intersection of the slice plane and the scanner rotation axis with the positions of the main detector and the scattered ray detector. 2. The X-ray CT apparatus according to claim 1, wherein the ring-shaped case is provided with an opening having an area that sufficiently covers the area surrounded by the straight line. (3) The X-ray CT apparatus according to claim 1, wherein an arbitrary point on the slice plane is set between the intersection point in the subject and the outer end of the maximum diameter of the subject. (4) The scattered radiation detector is arranged on an arc within a distance L from the position of the main detector, where L is the distance between the outer end and the position of the main detector. Section or 3rd
The X-ray CT apparatus described in 2.