JPH0445044B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a radiation CT apparatus that obtains tomographic images of objects using radiation.

[Technical background of the invention and its problems] Conventional X-ray CT devices emit X-rays from an X-ray tube toward an object to be examined, and detect multiple X-rays from the X-rays that have passed through the object. This is an inspection device that converts X-rays to electricity using a device and obtains a tomographic image of the object using a computer. The X-ray detector used in this inspection device has a plurality of X-ray/electrical converters arranged closely together. Normally
The ray detector is equipped with 10 to 1000 X-ray/electrical converters depending on the system. These multiple X-ray/electrical transducers are manufactured to theoretically have the same characteristics. However, in reality, the characteristics of all X-ray/electrical converters are not uniform due to manual work and parts used. The heterogeneity of these properties is
This results in errors when the computer reconstructs the tomographic image of the subject, resulting in inaccurate testing.

In addition, there is a so-called first generation CT device that uses an X-ray tube with a single X-ray/electrical converter and performs linear scanning and rotational movements alternately, but this system does not have problems due to non-uniformity of detector characteristics. However, there was a problem in that it took more than 200 seconds to obtain a single tomographic image, making the examination time-consuming.

[Object of the Invention] The present invention has been made based on the above-mentioned circumstances, and it is possible to perform multiple
It is an object of the present invention to provide a radiation CT apparatus that can reduce errors and obtain reliable tomographic images even if the characteristics of the wire/electrical transducer are uneven.

[Summary of the Invention] In order to achieve the above object, the present invention includes a pedestal fixing part having a cylindrical opening, a pedestal fixing part rotatably supported by the pedestal fixing part, and centered around the central axis of the cylindrical shape. , a gantry rotating part that rotates along the circumference of the cylindrical shape; a radiation source that is provided on the gantry rotating part and emits fan-shaped radiation having a predetermined spread angle toward the central axis; a subject mount that supports a subject near an axis and rotates the subject in the same direction and at half the rotational speed of the rotation of the gantry rotating section; This is a radiation CT device equipped with a detector that detects radiation transmitted through a specimen.

[Embodiment of the Invention] An embodiment of the present invention will be described with reference to the drawings.

First, regarding the concept of the present invention, FIGS. 1A and B
Refer to and explain.

In Fig. 1 A, the subject M has a protrusion on a part of the square.
, an X-ray tube Sp that rotates around the subject M with the center O of the subject M as an axis, and, for example, 1024 X-rays arranged in a densely fixed manner on the circumferential orbit of the X-ray tube Sp. Detectors D ₁ -D ₁₀₂₄ are shown. The center of this subject M is O, and the horizontal direction of the figure is the Xp axis.
The vertical direction is the Yp axis. The subject M rotates counterclockwise around O at an angular velocity ω. center O to r
There is an X-ray tube Sp in a remote location. X-ray tube Sp is O
The angular velocity ω of the object along the circumference of radius r centered on
It rotates counterclockwise with an angular velocity of 2ω, which is twice the
At that time, the X-ray emitting direction of the X-ray tube Sp is always at the center O.
, and emit fan-shaped X-rays with a predetermined spread angle centered at O.

Now, focusing on the detector _D2 , the X-rays emitted from the X-ray tube Sp and transmitted through the subject M enter the detector _D2 . The locus of the X-rays transmitted through the subject M is assumed to be parallel to the X-axis.

Next, FIG. 1B shows the state t seconds after FIG. 1A. Since the detector is fixed, in FIG. 1B, the subject M is in the Xt, Yt axis system rotated counterclockwise by an angle ωt from the Xp, Yp axis system. Since the X-ray tube Sp is rotating at twice the angular velocity of the subject, it is at a position St that has been rotated by 2ωt, which is twice the angle ωt, from the position Sp t seconds ago. When X-rays are irradiated from this position St, the subject M
and enters the detector _D2 . The trajectory of the X-rays is parallel to the X-axis.

Focusing on the detector _D2 in this manner, if the X-ray tube emits radiation while rotating, all of the radiation passes through the subject M in parallel to the subject M.
In other words, one detector can obtain parallel beams in one direction while the X-ray tube goes around the circumference of radius r while emitting radiation. By arranging 1024 detectors on the circumference of a radius r, 1024 types of parallel beams are obtained. Since the parallel beam data obtained in this way is obtained by the same X-ray detector, these parallel beam data are not affected by the non-uniformity of the X-ray detector. Furthermore, the number of parallel beams can be determined by the number of irradiations during one rotation of the X-ray tube.

FIG. 2 shows an embodiment based on the above concept. In FIG. 2, there is a substantially cylindrical frame fixing part 1 with a circular hole in the center. There is a gantry rotating part 2 on the outer circumferential surface of this gantry fixing part 1, and a motor 8
angular velocity in the counterclockwise direction along its outer circumferential surface.
Rotates at 2ω. The gantry fixing section 2 is provided with an X-ray tube 5 that irradiates X-rays toward the subject 4 . The subject 4 is placed on a subject mount 7 and rotated counterclockwise by a motor 6 at an angular velocity ω. Detector 3
is a donut-shaped detection group in which 1024 X-ray detectors are densely arranged, and detects the X-rays that have passed through the subject 4. The detector 3 operates by moving up and down using four pistons provided on the gantry fixing part 1 so that the detection point facing the X-ray tube is always parallel to the X-ray tube 5. A so-called nu-tate operation is performed so that the rotation radius of the X-ray tube 5 and the radius of the detector 3 do not overlap, so that the X-rays transmitted through the subject can be detected.

In this way, since the data for a set of parallel beams are obtained by the same X-ray detector, the data for these parallel beams are not affected by the non-uniformity of the X-ray detector. Furthermore, although there is an influence due to the non-uniformity of the X-ray detector between each set of parallel beam data, there is no variation in each parallel beam data, so no artifacts occur.

The parallel beam data in each direction obtained by the 1024 X-ray detectors in the detector 3 is reconstructed by a processing device (not shown) and displayed as a tomographic image of the subject 4.

[Effects of the Invention] According to the present invention, even if the characteristics of a plurality of X-ray/electrical converters are uneven, errors can be reduced and reliable tomographic images can be obtained without spending a long time on inspection.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the concept of a radiation CT apparatus according to the present invention, and FIG. 2 is a cross-sectional perspective view of one embodiment of the radiation CT apparatus according to the invention. 1... Frame fixing part, 2... Frame rotating part, 3...
X-ray detection unit, 4... Subject, 5... X-ray tube, 7...
...Subject mount.

Claims (1)

[Claims] 1. A pedestal fixing part having a cylindrical opening, and a pedestal rotating part rotatably supported by the pedestal fixing part and rotating along the circumference of the cylindrical shape, with the central axis of the cylindrical shape as an axis. and a radiation source that is provided on the gantry rotating part and that emits fan-shaped radiation that has a predetermined spread angle toward the central axis;
a subject mount that supports the subject near the central axis and rotates the subject in the same direction and at half the rotational speed of the rotation of the gantry rotating section;
A radiation CT apparatus comprising: a detector located on a rotating orbit of the radiation source and detecting radiation transmitted through the subject.