X-ray tube for CT apparatus

DETAILED DESCRIPTION This invention has been made having regard to the state of the art noted above, and its object is to provide an X-ray tube for a CT apparatus, which is capable of a high-speed scan of X-ray generating positions circumferentially of an examinee, and yet has a compact construction having a reduced length axially of an examinee.
The above object is fulfilled, according to this invention, by an X-ray tube for a CT apparatus for scanning X-ray generating positions along a circumference of an examinee, comprising a ring-shaped vacuum tube; a fixed cathode mounted in the vacuum tube and having a first thermion emitting surface; a ring-shaped fixed anode mounted in the vacuum tube; a ring-shaped rotatable cathode having a first thermion receiving surface opposed to the first thermion emitting surface, and a thermion emitting portion opposed to the fixed anode; a lifting device for suspending the ring-shaped rotatable cathode to a non-contact state; and a driving device for rotating the ring-shaped rotatable cathode.
Specifically, the first thermion emitting surface is formed by a filament disposed on the fixed cathode.
The fixed cathode may be shaped otherwise than ring-shaped as long as the first thermion emitting surface is formed opposite the first thermion receiving surface formed on the ring-shaped rotatable cathode.
The thermions emitted from the first thermion emitting surface of the fixed cathode impinge on the first thermion receiving surface formed on the ring-shaped rotatable cathode.
In order to reduce the difference in electric potential between the fixed cathode and rotatable cathode, it is desirable that the opposed first thermion emitting surface and thermion receiving surface have as large an area as possible, with a minimal spacing therebetween.
The thermions having entered the rotatable cathode are emitted from the thermion emitting portion of the rotatable cathode toward the fixed anode.
At this time, the thermion emitting portion is heated by a suitable heating device