JPH0824675B2 - X-ray CT system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention is directed to scattered radiation detection for detecting X-rays other than X-rays that have linearly transmitted through an object from an X-ray source. X-ray CT apparatus having a detector.

(Prior Art) As a conventional X-ray CT apparatus, one having a configuration as shown in FIGS. 5 and 6 is known. FIG. 5 is a front view and FIG. 6 is a side view, in which an X-ray main detector 4 composed of a plurality of channels is arranged so as to face the X-ray tube 1.
A plurality of scattering detectors 7 each having a single channel are arranged in proximity to at least one side along the length direction (rotational direction) Z of the main detector 4. Both the main detector 4 and the scattered radiation detector 7 are constituted by scintillation detectors including, for example, scintillators and photodiodes.

The collimator 2 and the subject 3 are arranged between the X-ray tube 1 and the main detector 4, and the X-ray tube 1, the collimator 2 and the main detector 4 are arranged.
And the scattered radiation detector 7 are integrated together while rotating around the subject 2 with the central axis X in the subject 2 as a rotation axis,
The subject 2 is exposed to X-rays and scanned. The X-ray emitted from the X-ray tube 1 and controlled by the collimator 2 into a beam having a desired slice thickness W and a fan angle θ passes through the subject 3 and enters the main detector 4 or the scattered ray detector 7. Here, the main detector 4 linearly extends from the X-ray tube 1 to the subject 3
It is desirable to detect only the X-rays (main lines) that have passed through and to perform image processing based on the detected X-ray absorption coefficient data.

However, in reality, the X-rays incident on the main detector 4 are scattered other than the main line and arrive at the subject 3 or arrive at the subject 3 without passing through the subject 3 (hereinafter, these Is referred to as scattered radiation). Therefore, in order to perform accurate image processing, it is necessary to perform correction processing in consideration of these scattered rays, and for this reason, the scattered ray detector 7 is arranged close to the main detector 4. Since the scattered ray detector 7 is arranged outside the passage path of the beam having the slice thickness W, the main ray does not enter, but only the scattered ray enters. Further, unlike the main detector, these scattered radiation detectors do not need to be densely arranged, and the objects can be achieved even if they are arranged at intervals, so that there is an advantage that the cost can be reduced. In this case, the detection value at the intermediate position where the scattered radiation detector is not arranged is estimated by interpolation.

Here, when performing the correction process by the scattered radiation detector 7,
The scattered radiation detected by the scattered radiation detector 7 is the main detector 4
It is a prerequisite that the same is detected by. If there are scattered rays that can be detected only by the scattered ray detector, an erroneous correction process will be performed, so that an artifact will occur in the obtained image.

By the way, in the conventional X-ray CT apparatus, the plurality of scattered radiation detectors 7 are arranged with a straight line Y connecting the X-ray tube 1 and the scan rotation axis X of the subject 3 as a center, as shown in FIG. In many cases, for example, three pieces 7a, 7b, 7c and 7'a, 7'b, 7'c are arranged at equal intervals at the left and right positions.

Although it is arranged so as to overlap the main detector 4 in the figure,
Actually, both detectors 4 and 7 are separated as shown in FIG. The distribution of scattered dose detected by these scattered ray detectors 7a to 7c and 7'a to 7'c is as shown in FIG. Each value Ma
To Mc and M'a to M'c are scattered ray detectors 7a to 7c and 7 ', respectively.
Since the values are actually measured by a to 7'c, the detection accuracy is high. However, since the values N _{1 to} N ₅ between the adjacent scattered ray detectors are estimated values by interpolation, the detection accuracy is low.

In such an X-ray CT apparatus, when a subject 3 having a small width D in the direction orthogonal to the straight line Y is scanned as shown in FIG. 7, all scattered radiation detectors have a width of the subject 3. Since it is not arranged at the position corresponding to D, the scattered radiation for the subject 3 is corrected by using the interpolation value of the portion A in FIG. Therefore, it is highly possible that the correction with low accuracy is performed.

(Problems to be Solved by the Invention) As described above, in the conventional X-ray CT apparatus, when a subject having a width smaller than the arrangement interval of the scattered ray detector is scanned, the scattered ray can be accurately corrected. There is a problem that it is not done.

The present invention has been made to address the above problems, and an object of the present invention is to provide an X-ray CT apparatus capable of accurately correcting scattered rays even when scanning an object having a small width. Is.

[Structure of Invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a plurality of scattered radiation detectors in the outward direction about a straight line connecting the X-ray source and the scan rotation axis of the subject. It is characterized in that they are arranged such that the distance between adjacent ones becomes smaller as they move toward each other.

(Operation) Since multiple scattered ray detectors are arranged not at equal intervals but at closer intervals as they approach the straight line, the position corresponding to any small width of the object to be scanned A scattered radiation detector can be placed in the. As a result, the correction based on the measured value is always performed, so that the correction can be performed with high accuracy.

(Embodiment) FIG. 1 is a front view showing an X-ray CT apparatus according to an embodiment of the present invention.
A main detector 24 and a scattered radiation detector 27 are arranged facing the X-ray tube 21. A collimator 22 and a subject 23 are arranged between the X-ray tube 21 and both detectors 24 and 27. X-ray detector 27
With respect to the straight line Y connecting the line tube 21 and the scan rotation axis X of the subject 23 as a center, for example, three pieces 27a, 27 are provided at the left and right positions.
b, 27c and 27'a, 27'b, 27'c are arranged so that the adjoining ones become closer to each other from the straight line Y toward the outside as shown in the drawing. That is, 27c-2
When the distance of 7'c is L ₁ , the distance of 27c-27b and 27'c-27'b is L ₂ , and the distance of 27b-27a and 27'b-27'a is L ₃ , then L ₁ <L Each is arranged so that the relation of ₂ <L ₃ is satisfied.

 Next, the operation of this embodiment will be described.

By integrally rotating the X-ray tube 21, the main detector 24, and the scattered radiation detector 27 about the scan rotation axis X to perform scanning, the distribution characteristic of scattered dose as shown in FIG. 2 is obtained. Since the corresponding values m _{a to} m _c , m _a ′ to m _c ′ on the scattered ray detectors 27a to 27c, 27'a to 27'c are values measured by the scattered ray detectors, the detection accuracy is high. Become. Further, the values n _{1 to} n ₅ between the adjacent scattered radiation detectors are estimated values by interpolation. According to the present embodiment as described above, even when the object 23 having a small width is targeted, the scattered radiation detector can always be arranged at a position corresponding to the object 23. If the object 23 is the object, two scattered radiation detectors 27c and 27'c can be arranged. Therefore, since the correction can be performed by the measured values m _c and m _c ′ corresponding to the 27 _c and 27 ′ _c , highly accurate correction can be performed.

FIG. 3 shows another embodiment of the present invention, in which the main detector
24 is arranged in a ring shape around the subject 23 over 360 °, and the scattered radiation detectors 27a to 27c and 27'a to 27'c arranged on at least one side of the subject 23 are integrated with the X-ray interval 21 to form the subject 23.
This is an example of application to a so-called fourth-generation X-ray CT apparatus in which the periphery of is scanned for scanning.
The scattered radiation detectors 27a to 27c and 27'a to 27'c are arranged under the same conditions as in the embodiment of FIG.

According to this embodiment, the same effect as the above embodiment can be obtained.

In each of the above embodiments, scattered ray detectors such as 27a, 27b, 27'a, 27'b are also provided outside the fan angle .theta.
It is desirable to arrange. This is because scattered rays are also emitted outside the fan angle θ during scanning, so if the scattered ray detector is arranged only at the position corresponding to the fan angle θ, correct correction cannot be performed at the end of θ. This is because. When the scattered radiation detectors 27a, 27b, 27'a, and 27'b are arranged as described above, as shown in FIG. Correct correction will be performed.

Further, in each of the embodiments, the scattered radiation detector 27 is preferably arranged so that the direction showing the maximum sensitivity thereof is directed to the section connecting the scan rotation axis X and the X-ray tube 21 as shown in FIG. As a result, the performance of the scattered radiation detector 27 can be maximized.

〔The invention's effect〕

As described above, according to the present invention, since a plurality of scattered radiation detectors are arranged sparsely so that the adjacent intervals are outwardly oriented with the reference line as the center, the accuracy of scattered radiation can be improved even for an object having a small width. High correction can be performed.

[Brief description of drawings]

FIG. 1 is a front view showing an X-ray CT apparatus according to an embodiment of the present invention, and FIG.
FIG. 4 is a characteristic diagram for explaining the present invention, FIG. 3 is a front view showing another embodiment of the present invention, FIG. 4 is a schematic diagram for explaining the present invention, and FIGS. FIG. 7 is a front view and a side view showing a conventional example, and FIGS. 7 and 8 are a front view and a characteristic view showing the conventional example. 21 ... X-ray tube, 23 ... Subject, 27,27a, 27b, 27c, 27'a, 27'b, 27'c ... Scattered ray detector, X ... Scanner rotation axis, Y ... Scanner A straight line connecting the rotation axis X and the X-ray tube 21.

Claims (1)

[Claims] 1. A main detector for detecting X-rays directly transmitted from an X-ray source and a plurality of scattered detectors arranged along the main detector for detecting X-rays other than the X-rays. In an X-ray CT device with a scanning device, a plurality of scattered radiation detectors become closer to each other toward the outer side with respect to a straight line connecting the X-ray source and the scan rotation axis of the subject, and the intervals between adjacent ones become sparse. X-ray CT device characterized in that