JPH04301399A - Medical x-ray tube device - Google Patents

Abstract

PURPOSE:To prevent the offset of a X-ray focus and the drift of the distance between a cathode and a target owing to the thermal expansion of the target and the like. CONSTITUTION:The axial and the radial drifts owing to the thermal expansion of a target 1 are detected by gap sensors S3, S4, and based on the detected signals, a magnetic bearing control circuit 20 controls the current fed to a radial bearing 7 and a thrust bearing 8, which forms a magnetic bearing structure, so as to compensate the drift. On a cathode 2, the drift owing to the thermal expansion is likewise compensated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an X-ray tube device used in the medical field.

0002

2. Description of the Related Art As is well known, a medical X-ray tube device, for example, a rotating anode X-ray tube device, rotates an anode target to increase the effective load area, thereby instantaneously producing a small focal point. It is constructed to withstand heavy loads. Even with a rotary anode X-ray tube device configured in this way, if a load is continuously applied, the target will exceed the allowable limit temperature, so the controller of the rotary anode X-ray tube device will The anode storage heat capacity is set in advance, and the tube current, tube voltage, exposure time, and exposure stop time are controlled so as not to exceed this anode storage heat capacity.

0003

However, the conventional medical X-ray tube apparatus has the following problems. Even if a rotating anode X-ray tube device is used under the control described above, the temperature of the target will rise to about 1000-1200°C, so as shown in Figure 4, a considerable amount of heat is generated in the target etc. Expansion occurs. In FIG. 4, reference numeral 2 is a cathode fixedly installed in a vacuum container (not shown), 4 is a part of a rotationally driven target, solid lines indicate the position in the cold state, and broken lines indicate the position in the heated state, respectively. There is. Further, the symbol S is the position of the X-ray focal point in the cold state, and S' is the position of the X-ray focal point in the heated state. In this way, the X-ray focal point moves by Δx in the X direction and Δy1 in the Y direction due to the thermal expansion of the target 4. In addition, the cathode 2 is also heated by the radiant heat from the target 4, and in FIG.
is undergoing thermal expansion.

As mentioned above, when the X-ray focal point moves due to thermal expansion of the target 4, the X-ray irradiation field and dose distribution change, so the photographed image also changes, especially in the case of an X-ray tomography image. Image quality deteriorates significantly.

[0005] Furthermore, because the distance between the target 4 and the cathode 2 becomes shorter due to thermal expansion of the target 4 and the cathode 2, a tube current larger than a preset value may flow and exceed the anode storage heat capacity. There is also.

Furthermore, when the distance between the target 4 and the cathode becomes shorter, the effect of radiant heat from the target 4 causes the cathode 2 to become shorter.
Since the temperature of the filament increases further in addition to the temperature increase due to the filament heating current, this also causes a tube current larger than the set value to flow, which may exceed the anode storage heat capacity.

The present invention was made in view of the above circumstances, and provides medical X-rays that can avoid displacement of the X-ray focal point and fluctuations in the distance between the target and the cathode due to thermal expansion of the target, etc. The purpose is to provide pipe equipment.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration. That is, the present invention provides a medical X-ray tube device that includes a cathode and an anode in a vacuum container, and includes a magnetic bearing structure that supports at least one of the cathode and the anode so as to be movable in the axial direction and the radial direction of the tube. , a position detection means for detecting a position change due to thermal expansion of at least one of the cathode or the anode, and controlling the magnetic bearing structure so as to eliminate the position change due to thermal expansion based on an output from the position detection means. , and control means for correcting the position of at least one of the cathode and the anode.

[0009]

[Operation] The operation of the present invention is as follows. That is, according to the present invention, a positional change due to thermal expansion of at least one of the cathode or anode is detected by the position detecting means, and the control means controls the magnetic bearing structure so as to eliminate the positional change. Since at least one of the positions is corrected, the distance between the cathode and anode and the position of the X-ray focal point are maintained at constant values even if the cathode and anode expand thermally.

0010

[Example] Hereinafter, with reference to the drawings, medical X according to the present invention will be described.
An example of a wire tube device will be described. FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a rotating anode X-ray tube device according to an embodiment. In the figure, reference numeral 1 denotes a vacuum vessel, and within this vacuum vessel 1 are provided a cathode 2 and an anode 3 supported by a magnetic bearing structure. In the anode 3, 4 is a target, and a cylindrical rotating shaft 5 is connected to this target 4.
A flange portion 6 that projects outward is formed at the tip portion of the holder. The rotating shaft 5 and the collar 6 are made of magnetic material.

A radial bearing 7 formed of an electromagnetic magnet is provided around the circumference of the vacuum vessel 1 surrounding the rotating shaft 5 to support the anode 3 by magnetically levitating it so as to be movable in the radial direction. As shown in the cross-sectional view of FIG. 2, the radial bearing 7 is composed of four electromagnetic magnets 7a arranged at equal intervals in the circumferential direction. A thrust bearing 8 consisting of a pair of electromagnetic magnets for moving the anode 3 in the axial direction is provided around the periphery of the vacuum vessel 1 surrounding the flange 6. Note that the reference numeral 9 in FIG. 1 is a stator for rotationally driving the magnetically levitated anode 3.

Further, S1 and S2 are gap sensors serving as position detecting means for detecting a positional change in the axial direction and a positional change in the radial direction of the cathode 2, respectively. S3 and S4 are gap sensors serving as position detecting means for detecting positional changes in the axial direction and radial direction of the target 4, respectively. S5,
S6 is a pair of gap sensors arranged at an angle of 90 degrees, and detects the displacement of the rotating shaft 5 in orthogonal radial directions.

Inside the rotating shaft 5, there is a support shaft 10 fixed to the inner wall of the vacuum vessel 1, and a touchdown bearing 11 is fitted into the support 10. When the magnetic levitation of the anode 3 is released, the touchdown bearing 11
This is for supporting the anode 3 from inside the rotating shaft 5. Further, reference numeral 12 in FIG. 1 is a tube current conduction path through which tube current flows due to a discharge phenomenon.

Next, the magnetic bearing structure of the cathode 2 will be explained with reference to FIG. A support shaft 13 is erected on the inner wall of the vacuum chamber 1 in which the cathode 2 is provided, and a radial/thrust bearing 14 composed of an electromagnetic magnet divided into four parts in the circumferential direction is attached to the support shaft 13. It is being The cylindrical body 15a of the cathode body 15 is fitted into the support shaft 13, and the radial/thrust bearing 14 is inserted into the radial/thrust bearing 14 with the convex portion 15b provided inside the cylindrical body 15a being slightly shifted in the axial direction. It faces each electromagnetic magnet. In addition, Figure 3
Inside, 16 is a filament, 17 is an elastic filament wiring for absorbing displacement of the cathode 2, and S7 is a pair of gap sensors as position detection means for detecting displacement of the cathode 2 in the radial direction. In FIG. 3, the gap sensors S7 are shown facing each other (with a 180-degree positional relationship) for convenience, but in reality, they are arranged at a 90-degree angle.

The bearings 7, 8, 14 of the cathode 2 and anode 3 described above are controlled by a magnetic bearing control circuit 20 which is supplied with detection signals from the gap sensors S1 to S7. Next, the operation of the above-described device will be explained. For example, if the target 4 is heated and thermally expands as shown in FIG. 4, and the X-ray focal point is displaced from point S to point S', the gap sensor S4 shown in FIG.
The amount of deviation Δx of the X-ray focal point in the direction (radial direction) is detected, and the detection signal is output to the magnetic bearing control circuit 20. Based on this, the magnetic bearing control circuit 20 controls the current flowing through the radial bearing 7 to displace the anode 3 by Δx in the −X direction, thereby correcting the displacement of the target 4 in the X direction. At this time, the amount of displacement of the anode 3 in the X direction is detected by gap sensors S5 and S6.

Furthermore, the amount of deviation Δy1 of the X-ray focal point in the Y direction (axial direction) is detected by a gap sensor S3. Based on this detection signal, the magnetic bearing control circuit 20 controls the current flowing through the thrust bearing 8 to move the anode 3 in the −Y direction by Δ
By displacing y1, Y of target 4
Correct the misalignment. At this time, the amount of displacement of the anode 3 in the Y direction is detected by the gap sensor S3.

The amount of deviation Δx of the cathode 2 in the X direction is detected by the gap sensor S2, and based on this detection signal, the magnetic bearing control circuit 20 controls each of the left and right electromagnetic magnets of the radial/thrust bearing 14 shown in FIG. The above deviation amount Δx is corrected by changing the balance of the current flowing in the . Further, the displacement amount Δy2 of the cathode 2 in the -Y direction is detected by the gap sensor S1, and based on this detection signal, the magnetic bearing control circuit 20 controls the current flowing through the upper and lower electromagnetic magnets of the radial/thrust bearing 14. By changing the balance, the above deviation amount -Δy2
Correct.

With each of the above corrections, the position of the X-ray focal point becomes S
' Return to the original point S.

Note that when the temperature of the filament of the cathode 2 increases due to radiant heat from the target 4 and the tube current increases, by moving the cathode 2 in the Y direction,
It is also possible to correct the increase in tube current.

Further, in the above embodiment, the cathode 2 and the anode 3 are displaced to correct the shift of the X-ray focus.
If the thermal expansion of the cathode 2 is so small that it is not a problem,
It is sufficient to displace only the anode 3.

Furthermore, in the above-described embodiment, both the cathode 2 and the anode 3 are provided with a magnetic bearing structure, but the present invention does not necessarily require the magnetic bearing structure to be provided on both, but only on either the cathode 2 or the anode 3. But that's fine.

Furthermore, although the embodiments have been described using a rotating anode X-ray tube device as an example, the present invention can also be applied to a fixed anode X-ray tube device. In this case, as shown in FIG. 3, a magnetic bearing structure may be adopted for the cathode.

Further, in the embodiment, a gap sensor is used to detect the displacement of the cathode 2 and anode 3, but the present invention is not limited to this, and the amount of heat applied to the target 4 is calculated from the X-ray imaging conditions, Based on this, the amount of thermal expansion of the target 4 may be determined, and each magnetic bearing may be controlled to correct this.

[0024]

Effects of the Invention As is clear from the above description, according to the present invention, a magnetic bearing structure is provided so as to detect a positional change due to thermal expansion of at least one of the cathode or anode and eliminate the positional change. control and correct the position of at least one of the cathode and anode to adjust the distance between the cathode and anode and
Since the position of the line focus is maintained at a constant value, there will be no change in image quality due to positional deviation of the X-ray focus or overload due to an increase in tube current.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a schematic configuration of a rotating anode X-ray tube device according to an embodiment.

FIG. 2 is a cross-sectional view showing the magnetic bearing structure of the anode.

FIG. 3 is a longitudinal sectional view showing the magnetic bearing structure of the cathode.

FIG. 4 is a diagram for explaining conventional problems.

[Explanation of symbols]

1...Vacuum container
2...Cathode 3...Anode
4...Target 5...Rotation axis
6...
Flange part 7...Radial bearing
8... Thrust bearing 9... Stator
14...Radial/thrust bearing 20...Magnetic bearing control circuit (control means)

Claims (1)

[Claims] 1. A medical X-ray tube device comprising a cathode and an anode in a vacuum container, comprising: a magnetic bearing structure that supports at least one of the cathode and the anode so as to be movable in the axial direction and the radial direction of the tube; a position detection means for detecting a position change due to thermal expansion of at least one of the cathode or anode, and controlling the magnetic bearing structure so as to eliminate the position change due to thermal expansion based on the output from the position detection means, A medical X-ray tube apparatus comprising: a control means for correcting the position of at least one of the cathode and the anode.