Patent Application
20130182825
X-ray tubes are extremely valuable tools that are used in a wide variety of applications, both industrial and medical. An x-ray tube typically produces x-rays in an omnidirectional fashion where the useful portion ultimately exits the x-ray tube through a window in the x-ray tube, and interacts with a subject, such as a material sample or a patient, in order to create an x-ray image.
During the operation of some x-ray tubes, the x-ray tube is translated or rotated about a subject in order to produce x-ray images of the subject at various angles. Unfortunately, however, the motion of the x-ray tube can result in an effective increase of the focal spot size. This effective increase in the focal spot size, also known as motion blurring of the focal spot, can result in reduced resolution of the imaging of the subject.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced.
In general, example embodiments relate to an x-ray tube cathode with magnetic electron beam steering. The example cathode disclosed herein is configured to create and steer a beam of electrons during beam formation. This steering can, in at least some example embodiments, enable an x-ray tube to translate or rotate on a gantry about a subject while the beam of electrons is steered so that a mean position of a focal spot of the beam of electrons remains stationary in the subject's frame of reference despite the motion of the x-ray tube, resulting in consistent imaging of the subject.
In one example embodiment, an x-ray tube cathode includes a cathode head and an electron emitter. The cathode head includes electrically conductive and non-magnetic material integrated with magnetic material. The cathode head defines an emitter slot in a portion of electrically conductive and non-magnetic material positioned between two portions of magnetic material. The electron emitter is positioned within the emitter slot. The electron emitter is configured to emit a beam of electrons. The beam of electrons is configured to be both focused by the electrically conductive and non-magnetic material and steered during beam formation by the magnetic material.
In another example embodiment, an x-ray tube cathode includes a magnetic yoke, a cathode head, and an electron emitter. The magnetic yoke includes a core and a coil. The core has a base and two ends formed from a magnetic material. The coil is wound around the base of the core. The two ends are configured to function as magnetic poles when an electric current is passed through the coil. The cathode head includes electrically conductive and non-magnetic material integrated with the two ends. The cathode head defines an emitter slot positioned between the two ends. The electron emitter is positioned within the emitter slot. The electron emitter is configured to emit a beam of electrons. The beam of electrons is configured to be both focused by the electrically conductive and non-magnetic material and steered during beam formation by the magnetic poles.
In yet another example embodiment, an x-ray tube includes an evacuated enclosure, an anode positioned within the evacuated enclosure, and a cathode. The cathode includes a magnetic yoke, a cathode head, and an electron emitter. The magnetic yoke includes a core and a coil. The core has a base and two ends formed from a magnetic material. The coil is wound around the base of the core. The coil and the base are positioned outside the evacuated enclosure. The two ends are positioned within the evacuated enclosure. The two ends are configured to function as magnetic poles when an electric current is passed through the coil. The cathode head includes electrically conductive and non-magnetic material integrated with the two ends. The cathode head defines an emitter slot in the electrically conductive and non-magnetic material positioned between the two ends. The electron emitter is positioned within the emitter slot and is configured to emit a beam of electrons. The electron emitter is immersed in a uniform magnetic field created by the magnetic yoke that is configured to steer the beam of electrons during beam formation
These and other aspects of example embodiments of the invention will become more fully apparent from the following description and appended claims.
To further clarify certain aspects of the present invention, a more particular description of the invention will be rendered by reference to example embodiments thereof which are disclosed in the appended drawings. It is appreciated that these drawings depict only example embodiments of the invention and are therefore not to be considered limiting of its scope. Aspects of example embodiments of the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
Example embodiments of the present invention relate to an x-ray tube cathode with magnetic electron beam steering. Reference will now be made to the drawings to describe various aspects of example embodiments of the invention. It is to be understood that the drawings are diagrammatic and schematic representations of such example embodiments, and are not limiting of the present invention, nor are they necessarily drawn to scale.
With reference first to
As disclosed in
With continued reference to
The focal track 110 is oriented so that many of the emitted x-rays are collimated by the x-ray tube window 104. As the x-ray tube window 104 is comprised of an x-ray transmissive material, the x-rays emitted from the focal track 110 pass through the x-ray tube window 104 in order to be attenuated in a subject, such as a material sample or a patient (not shown), and then imaged on an image detector (not shown) in order to produce an x-ray image (not shown). The window 104 therefore hermetically seals the vacuum of the evacuated enclosure 106 of the x-ray tube 100 from the atmospheric air pressure outside the x-ray tube 100 and yet enables the x-rays generated by the rotating anode 108 to exit the x-ray tube 100.
Although the example x-ray tube 100 is depicted as a rotatable anode x-ray tube, example embodiments disclosed herein may be employed in other types of x-ray tubes. Thus, the example electron emitters disclosed herein may alternatively be employed, for example, in a stationary anode x-ray tube. Further, although the electron emitter 202 is disclosed as a helical filament, it is understood that the electron emitter 202 may instead be a flat filament.
With continued reference to
As disclosed in
During operation of the example x-ray tube 100, an electric current may be intermittently passed through the coil 216 (wire or tap wound). When the electric current is passed through the coil 216, the two portions of magnetic material 208 and 210 function as ends of the core and magnetic poles. For example, the coil 202 may be configured to have a magnetomotive force of about 200 ampere-turns. As disclosed in
The establishment of the uniform magnetic field of magnetic flux density “B”, considered in connection with the direction of travel of the beam of electrons “e” emitted by the electron emitter 202, results in the ability, through the control of the uniform magnetic field, to deflect the beam of electrons “e” laterally, as indicated by the dashed arrow. Moreover, varying the electric current that is passed through the coil 216 enables reliable control over the extent to which the beam of electrons “e” is laterally deflected.
The positions of the two portions of magnetic material 208 and 210 are such that the uniform magnetic field immerses the electron emitter 202 and is configured to steer the trajectory of the beam of electrons “e” produced by the electron emitter 202 during beam formation. Thus, the beam of electrons “e” is simultaneously formed and steered, instead of being steered after formation. For example, the example cathode 200 may be configured such that the trajectory of the beam of electrons “e” is deflected during formation by the uniform magnetic field created by the magnetic poles to achieve up to about 5 mm of beam steering. At the same time, the electrically conductive and non-magnetic material 206 is configured to focus the beam of electrons “e”.
Although the deflection of the trajectory of the beam of electrons “e” can be accomplished by passing an electric current through the coil 216, it is understood that the two portions of magnetic material 208 and 210 may be configured to deflect the trajectory of the beam of electrons “e” simply by virtue of their proximity to the electron emitter 202 without passing an electric current through the coil 216.
The intermittent steering of the beam of electrons “e” by the example cathode 200 can help maintain stationary the mean position of a focal spot in the subject's reference frame. This steering can be particularly useful in application where the example x-ray tube 100 is rotated during operation about a subject in order to produce x-ray images of the subject at various angles, with the direction of motion during rotation, using a gantry for example, being in the direction of the dashed arrow in
The example embodiments disclosed herein may be embodied in other specific forms. The example embodiments disclosed herein are therefore to be considered in all respects only as illustrative and not restrictive.
