X-ray or gamma ray systems or devices – Source – Electron tube
Reexamination Certificate
1999-03-29
2001-07-03
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Source
Electron tube
C378S119000, C378S121000
Reexamination Certificate
active
06256375
ABSTRACT:
TECHNICAL FIELD
The present invention relates to rotating x-ray tubes and, more particularly, to rotating x-ray tubes which employ an angled cathode structure to maintain parallelism of the surface between the cathode and the x-ray target.
BACKGROUND ART
X-ray tubes used in medical diagnostic imaging are built with a rotating anode structure for the purpose of distributing the heat generated at the focal spot. The anode is rotated by an induction motor consisting of a cylindrical rotor built into a cantilevered axle that supports the disc shaped anode target, and an iron stator structure with copper windings that surrounds the elongated neck of the x-ray tube that contains the rotor. The rotor of the rotating anode assembly being driven by the stator which surrounds the rotor of the anode assembly is at anodic potential while the stator is referenced electrically to ground. The X-ray tube cathode provides a focused electron beam which is accelerated across the anode-to-cathode vacuum gap and produces X-rays upon impact with the anode.
In designing the cathode for an x-ray tube, the surface of the cathode is typically desired to be parallel to the target. However, there are instances that the surface between the cathode and the target are not paralleled by design. Unfortunately, if the surface between the cathode and the target is not paralleled, the focal spot will be skewed. The skew of the focal spot could cause the tube to be out of specification, resulting in failure. The focal skew is caused by the electron beams accelerating from the cathode and landing at different coordinates on the target because of the non-parallel surface.
In order to minimize focal skew, it is desirable for the surface between the cathode and the target to be parallel.
BRIEF SUMMARY OF THE INVENTION
The present invention provides for a target angle matching cathode design for an x-ray tube, for generating the desired parallel surface between the cathode and the target. Using the target angle matching technique to maintain parallelism of the surface between the cathode and the target minimizes the opportunity of the focal spot from being skewed.
A rotating x-ray tube comprises an anode assembly and a target. The target, associated with the anode assembly, distributes heat generated at a focal spot. A cathode produces X-rays upon impact with the anode. A target angle matching cathode cup creates a parallel surface between the cathode and the target. The target angle matching cathode cup maximizes the gap between a frame containing the cathode and anode, and the cathode. The angled cathode cup configuration also minimizes focal spot skew.
Accordingly, the present invention provides a parallel surface between the cathode and the target. This provides the advantage of minimizing focal skew.
REFERENCES:
patent: 4736400 (1988-04-01), Koller et al.
patent: 5136625 (1992-08-01), Heiting et al.
patent: 5384818 (1995-01-01), One et al.
patent: 5384819 (1995-01-01), Ono
patent: 5668849 (1997-09-01), Sugiura et al.
Gravelle Stephen W.
Lu Quan N.
Waite Stephen S.
Cabou Christian G.
General Electric Company
Haushalter Barbara Joan
Ho Allen C.
Kim Robert H.
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