Patent Application
20120190233
The subject matter disclosed herein relates to high voltage cable assemblies, and in particular, to ultra-low capacitance cable assemblies for CT systems
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. A steering magnet assembly within the X-ray tube may control the size and location of the electron stream as it hits the target. Once the target is bombarded with the stream of electrons, it produces X-ray radiation.
The 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.
One method of imaging in CT systems includes dual energy imaging. In a dual energy application, data is acquired from an object using two operating voltages of an X-ray source to obtain two sets of measured intensity data using different X-ray spectra, which are representative of the X-ray flux that impinges on a detector element during a given exposure time. Since projection data sets corresponding to two separate energy spectra must be acquired, the operating voltage of the X-ray tube is typically switched rapidly.
One obstacle associated with CT systems using the fast voltage switching methods is the time required to charge and discharge the high voltage cable and the X-ray tube. Once a generator capacitance is reduced to an acceptable level, within the CT system, cable capacitance becomes a bottleneck that limits the further increase in switching frequency. Accordingly, a need exists for low capacitance high voltage cables for CT systems that will require less time to charge and discharge.
In one embodiment, a high voltage cable assembly is provided that includes a cable having first and second ends, a first connector terminating the first end, and a second connector terminating the second end. The cable includes a protective jacket, an electromagnetic compatibility shield layer disposed inside the jacket, an outer semi-conducting layer disposed inside the electromagnetic compatibility shield layer, and a main cable insulating layer disposed inside the outer semi-conducting layer. The main cable insulating layer includes a low-permittivity insulation material. An inner cable core assembly is disposed inside the main cable insulating layer, and includes an inner semi-conducting layer, one or more filament conductors, one or more bias conductors, and one or more high voltage common conductors. The filament conductors, bias conductors, and high voltage common conductors are disposed inside the inner semi-conducting layer and are insulated from each other. In another embodiment, a high voltage cable assembly is provided that includes a cable having first and second ends, a first low capacitance connector terminating the first end and a second low capacitance connector terminating the second end. The cable includes a protective jacket, an electromagnetic compatibility shield layer disposed inside the jacket, an outer semi-conducting layer disposed inside the electromagnetic compatibility shield layer, a main cable insulating layer disposed inside the outer semi-conducting layer, and an inner cable core assembly disposed inside the main cable insulating layer. The inner cable core assembly includes an inner semi-conducting layer, one or more filament conductors, one or more bias conductors, and one or more high voltage common conductors. The filament conductors, bias conductors, and high voltage common conductors are disposed inside the inner semi-conducting layer and are insulated from each other. Additionally, the low capacitance connectors each include an internal cup and low permittivity material at least partially surrounding each cup.
In a third embodiment, a cable assembly is provided that includes a connection pipe and a cable core disposed inside the connection pipe. The cable core has a first and a second end. The cable core includes one or more bias conductors, one or more filament conductors, and one or more high voltage common conductors. The conductors are insulated from each other. Additionally, the cable assembly includes a first low capacitance connector which may receive the first end of the cable core in a first internal cup and a second low capacitance connector that may receive the second end of the cable core in a second internal cup. A low-permittivity insulation medium, more specifically vacuum or gas insulation, at least partially surrounds the first and second internal cups and surrounds the cable core inside the connection pipe.
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:
X-ray systems utilizing fast voltage switching capabilities are oftentimes limited in how fast voltage switching may occur, by the X-ray system cable capacitance. When switching voltages, a cable with high capacitance may cause the system to be unable to switch voltages in a timely manner.
In the present context, utilizing low-permittivity materials within the cable assembly and designing a cable aspect ratio and length that further reduces cable capacitance may have the effect of significant reduction in charging and discharging time within the cable, and thus speed up voltage switching within the X-ray system. Low-permittivity materials are materials that have very low dielectric constants, reducing capacitance. In preferred embodiments, the dielectric constants will be approximately 2.1-2.3, but may include any materials with a dielectric constant less than 2.8.
Turning now to the figures,
Various elements in the high voltage cable 16 can provide a low capacitance high voltage cable.
Another factor that plays a role in overall cable capacitance, is the aspect ratio of the main cable insulating layer 26 and the inner cable core assembly 20, as shown in
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.
