JPS60158837A - Ct scanner - 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 a CT scanner, and more specifically, to a CT scanner, in which a radiation source and a radiation detector are fixed in relative position, and an object to be inspected between them is So-called roti-john roti-joon OCT, which is rotated in a circular motion.
It's about the scanner.

C. Background of the Invention] In this type of CT scanner, an ionization box type is widely used as a radiation detector. This radiation detector includes a large number of signal electrode plates and high voltage electrode plates arranged alternately and at regular intervals. A signal electrode plate and a high voltage electrode plate constitute one detection element, and a radiation detector includes, for example, 576 such detection elements. Due to processing accuracy and the need to deal with the occurrence of defective detection elements, radiation detectors are made up of multiple detection element arrays, and after each array is assembled, these arrays are lined up to form a single detector. . That is, each array is created by preparing a pair of insulating plates with a large number of grooves, placing these insulating plates in parallel so that the grooves face each other, and inserting and fixing an electrode plate between the facing grooves. I'm being kicked. A radiation detector is constructed by arranging a plurality of such thin arrays so that the distance between the signal electrode plate and the high voltage electrode plate at the edges of adjacent arrays matches that in the array. The detection elements between adjacent arrays are arranged symmetrically with respect to the central axis of the radiation detector, for example, each array has the same number of detection elements, and the installation of the radiation i detector in the frame is arranged symmetrically with respect to the central axis of the radiation detector. The central axis of the detector is made to coincide with the center of the radiation flux passing through the focus of the radiation source and the central axis of rotation of the frame.

The simple problem of a CT scanner with such a radiation detector is that the array must be arranged so that the spacing between the electrode plates at the ends of the adjacent four-detection element arrays precisely matches that within the array. Otherwise, a ring-like artifact will appear on the CT image. However, in a rotation-rotation OCT scanner, detection elements located at the same distance from the central axis of the radiation flux determine the CT values of picture elements located at the same radius on the CT image.
If the detection elements between the arrays are defective, the error of the detection elements between the arrays will be doubled at the corresponding radius on the CT image, creating a ring-shaped artifact in the CT image that will lead to misdiagnosis. .

[Object of the present invention]

The present invention is based on detection element defects between detection element arrays (
An improved CT scanner is provided that can minimize the occurrence of ring artifacts on CT images.

[Summary of the invention]

The OCT scanner of the present invention is characterized in that the detection elements between adjacent detection element arrays are arranged asymmetrically with respect to the central axis of the radiation flux passing through the focal point of the radiation source and the central axis of rotation of the frame.

With this arrangement of detection elements, the detection elements between adjacent detection element arrays are located at different distances from the frame's rotational center axis, so even if these detection elements are defective, the conventional The error will be halved compared to an OCT scanner. Ring-shaped artifacts on CT images occur in numbers corresponding to the number of detection elements between arrays.However, if the arrangement precision of the arrays is the same, the artifacts can be significantly reduced; If this is allowed, the arrangement accuracy of the array can be relaxed.

The asymmetrical arrangement of the detection elements can be achieved, for example, by incorporating each play into the radiation detector such that the center axis of one thick array formed in the detection element play is offset from the center axis of the radiation detector. This can also be achieved by arranging the detection element relays symmetrically with respect to the central axis of the radiation detector, and installing the radiation detector in a frame with its central axis offset relative to the central axis of the radiation flux. This can also be done by varying the number of sensing elements within each array. If the deviation is small, the ring-shaped artifacts will be concentrically and closely arranged and wide, whereas if the deviation is large, the number of invalid detection elements that are out of the radiation flux will increase.
Although it depends on the number of C detection elements employed, it is generally desirable that the number of detection elements be around five.

An embodiment of the OCT scanner of the present invention will be described below with reference to the accompanying drawings.

[Embodiments of the invention]

In FIGS. 1 and 2, 10 represents a frame, 11 represents a radiation source, and 12 represents a radiation detector.

The frame is disc-shaped, and its peripheral surface is supported by rollers 16 on a base set on the floor, etc., and can rotate on the rollers about the central axis 14 of the frame. The radiation source includes an x-ray tube and an aperture mechanism. The X-ray tube has its focal point as axis 1
A constriction mechanism located in a plane perpendicular to the plane 4 and supported by the frame constricts the X-ray flux from the X-ray tube into a fan beam line 15 extending within said plane. The radiation detector is in the form of an ionization box having a large number of detection elements, and is disposed on the frame so as to face the radiation source across the rotation center axis 14 of the frame.

In the measurement, the object to be inspected 16 is placed between the radiation source 11 and the detector A with the measurement site aligned with the plane, and the frame 10 is rotated to perform rotation d, for example.
This is accomplished by meshing a large gear provided on the side of the frame with a pinion coaxial with one of the rows 216, and rotating the pinion by an electric motor on the base. X-rays are emitted every time the frame is rotated by an angle corresponding to nine angles θ, and each detection element receives electricity related to the absorption of X-rays at the diagnostic site of the subject by one rotation of the frame. I can get a signal.

As mentioned above, the radiation detector is in the form of an ionization box. FIG. 6 shows the detection element array. This detector includes, for example, three detection element arrays 21&,
It is composed of 21b' and 21e.

Each array has 200 detection elements, and the number of detection elements is 602, including the detection elements formed by the electrode plates at the ends of the adjacent arrays. As clearly shown in FIGS. 4 and 5, each detection element array has signal electrode plates 22 and high voltage electrode plates 23 arranged alternately and at a constant interval. The electrode plates are arranged vertically in a row, and this electrode plate group is inserted and fixed into each of the grooves provided facing the pair of insulating plates 24 and 25. Each play is arranged on the lid 27 of the pressure vessel such that the spacing between the signal electrode plate and the high voltage electrode plate at adjacent ends is equal to the spacing between the signal electrode plate and the high voltage electrode plate of the play. At the same time, it is fixed to the lid by an adhesive layer 28 or bolts 29, and is housed in the main body by covering the lid with the main body 26, and an ionized gas such as xenon gas is sealed in the internal space. . This pressure vessel main body is fixed to a frame.

According to the present invention, in the CT scanner, the detection elements between adjacent detection element arrays are arranged asymmetrically with respect to the radiation center axis passing through the focal point of the radiation source and the rotation center axis of the frame. FIG. 6 shows the details. Each of the electrode plates 22 and 25 in the detection element array is arranged radially so as to be located on a straight line passing through the focal point 60 of the X-ray tube, and arranged at equal angles with respect to the focal point 30. The arrays are arranged so that the signal electrode plates and high voltage electrode plates at the edges of adjacent arrays also form the same angle as those in the array. But array"' + 21b.

The central axis 34 of one large array constituted by 21e is at an angle relative to the focal point 3o with respect to the axis passing through the focal point 3o of the X-ray tube and the central axis of rotation 14 of the frame, or with respect to the central axis 66 of the fan beam X-ray 15. It is shifted by an angle A. To be more specific, this large array is located at a distance of 5.5 mm from the central axis 33 of the fan beam
The detection elements are shifted along an arc centered on the focal point 3o. Only 576 of the total 602 detection elements are covered by the fan beam X-ray 15 and connected to the image processing device or the image reconstruction device. 7 The remaining 24 detection elements that are off the beam X#, that is, the 7 detection elements located in the shaded area 34 of the array 21a, and the 17 detection elements located in the same area 35 of the small array 21c, are grounded. There is. In a CT scanner having such a radiation detector, the detection element 31 constituted by electrode plates at adjacent ends of the detection element arrays 21a and 21b detects CT values on the circumference indicated by the broken line on the cT image, Further, the detection elements 32 between the arrays each determine the CT value on the circumference indicated by the chain line. Therefore, even if these detection elements 31 and 32 become defective detection elements, the error in CT values on the circumference on the CT image corresponding to each detection element can be halved compared to conventional CT scanners. be able to.

〔Effect of the invention〕

As described above, in the OCT scanner of the present invention, the detection elements between the detection element arrays constituting the radiation detector are arranged asymmetrically with respect to the central axis of the radiation flux. It is possible to reduce ring-shaped artifacts by half, and also to reduce the precision required for array arrangement.

[Brief explanation of the drawing]

The drawing shows an embodiment of the OCT scanner of the present invention.
FIG. 1 is a front view, FIG. 2 is a side view, FIG. 3 is a perspective view of the detection element array of the radiation detector, FIG. 4 is a partially cutaway perspective view showing the configuration of the radiation detector, and FIG. Figure 5 is Figure 3 V
FIG. 6 is an enlarged cross-sectional view taken along the line -V, and is a diagram for explaining the arrangement of the detection elements between the small arrays constituting the detection element array. DESCRIPTION OF SYMBOLS 10... Frame, 11... Radiation source, 12 River radiation detector, 14... Rotation center axis of frame, 15...
- Radiation flux, 21 & , 21b, 21e...Detection element array, 3o...Focus of radiation source, 31.32
...Detection element between arrays, 33... Central axis of radiation. Agent Patent Attorney Tadashi Akimoto Figure 1 Figure 1 Figure 2 Figure 5 Figure 6

Claims (1)

[Claims] 1. A rotating frame, a radiation source disposed on the frame with its focal point located within a plane perpendicular to the central axis of rotation of the frame, and a radiation source disposed on the frame such that the radiation source within the plane is detected as a branched beam. and an ionization box-type radiation detector arranged in the form of an ionization chamber, the radiation detector being composed of a plurality of detection element arrays, and in which detection elements are also formed on adjacent electrode plates at the ends of adjacent detection element arrays. A CT scanner is characterized in that the detection elements between the detection element arrays are arranged asymmetrically with respect to the central axis of the radiation flux passing through the focal point of the radiation source and the central axis of rotation of the frame.