JPH11185680A - X-ray tube assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a X-ray tube structure to reduce extrafocal radiation which is X-ray radiation from a site inside a X-ray tube other than a focal spot. SOLUTION: In an X-ray tube having an anode assembly with an anode, and a cathode assembly generating a converged X-ray beam directed to the anode, a cut-out part 28 for reducing extrafocal radiation is provided on the upper face of an anode target 12b for generating an X-ray when an electron beam is accelerated so that an electron collides.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates generally to x-ray tubes, and more particularly to x-ray tube targets for reducing out-of-focus radiation.

[0002]

BACKGROUND OF THE INVENTION X-ray tubes have become essential for medical diagnostic imaging applications, medical applications, and various medical testing and material analysis applications. A typical X-ray tube is
Includes a rotating anode structure for distributing the heat generated at the focal spot. The anode is rotationally driven by an induction motor.
The induction motor includes a cylindrical rotor assembled on a cantilever beam shaft supporting a disk-shaped anode target,
Includes a stator core with copper windings surrounding an elongated neck of the x-ray tube containing the rotor. The rotor of the rotating anode assembly is driven by a surrounding stator. The cathode of the X-ray tube provides a focused electron beam that is accelerated across a large anode-cathode vacuum gap and generates X-rays upon impact on the anode.

[0003] X-ray images, especially computed tomography (C
T) One of the factors that degrade the image is out-of-focus radiation, that is, X-ray radiation from a location in the X-ray tube other than the focal spot. Most of this out of focus radiation is caused by electrons scattered from the focal spot and striking the target and other parts of the X-ray tube. In CT, this out-of-focus radiation produces image artifacts near the bone-brain interface, especially in head scans, which can obscure the trauma or manifest itself as a false medical problem. Current X-ray tube designs with software correction algorithms are less than satisfactory. The new CT device under development uses a wide X-ray beam corresponding to the multi-slice detector and has a short shape, so that the influence of out-of-focus radiation is increased. Of particular importance is the need for a uniform x-ray beam in the z-direction of the detector. Out-of-focus radiation creates extra non-uniformities, which require wider collimation, and thus increase the patient's X-ray exposure to prevent non-uniformities. Increasing non-uniformity also increases the need for sophisticated software correction and collimation equipment.

[0004]

Accordingly, it is desirable to provide an X-ray tube structure that reduces out of focus radiation.

[0005]

According to the present invention, a standard X
A cutout is provided at the top of the anode to significantly reduce out-of-focus radiation compared to a tube. According to one aspect of the invention, in an X-ray tube assembly having an anode assembly having an anode and a cathode assembly for producing a focused X-ray beam directed to the anode, the anode assembly accelerates the electron beam. And an anode target that generates X-rays when electrons collide with the target. A cutout is provided on the upper surface of the anode target to reduce out-of-focus radiation.

Therefore, according to the present invention, the out-of-focus radiation is significantly reduced as compared with a standard X-ray tube. Another advantage is that
The reduced variation in out-of-focus radiation intensity with the detector z-axis position eliminates the need for multiple kernels for correction in multi-slice CT systems. In addition, multi-slice CT
X-ray beam umbra required by the system
The flatness of the area is improved, thereby minimizing excessive x-ray exposure of the patient.

[0007] Other objects and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotating X-ray tube using a rotating anode assembly and a cathode assembly. It is an object of the present invention to reduce out-of-focus radiation of an X-ray tube. Referring to the drawings, FIG. 1 shows a typical conventional X-ray tube anode assembly 10. X-ray tube anode assembly 10 typically includes a rotating target assembly 12 having a mandrel 14 to distribute heat generated at focal spot 16.
A typical X-ray tube is further accelerated across an anode-cathode vacuum gap and impinges on a target by X-rays.
An X-ray tube cathode assembly (not shown) that produces a focused electron beam to produce the radiation.

The anode assembly 10 is rotationally driven by an induction motor, which is typically a cantilevered shaft 20.
Including a cylindrical rotor 18 assembled therearound. The cantilevered shaft 20 supports a disk-shaped anode target 22 connected to a cylindrical rotor 18 and a bearing assembly 24 via a mandrel 14 and a hub 22. Bearing assembly 24 includes bearings that facilitate rotation. Rotating anode assembly 10
Is driven by the stator of the induction motor, and the cylindrical rotor 18 is at anodic potential.

Referring now to FIG. 2, out-of-focus radiation tends to be emitted most strongly by the upper surface 32a of the target 12a. In a conventional X-ray tube, out-of-focus radiation from almost the entire upper surface 32a of the target 12a can be viewed by the detector 26. As the ratio of the focus trajectory area visible at the detector 26 to the area of the target upper surface 32a decreases, it becomes more important to block out-of-focus radiation generated at the target upper surface 32a.

Referring to FIG. 3, there is shown a target 12b according to the present invention for reducing out-of-focus radiation caused by a standard x-ray tube anode structure as shown in FIG. A cutout portion 28 is provided on the upper surface of the target, and the cutout portion 28 blocks the line of sight from the detector 26 to the upper surface of the target 12b, that is, the upper surface of the target 12b is not visible from the detector 26, Detector 2
6 do not receive out-of-focus radiation from the top surface of the target. As can be seen from FIGS. 2 and 3, the nut 30 shown in FIG. 2 has been removed from the target 12b of FIG. 3, so that the cutout 28 obscures the entire top surface of the anode assembly.

In a preferred embodiment of the present invention, the depth of the cutout 28 is such that the top of the target 12b is not visible from the detector 26. The minimum depth is about 2.3 mm in one embodiment, and may be deeper or shallower depending on the shape of the x-ray tube. Cutouts shallower than the minimum depth can reduce the out-of-focus radiation received by the detector, but are ineffective in making the out-of-focus radiation invisible. Conversely, if the depth of the cutout is greater than the minimum depth, the effect is the same as that of the minimum depth in that the out-of-focus radiation is invisible, but the strength and heat capacity of the target increase as the depth increases. May be damaged. Accordingly, the depth of the cutout is calculated such that its surface is hidden from the edge of the detector, and such that the cutout does not adversely affect the heat capacity of the target anode.

Although it is contemplated that the target cutout 28 may be of various shapes, a rectangular shape as shown in FIG. 3 is easier to inspect and process than, for example, a curved surface. Typically, cutting is performed at the final processing stage of the target, before attaching to the anode assembly. The present invention has the advantage of reducing out-of-focus radiation since radiation from the top surface of the anode is blocked and does not reach the detector. The present invention has the advantage that a more uniform X-ray beam is obtained, thus lowering the fractional dose and making the intensity of the out-of-focus radiation independent of the z-axis position of the detector.

While the invention has been described in detail with reference to certain preferred embodiments, it will be understood that various changes and modifications may be made within the spirit and scope of the invention. For example, the present invention may include utilizing a low atomic number material such as titanium, graphite, ceramic, etc. on the top surface of the target.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a typical conventional X-ray tube anode assembly.

FIG. 2 is a side view showing a conventional target assembly part of the X-ray tube anode assembly of FIG. 1;

FIG. 3 is a side view of a target assembly according to the present invention for use in the X-ray tube anode assembly of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 X-ray tube anode assembly 12 Rotary target assembly 12a, 12b Target 14 Mandrel 16 Focus spot 18 Cylindrical rotor 20 Cantilever shaft 22 Hub 24 Bearing assembly 26 Detector 28 Cutout 32a Target upper surface

 ──────────────────────────────────────────────────続 き Continuing the front page (72) Inventor Willi Walta Hampel United States, Wisconsin, Saint Francis, South Lower Avenue, No. 3686 (72) Inventor Stephen Gravel Mech, Wisconsin, United States On, North Solar Avenue, No. 11754 (72) Inventor Wayne F. Block, Wisconsin, United States, Sassex, Pine Terrace, W236, N6210 (no address)

Claims (7)

[Claims] An X-ray tube assembly having an anode assembly having an anode and a cathode assembly for producing a focused X-ray beam directed to the anode, wherein the anode assembly accelerates an electron beam. An X-ray tube assembly comprising: an anode target that generates X-rays when electrons collide with the target; and a cutout for reducing out-of-focus radiation is provided on an upper surface of the anode target. 2. The X-ray tube assembly according to claim 1, further comprising a detector for receiving X-rays generated by said anode target. 3. The X-ray tube assembly according to claim 2, wherein the shape of the cutout is rectangular. 4. The X according to claim 3, wherein the detector is arranged along a line of sight along an upper surface of the anode target.
Wire tube assembly. 5. The X-ray tube assembly according to claim 4, wherein a surface of the cutout has a depth sufficient to block a line of sight from the detector to an upper surface of the anode target. 6. The X-ray tube assembly according to claim 5, wherein a depth of the cutout is a minimum depth that blocks a line of sight from the detector to an upper surface of the anode target. 7. The X-ray tube assembly according to claim 4, wherein the cutout is configured to prevent out-of-focus radiation from the anode target from reaching the detector.