JP4356964B2 - X-ray CT system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray CT apparatus mainly used in fields such as industry and medicine.
[0002]
[Prior art]
Some X-ray CT apparatuses that have been widely used in the fields of industry and medicine in the past are equipped with an ionization chamber type X-ray detector.
In this ionization chamber type X-ray detector, the halogen gas is sealed in the gas chamber, the X-ray is made incident in the gas chamber, and the difference in the amount of current generated by the ionization action of the gas according to the incident X-ray dose. Since the gas concentration in the gas chamber is uniform, the sensitivity distribution in the rotation direction of the rotating plate provided in the X-ray CT apparatus is uniform. Since the level is not sufficient, a highly sensitive detector is required to improve the image quality of the X-ray CT apparatus.
[0003]
Therefore, as a highly sensitive detector, a solid state detector using a fluorescent semiconductor element has been developed and has been popularized in recent years.
However, while the solid state detector is highly sensitive, it uses a semiconductor, so when used in the X-ray detector of the X-ray CT apparatus due to partial characteristic variations of the substance, Sensitivity distribution is not uniform.
[0004]
For this reason, conventionally, when performing image processing, a calibration operation is performed in which correction data is created by capturing image data in advance without placing the subject.However, when imaging of the subject is actually started, The X-ray focal point position may move for the following reason, and the amount of movement may exceed the allowable range of correction data obtained by the calibration operation.
FIG. 6 shows a cross section of a conventional X-ray CT apparatus, which has a cylindrical rotating body c rotatably supported by a support base a via a bearing b, and an outer peripheral portion of the rotating body C. The X-ray detector e is mounted on the rotary anode X-ray tube d at a position facing the rotary anode X-ray tube d across the center of the rotating body c.
The rotary anode X-ray tube d is installed so that the rotary anode f and the cathode g are opposed to each other, and X-rays generated from the rotary anode f are reduced by a collimator h as shown in FIG. As a result, the X-ray beam i is configured to reach the X-ray detector e.
[0006]
[Problems to be solved by the invention]
In the X-ray CT apparatus configured as described above, the rotating body c is rotated at a high speed in order to reduce the X-ray exposure amount of the subject and to shorten the output time of the image data.
For this reason, a centrifugal force proportional to the square of the rotational speed acts on the rotating anode X-ray tube d and the X-ray detector e mounted on the rotating body c.
When the bracket j supporting the rotating anode f is bent by this centrifugal force, the position of the focal point f ′ of the rotating anode f and the pinhole h ′ of the collimator h is shifted as shown in FIG. The line beam i is displaced from the center e ′ of the X-ray detector e.
[0007]
The rotating body c also has an end opposite to the end supported by the bearing b due to the centrifugal load acting on the mounted rotating anode X-ray tube d and X-ray detector e in FIG. As shown in the figure, it expands and deforms into a cone shape. As a result, the X-ray beam i deviates further from the center e ′ of the X-ray detector e and exceeds the allowable range of the correction data obtained by the calibration operation. Therefore, there is a problem that a ring artifact occurs in the CT image, the image deteriorates, and a high-quality tomographic image cannot be obtained.
[0008]
The present invention has been made in order to improve such a conventional problem, and provides an X-ray CT apparatus that suppresses focal movement by changing the position of the rotating anode so that a high-quality tomographic image can be obtained. The purpose is to make it.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an X-ray CT apparatus of the present invention comprises a cylindrical rotating body whose one end is rotatably supported by a support frame, a rotating anode having a rotating shaft, and a rotation center axis of the rotating body. A rotating anode X-ray tube mounted on the outer periphery of the rotating body so as to be parallel to the rotating shaft, a collimator for narrowing an X-ray beam generated from the rotating anode of the rotating anode X-ray tube, and the rotating anode An X-ray CT apparatus comprising: an X-ray detector that detects an X-ray beam generated in an X-ray tube and narrowed down by the collimator, wherein the X-ray CT apparatus has a substantially inverted L-shape provided with a rotating anode on one end side. the other end of the bracket, so that the rotating body is offset by the deformation of the rotating body due to the centrifugal load generated during rotation and deformation of the bracket, the movement of the focal point of the X-ray beam is suppressed, The X-ray detector is illuminated from the rotating anode. With respect to the X-ray beam, characterized by being supported by the rotating anode X-ray tube with bearing portion side of the rotating body.
[0010]
With the above configuration, even if the rotating body is deformed so that the end on the side opposite to the support portion is expanded due to the centrifugal load generated when the rotating body rotates at a high speed, the rotating anode is on the support portion side. Since the rotary anode X-ray tube is mounted on the X-ray detector, the amount of movement of the focal point of the X-ray beam irradiated to the X-ray detector is suppressed, and thus the allowable range of the correction data obtained by the calibration operation is set to the focal position. Therefore, it is possible to easily obtain a high-quality tomographic image without image degradation due to the occurrence of ring artifacts.
Moreover, since the movement of the focal point of the X-ray beam can be suppressed only by mounting the rotating anode X-ray tube on the rotating body so that the rotating anode is on the support portion side, it can be easily implemented and the conventional rotating anode X It is economical because the tube can be used as it is.
[0012]
With the above configuration, the amount of movement of the focal point can be greatly reduced because the amount of deformation of the bracket deformed by the centrifugal force and the amount of deformation of the rotating body cancel each other.
[0013]
Embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a perspective view of an X-ray CT apparatus, FIG. 2 is a cross-sectional view, FIG. 3 is a schematic view, and FIGS.
In the X-ray CT apparatus shown in FIGS. 1 and 2, a support frame 1 is installed in a case (not shown), and a rotating body 2 formed in a cylindrical shape is freely rotatable on the support frame 1 via a bearing 3. It is supported by.
A rotating anode X-ray tube 4, a high-voltage power source 5 that supplies power to the rotating anode X-ray tube 4, a cooler 6 that cools the rotating anode X-ray tube 4, and the like are mounted on the outer periphery of the rotating body 2. An X-ray detector 7 made of a solid detector is mounted at a position facing the rotary anode X-ray tube 4 across the center of the rotating body 2.
Rotating anode X-ray tube 4, bearing a rotating anode 4a therein as shown in FIG. 2, be more and installed cathodic 4b so as to face the rotating anode 4a and the horizontal direction, rotating anode 4a is a rotating body 2 The rotating anode X-ray tube 4 is mounted on the rotating body 2 so that the cathode 4b is positioned on the bearing 3 side and the cathode 4b on the opposite side of the bearing 3.
[0014]
The rotary anode 4a in the rotary anode X-ray tube 4 is adapted to generate X-rays at the focal position 4d by being rotated by a rotary drive source 4c such as a motor, and the X generated by the rotary anode 4a. The line is configured to enter the center 7 a of the X-ray detector 7 as a fan-shaped X-ray beam 9 from the focal position 4 d through the slit 8 a of the collimator 8.
The rotating anode 4a is fixed in the rotating anode X-ray tube 4 by a bracket 4e formed in a substantially inverted L shape.
[0015]
Next, the operation of the X-ray CT apparatus constructed as described above will be described with reference to FIGS.
When imaging a subject (not shown), the rotating body 2 is rotated at a high speed by a rotational drive source (not shown) in order to reduce the X-ray exposure amount of the subject and simultaneously reduce the output time of image data. Considering the deformation of the rotating body 1 due to the centrifugal load generated at this time, a calibration operation is performed in which correction data is generated by capturing image data without placing a subject in advance before performing image processing.
[0016]
When the calibration operation is finished, the subject is carried into the opening 2a of the rotating body 2 and imaging of the subject is started. The subject is generated from the rotating anode 4a of the rotating anode X-ray tube 4 and condensed by the collimator. The X-ray beam is set to irradiate the center of the X-ray detector 7 as shown in FIG. 4A when the rotator 2 is not rotating, but the rotator 2 rotates. When started, the centrifugal force generated by the rotation acts on the rotating anode X-ray tube 4 mounted around the rotating body 2.
[0017]
In the rotating anode X-ray tube 4, there is provided a rotating anode 4a that is cantilevered by a substantially inverted L-shaped bracket, and the bracket is shown in FIG. 4B by centrifugal load acting on the rotating anode 4a. As shown in the figure, the bracket that supports the rotating anode 4a is installed on the support portion side (bearing 3 side) of the rotating body 2, so that the focal point of the X-ray beam reaching the X-ray detector 7 is Contrary to the conventional X-ray CT apparatus shown in FIG. 7B, the X-ray detector 7 moves from the center 7a to the bearing 3 side by substantially the same amount as the conventional X-ray CT apparatus.
[0018]
Thereafter, when the rotating body 2 is further rotated at a high speed, the open end opposite to the support portion of the rotating body 2 is expanded, and the rotating body 2 is deformed into a substantially cone shape as shown in FIG. However, since the deformation of the rotating body 2 is in a direction to cancel the deformation of the bracket that supports the rotating anode 4a, the X-ray beam that has shifted from the center 7a of the X-ray detector 7 to the bearing 3 side due to the deformation of the bracket. Is moved toward the center 7a of the X-ray detector 7 as shown in FIG.
As a result, even if the rotating body 2 is deformed into a cone shape due to the centrifugal load generated when the rotating body 2 is rotated at a high speed, the movement of the focal point of the X-ray beam is suppressed, and a focus shift is obtained by the calibration operation. Since the allowable range of the corrected data is not exceeded, image degradation due to the occurrence of ring artifacts is reduced, and a high-quality tomographic image can be obtained in a short time.
[0019]
FIG. 5 is a line comparing the deviation of the focal position of the X-ray beam due to the bending of the bracket supporting the rotating anode and the bending of the rotating body 2 of the X-ray CT apparatus according to the embodiment of the present invention and the conventional X-ray CT apparatus. In the figure, curve A represents the present invention and curve B represents the conventional one.
As is clear from this figure, when the bracket supporting the rotating anode 4a is deformed by centrifugal force, the focal point of the X-ray beam moves to the (−) side from the center 7a of the X-ray detector 7, and the rotating body 2 Is deformed by centrifugal force, the deformation of the rotating body 2 is absorbed by the amount of deformation of the bracket, so that the substantial shift amount is greatly reduced as compared with the conventional X-ray CT apparatus.
[0020]
【The invention's effect】
As described in detail above, the present invention suppresses the movement of the rotating anode X-ray tube and the focal point of the X-ray beam caused by the rotation of the rotating body on the cylindrical rotating body whose one end is rotatably supported by the support frame. both the provision focus movement restraining portion which, in the X-ray detector so as to face the rotating anode X-ray tube that is mounted to the rotating body, the movement amount of the focus of the X-ray beam irradiated onto the X-ray detector It is possible to easily obtain a high-quality tomographic image that is suppressed and has no image degradation due to the occurrence of ring artifacts.
[0021]
Moreover, since the movement of the focal point of the X-ray beam can be suppressed only by mounting the rotating anode X-ray tube on the rotating body so that the rotating anode is on the support portion side, the conventional rotating anode X can be easily implemented. It is economical because the tube can be used as it is, and since the rotating anode is supported in the rotating anode X-ray tube by a bracket formed in an approximately inverted L shape, the amount of deformation of the bracket that is deformed by centrifugal force Since the deformation amount of the rotating body cancels each other, the moving amount of the focal point can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a perspective view of an X-ray CT apparatus according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of an X-ray CT apparatus according to an embodiment of the present invention.
FIG. 3 is a configuration diagram of an X-ray CT apparatus according to an embodiment of the present invention.
FIGS. 4A to 4C are operation explanatory views of an X-ray CT apparatus according to an embodiment of the present invention.
FIG. 5 is a diagram comparing the amount of movement of a focal point due to bending of an X-ray CT apparatus according to an embodiment of the present invention and a conventional X-ray CT apparatus.
FIG. 6 is a configuration diagram of a conventional X-ray CT apparatus.
FIGS. 7A to 7C are operation explanatory views of a conventional X-ray CT apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Support stand 2 Rotating body 4 Rotating anode X-ray tube 4a Rotating anode 4e Bracket 7 X-ray detector 8 Collimator 9 X-ray beam

Claims (1)

A cylindrical rotating body whose one end is rotatably supported on a support frame, and a rotating anode having a rotating shaft, and an outer periphery of the rotating body so that the rotation center axis of the rotating body and the rotating shaft are parallel to each other A rotary anode X-ray tube mounted on the rotary anode, a collimator for narrowing the X-ray beam generated from the rotary anode of the rotary anode X-ray tube, and the X-ray generated by the rotary anode X-ray tube and throttled by the collimator An X-ray CT apparatus including an X-ray detector for detecting a beam, wherein the rotating body rotates on the other end side of a substantially inverted L-shaped bracket provided with the rotating anode on one end side. and deformation of the rotor by the centrifugal load and the deformation of the bracket is offset to occur, as described above movement of the focal point of the X-ray beam is suppressed, the irradiated said to more rotary anode the X-ray detector For the X-ray beam, X-ray CT apparatus characterized by Seung side that you were supported on the rotary anode X-ray tube.

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