X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1998-12-10
2001-01-30
Porta, David P. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S121000
Reexamination Certificate
active
06181765
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to X-ray tubes and, more particularly, is concerned with an X-ray tube assembly.
Medical X-ray devices, including those employed in computed tomography, generally contain an X-ray tube. An X-ray tube typically includes a cathode, an anode and a stationary frame surrounding the cathode and anode. The cathode is stationary while the anode rotates relative to the cathode. The surrounding frame contains a vacuum chamber and has an X-ray transparent window. The anode has a target surface which faces the cathode. The cathode emits electrons which strike the target surface of the anode and produce X-rays. Some of the X-rays exit the frame as an X-ray beam through the X-ray transparent window.
Load-carrying bearings are located inside the vacuum chamber between the frame and a stem of the anode. The bearings must be lubricated. The target surface of the anode is heated by the impinging electrons. The heat of the target surface is dissipated by thermal radiation and conduction to the frame. The heated frame is cooled by a liquid coolant, such as oil or water, located between the frame and a surrounding casing.
Thermal management requirements have caused the mass and the speed of rotation of the anode to increase dramatically in recent years which adversely affects the performance of bearings over time. Current X-ray tube designs are close to the limits of X-ray tube bearing technology and to the limits of technology available for thermal management.
Consequently, a need exists for an X-ray tube design which will avoid the problems associated with current X-ray tube designs in terms of bearing technology and thermal management without introducing any new problems in place thereof.
BRIEF SUMMARY OF THE INVENTION
The present invention provides an X-ray tube assembly designed to satisfy the aforementioned need. The X-ray tube assembly of the present invention has no moving parts and, therefore, does not need bearings. The X-ray tube assembly includes a ring-shaped stationary anode and cathode. The X-ray tube assembly has a frame which can be cooled by a liquid. The X-ray tube assembly can also be grounded to allow for water cooling. The frame has an annular configuration providing the X-ray tube assembly with an overall donut shape. The annular configuration of the frame, the stationary anode and cathode rings, and the lack of bearings enables the X-ray tube assembly to overcome the problems associated with the prior art in regard to the limits of X-ray tube bearing technology and of the technology available for thermal management.
In an exemplary embodiment of the present invention, an X-ray tube assembly comprises a hermetically-sealed frame and anode and cathode rings stationarily disposed in the frame. The frame has a substantially curved configuration and surrounds an exterior central passage through the frame for receiving a patient therethrough. The frame defines an interior chamber with a vacuum therein and has an X-ray transparent window ring surrounding and facing the central passage of the frame. The frame has a substantially annular configuration and spans up to 360 degrees.
The cathode ring is mounted to the frame and disposed within the interior chamber. The cathode ring has an electron emitting portion and a first electrical potential. The anode ring is also mounted to the frame and disposed within the interior chamber. The anode ring is spaced apart from the cathode ring and has a target portion and a second electrical potential more positive than the first electrical potential of the cathode ring.
The X-ray tube assembly also comprises means for excitation of electrons from the electron emitting portion of the cathode ring to cause the excited electrons to flow in an e-beam from the electron emitting portion of the cathode ring to the target portion of the anode ring. Impact of excited electrons with the target portion of the anode ring produces an X-ray beam that exits the interior chamber of the frame and passes through the transparent window ring and across the central passage of the frame.
The transparent window ring also spans up to substantially 360 degrees as do the cathode and anode rings. In an example, the transparent window ring is disposed between and radially inwardly of the cathode and anode rings, and the target portion of the anode ring faces the electron emitting portion of the cathode ring. In another exemplary embodiment of the present invention, the electron emitting portion of the cathode ring includes a series of circumferentially arranged side-by-side filaments each separately and consecutively excitable by the electron citation means such that the X-ray beam is movable around the patient disposed within the central passage.
REFERENCES:
patent: 5125012 (1992-06-01), Schittenhelm
patent: 5483570 (1996-01-01), Renshaw et al.
patent: 5652778 (1997-07-01), Tekriwal
patent: 5995584 (1999-11-01), Bhatt
Sribar Rok
Vlatkovic Vlatko
General Electric Company
Hobden Pamela R.
Porta David P.
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