Refrigeration – Storage of solidified or liquified gas – Including cryostat
Reexamination Certificate
1999-10-27
2001-08-21
Doerrler, William (Department: 3744)
Refrigeration
Storage of solidified or liquified gas
Including cryostat
C062S331000, C062S259200, C378S015000
Reexamination Certificate
active
06276145
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the art of medical diagnostic imaging. It finds particular application in conjunction with computed tomography (CT) scanners, and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications.
Generally, CT scanners have a defined examination region or scan circle in which a patient, phantom or like subject being imaged is disposed. A thin beam of radiation is transmitted across the examination region from an radiation source, such as an x-ray tube, to oppositely disposed radiation detectors. The source, or beam of radiation, is rotated around the examination region while data is collected from the radiation detectors receiving x-ray radiation passing through the examination region and the subject disposed therein. Rotation of the radiation source is often achieved by mounting the radiation source to a rotating gantry which is rotated on a stationary gantry.
The sampled data is typically manipulated via appropriate reconstruction processors to generate an image representation of the subject which is displayed in a human-viewable form. Commonly, the x-ray data is transformed into the image representation utilizing filtered back projection. A family of rays extending from source to detector is assembled into a view. Each view is filtered or convolved with a filter function and backprojected into an image memory. Various view geometries have been utilized in this process. In a rotating, fan-beam-type scanner in which both the source and detectors rotate (i.e. a third generation scanner), each view is made up of concurrent samplings of an arc of detectors which span the x-ray beam when the x-ray source is in a given position to produce a source fan view. Alternately, with stationary detectors and a rotating source (i.e. a fourth generation scanner), a detector fan view is formed from the rays received by a single detector array as the x-ray source passes behind the examination region opposite the detector.
In any event, accurate reconstruction is dependant upon acquiring data views from a range of accurately resolved angular orientations or positions of the source as it rotates about the examination region. Reconstruction algorithms have been developed which use data collected over numerous helical rotations, 360 degrees of source rotation, 180 degrees plus the angle or spread of the fan of radiation, and the like. Therefore, scan times are constrained by the speed of rotation of the source.
In previously developed CT scanners, commonly the rotating gantry is supported on the stationary gantry via a mechanical bearing including rolling elements or balls interposed between two raceways. However, with increased rotational speed of the rotating gantry, noise levels associated which such mechanical bearings reach unacceptable levels. In continuously rotating systems, friction related heating can restrict the length of scans. Moreover, the accompanying friction causes wearing of parts in physical contact with one another thereby incurring disadvantageous maintenance requirements and a limited lifetime.
In another type of CT scanner, the rotating gantry is suspended via electromagnetic levitation. However, such a technique tends to be unstable and employs complex feedback controls to maintain stability. Moreover, the size and cost associated with such a system can be prohibitive when rotating loads of the size desired for many CT scanners, e.g., in the neighborhood of 1000 lbs.
The present invention contemplates a new and improved gantry suspension technique which overcomes the above-referenced problems and others.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a CT scanner for obtaining a medical diagnostic image of a subject is provided. The CT scanner includes a stationary gantry, and a rotating gantry rotatably supported on the stationary gantry for rotation about the subject. A fluid bearing is interposed between the stationary and rotating gantries. The fluid bearing provides a fluid barrier which separates the rotating gantry from the stationary gantry.
In accordance with a more limited aspect of the present invention, the fluid barrier is a gas.
In accordance with a more limited aspect of the present invention, the gas is air.
In accordance with a more limited aspect of the present invention, the fluid barrier is a liquid.
In accordance with a more limited aspect of the present invention, the liquid is oil.
In accordance with a more limited aspect of the present invention, the CT scanner further includes a reservoir containing the fluid which is supplied from the reservoir to the fluid bearing to create the fluid barrier.
In accordance with a more limited aspect of the present invention, the fluid is supplied to the fluid bearing through distribution pads which distribute the fluid between the stationary and rotating gantries.
In accordance with a more limited aspect of the present invention, the distribution pads have a beveled edge along a leading side thereof relative to a direction of rotation of the rotating gantry.
In accordance with a more limited aspect of the present invention, the CT scanner further includes opposing surfaces on the stationary and rotating gantries which face one another across the fluid barrier. The opposing surfaces define the shape of the fluid bearing.
In accordance with a more limited aspect of the present invention, the shape of the fluid bearing is symmetrical with respect to an axial plane which is normal to an axis of rotation of the rotating gantry.
In accordance with a more limited aspect of the present invention, the shape of the fluid bearing is defined by two conic sections which meet at the axial plane to form an annular V-shaped trough.
In accordance with a more limited aspect of the present invention, the CT scanner further includes a recovery system which collects fluid escaping from the fluid bearing.
In accordance with a more limited aspect of the present invention, the CT scanner further includes a radiation source attached to the rotating gantry. The radiation source produces a beam of penetrating radiation which irradiates the subject as the rotating gantry rotates. A cooling system circulates a cooling fluid past the radiation source. The cooling fluid draws heat from the radiation source as the cooling fluid is circulated past the radiation source. A heat exchanger, interfacing the cooling system with the recovery system, transfers heat from the cooling fluid in the cooling system to the fluid collected by the recovery system.
In accordance with a more limited aspect of the present invention, the recovery system returns fluid collected thereby to the fluid bearing.
In accordance with another aspect of the present invention, a method of rotating a source of radiation about an axis is provided. The method includes suspending a second gantry from a first gantry while the second gantry has the source of radiation mounted thereto. Thereafter, a fluid is fed in between the first and second gantries such that they are spaced apart from one another by a layer of the fluid, and the second gantry is then rotated.
In accordance with a more limited aspect of the present invention, the method further includes controlling the rate at which the fluid is fed in between the first and second gantries.
In accordance with a more limited aspect of the present invention, the method further includes storing a reserve of the fluid such that the fluid is fed in between the first and second gantries from the stored reserve.
In accordance with a more limited aspect of the present invention, the method further includes generating dynamic forces which radially stabilize the second gantry as it rotates.
In accordance with a more limited aspect of the present invention, the method further includes collecting the fluid as it escapes from in between the first and second gantries, and returning the fluid for further use.
In accordance with a more limited aspect of the prese
Brunnett William Charles
Sharpless Ronald Bryan
Doerrler William
Fay Sharpe Fagan Minnich & McKee LLP
Picker International Inc.
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