Patent Application
20120177186
The subject matter disclosed herein relates to X-ray tubes and, in particular, to attenuation features for secondary discharges of X-rays within an X-ray tube.
In non-invasive imaging systems, X-ray tubes are used in fluoroscopy, projection X-ray, tomosynthesis, and computer tomography (CT) systems as a source of X-ray radiation. Typically, the X-ray tube includes a cathode and a target. A thermionic filament within the cathode emits a stream of electrons towards the target in response to heat resulting from an applied electrical current, with the electrons eventually impacting the target. Once the target is bombarded with the stream of electrons, it produces focal and off-focal X-ray radiation.
The focal X-ray radiation traverses a subject of interest, such as a human patient, and a portion of the radiation impacts a detector or photographic plate where the image data is collected. Generally, tissues that differentially absorb or attenuate the flow of X-ray photons through the subject of interest produce contrast in a resulting image. In some X-ray systems, the photographic plate is then developed to produce an image which may be used by a radiologist or attending physician for diagnostic purposes. In digital X-ray systems, a digital detector produces signals representative of the received X-ray radiation that impacts discrete pixel regions of a detector surface. The signals may then be processed to generate an image that may be displayed for review. In CT systems, a detector array, including a series of detector elements, produces similar signals through various positions as a gantry is displaced around a patient.
Despite the electron stream colliding with the target in the proper location, some X-rays do not exit through the window, but instead are projected back through the X-ray tube, and may result in secondary radiation. This off-focal X-ray radiation generated in the X-ray tube must be contained within the unit so that the X-rays do not exit to the environment. Traditionally, X-ray attenuation has been provided through the use of lead linings placed along the outer periphery of the tube unit. Environmental awareness and regulation has made these techniques less desirable. Furthermore, full enclosure shielding can be bulky, requiring a large amount of shielding material. Accordingly, a need exists from improved off-focal X-ray shielding in X-ray tubes.
In one embodiment, an X-ray tube is provided. The X-ray tube includes a cathode configured to output an electron beam and a target configured to receive the electron beam and to generate X-rays. Additionally, the X-ray tube includes a magnetic focal spot control unit disposed between the cathode and the target. The magnetic focal spot control unit may generate electromagnetic fields to affect the electron beam. The magnetic focal spot control unit includes at least one electromagnet encased in a resin loaded with an X-ray attenuating material.
In another embodiment, an electromagnet for an X-ray tube is provided. The electromagnet includes an electromagnet assembly for a magnetic focal spot control unit designed to be disposed between a cathode and a target of an X-ray tube. The electromagnet assembly may generate electromagnetic fields to affect the electron beam. Additionally, the electromagnet is encased in a resin loaded with an X-ray attenuating material.
In a further embodiment, a method of forming an electromagnet is provided. The method generally includes doping a resin with an X-ray attenuating material, winding a coil around a magnet core, and encasing the magnet core and the coil in the loaded resin.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
The present approach is directed towards a system and method for attenuating off-focal X-rays produced in an X-ray tube. For example, in embodiments of an X-ray tube wherein a magnetic focal spot control unit is present, attenuation materials surrounding the electromagnets within the magnetic focal spot control unit may provide the attenuation desired to contain the off focal, or secondary, X-rays.
The secondary discharge attenuation techniques discussed herein may be utilized in an X-ray tube, such as X-ray tubes utilized in projection X-ray imaging systems, fluoroscopy imaging systems, CT imaging systems, and so on.
In the embodiment illustrated in
As noted above, the present embodiments are directed towards attenuation of the off-focal X-ray radiation produced within the X-ray tube 10. In accordance with the embodiments disclosed herein, attenuation may be performed by placing attenuation materials within the magnetic focal spot control unit 14.
In some embodiments, the electromagnets 22 within the magnetic focal spot control unit 14 may be formed into a magnet assembly.
As previously discussed, the electromagnets within the electromagnetic focal spot control unit 14 may attenuate the off-focal X-ray radiation 28. Providing attenuation within the magnetic focal spot control unit 14 may provide more efficient X-ray shielding than shielding external to the X-ray tube, by attenuating the off-focal X-rays at a sight of greater flux. The attenuation features of the electromagnets 22 and ultimately the electromagnet assembly 36 may be achieved by providing a resin encasement for the electromagnets 22, where the resin 46 is loaded with X-ray attenuating materials. The X-ray attenuating materials incorporated into the resin 46 may consist of high-density, non-magnetic materials that have a low magnetic permeability. Additionally, it may be desirable that the attenuating materials have little to no electrical conductance, as conductive materials may affect the electromagnetic field generated by the electromagnets 22. For example, tungsten, while high density and capable of X-ray attenuation, is also conductive and thus may interfere with the electromagnetic field produced by the electromagnets 22. Examples of a few suitable attenuating materials may include bismuth oxide, lead oxide, or barium sulfate. The ratio of resin 46 to attenuating materials may affect the attenuation characteristics of the electromagnets 22. Increasing the percent by volume of attenuating materials may increase the attenuation capabilities of the resin. Furthermore, the percent by volume of attenuating materials may be controlled based upon the desired thickness of the resin 46 loaded with the attenuating material or based upon the amount of attenuation desired by the encased electromagnets 22. For example, in one embodiment, the resin may have a thickness of 9 mm. At a 9 mm thickness level, to obtain full attenuation, it may beneficial for the resin 46 to contain at least approximately 50% bismuth oxide by volume. The percent by volume may be reduced if full attenuation is not required. For example, if full attenuation is not necessary, the amount of bismuth oxide may be reduced to approximately 40% by volume, providing approximately 99% attenuation.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
