JP4231706B2 - X-ray tube apparatus and X-ray CT apparatus using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray tube apparatus used in an X-ray CT apparatus and the like, and more particularly, to an improvement in the rotary anode structure of a rotary anode X-ray tube housed in the X-ray tube apparatus.
[0002]
[Prior art]
In recent years, the performance of X-ray CT apparatuses has been remarkably improved, and image processing technology has been particularly advanced. For X-ray detectors that capture X-ray measurement data, solid-state X-ray detectors using semiconductors with high photosensitivity are used instead of gas chamber X-ray detectors that apply gas ionization by X-rays. This contributes greatly to improving the image quality of X-ray CT equipment. In response to such technological advances, the X-ray tube apparatus that is an X-ray generation source has the following problems.
[0003]
In an X-ray CT device, a fan-shaped X-ray with a thickness of about 1 to 10 mm radiated from the X-ray tube device passes through the examination site of the subject and is attenuated by the subject, and then received by the X-ray detector. Then, an X-ray attenuation signal (X-ray measurement data) is output from the X-ray detector, and this X-ray attenuation signal is subjected to image reconstruction processing to obtain a tomographic image of the imaging region of the subject. In this process, since the focus of the X-ray source is moved in the conventional X-ray tube apparatus, an artifact is generated on the tomographic image, which hinders the improvement of the image quality of the X-ray CT apparatus.
[0004]
Recently, solid-state X-ray detectors have become mainstream as X-ray detectors, and in order to fully demonstrate the high sensitivity of this solid-state X-ray detector and provide the highest image quality, It is necessary to solve the problem of tube device focal shift.
[0005]
The above focal movement occurs in the axial direction of the X-ray tube and occurs because heat accumulates in the rotating anode during use of the X-ray tube and the rotating anode thermally expands. In the X-ray CT apparatus, when performing tomographic image processing, a calibration operation is performed in which X-ray measurement data is acquired and a correction coefficient is determined without inserting a subject in advance. When tomography is actually started, in the X-ray tube apparatus, heat is generated in the target of the rotating anode of the X-ray tube along with the X-ray exposure. By repeating this X-ray exposure, heat accumulates on the target and the temperature of the target rises to 950-1000 ° C. Due to the temperature rise of the target, the rotating anode itself thermally expands in the X-ray tube axis direction, and the focal point on the target moves.
[0006]
In the current X-ray tube apparatus, this focal shift amount is about 200 to 400 μm. On the other hand, the allowable range of the focus movement amount that can be allowed by the correction coefficient determined by the calibration operation is within about 100 μm. If the focal position moves beyond this allowable range, artifacts and the like occur on the tomographic image, and image degradation occurs.
[0007]
Next, the specific contents of focus movement in the conventional X-ray tube apparatus will be described with reference to FIG. FIG. 10 is a diagram showing the relationship between the structure of a rotary anode X-ray tube inserted in a conventional X-ray tube apparatus and the collimator of the X-ray CT apparatus. In FIG. 10, a rotary anode X-ray tube 1 is composed of a rotary anode 2, a cathode 3 disposed opposite thereto, and an envelope 4 that encloses the rotary anode 2 and the cathode 3 in a vacuum-tight manner. During use of the rotating anode X-ray tube 1, a high voltage is applied between the rotating anode 2 and the cathode 3, and an electron flow 5 due to thermoelectrons emitted from the filament of the cathode 2 is applied to the target 6 of the rotating anode 2. Collides and emits X-rays 8. The portion where the electron flow 5 from the cathode 3 collides is the focal point 7, and the X-ray 8 is emitted outside through the X-ray emission window 9 of the envelope 4 with the focal point 7 as an X-ray source.
[0008]
When using the X-ray tube device with the rotary anode X-ray tube 1 inserted in the X-ray CT device, the X-ray 8 is required by the slit 11 of the collimator 10 attached to the X-ray CT device. The fan-shaped X-ray beam 8 is reduced in thickness. Since the number of X-ray exposures is small at the start of use of the X-ray tube device, the rotating anode 2 hardly thermally expands, the target 6 is in the position of the solid line, and the X-ray beam 8 is the X-ray detector 12 Radiated to point A. However, when the number of X-ray exposures increases, the temperature of the rotating anode 2 including the target 6 increases, and the members constituting the rotating anode 2 thermally expand. As a result, the position of the target 6 moves to the position of the target 6A indicated by the broken line, and accordingly, the focal point 7 also moves to the position of the focal point 7A on the target 6A.
[0009]
Due to the movement of the position of the focal point 7A, the X-ray beam 8 passing through the slit 11 of the collimator 10 also moves to the position of the X-ray beam 8A and is emitted toward the point B of the X-ray detector 12. The X-ray detector 12 that detects the X-ray beam 8 detects the movement amount ΔL13 of the position of the X-ray beam 8, that is, the distance between the points A and B, and detects the focal movement amount from this movement amount ΔL13. To do. In addition, if the movement amount ΔL13 exceeds the allowable range, the tomographic image processing is adversely affected. For this reason, an allowable value of the focal movement amount is set corresponding to the allowable value of the movement amount ΔL13.
[0010]
As an example of a technique for dealing with the above-described focus movement problem, there is a technique in which a mechanism for moving the entire X-ray tube apparatus in the tube axis direction of the rotary anode X-ray tube is added. In this technology, a mechanism that can be moved in the X-ray tube axis direction by a motor drive is provided on the X-ray CT device support base of the X-ray CT device, and the focus movement amount is adjusted in accordance with the measurement result of the focus movement amount. The X-ray tube device is moved in a direction opposite to the direction to compensate for the focal shift amount. As another example of the above-described countermeasure technique, a technique for moving the X-ray detector in the X-ray tube axis direction in correspondence with the measurement result of the focal movement amount is also put into practical use.
[0011]
However, these techniques mechanically move the X-ray tube apparatus and the X-ray detector with an accuracy of several hundred μm, so that the drive mechanism becomes complicated and the support portion becomes large. As a result, the cost of the X-ray CT apparatus is increased, and the miniaturization of the X-ray CT apparatus is hindered.
[0012]
In addition, as a technique for dealing with the above-mentioned focus movement problem with the X-ray detector, a part of the arrangement of the radiation detection elements is changed, the changed part is dedicated to the reference of the X-ray intensity distribution, and the measurement data is fed back to the image. Some perform processing correction (for example, refer to Patent Document 1).
[0013]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-290308
[0014]
However, in the case of this technology, the number of correction programs increases, and the calculation time of image processing increases. In the latter case, the X-ray dose incident on the detector is reduced, which may lead to deterioration in image quality. There are problems such as low efficiency.
In addition, there is a technique that narrows down the width of X-rays irradiated to the detector and uses only a uniform portion of the X-ray intensity distribution (see, for example, Patent Document 2).
[0015]
[Patent Document 2]
Japanese Patent Laid-Open No. 11-295430
[0016]
However, in the case of the present technology, there is a problem that the structure of the detector itself becomes complicated and causes a cost increase.
In addition, as a coping technique in the X-ray tube apparatus itself for the above-mentioned focal movement problem, a part extending in the direction opposite to the moving direction of the focal point is part of the components constituting the rotary anode of the rotary anode X-ray tube. And a structure that increases the length of the portion and cancels the amount of extension in the focal movement direction (see, for example, Patent Document 3).
[0017]
[Patent Document 3]
JP2000-40480
[0018]
However, the structure of the rotating anode has problems such as restrictions on the structural length of the X-ray tube, complicated parts structure and difficulty in manufacturing, and lower rigidity than an integral part.
In addition, the fixed part of the rotating anode has a double tube structure, the inner cylinder part is made of a metal material with high thermal conductivity, and the outer cylinder part is made of a metal material with high strength and low thermal expansion coefficient, thereby reducing the amount of focal movement. Some have aimed at improving the strength of the rotating anode (for example, see Patent Document 4).
[0019]
[Patent Document 4]
JP 2000-340148
[0020]
However, merely improving the structure of the fixed part is not sufficient to solve the problem of the focal shift amount of the entire rotating anode.
Furthermore, by attaching a heater to the member that supports the rotating anode of the X-ray tube in the X-ray tube device and heating it, this member is thermally expanded in the direction opposite to the focal movement direction, thereby canceling the focal movement amount. Some methods have been adopted (see, for example, Patent Document 5).
[0021]
[Patent Document 5]
JP 9-63522 A
[0022]
However, there is a problem that it is difficult to follow the change in the focal point movement amount of the heater heating operation, and the cost increases due to the necessity of providing a separate controller or the like. On the other hand, in recent X-ray CT systems, in order to obtain many tomographic images in a short time, an X-ray tube with a target with a large heat capacity of 5 million heat units (HU: about 0.71 joule) is used. A technique has been developed to mount an interpolated X-ray tube device and take one tomogram in 0.5 seconds (or to perform one scan in 0.5 seconds). In this technology, the scanner equipped with the X-ray tube device rotates at a speed that is approximately twice as high as that of conventional products, so the centrifugal force applied to the X-ray tube device increases in proportion to the square of the scan speed. In addition, since the target becomes larger due to an increase in the heat capacity of the target and a large load is applied to a portion supporting the target, it is necessary to improve the mechanical strength of the rotating anode of the X-ray tube.
[0023]
In order to cope with this, regarding the structure of the X-ray tube itself inserted in the X-ray tube apparatus, the rotor and the heat insulating portion (rotor and rotating shaft and rotor) of the rotating anode are required due to the necessity of improving the strength and reducing the focal movement amount. In order to improve the rigidity by increasing the diameter of the connecting portion), a metal material having a high strength and a low coefficient of thermal expansion such as molybdenum is used as a rotor material.
[0024]
Here, in order to balance the rotation of the rotating anode, the rotor and the heat insulating portion generally adopt a fitting structure with a small tolerance. As a result, if a heat insulating part using a material with a relatively high coefficient of thermal expansion is fitted to a rotor using a material with a low coefficient of thermal expansion, the heat insulating part is tightened by the rotor as the temperature rises, and the rotor is deformed. There is a problem of doing. On the other hand, it is also possible to increase rigidity and prevent deformation by increasing the thickness of the heat insulating part or shortening the length. However, such a method has problems such as a decrease in the heat insulation effect of the heat insulating portion and an increase in the amount of focal movement due to a decrease in the amount of thermal elongation in the reverse direction in the heat insulating portion.
[0025]
[Problems to be solved by the invention]
As described above, various improvements have been made to the problem of the focus movement of the X-ray tube apparatus mounted on the X-ray CT apparatus and the problem of an increase in the load on the rotating anode accompanying the increase in the capacity of the target. However, it is still insufficient. A problem in the conventional X-ray tube apparatus will be described with reference to FIG. FIG. 11 shows an example of the structure of a rotating anode of a rotating anode X-ray tube inserted in a conventional X-ray tube apparatus. In FIG. 11, the rotating anode 2 includes a disk-shaped target 6, a rotor 20 that supports the target 6, a rotating shaft 26 that supports the rotor 20, and a heat insulating cap 24 that connects the rotor 20 and the rotating shaft 26. The bearing 27 includes two bearings 27 that rotatably support the rotating shaft 26, and a fixing portion 28 that fixes and supports the bearing 27. The rotor 20 includes a target support shaft 21, a rotor shoulder portion 22, and a cylindrical portion 23, and each component of the rotor 20 is connected by casting or brazing. Among these components, the components involved in the focal movement are the target 6, the target support shaft 21 and the rotor shoulder 22 of the rotor 20, the heat insulating cap 24, the rotating shaft 26, and the fixed portion 28.
[0026]
These components thermally expand when the temperature of the rotary anode 2 rises, but the target 6, the target support shaft 21, the rotor shoulder 22, the rotary shaft 26, and the fixed portion 28 thermally expand in the direction of increasing the focal shift amount, The heat insulating cap 24 is thermally expanded in a direction to reduce the focal amount. As for the material of the parts related to the focal movement of these parts, the target 6 and the target support shaft 21 are made of a high heat resistant metal material such as molybdenum or a molybdenum alloy, and the rotor shoulder portion 22 and the heat insulating portion 24 are made of stainless steel. A high-strength metal material such as heat-resistant steel is used for the rotating shaft 26, and a highly heat-conductive metal material such as copper is used for the fixed portion 28.
[0027]
In the conventional X-ray tube apparatus in which the rotary anode X-ray tube using the rotary anode 2 is inserted, the focal shift amount when the temperature of the target 6 rises to about 1,000 ° C. is about 350 μm. In the X-ray tube apparatus, the parts involved in the focal movement include the rotary anode 2 of the rotary anode X-ray tube and the anode support structure (not shown) of the X-ray tube container. According to experiments, the former thermally expands in the direction of increasing the focal shift amount, while the latter thermally expands in the direction of decreasing the focal shift amount. In the experimental example, the thermal elongation amount of the rotating anode 2 is about 480 μm, and the thermal elongation amount of the anode support structure is about 130 μm in the direction opposite to the thermal elongation direction of the rotating anode 2, so that the difference between the two as a whole. Is about 350μm. Further, about 310 μm (about 65%) of the elongation due to the thermal expansion of the rotating anode 2 is the largest portion of the rotor 20.
[0028]
In order to reduce the amount of thermal expansion of the rotor 20, it is conceivable to apply a material having a low coefficient of thermal expansion to the rotor shoulder portion 22. For example, when molybdenum or molybdenum alloy is selected as the material, the coefficient of thermal expansion is 4.5 × 10-6 (1 / ° C), which is about 1/3 of 13.6 × 10-6 (1 / ° C) of stainless steel. The elongation amount due to the thermal expansion of the rotor 20 can be significantly reduced.
[0029]
Furthermore, if the rotor shoulder 22 is made of molybdenum or a molybdenum alloy instead of conventional stainless steel, the elastic modulus will increase by about 1.5 times and the rigidity will increase, so it will be added when mounted on an X-ray CT system and scanned at high speed. It can withstand centrifugal force, and the amount of deflection of the rotating anode 2 can be reduced.
[0030]
However, as described above, when molybdenum or a molybdenum alloy is applied as the material of the rotor shoulder 22, the heat insulating cap 24 fitted inside expands more than the rotor shoulder 22 when the temperature of the rotary anode 2 rises. A problem arises in that the tightening stress acts on the cap 24 to cause deformation, and the rotational balance of the rotating anode 2 is lost.
[0031]
Furthermore, the heat insulating cap 24 is connected to the rotor shoulder 22 with several thin screws 25 made of stainless steel, but since this screw 25 has a higher coefficient of thermal expansion than the material of the rotor shoulder 22, There is a problem that the amount of thermal elongation becomes larger than that of the rotor shoulder 22 and the screw 25 is loosened when the temperature rises.
[0032]
As a technique for dealing with the above problem, regarding the loosening of the latter screw 25, the amount of thermal elongation can be reduced by shortening the length of the screw 25. For example, when the length of the portion for fixing the rotor shoulder portion 22 of the screw 25 is about 1 mm, the temperature during use is about 550 ° C., so the amount of thermal elongation is about 5 μm. When tightening using elastic deformation of the screw beyond this amount of elongation, the stress of approximately 980 MPa (100 kg / mm2) is applied to the screw 25, and the stainless steel screw exceeds the yield point and causes plastic deformation. As a result, the tightening force is reduced, and as a result, the screws are loosened.
[0033]
In addition, regarding the problem of the tightening of the former heat insulating cap 24, in order to prevent deformation, the thin cylindrical portion of the heat insulating cap 24 is made thicker and the length in the X-ray tube axial direction is shortened to increase rigidity. Can be considered. However, this method reduces the effect of reducing the heat flow to the bearing 27 for the purpose of protecting the lubricant of the bearing 27, which is the original purpose of the heat insulating cap 24. I can't say that.
[0034]
In view of the above, the present invention improves the structure of the rotating anode of the X-ray tube, greatly reduces the amount of focal movement, and mechanical strength that can withstand the centrifugal force during the 0.5 second scan of the X-ray CT apparatus It is an object to provide an X-ray tube apparatus having an X-ray tube and an X-ray CT apparatus using the same.
[0035]
[Means for Solving the Problems]
In order to achieve the above object, an X-ray tube apparatus of the present invention includes a disk-shaped target, a rotor that supports the target, a rotating shaft that supports the rotor, a bearing that rotatably supports the rotating shaft, and a bearing. A rotating anode having a fixed part to support; a cathode that emits an electron stream to form a focal point that becomes an X-ray source on the target; and an envelope that insulates and supports the rotating anode and the cathode and is sealed in a vacuum-tight manner In an X-ray tube device that stores and supports a rotating anode X-ray tube in an X-ray tube container having an X-ray and electric shock structure, the rotor supports a target, and is highly heat-resistant and mechanical. A target support portion made of a metal material having a high strength, a heat insulation portion joined to the target support portion at one end and supported by the rotating shaft at the other end and made of a metal material having a high mechanical strength, and a target of the heat insulation portion The joint with the support A cylindrical portion having substantially the same outer diameter, connected to the heat insulating portion and made of a metal material having a high conductivity, and the target support portion includes a small diameter portion for supporting a target, and the heat insulating portion. A flange that has a large-diameter portion that is joined to the portion and has a circular hole that accommodates most of the heat-insulating portion on the large-diameter portion side, and the heat-insulating portion is joined to the large-diameter portion of the target support portion A thin cylindrical portion for reducing heat transfer from the target support portion, and a flat portion that forms the bottom of the thin cylindrical portion and is coupled to the rotation shaft, and the target support portion and the heat insulating member. At the joint with the two parts, one has two or more annular projections (hereinafter referred to as annular tooth parts), and the other has one or more, and between the two annular tooth parts. The other one annular tooth portion is brazed in a fitted state (Claim 1).
[0036]
In this configuration, an annular tooth portion that meshes with each other is provided at the joint portion between the target support portion and the heat insulation portion of the rotor that constitutes the rotary anode of the rotary anode X-ray tube inserted in the X-ray tube device, and the target support portion The heat insulation part is made of a high-strength metal material, and the annular tooth parts of both are fitted and brazed, so the rigidity of the joint part of both is improved and the centrifugal force applied when mounted on the X-ray CT system The deflection of the rotating anode caused by the above can be greatly reduced.
[0037]
In the X-ray tube apparatus of the present invention, the target support portion of the rotor is made of a metal material having a high mechanical strength and a low coefficient of thermal expansion, and the heat insulating portion is a metal material having a low thermal conductivity and a high coefficient of thermal expansion. (Claim 2).
[0038]
In this configuration, the target support part of the rotor that constitutes the rotary anode of the rotary anode X-ray tube inserted in the X-ray tube device has an integrated structure including the conventional rotor shoulder, and is made of a metal material having a low coefficient of thermal expansion. Therefore, the amount of thermal elongation of the rotor is greatly reduced, and the amount of focal movement is greatly reduced.
[0039]
In the X-ray tube device of the present invention, the rotor further includes an outer peripheral surface of the annular tooth portion of the target support portion and an annular tooth portion of the heat insulating portion at a joint portion between the target support portion and the heat insulating portion of the rotor. The former fitting portion has at least one fitting portion between the fitting portion with the peripheral surface, the inner peripheral surface of the annular tooth portion of the target support portion, and the outer peripheral surface of the annular tooth portion of the heat insulating portion. In FIG. 2, both the peripheral surfaces are substantially in contact with each other at room temperature, and the latter fitting portion is formed so that both the peripheral surfaces are substantially in contact with each other at a brazing temperature.
[0040]
In this configuration, the annular tooth portion of the target support portion of the rotor and the annular tooth portion of the heat insulating portion are substantially in contact with the outer peripheral surface of the former at the room temperature and the inner peripheral surface of the latter at the time of brazing. Because the outer peripheral surface of the latter is almost in contact, it is fitted with high accuracy in the central axis direction, so the rotor shaft center can be brought out with high accuracy over the entire temperature range during use of the X-ray tube device. The rotational balance of the rotating anode can be improved.
[0041]
In the X-ray tube device of the present invention, two annular tooth portions of the target support portion of the rotor and two annular tooth portions of the heat insulating portion are formed. In this configuration, since the joint portion between the target support portion and the heat insulation portion of the rotor has a meshing structure of two annular tooth portions of both, the strength and rigidity of both joint portions are improved, The axis of the rotor can be obtained with high accuracy.
[0042]
In the X-ray tube apparatus of the present invention, the length of the portion parallel to the central axis of the target support portion of the rotor and the annular tooth portion of the heat insulating portion is larger than the radial width thereof. Is formed.
[0043]
In this configuration, since the length dimension of both of the annular tooth portions is larger than the width dimension at the joint portion between the target support portion and the heat insulating portion of the rotor, the meshing engagement structure of both of the annular tooth portions is provided. The strength and rigidity of the rotor and the accuracy of the shaft center can be improved.
[0044]
In the X-ray tube device of the present invention, the length of the annular tooth portion arranged outside the target support portion of the rotor is longer than that of the annular tooth portion arranged inside. In this configuration, at the joint between the target support part and the heat insulation part of the rotor, the outer ring tooth part of the target support part made of a material having high heat resistance and high strength is fitted so that it enters the heat insulation part more deeply. Therefore, it is possible to suppress deformation in the radial direction at the joint portion between the two due to thermal stress at the time of temperature rise.
[0045]
In the X-ray tube device of the present invention, the length of the annular tooth portion arranged inside the heat insulating portion of the rotor is longer than the length of the annular tooth portion arranged outside. In this configuration, at the joint portion between the target support portion and the heat insulation portion of the rotor, the annular tooth portion inside the heat insulation portion is fitted so as to enter deeper into the target support portion. The deformation in the radial direction can be suppressed.
[0046]
In the X-ray tube device according to the present invention, the annular tooth portion disposed inside the heat insulating portion of the rotor is formed to be thicker than the annular tooth portion disposed outside. In this configuration, at the joint portion between the target support portion and the heat insulating portion of the rotor, the annular tooth portion inside the heat insulating portion made of a material having lower strength at high temperature is reinforced and reinforced. Since the annular tooth portion is fitted, the rigidity of the joint portion between them can be increased, and deformation of the joint portion can be suppressed.
[0047]
In the X-ray tube apparatus according to the present invention, further, at the joint portion between the target support portion and the heat insulating portion of the rotor, a gap in the central axis direction where both the annular tooth portions are fitted to each other is wider than a gap in the radial direction. In addition, the thickness of the brazing material filled in the gap in the central axis direction is made larger than the thickness of the brazing material filling the gap in the radial direction.
[0048]
In this configuration, since the thickness of the brazing material filled in the gap in the central axis direction in which the annular tooth portions of both the joints of the target support portion and the heat insulating portion of the rotor are fitted is increased. Due to the relatively high ductility of the material, it is possible to relieve the stress in the radial direction at the joint between them.
[0049]
In the X-ray tube apparatus of the present invention, the tip of at least one of the annular tooth portions of the target support portion and the heat insulating portion of the rotor is chamfered for stress relaxation. In this configuration, since the corners at the tips of the annular tooth portions are chamfered at the joint between the target support portion and the heat insulating portion of the rotor, stress concentration around the tips of the annular tooth portions is alleviated. , Peeling of the joint surface between the two is prevented.
[0050]
In the X-ray tube apparatus of the present invention, three or more annular tooth portions of the target support portion of the rotor and three or more annular tooth portions of the heat insulating portion are formed. In this configuration, the number of the annular tooth portions of the target support portion and the heat insulating portion of the rotor is increased, so that the mechanical strength of the rotor can be improved and the target support portion and the heat insulating portion are increased by increasing the brazing area. The joint strength with the part can be improved.
[0051]
In the X-ray tube device of the present invention, the length of the annular tooth portion arranged inside the heat insulating portion of the rotor is shorter than the annular tooth portion arranged outside. . In this configuration, since the length of the annular tooth portion inside the heat insulating portion of the rotor is shortened, the strength and rigidity of the entire joint portion between the target support portion and the heat insulating portion are slightly reduced. The workability of the annular tooth part of the heat insulating part is improved, contributing to cost reduction.
[0052]
In the X-ray tube device of the present invention, the annular tooth portion of the target support portion of the rotor further includes an outer tooth portion and an inner tooth portion, and the annular tooth portion of the heat insulating portion includes the outer tooth portion and the inner tooth portion. In the case where the inner teeth of the target support part, the inner teeth of the heat insulation part, the outer teeth of the target support part, and the outer tooth part of the heat insulation part are meshed in this order from the inside, The contact surface between the inner tooth portion of the target support portion and the inner tooth portion of the heat insulation portion, or the contact surface of the inner tooth portion of the heat insulation portion and the outer tooth portion of the target support portion is tapered with respect to the central axis direction of the rotating anode. ing. That is, the joint portion between the target support portion and the heat insulating portion has a fitting structure in which the cross section is Z-shaped and meshes in an annular shape. In this configuration, since stress applied to each part of the fitting structure can be reduced, fatigue failure can be prevented.
[0053]
In the X-ray tube device of the present invention, the target support portion of the rotor is made of molybdenum or a molybdenum alloy, and the heat insulating portion is made of stainless steel. In this configuration, since the material of the target support portion of the rotor is molybdenum or a molybdenum alloy, the amount of thermal elongation of the rotor can be significantly reduced. In addition, by using stainless steel as the material of the heat insulating part, the strength of the joint part of the target support part is improved in cooperation with the high heat resistant high strength material of the target support part, and the mechanical strength and rigidity of the entire rotor are improved. be able to.
[0054]
In the X-ray tube device of the present invention, the fixed portion further includes an inner cylinder portion that supports the bearing and an outer cylinder portion that covers the outer periphery of the inner cylinder portion, and the inner cylinder portion is a metal having a high thermal conductivity. The outer cylinder portion is made of a metal material having a high mechanical strength and a low coefficient of thermal expansion (claim 3). Moreover, the outer cylinder part has covered the range which is supporting the bearing of an inner cylinder part at least among the length of a fixing | fixed part.
[0055]
In this configuration, the rotating part of the rotating anode X-ray tube inserted in the X-ray tube device has a double cylindrical structure, and a metal material having a high mechanical strength and a low coefficient of thermal expansion is used for the outer cylinder part. Because it is used, the range covered by the outer cylinder occupying most of the length of the fixed part, such as the range supporting the bearing of the inner cylinder part, because the amount of thermal expansion is greatly reduced, The amount of focus movement of the X-ray tube device is greatly reduced. Moreover, since a metal material having a large thermal conductivity is used for the inner cylinder part, the temperature rise of the fixed part in use is suppressed, and accordingly, the temperature rise of the bearing supported by the inner cylinder part is also suppressed, Long life of the bearing is secured.
[0056]
In the X-ray tube device of the present invention, the inner cylindrical portion of the fixed portion is made of copper, and the outer cylindrical portion is made of molybdenum or a molybdenum alloy. In this configuration, the outer cylindrical portion of the fixed portion is made of molybdenum or molybdenum alloy having a high mechanical strength and a low coefficient of thermal expansion, and the inner cylindrical portion is made of copper having a high thermal conductivity. Along with a significant reduction in the amount of focal movement of the X-ray tube device, which is the objective, it is possible to achieve a long bearing life.
[0057]
An X-ray CT apparatus of the present invention includes a scanning gantry in which the X-ray tube apparatus of the present invention and an X-ray detector are mounted so as to face each other across an opening into which a subject is inserted, and the X-ray tube An X-ray controller for applying a high voltage load to the apparatus; an imaging table for inserting a placed subject into the opening; the scanning gantry; the X-ray controller and the imaging table; And an operation console for reconstructing a tomographic image of the subject based on the X-ray measurement data collected in (4).
[0058]
In this configuration, since the X-ray tube apparatus of the present invention is used as the X-ray tube apparatus mounted on the X-ray CT apparatus, the amount of focal movement of the X-ray tube apparatus is greatly reduced, and the mechanical strength of the rotating anode is increased. In addition, since the rigidity is improved, a high-quality tomographic image free from artifacts due to focus movement can be obtained, and an X-ray CT apparatus capable of high-speed scanning such as 0.5 second scanning can be realized.
[0059]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, about the code | symbol of drawing, it decided to use the same code | symbol for what has a substantially the same function and a substantially the same structure as a conventional product.
[0060]
A first embodiment of an X-ray tube apparatus according to the present invention will be described with reference to FIGS. In the present invention, since the structure of the rotating anode of the rotating anode X-ray tube inserted in the X-ray tube apparatus is different from that of the conventional example, the following description will focus on the structure of the rotating anode. FIG. 1 is an overall structural view of a rotating anode X-ray tube inserted in the first embodiment of the X-ray tube apparatus according to the present invention, and FIG. 2 is an enlarged sectional view of the structure of the rotating anode in FIG.
[0061]
In FIG. 1, a rotating anode X-ray tube 40 of this embodiment includes a rotating anode 41 having a target 6, a cathode 3 that emits an electron beam to form a focal point that becomes an X-ray source on the target 6, and a rotating anode. An envelope 4 is provided that insulates and supports 41 and the cathode 3 and is sealed in a vacuum-tight manner. Since the structure of the rotating anode 41 is a main part of the present invention, it will be described in detail later with reference to FIG. The cathode 3 and the envelope 4 have the same structure as the conventional example.
[0062]
In FIG. 1, the cathode 3 supports a filament that emits thermoelectrons and focuses a thermoelectron emitted from the filament, a focusing electrode 3A, a holder 3B that supports the focusing electrode 3A, and an insulating support for the holder 3B. It is composed of a stem 3C or the like coupled to the envelope 4. Although the filament is not shown in the drawing, a thin tungsten wire wound in a coil shape is usually used, and thermal electrons are emitted by energizing and heating the filament. The focusing electrode 3A has a semicircular or rectangular focusing groove, and a filament is installed in the focusing groove, and the thermoelectrons from the filament are focused by an electric field formed in the focusing groove to form an electron beam 5, which is a target. Collides with 6 to form focal point 7. The focusing electrode 3A and the holder 3B are made of a metal material such as iron or stainless steel. Most of the stem 3C is made of an insulating material such as heat-resistant glass or ceramic, and a lead for power feeding is embedded in the center portion in a vacuum-tight manner. Power is supplied to the filament and the focusing electrode (cathode potential) through this lead.
[0063]
The envelope 4 includes a body portion 4A made of a metal material such as stainless steel or copper, an anode cylindrical portion 4B that is coupled to an end portion of the rotating anode 41, and insulates and supports it, and a stem 3C of the cathode 3 The cathode cylindrical portion 4C and the like are joined and insulated and supported. The anode cylindrical portion 4B and the cathode cylindrical portion 4C are made of an insulating material such as heat resistant glass or ceramic. An X-ray emission window 12 is attached to a portion near the position of the focal point 7 of the target 6 at the center outer peripheral portion of the body portion 4A. The X-ray radiation window 12 is made of a material having good X-ray transparency such as beryllium, and is coupled to the body portion 4A by brazing or welding. X-rays generated at the focal point 7 are extracted from the X-ray emission window 12 to the outside.
[0064]
Next, with reference to FIG. 2, the structure of the rotating anode 41 that is a main part of the present embodiment will be described. 2, FIG. 2 (a) is an enlarged cross-sectional view of the rotating anode 41 of FIG. 1, and FIG. 2 (b) is an enlarged view of a circle A portion of FIG. 2 (a). In FIG. 2 (a), the rotating anode 41 of the present embodiment includes a disk-shaped target 6, a rotor 44 that supports the target 6 by fixing it with a nut 19, a rotating shaft 26 that supports the rotor 44, and a rotating shaft. The bearing 27 includes a bearing 27 that rotatably supports the bearing 26, and a fixing portion 28 that supports the bearing 27. The feature of this embodiment is the structure of the rotor 44, which is a structure in which the rotor 20 and the heat insulating cap 48 in the conventional product of FIG. 9 are integrated.
[0065]
The rotor 44 of this embodiment includes a target support shaft 46, a heat insulating cap 48, and a cylindrical portion 23. The target support shaft 46 integrates the conventional target support shaft 21 and the rotor shoulder 22, and the heat insulating cap 48 has substantially the same function as the conventional heat insulating cap 24. The cylindrical portion 23 is the same as that of the conventional product, but is coupled to the flange portion of the heat insulating cap 48 in this embodiment.
[0066]
Since the target support shaft 46 has a structure in which the conventional target support shaft and the rotor shoulder are integrated, the portion 46A that supports the target 6 at one end has a narrow outer diameter (hereinafter referred to as a small diameter portion) from the target 6. The part 46B that suppresses heat conduction and joins the heat insulating cap 48 at the other end has a large outer diameter (hereinafter, referred to as a large diameter part) that is almost the same as the cylindrical part 23, and can be easily connected to the heat insulating cap 48 and the cylindrical part 23. I have to. The large-diameter portion 46B of the target support shaft 46 corresponds to a conventional rotor shoulder, and the large-diameter portion 46B is provided with a circular hole 46C that accommodates most of the heat insulating cap 48.
[0067]
The heat insulating cap 48 is joined to the large diameter portion 46B of the target support shaft 46, a thin cylindrical portion 48B connected to the flange portion 48A, and connected to the thin cylindrical portion 48B and fastened to the rotary shaft 26. And bottom surface portion 48C. Except for the structure of the flange portion 48A, it has almost the same structure as the conventional product. The thin cylindrical portion 48B is processed into a thin cylindrical shape for the purpose of heat insulation and extends from the flange portion 48A to the target 6 side. . The bottom surface portion 48C forms the bottom surface of the thin-walled cylindrical portion 48B, is processed into a flat shape, and is fastened to the rotary shaft 26 with a screw or the like at the flat surface portion. The thin cylindrical portion 48B and the bottom surface portion 48C are accommodated in the hole 46C of the large diameter portion 46B of the target support shaft 46.
[0068]
The target support shaft 46 is made of a metal material having a low coefficient of thermal expansion, high heat resistance, and high mechanical strength, such as molybdenum or a molybdenum alloy. The heat insulating cap 48 is made of a metal material having a relatively high coefficient of thermal expansion and high mechanical strength, such as stainless steel. The connecting portion between the large diameter portion 46B of the target support shaft 46 and the flange portion 48A of the heat insulating cap 48 has a cross-sectional fitting structure as shown in FIG. That is, both have two-layered annular protrusions (hereinafter referred to as “annular teeth”), and the respective annular teeth are engaged with each other.
[0069]
In FIG. 2 (b), the target support shaft 46 has two layers of annular tooth portions 47 of substantially the same length, that is, an outer annular tooth portion 47A and an inner annular tooth portion 47B, and the heat insulating cap 48 also has two layers. An annular tooth portion 49 having substantially the same length, that is, an outer annular tooth portion 49A and an inner annular tooth portion 49B, and a heat insulating cap 48 between the two annular tooth portions 47A and 47B of the target support shaft 46. The inner annular tooth portion 49B is fitted, and the outer annular tooth portion 47A of the target support shaft 46 is fitted between the two annular tooth portions 49A and 49B of the heat insulating cap 48. The cross-sections of the respective annular tooth portions 47A, 47B, 49A, 49B are rectangular with the long axis in the central axis direction of the rotating anode 41. That is, the length of the annular tooth portion in the central axis direction is larger than the radial width. Moreover, although the radial width method of an annular tooth part is usually made with the substantially same dimension, it cannot be overemphasized that it may make with a different dimension.
[0070]
The target support shaft 46 and the heat insulating cap 48 are joined by brazing using, for example, copper 50 having a melting point of 1,083 ° C. in a state where the annular tooth portions 47 and 49 of the target support shaft 46 are fitted. The radial fitting dimensions of the annular teeth 47, 49 before brazing are the outer circumference of the outer annular teeth 47A of the target support 46 and the inner circumference of the outer annular teeth 49A of the heat insulating cap 48. And the gap between the outer periphery of the inner annular tooth portion 47B of the target support portion 46 and the inner periphery of the inner annular tooth portion 47B of the heat insulating cap 48 are almost eliminated so that the two substantially come into contact with each other. By doing in this way, the axial center of the target support shaft 46 and the heat insulation cap 48 can be taken out with high precision. In the above, the high-precision fitting of the annular tooth portions of the target support shaft 46 and the heat insulating cap 48 is performed at two locations, the outer annular tooth portions and the inner annular tooth portions. In this case, it is not always necessary to carry out at two places, and only one of the outer ring tooth portions or the inner ring tooth portions may be used.
[0071]
In addition, the gap between the outer circumference of the outer annular tooth portion 47A of the target support portion 46 and the outer circumference of the inner annular tooth portion 49B of the heat insulating cap 48 is a loose fitting at room temperature, and the brazing material (copper) 50 The melting point is set in consideration of the difference in thermal expansion coefficient between the target support shaft 46 and the heat insulating cap 48 so that the two are almost in contact with each other. By adopting such a fitting structure, the target support shaft 46 and the heat insulating cap 48 have concentric cylindrical contact surfaces at both the fitting assembly time and the brazing temperature. The deviation can be almost completely eliminated.
[0072]
In the above, the number of the annular tooth portions 47 and 49 of the target support shaft 46 and the heat insulating cap 48 has been described as two layers each, but the meshing fitting structure of the annular tooth portions 47 and 49 of the present invention is as follows. One of the target support shaft 46 and the heat insulating cap 48 can be realized by having two layers of annular teeth, and the other has one layer of annular teeth. The minimum requirement is that one has two layers of ring teeth and the other has one layer of teeth.
[0073]
Further, regarding the high-precision fitting at the time of fitting and assembly of the annular tooth portions 47 and 49 of the target support shaft 46 and the heat insulation cap 48, both of the target support shaft 46 and the heat insulation cap 48 are included. This can be realized by having one ring tooth part with one layer and one ring tooth part with the other. However, since both of them have two layers of annular teeth 47 and 49, the accuracy and safety of high-precision fitting are improved. Therefore, in the following explanation, both have two layers of annular teeth. An example of having a part is shown.
[0074]
The fitting structure of the target support shaft 46 of the rotor 44 of the rotating anode 41 and the heat insulating cap 48 of the present embodiment has both a surface parallel to and perpendicular to the central shaft 52 of the rotating anode 41. Compared to the conventional fitting structure with only parallel surfaces, the joint area between the two is increased, and since the both ring teeth engage with each other, it has a fitting shape. The structure is more able to withstand tensile or compressive thermal stress in all directions generated by a large difference in thermal expansion. Furthermore, by improving the rigidity of the joint between the target support shaft 46 and the heat insulating cap 48, the deflection of the rotating anode 41 caused by the centrifugal force applied when the X-ray tube device is mounted on the X-ray CT device can be greatly reduced. The effect that it can do is also acquired.
[0075]
Further, in the structure of the rotor 44 described above, since the heat insulating cap 48 is structured to clamp the target support shaft 46 isotropically in the radial direction when cooled to room temperature after brazing, it is placed on the periphery of the heat insulating cap like the conventional product. Uneven deformation can be prevented.
[0076]
Further, in FIG. 2, the heat insulating cap 48 has a thin cylindrical portion 48B for heat insulation as described above, and by improving the strength of the target support shaft 46 itself and improving the strength of the joint portion between the target support shaft 46 and the heat insulating cap 48, The length of the large-diameter portion 46B of the target support shaft 46 can be lengthened, and the thin cylindrical portion 48B can be lengthened, and the heat insulation effect in this portion can be improved. Further, in this embodiment, a gap 56 for preventing contact is formed between the outer peripheral surface 54 of the thin cylindrical portion 48B of the heat insulating cap 48 and the inner cylindrical surface 55 of the inner annular tooth portion 47B of the target support shaft 46. To secure the heat insulation effect.
[0077]
Further, in the rotating anode 41 of the present embodiment, the length of the large diameter portion 46B of the target support shaft 46 can be increased as described above, so that the length of the thin cylindrical portion 48B of the heat insulating cap 48 is increased, The amount of thermal expansion in the direction opposite to the movement can be increased, and the amount of focal movement can be reduced. In this case, if the length of the thin cylindrical portion 48B of the relatively thin heat insulating cap 48 is extended, the rigidity of the rotary anode 41 is reduced.In contrast, by increasing the thickness of the thin cylindrical portion 48B, The problem can be avoided. In addition, the heat insulating effect of the heat insulating cap 48 at this time is maintained by offsetting the negative thickness portion because the length of the thin cylindrical portion 48B is extended.
[0078]
Next, second to seventh embodiments of the X-ray tube apparatus according to the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view of the main part of the rotating anode of the second to seventh embodiments of the X-ray tube apparatus according to the present invention. First, a second embodiment of the X-ray tube apparatus of the present invention will be described with reference to FIG. FIG. 3 (a) shows a cross-sectional view of the joint portion between the target support shaft of the rotor and the heat insulating cap, which is the main part of the present embodiment. In FIG. 3 (a), the rotor 60 of the rotating anode of the present embodiment has almost the same structure as that of the first embodiment, and the joint portion between the target support shaft 62 and the heat insulating cap 64 is a ring tooth of both. Each part has a fitting structure that meshes with each other. In the present embodiment, the length of the outer ring tooth portion 63A of the target support shaft 62 in the central axis direction is longer than the length of the inner ring tooth portion 63B, and the outer ring tooth portion 63A is the outer circle of the heat insulating cap 64. The ring tooth portion 65A and the inner ring tooth portion 65B are fitted deeply.
[0079]
When two members with different thermal expansion are brazed with a fitting structure, complicated thermal stresses with different directions and sizes are generated due to the difference in thermal expansion of the brazed member and the rise and fall of the temperature. In the embodiment, the length of the outer annular tooth portion 63A of the target support shaft 62 made of a material having high heat resistance and high strength is extended to be fitted deeply into the heat insulating cap 64. Deformation in the direction can be suppressed.
[0080]
FIG. 3 (b) shows a cross-sectional view of the joint portion between the target support shaft of the rotor and the heat insulating cap, which is the main part of the third embodiment of the X-ray tube apparatus according to the present invention. In FIG. 3 (b), at the joint portion between the target support shaft 68 and the heat insulation cap 70 of the rotor 66 of the rotary anode of the present embodiment, the length in the central axis direction of the inner annular tooth portion 71B of the heat insulation cap 70 is outside. It is longer than the length of the annular tooth portion 71A, and this inner annular tooth portion 71B is fitted deeply between the outer annular tooth portion 69A and the inner annular tooth portion 69B of the target support shaft 68. . Also in the present embodiment, the inner annular tooth portion 71B of the heat insulating cap 70 has a shape that fits deeply into the target support shaft 68, and therefore, deformation in the radial direction at the joint portion between them can be suppressed.
[0081]
FIG. 3 (c) shows a cross-sectional view of the joint portion between the target support shaft of the rotor and the heat insulating cap, which is the main part of the fourth embodiment of the X-ray tube apparatus according to the present invention. In FIG. 3 (c), the radial width of the inner annular tooth portion 77B of the heat insulating cap 76 is particularly wide at the joint between the target support shaft 74 of the rotor 72 of the rotating anode of this embodiment and the heat insulating cap 76. The outer annular tooth portions 75A and 77A of both are narrowed and fitted in the radial direction. In this embodiment, by increasing the width of the inner annular tooth portion 76B of the heat insulating cap 76 made of a material (such as stainless steel) having a lower strength than the material of the target support shaft 74 (such as molybdenum), the rigidity is increased. , Deformation of the joint between the two can be suppressed.
[0082]
FIG. 3 (d) shows a cross-sectional view of the joint portion between the target support shaft of the rotor and the heat insulating cap, which is the main part of the fifth embodiment of the X-ray tube apparatus according to the present invention. In FIG. 3 (d), the joint structure between the target support shaft 80 and the heat insulating cap 82 of the rotor 78 of this embodiment is almost the same as that of the fourth embodiment except for the gap. ing. That is, the fitting structure in the radial direction is exactly the same, and in the central axis direction, it is the same structure except that the gap into which the brazing material (copper) 50 enters is slightly wider than in the radial direction.
[0083]
In the present embodiment, as shown in the drawing, the two layers of annular teeth 81A, 81B of the target support shaft 80 and the two layers of teeth of teeth 83A, 83B of the heat insulating cap 82 are fitted to each other in the direction of the central axis. The gaps 84A to 84D into which the brazing material 50 enters when brazing between the two are set slightly wider. By brazing with these slightly wider gaps 84A to 84D, the gaps 84A to 84D are filled with the brazing material 50 thicker. Since a relatively high ductility material such as copper is used for the brazing material 50, the brazing material 50 corresponding to the thickness of the gaps 84 </ b> A to 84 </ b> D has an effect of relieving the radial stress at the joint surfaces of both. In the illustrated example, the dimensions of the gaps 84A to 84D are substantially the same, but it goes without saying that the dimensions may be increased or decreased for some of the gaps.
[0084]
FIG. 3 (e) shows a cross-sectional view of the joint portion between the target support shaft of the rotor and the heat insulating cap, which is the main part of the sixth embodiment of the X-ray tube apparatus according to the present invention. In FIG. 3 (e), at the joint portion between the target support shaft 88 and the heat insulation cap 90 of the rotor 86 of the present embodiment, the outer ring tooth portion 89A of the target support shaft 88 and the inner ring tooth portion 91B of the heat insulation cap 90. The tips 92 and 93 are semicircular, and the bottoms of the annular groove portions into which the respective annular tooth portions 89A and 91B are fitted are also brazed as a semicircular shape.
[0085]
When the cross-sectional shape of the annular tooth portion is rectangular, stress concentrates on the corner of the tip. For this reason, as in the present embodiment, the tips 92 and 93 of the annular tooth portions 89A and 91B are made semicircular and rounded, so that the corner portions of the tips 92 and 93 of the annular tooth portions 89A and 91B are formed. The stress concentration is relaxed, and peeling of the joint surface between the target support shaft 88 and the heat insulating cap 90 can be prevented. In the drawing, the entire tips 92 and 93 of the annular tooth portions 89A and 91B are semicircular. However, the corners of the tips 92 and 93 have the same effect even if they are rounded or rounded less than the semicircular shape. Is obtained. Further, when the radial width is narrow like the annular tooth portion 89A of the target support shaft 88, the same effect can be obtained even if the semicircular machining of the bottom of the annular groove portion into which it is fitted is omitted.
[0086]
In the fifth embodiment shown in FIG. 3 (d) and the sixth embodiment shown in FIG. 3 (e), the radial width of the annular tooth portion is set in the fourth embodiment in FIG. 3 (c), respectively. Although the same as the examples, the technical contents of these embodiments can be applied to a configuration different from the fourth embodiment, such as the first to third embodiments.
[0087]
FIG. 3 (f) shows a cross-sectional view of the joint portion between the target support shaft of the rotor and the heat insulating cap, which is the main part of the seventh embodiment of the X-ray tube apparatus according to the present invention. This embodiment is obtained by increasing the number of annular tooth portions as compared with the first embodiment of FIG. In FIG. 3 (f), the target support shaft 96 of the rotor 94 has four annular teeth 97A to 97D, and the heat insulating cap 98 also has four annular teeth 99A to 99D. The portions are alternately meshed and brazed with a brazing material 50 such as copper.
[0088]
In the illustrated example, the number of the annular tooth portions is four, but it goes without saying that other numbers may be used. The number of annular teeth is limited by the size of the rotor 94 (particularly the outer diameter) and the workability of the member, but by increasing this number as much as possible, the mechanical strength of the rotor 94 is improved. In addition, since the brazing area is further increased, the bonding strength between the target support shaft 96 and the heat insulating cap 98 can be improved. As a result, it is possible to improve safety when the X-ray tube apparatus is mounted on the X-ray CT apparatus and used.
[0089]
Next, an eighth embodiment of the X-ray tube apparatus according to the present invention will be described with reference to FIG. FIG. 4 is an enlarged cross-sectional view of the structure of the rotating anode of the eighth embodiment of the X-ray tube apparatus according to the present invention. FIG. 4 (a) shows a cross-sectional view of the entire rotating anode, and FIG. 4 (b) shows an enlarged view of a circle A portion in FIG. 4 (a). In FIG. 4 (a), the rotary anode 100 of the present embodiment has the same structure as the rotary anode 41 of the first embodiment, except for the rotor 101. FIG. 4B is an enlarged cross-sectional view of a joint portion between the target support shaft 102 and the heat insulating cap 104 of the rotor 101, which is a main part of the present embodiment. In FIG. 4 (b), in the rotor 101 of the present embodiment, the length of the inner annular tooth portion 105B of the heat insulating cap 104 in the central axis direction is made shorter than that of the outer annular tooth portion 105A, and the target support shaft 102 has an annular shape. The teeth 103A and 103B are fitted and brazed.
[0090]
In the case of the present embodiment, since the length of the inner annular tooth portion 105B of the heat insulating cap 104 is shortened, the rigidity of the entire joint portion is slightly lower than that of the first embodiment, but the target support shaft 102 and The workability of the annular teeth 103A, 103B, 105A, 105B of the heat insulating cap 104 is improved. For this reason, it is effective when the stress generated at the joint of the rotor 101 is relatively low, such as when the outer diameter of the rotor 101 is thin or when the operating temperature is low.
[0091]
Next, a ninth embodiment of the X-ray tube apparatus according to the present invention will be described with reference to FIG. FIG. 5 is an enlarged sectional view of the structure of the rotating anode of the ninth embodiment of the X-ray tube apparatus according to the present invention. FIG. 5 (a) shows a sectional view of the entire rotating anode, and FIG. 5 (b) shows an enlarged view of a circle A portion in FIG. 5 (a). In FIG. 5 (a), the rotary anode 200 of the present embodiment has the same structure as the rotary anode 41 of the first embodiment, except for the rotor 201. FIG. 5 (b) is an enlarged cross-sectional view of a joint portion between the target support shaft 202 and the heat insulating cap 204 of the rotor 201, which is a main part of the present embodiment. In FIG. 5 (b), the annular teeth of the target support shaft 202 have outer teeth 203A and inner teeth 203B. On the other hand, the annular teeth of the heat insulating cap 204 have outer teeth 205A and inner teeth 205B. The mutual fitting is a structure in which the inner teeth 203B, the inner teeth 205B, the outer teeth 203A, and the outer teeth 205A are engaged with each other in this order from the inside. In this structure, the contact surface 237 between the outer teeth 203A of the target support shaft 202 and the inner teeth 205B of the heat insulation cap 204 has a structure (taper surface 237) that is tapered with respect to the central axis direction of the rotary anode X-ray tube. The joint between the target support shaft 202 and the heat insulating cap 204 has a fitting structure in which the cross section is Z-shaped and meshes in an annular shape.
[0092]
In this embodiment, the stress applied to each part of the fitting structure is reduced. The principle will be described with reference to FIG. However, FIG. 6 (a) shows a structure in which only the radial surfaces are butted, FIG. 6 (b) shows a rectangular ring-shaped protrusion 331 on the heat insulating cap 314A, and a ring-shaped groove 332 on the rotor shoulder 318A. When the two are fitted and brazed together (substantially the same as in Example 8), FIG. 6 (c) is this example.
[0093]
In the structure in which only the radial surfaces in FIG. ² A degree of shear stress 330 is generated along the brazed surface. There is a problem in that the fatigue stress is caused by the amplitude of the shear stress 330 that is applied or not applied when the anode X-ray tube is used or not used. When the brazed part breaks, there is a problem that the axis of the rotor bends to cause unbalance of the anode and rotational vibration becomes large.
[0094]
For example, when the heat insulating cap 314A is provided with a rectangular ring-shaped protrusion 331 and the rotor shoulder 318A is provided with a ring-shaped groove 332, and the two are fitted and brazed (see FIG. 6 (b)). )) Is considered. In this structure, since the ring suppresses the thermal expansion in the radial direction with respect to the rotation axis, the shear stress 333 generated in the brazing radial direction can be reduced. However, since the ring-shaped protrusion 331 itself undergoes thermoelastic-plastic deformation due to a temperature change, the stress at that portion increases. Therefore, as a result of stress analysis, the brazed portion 334 on the upper surface of the ring-shaped protrusion 331 has a 40 kg / mm perpendicular to the surface. ² Since a certain degree of tensile stress 335 is generated on the entire surface, the problem of causing fatigue failure remains.
[0095]
In order to solve this problem, the structure of this embodiment (FIG. 6c) reduces the tensile stress 335 on the entire brazed part, particularly the upper surface of the ring, thereby preventing fatigue failure. As described with reference to FIG. 5, the ring-shaped protrusion 336 is fitted and brazed in a Z shape, and the thermal expansion and contraction of the ring-shaped protrusion 336 itself is suppressed by the taper surfaces 337 being caught together. The tensile stress 339 on the ring upper surface is 30 kg / mm ² The distribution range is reduced to about 1/5 instead of the entire surface. As a result, the stress of the entire brazed surface is reduced, and fatigue failure can be prevented. This embodiment is not limited to the case where there are two annular teeth on the target support shaft side and the heat insulating cap side as shown above, but also applicable to other numbers as shown in the seventh embodiment. Needless to say, you can.
[0096]
Next, an analysis result example of the thermal expansion amount of the rotating anode of the first to ninth embodiments of the X-ray tube apparatus according to the present invention described above will be described with reference to FIG. FIG. 7 compares the analysis results of the thermal elongation of the rotating anodes of the first example of the present invention and the conventional example. FIG. 7 (a) is a calculation example for the rotating anode of the first embodiment of the present invention, and FIG. 7 (b) is a calculation example for the rotating anode of the conventional example. In the rotating anodes of the first to ninth embodiments of the present invention, the amount of thermal elongation is structurally substantially the same, so that the first embodiment is shown here as a representative example. In the rotary anode 41 of the first embodiment, the target support shaft 46 of the rotor 44 is an integration of the target support shaft 21 and the rotor shoulder 22 of the rotary anode 2 of the conventional example. In order to make the comparison with the anode 2 easier to understand, in the calculation example of FIG. 7 (a), the target support shaft 46 is divided into a portion corresponding to the target support shaft 21 of the conventional example and a portion corresponding to the rotor shoulder portion 22. Showed.
[0097]
In FIG. 7, the thermal elongation amount of the rotating anode 2 of the conventional example is about 480 μm, whereas the thermal elongation amount of the rotating anode 41 of the first embodiment is about 320 μm, and the thermal elongation amount is reduced by about 160 μm. ing. This reduction effect is obtained due to the improvement of the rotor structure. Therefore, in the present invention, the strength of the rotating anode is improved and the amount of thermal elongation is reduced.
[0098]
When the calculation result of the thermal elongation amount of the rotating anode shown in FIG. 7 is evaluated as the focal point movement amount of the entire X-ray tube apparatus, the thermal elongation amount inside the X-ray tube container when using the X-ray tube apparatus, in particular, X It is necessary to consider the amount of thermal elongation of the anode support part of the tube. This amount of thermal elongation is about 130 μm in the direction of reducing the amount of focal movement, as described in the prior art section. In consideration of this, the focal point movement amount of the entire X-ray tube apparatus of the first embodiment is about 190 μm, compared to about 350 μm in the conventional example.
[0099]
Next, a tenth embodiment of the X-ray tube apparatus according to the present invention will be described with reference to FIG. FIG. 8 is an enlarged cross-sectional view of the rotating anode of the tenth embodiment of the X-ray tube apparatus according to the present invention. In this embodiment, the structure of the rotor and the fixed part of the rotating anode is improved. In FIG. 8, the rotating anode 110 of the present embodiment has the same structure as the rotating anode 41 of the first embodiment shown in FIG. 2 except for the fixed portion 112. It has a double cylindrical structure composed of an outer cylindrical portion 116. In the following, the structure of the fixing portion 112 will be described mainly.
[0100]
The structure of the fixing portion 112 of this embodiment employs a structure similar to the double cylinder structure previously proposed by the inventors of the present invention in Japanese Patent Laid-Open No. 2000-340148. In FIG. 8, the entire structure of the fixing portion 112 is substantially the same as that of the first embodiment of the present invention shown in FIG. 2, but the fixing portion 112 is an inner cylinder portion 114 that supports the outer periphery of the bearing 27. And an outer cylinder portion 116 partially covering the outer periphery of the outer cylinder. The inner cylinder portion 114 is made of a metal material such as copper having a high thermal conductivity, and the outer cylinder portion 116 is made of a metal material such as molybdenum or molybdenum alloy having a high mechanical strength and a low thermal expansion coefficient. The structure of the hole 118 into which the bearing 27 of the inner cylinder part 114 is inserted and the anode end 34 are substantially the same as those of the fixed part 28 of the conventional example. The outer cylinder part 116 covers the most range of the outer peripheral part of the inner cylinder part 114 in the central axis direction. In the illustrated example, the outer cylinder part 116 covers from the entrance of the hole 118 of the inner cylinder part 114 to the vicinity of the anode end 34. The range covered by the outer cylindrical portion 116 is preferably as long as possible, but it is difficult to make the entire length of the fixed portion 112 due to the connection with the envelope. From the entrance of the hole 118 to the front of the connection portion with the envelope. Further, although the covering range of the outer cylinder part 116 is effective even if it is short, it is appropriate to cover the entire hole part 118 of the inner cylinder part 114 because of the structure of the fixing part 112.
[0101]
As described above, the fixing portion 112 has a double cylindrical structure, and the inner cylinder portion 114 made of copper having a low mechanical strength is covered with the outer cylinder portion 116 made of molybdenum or a molybdenum alloy having a high mechanical strength. In addition, the mechanical strength and rigidity of the fixing portion 112 can be significantly improved.
[0102]
In the present embodiment, since the fixing portion 112 has a double cylindrical structure, the large thermal expansion of copper or the like that is the material of the inner cylinder portion 114 is small such as molybdenum or molybdenum alloy that is the material of the outer cylinder portion 116. The mechanism is suppressed by thermal expansion. For this reason, the elongation amount due to the thermal expansion of the portion of the fixed portion 112 covered by the outer cylinder portion 116 is substantially the same as the elongation amount due to the low thermal expansion of the outer cylinder portion 116 such as molybdenum or molybdenum alloy. In addition, the temperature rise of each part of the fixing part 112 is suppressed to the same level as that of the fixing part 28 of the conventional example due to the effect of the inner cylinder part 114 made of a material having high thermal conductivity such as copper as described above. Is done. As a result, when the lengths of the fixing portion 112 and the outer cylindrical portion 116 are, for example, 110 mm and 90 mm, respectively, the thermal elongation amount in the fixing portion 112 is about 80 μm, which is about 120 μm compared to about 200 μm in the conventional example. Reduced.
[0103]
Therefore, in the X-ray tube apparatus of the present embodiment, the amount of focal movement is further reduced by about 120 μm to about 70 μm compared to about 190 μm of the first embodiment, so that the focal movement amount can be reduced to 100 μm or less. It becomes possible. As a result, the fluctuation of the focal shift amount falls within the applicable range of the correction coefficient determined by calibration at the time of image processing, so that high image quality without image degradation such as artifacts in practical use with X-ray CT equipment. Can be obtained.
[0104]
FIG. 9 shows an example of a configuration diagram of an X-ray CT apparatus equipped with the X-ray tube apparatus according to the present invention. In FIG. 9, an X-ray CT apparatus 120 includes an X-ray tube apparatus 122 according to the present invention, irradiates a subject with X-rays and collects X-ray measurement data, and an operation of the scanning gantry 124. An operation console 126 for creating a tomogram from the control and the image data, an imaging table 128 for mounting the subject, and the like are included.
[0105]
The scanning gantry 124 includes an X-ray tube device 122 and an X-ray detector 130 that are arranged so as to face each other around the opening 132A and mount the scanner 132 to rotate around the subject, and to control the rotation of the scanner 132. A rotation controller 134, an X-ray controller 136 that controls the X-ray output of the X-ray tube device 122, a collimator 10 that narrows the X-ray into a fan-shaped beam, a collimator controller 138 that controls the irradiation range of the X-ray beam, The data detector 140 is configured to collect X-ray measurement data by the line detector 130 and send it to the operation console 126.
[0106]
The operation console 126 includes a central processing unit 142 that processes image data and various types of data for controlling the operation of the X-ray CT apparatus, a display device 144 that displays a tomographic image, and data such as a tomographic image. Enter the storage device 146 to save, the data collection buffer 148 to temporarily save the X-ray measurement data from the data collection unit 140, the operation control data of the X-ray CT device, etc. An operation device 130 for operating the device, a control gantry 124 based on control data from the operation device 150, a control interface 152 for controlling the operations of various controllers 134, 136, 138 and an imaging table 128 included therein, and the like Is done. The imaging table 128 inserts the subject on the bed 132A into the opening 132A provided at the center of the scanner 132.
[0107]
In FIG. 9, the X-ray tube device according to the present invention is used as the X-ray tube device 122 mounted on the scanner 132 of the scanning gantry 124. Therefore, the mechanical strength and rigidity of the rotating anode during use of the X-ray tube device 122 are remarkably improved compared to the conventional product, and the focal shift amount of the X-ray tube device 122 as a whole is greatly reduced compared to the conventional product. ing.
[0108]
In taking a tomographic image with the X-ray CT apparatus 120, the X-ray tube apparatus 122 is mounted on the scanner 132 of the scanning gantry 124 opposite to the X-ray detector 130, and under the control of the rotation controller 134, The subject rotates on the imaging table 128 and rotates around the subject inserted into the opening 132A of the scanner 132. At the same time, a high voltage load is applied to the X-ray tube device 122 under the control of the X-ray controller 136, and the subject is irradiated with X-rays. The X-ray transmitted through the subject is measured by the X-ray detector 130, and the X-ray measurement data is sent to the operation console 126 via the data collection unit 140 and reconstructed as a tomographic image by the central processing unit 142. .
[0109]
If the tomographic imaging of the subject is continued, the rotating anode of the X-ray tube device 122 is heated. However, in the X-ray tube device 122 of the present invention, the amount of focal movement is small, so there is no artifact in the tomographic image. A high-quality tomographic image can be obtained. As a result, unlike the conventional X-ray CT apparatus, a mechanism for correcting the focal movement by moving the X-ray tube apparatus itself in the X-ray tube axis direction becomes unnecessary, thereby reducing the cost of the X-ray CT apparatus. Can do.
[0110]
Further, in the X-ray CT apparatus 120 equipped with the X-ray tube apparatus 122 of the present invention, as described above, the mechanical strength of the rotating anode of the X-ray tube apparatus 122 is improved and the rigidity is increased. The resistance to stress caused by centrifugal force applied to the rotating anode when the scanner 132 of 124 is rotated is further increased. As a result, the X-ray CT system can scan faster than before, and it is possible to perform imaging with a 0.5 second scan.
[0111]
【The invention's effect】
As described above, in the X-ray tube apparatus of the present invention, the structure of the rotor of the rotating anode of the insertion X-ray tube, particularly the structure of the joint portion between the target support portion and the heat insulating portion, includes a plurality of annular teeth. The mechanical strength and rigidity of the rotating anode could be greatly improved by providing a fitting structure in which the two annular tooth portions mesh with each other.
[0112]
In addition, in the X-ray tube apparatus of the present invention, along with the improvement of the rotor structure described above, the target support portion is made of a metal material having high heat resistance, high mechanical strength, and low thermal expansion coefficient, and the heat insulating portion is mechanical strength. With a high metal expansion coefficient, the mechanical strength and rigidity of the rotating anode can be improved, the amount of thermal elongation of the rotating anode can be greatly reduced, and the amount of focal movement can be greatly reduced. did it.
[0113]
Further, in the X-ray tube apparatus of the present invention, in addition to the improvement of the structure and material of the rotor of the rotary anode described above, the fixed part has a double cylindrical structure, the outer cylinder part has a high mechanical strength, and has a low thermal expansion coefficient. By configuring the inner cylinder with a material having a high thermal conductivity, the amount of thermal elongation of the rotating anode can be reduced, and the amount of focal movement can be greatly reduced.
[0114]
Moreover, in the X-ray CT apparatus of the present invention, since the X-ray tube apparatus of the present invention is mounted, the mechanical strength and rigidity of the rotating anode of the X-ray tube apparatus are greatly improved compared to the conventional products, Scanning gantry scanners can be rotated at high speed, and high-speed scanning of about 0.5 seconds is possible.
[0115]
Further, in the X-ray CT apparatus of the present invention, the amount of thermal elongation of the mounted X-ray tube apparatus is greatly reduced, and the amount of focal movement is significantly reduced, which is caused by focal movement during tomographic imaging. Occurrence of artifacts is eliminated and a high-quality tomographic image can be obtained. In addition, the rotor and fixed part of the rotating anode of the X-ray tube device can be used without a mechanism that moves the X-ray tube device in the X-ray tube axis direction due to a significant reduction in the amount of focal movement. The installation and control of these mechanisms are not required, and the image quality can be improved and the cost of the apparatus can be reduced.
[Brief description of the drawings]
FIG. 1 is an overall structural view of a rotary anode X-ray tube inserted in a first embodiment of an X-ray tube apparatus according to the present invention.
FIG. 2 is an enlarged cross-sectional view of the structure of the rotating anode in FIG.
FIG. 3 is a cross-sectional view of a main part of a rotating anode of second to seventh embodiments of an X-ray tube apparatus according to the present invention.
FIG. 4 is an enlarged cross-sectional view of the structure of a rotating anode of an eighth embodiment of the X-ray tube apparatus according to the present invention.
FIG. 5 is an enlarged cross-sectional view of the structure of the rotating anode of the ninth embodiment of the X-ray tube apparatus according to the present invention.
FIG. 6 is a principle diagram of stress reduction applied to a fitting structure portion.
FIG. 7 is a comparison of the amount of thermal elongation between the rotating anodes of the first embodiment of the present invention and the conventional example.
FIG. 8 is an enlarged cross-sectional view of the structure of the rotating anode of the ninth embodiment of the X-ray tube apparatus according to the present invention.
FIG. 9 is an example of a configuration diagram of an X-ray CT apparatus equipped with the X-ray tube apparatus according to the present invention.
FIG. 10 is a diagram showing the relationship between the structure of a rotary anode X-ray tube inserted in a conventional X-ray tube apparatus and the collimator of the X-ray CT apparatus.
FIG. 11 shows an example of the structure of a rotating anode of a conventional rotating anode X-ray tube.
[Explanation of symbols]
1, 40 ... Rotating anode X-ray tube (X-ray tube)
2, 41, 100, 110, 200 ... Rotating anode (anode)
3 ... Cathode
4 ... Envelope
5 ... Electron beam (electron current)
6, 6A ... Target
7,7A ... Focus
8, 8A ... X-ray (X-ray beam)
9 ... X-ray emission window
10 ... Collimator
11 ... Slit
12 ... X-ray detector
13 ... Movement amount △ L
20, 44, 60, 66, 72, 78, 86, 94, 101, 201 ... rotor
21, 46, 62, 68, 74, 80, 88, 96, 102, 202 ... target support shaft
22,318A ... Rotor shoulder
23 ... Cylindrical part
24, 48, 64, 70, 76, 82, 90, 98, 104, 314A ... Insulation cap
26 ... Rotation axis
27… Bearings
28, 112 ... fixed part
46A ... Small diameter part
46B, 62B, 68B, 74B, 80B, 88B, 96B, 102B, 202B ... large diameter part
47, 47A, 47B, 49, 49A, 49B, 63, 63A, 63B, 65, 65A, 65B, 69, 69A, 69B, 71, 71A, 71B, 75, 75A, 75B, 77, 77A, 77B, 81, 81A, 81B, 83A, 83B, 89, 89A, 89B, 91, 91A, 91B, 97, 97A, 97B, 97C, 97D, 99, 99A, 99B, 99C, 99D, 103, 103A, 103B, 105, 105A, 105B, 203, 203A, 203B, 205A, 205B ... Ring tooth
48A, 64A, 70A, 76A, 82A, 90A, 98A, 104A, 204A ... Flange
48B, 64B, 70B, 76B, 82B, 90B, 98B, 104B, 204B ... Thin cylindrical part
48C ... Bottom
50 ... Copper (brazing material)
84A, 84B, 84C, 84D ... Gap
92, 93 ... tip
114 ... Inner tube
116 ... Outer tube
118 ... hole
120 ... X-ray CT system
122 ... X-ray tube equipment
124 ... Scanning gantry
126… Operation console
128 ... Shooting table
130 ... X-ray detector
132 ... Scanner
136… X-ray controller
142 ... Central processing unit
237,337 ... Taper surface
330, 336 ... Ring-shaped protrusion
332 ... Ring-shaped groove
334, 338 ... Brazed portion on the upper surface of the ring-shaped protrusions 331, 336
335,339 ... tensile stress
336 ... Ring-shaped protrusion

Claims (2)

A disk-shaped target, a rotor that supports the target, a rotating shaft that supports the rotor, a bearing that rotatably supports the rotating shaft, and a rotating anode that has a fixed portion that supports the bearing, and an electron current emitted onto the target A rotating anode X-ray tube comprising a cathode forming a focal point as an X-ray source, and an envelope that insulates and supports the rotating anode and the cathode and is hermetically sealed in a vacuum-tight manner. In an X-ray tube device that is insulated and supported in a tube container, the rotor is supported by a target support portion that supports a target, and a heat insulating portion that is joined to the target support portion at one end and supported at the other end by the rotating shaft. And a cylindrical portion having substantially the same outer diameter as a joint portion of the heat insulation portion with the target support portion, and a cylindrical portion connected to the heat insulation portion, and the target support portion supports the target A diameter portion and a large diameter portion joined to the heat insulating portion, and provided with a circular hole for accommodating at least a part of the heat insulating portion on the large diameter portion side, the heat insulating portion of the target support portion A flange portion joined to the large-diameter portion, a thin cylindrical portion for reducing heat transfer from the target support portion, and a flat portion that forms the bottom of the thin cylindrical portion and is coupled to the rotating shaft. In addition, at the joint portion between the target support portion and the heat insulating portion, one has two or more annular tooth portions that are annular protrusions that mesh with each other, and the other has one or more, and the annular tooth portion is It is a structure having a taper in the direction of the rotation axis, and is brazed in a state where one or more annular tooth portions are fitted between two or more annular tooth portions , An X-ray tube device characterized in that the cross-section of the fitting portion is Z-shaped .   A scanning gantry in which an X-ray tube device and an X-ray detector are arranged opposite to each other across an opening into which a subject is inserted; an X-ray controller that applies a high voltage load to the X-ray tube device; An imaging table for inserting the placed subject into the opening, the scanning gantry, the X-ray controller, and the imaging table are controlled, and the tomogram of the subject is based on the X-ray measurement data collected by the X-ray detector. An X-ray CT apparatus comprising an operation console for reconstructing an image, wherein the X-ray tube apparatus is the X-ray tube apparatus according to claim 1.

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