Patent Application
20050175152
Not applicable.
1. Field of the Invention
The present invention relates generally to x-ray systems and devices. More particularly, embodiments of the invention concern a cathode head that includes features directed to facilitating implementation of focal spot control.
2. Related Technology
It is often desirable in various types of x-ray tubes to be able to deflect the beam of electrons emitted by the cathode, or other emitter, so that the focal spot created by the electron beam can be located at a particular place on the target surface of the anode at which the electron beam is directed. In some instances, the position of the focal spot on the target surface of the anode must be adjusted in order compensate for any changes to the focal spot location that may have resulted from environmental factors, or factors relating to the operation of the x-ray tube.
By way of example, the high speed motion associated with the operation of rotating anode x-ray tubes may cause undesirable variations to a location of the focal spot on the target surface. Further, misalignment of the focal spot on the target surface of the anode can occur over a period of time as the parts of the x-ray device experience operational wear and tear. A variety of other conditions or advance may likewise cause undesirable changes to the desired position of the focal sport on the target surface of the anode.
In yet other cases, it is desirable to move the position of the focal spot on the target surface of the anode so as to achieve a particular x-ray emissive effect or to overcome certain conditions that may be present. Accordingly, the ability to achieve and/or maintain such a desired effect is materially compromised by uncontrolled changes to the position of the focal spot. As an example, it may be desirable in some instances to modify the position of the focal spot in order to compensate for any localized deterioration or other shortcomings in the target surface of the anode. Finally, modification of the position of the focal spot on the target surface of the anode may be necessary in some instances to compensate for local electrical and/or magnetic effects.
Various systems and components have been devised in an effort to attain and maintain effective and reliable focal spot placement and control. For example, deflection of the emitted electron beam and, thus, changes to the position of the focal spot on the target surface of the anode may be implemented through the use of magnetic coils, or electromagnets located on the outside of the x-ray tube.
One significant problem with this type of implementation is that a relatively high level power is required to create the magnetic field necessary to move the focal spot to a desired location or position. Such high power levels relate to the fact that magnetic field strength diminishes over distance. In particular, magnetic coils located on the outside of the x-ray tube, or at other locations well away from the electron beam, require relatively more power to implement a particular electron beam effect than would a magnetic coil, or coils, located relatively closer to the electron beam.
Moreover, known x-ray tube configurations, and cathode assemblies and devices in particular, largely preclude arrangement of a magnetic coil near the electron beam. Further, it is not feasible to locate magnetic coils near the anode due to the high operating temperature of the anode and the presence of x-rays and backscatter electrons that could impair the operation of the coil.
Accordingly, what is needed is a cathode head that includes one or more magnetic elements that are located proximate the emitter so as to enable reliable control of electron beam focal spot location without requiring a significant amount of operational power.
In general, embodiments of the invention are concerned with a cathode head that includes features directed to facilitating implementation of focal spot control. More particularly, exemplary embodiments of the invention are directed to a cathode head that includes one or more magnetic elements that are located proximate an emitter, such as a filament, of the cathode so as to enable control of the location of the focal spot defined by an electron beam generated by the emitter.
In one exemplary embodiment of the invention, a cathode head is provide that is suitable for use in an x-ray device that includes an anode having a target surface configured and arranged to receive an electron beam from the cathode head. The cathode head may be constructed of magnetic or non-magnetic material and includes an emitter block carrying a filament that defines a longitudinal axis about which is disposed one or more magnetic elements, such as electromagnets. The filament is configured and arranged to emit an electron beam that defines a focal spot on the target surface of the anode.
In operation, the magnetic coils disposed about the longitudinal axis defined by the filament generate a magnetic flux that is generally perpendicular to the emitted electron beam and, thus, imparts a desired deflection to the electron beam. Alterations to the magnetic flux density, for example, associated with the magnetic coils, changes the extent to which the emitted electron beam is deflected and, thus, the location of the focal spot on the target surface of the anode. Moreover, the relatively close proximity of the magnetic coils with the filament enables a given electron beam deflection to be achieved using relatively weaker magnetic fields than would be required if the filament and magnetic coils were spaced some distance apart.
These and other, aspects of embodiments of the present invention will become more fully apparent from the following description and appended claims.
In order that the manner in which the above-recited and other advantages and features of the invention are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
Reference will now be made to the drawings to describe various aspects of exemplary embodiments of the invention. It is to be understood that the drawings are diagrammatic and schematic representations of such exemplary embodiments, and are not limiting of the present invention, nor are they necessarily drawn to scale.
In general, embodiments of the invention are concerned with a cathode head that includes one more magnetic elements that enable directional control of an electron bean generated by an associated emitter such as a filament. In this way, exemplary embodiments of the invention are able to effectively and reliably control the location of an electron beam focal spot on a target surface of an associated anon.
Directing particular attention now to
With more particular reference now to
With continuing attention to
The illustrated implementation of the cathode head 200 further includes one or more magnetic elements 208 arranged with respect to the filament 204 such that a magnetic field having a desired magnetic flux density “B” and orientation is created. As suggested in
As noted earlier, the exemplary implementation of the x-ray device 100 includes anode 300 positioned to receive the electron beam generated by the filament 204 of the cathode head 200. More particularly, the anode 300 includes a substrate 302 upon which a target surface 304 is positioned. In an exemplary implementation of the anode 300, the substrate 302 substantially comprises a carbon-based material or carbon compound, while the target surface 304 substantially comprises tungsten and/or other metals or compounds effective in generating x-rays.
It should be noted that embodiments of the cathode 200 are suitable for use in connection with a variety of different types of anodes 300. For example, embodiments of the cathode head 200 are suitable for use in connection both with rotating anode type x-ray devices, as well as with stationary anode type x-ray devices. Accordingly, the scope of the invention should not be construed to be limited to any particular anode or x-ray device configuration.
With attention now to
With continuing reference to
As suggested by the foregoing discussion of
As another example, modifications to the generated magnetic field, such as the strength and direction of the field, may be implemented by varying the arrangement of the magnetic elements 208 with respect to each other and/or with respect to the emitter block 202 and the filament 204. Thus, by modifying aspects of the generated magnetic field, changes to the positioning of the electron beam and, thus, the focal spot at which the electron beam impacts the target surface of the anode (see
Moreover, the relatively close physical proximity between the filament 204 and the magnetic elements 208 enables desired beam deflection effects to be implemented with relatively less power than would otherwise be required if the magnetic elements 208 were located relatively further away from the electron beam, as is typical in many known devices. That is, because the strength of the magnetic field diminishes over distance, the input power to the magnetic elements 208 that is required to establish and maintain a magnetic field of desired strength, necessarily increases as the distance between the electron beam and the magnetic elements increases.
Other variables, as well, can be adjusted to achieve certain effects with respect to the focal spot of the electron beam admitted by the filament 204. By way of example, aspects such as the number and polarity of the magnetic elements 208 can be changed as necessary to achieve a desired effect.
Directing attention now to
With continuing reference to
As suggested by
Additionally, the positioning and orientation of the magnetic element 406 relative to the filament 404 and the emitter block 402, as well as the power applied to magnetic element 406, in implementations where the magnetic element 406 comprises an electromagnet, may be desirably modified to achieve a particular effect with respect to the control of the focal spot of the emitted electron beam.
Finally, the orientation of the emitter block 402 inside the vacuum enclosure (see
It should be noted that the various magnetic elements, or combinations of magnetic elements, disclosed herein comprise exemplary structural implementations of a means for facilitating focal spot control. However, any other structures or combinations thereof effective in implementing control of the location of the focal spot may alternatively be employed. Accordingly, the scope of the invention should not be construed to be limited to the exemplary structural implementations disclosed herein.
With attention now to
That is, the flux lines that represent the magnetic flux density B of the magnetic field are generally oriented parallel to the filament 204 and generally perpendicular to the plane of the transmitted electron beam. As noted earlier, the strength and orientation of this magnetic field may be varied as desired to achieve a particular effect with respect to the location of the focal sport on the target surface 304 of the anode 300. Generally, this is due to the relationship between the magnetic field strength, or magnetic flux density, B and the force exerted on an electron passing through the magnetic field.
This relationship is sometimes expressed in the form F=qv×B, where F is the force exerted on a particle, such as an electron, of charge q moving at a velocity v perpendicular to, and through, a magnetic field having a magnetic flux density B. As the foregoing relation makes clear, the force F exerted on an electron varies directly as a function of the magnetic flux density B, so that as flux density increases, the force exerted on electrons passing through the magnetic field increases accordingly.
As indicated in
The described embodiments are to be considered in all respects only as exemplary and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
