Abstract:
A CT scanner comprises a beryllium window mounted on an x-ray insert, a cooling fluid circulation line, and a cooling fluid return line. A plurality of fins are mounted in the cooling fluid circulation line. The fluid circulation line is in fluid communication with one of an anode side cavity and a cathode side cavity and in fluid communication with a heat exchanger. The fluid return line is in fluid communication with the heat exchanger and in fluid communication with the other one of the anode side cavity and the cathode side cavity. A pump means circulates the cooling fluid through the heat exchanger, the suction and return lines, and the x-ray tube housing assembly.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the radiographic arts. It finds particular application in conjunction with x-ray tubes for computerized tomographic (CT) scanners and will be described with particular reference thereto. However, it is to be appreciated that the present invention may also be amenable to other applications. 
     CT scanners have commonly included a floor-mounted frame assembly which remains stationary during a scan and a rotatable frame assembly. An x-ray tube is mounted to the rotatable frame assembly which rotates around a patient receiving examination region during the scan. Radiation from the x-ray tube traverses the patient receiving region and impinges upon an array of radiation detectors. Using the position of the x-ray tube during each sampling, a tomographic image of one or more slices through the patient is reconstructed. 
     The x-ray tube typically comprises an x-ray tube insert holded a rotating anode and a stationary cathode and a lead lined housing. The x-ray tube insert is contained within the lead lined housing. Cooling oil is flowed between the x-ray tube insert and the housing. In large, high performance x-ray tubes, the x-ray insert may be a metal shell or frame with a window mounted or brazed thereon for allowing the transmission of x-rays from the x-ray tube. The window may be made of beryllium, titanium or any other x-ray transmitting material. Likewise, the housing defines an xray output window that is in alignment with the beryllium window of the metal frame such that x-rays pass directly through both the beryllium window and the x-ray output window. 
     During x-ray operation, electrons are emitted from a heated filament in the cathode and accelerated to a focal spot area on the anode. Upon striking the anode, some portion of the electrons, or secondary electrons, are bounced to the surrounding frame and converted into heat. The beryllium window receives the highest intensity of the secondary electron heating because the window is close to the focal spot on the anode. This heat is undesirable and is commonly termed waste heat. One of the persistent problems in CT scanners and other radiographic apparatus is dissipating the waste heat created while generating x-rays. 
     In order to remove the waste heat, a cooling fluid is often circulated between the housing and the metal frame intert to form a cooling flow path throughout the x-ray tube. For example, cooling oil is drawn through an output aperture located at one end of the housing, circulated through a radiator or heat exchanger and returned to an inlet aperture in the opposite end of the housing. The returned cooled fluid flows axially through the housing toward the outlet aperture, absorbing heat from the x-ray insert. 
     Removing waste heat in this manner is not always completely effective. More specifically, waste heat removal by merely forcing coolant to flow between the x-ray insert and the housing is particularly ineffective around the x-ray output window. The beryllium window and its environs, being the recipient of the secondary electrons and heat from the closely adjacent focal spot, is preferentially heated. Further, the beryllium window protrudes out from the frame and generally disrupts the flow of coolant around the window preventing optimal cooling. Additionally, the configuration of the x-ray output window on the housing disrupts coolant flow and, by its proximity to the beryllium window, limits the amount of coolant capable of passing over the beryllium window. 
     When the beryllium window is not sufficiently cooled, the heat can damage the braze joint between the beryllium window and the metal frame insert causing the x-ray tube to fail. Further, the coolant adjacent to the beryllium window may boil and leave a carbon residue on the beryllium window. Such a coating is undesirable as it may degrade the quality of the x-ray image. 
     The present invention provides a new and improved cooling system for overcoming the above-referenced drawbacks and others. 
     SUMMARY OF THE INVENTION 
     The present invention relates to the use of a cooling jacket and/or flow baffles around an x-ray insert to provide for the removal of undesirable waste heat from the x-ray tube insert, a beryllium window on the x-ray insert, and the area surrounding the beryllium window. 
     In accordance with one aspect of the present invention, a CT scanner comprises an x-ray tube mounted on a rotating frame portion. The x-ray tube includes an x-ray insert and a housing. The x-ray insert is mounted in the housing between an anode side cavity and a cathode side cavity with a cooling fluid path surrounding the x-ray insert and running between the anode and cathode side cavities. The x-ray tube has a beryllium window mounted on the x-ray insert, a cooling fluid circulation line, and a cooling fluid return line. The fluid circulation line is in fluid communication with one of the anode side cavity and the cathode side cavity and in fluid communication with a heat exchanger. The fluid return line is in fluid communication with the heat exchanger and in fluid communication with the other one of the anode side cavity and the cathode side cavity. The CT scanner additionally comprises a pump means and a plurality of fins mounted in the cooling fluid circulation line. The pump means circulates the cooling fluid through the heat exchanger, the suction and return lines, and the x-ray tube housing. 
     In accordance with another aspect of the present invention, an x-ray tube comprises a housing, an x-ray insert, and a plurality of baffles. The housing has an x-ray window and defines a housing cavity therein. The x-ray tube includes a vacuum envelope which holds an anode and a cathode. The vacuum envelope has a beryllium window adjacent the anode. The x-ray insert is mounted in the housing spaced from the housing by an annular fluid path with the beryllium window aligned with the x-ray window. The plurality of baffles is mounted in the flow path for directing cooling fluid toward the beryllium window. 
     In accordance with another aspect of the present invention, a method of cooling an x-ray tube is provided. A cooling fluid is circulated through an x-ray tube housing. Heat is removed from an x-ray insert disposed within the x-ray tube housing by allowing the circulating cooling fluid to flow adjacent the x-ray insert. Heat is removed from a beryllium window disposed on the x-ray insert by forcing the cooling fluid to converge toward the beryllium window. The forcing is caused by a plurality of baffles disposed angularly relative to the flow direction of the circulating cooling fluid. Heated cooling fluid is removed from the x-ray tube housing. Cooling fluid is cooled and recirculated through the x-ray tube housing. 
     The advantages of the present invention include the ability to prevent or reduce the risk of thermal damage to the joint between the beryllium window and the metal frame insert. 
     Another advantage resides in reducing or preventing failure of the x-ray insert due to overheating. 
     Another advantage of the present invention resides in reducing or preventing carbon build-up on the beryllium window due to overheating of the cooling fluid. 
     Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawing is only for purposes of illustrating a preferred embodiment and is not to be construed as limiting the invention. 
     FIG. 1 is a diagrammatic illustration of a CT scanner in accordance with the present invention; 
     FIG. 2 is a perspective view of the x-ray tube housing of the scanner of FIG. 1; 
     FIG. 3 is a diagrammatic cross-sectional illustration of the x-ray tube housing of FIG. 2, a contained x-ray insert, and a cooling jacket; 
     FIG. 4 is a top view in partial section of the x-ray insert and cooling jacket of FIG. 3; 
     FIG. 5 is a partial perspective view of a cooling jacket in accordance with the present invention; and 
     FIG. 6 is a partial perspective view of an alternate embodiment of the metal frame insert in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, a CT scanner includes a floor mounted or stationary frame portion A whose position remains fixed during data collection. An x-ray tube B is mounted on a rotating frame C rotatably mounted within the stationary frame portion A. Heat generated by the x-ray tube B is transferred to a heat exchanger D by a cooling fluid, such as oil, water, refrigerant gas, other fluids and combinations thereof. 
     The stationary frame portion A includes a bore  10  that defines a patient receiving examination region  12 . An array of radiation detectors  14  are disposed concentrically around the patient receiving region  12 . The stationary frame A with the rotating frame C can be canted or tipped to scan slices at selectable angles. A control console  16  contains an image reconstructing processor  18  for reconstructing an image representation of output signals from the detector array  14 , performing image enhancements, and the like. A video monitor  20  converts the reconstructed image representation into a human readable display. The console  16  also includes appropriate digital recording memory media for archiving the image representations. Various control functions, such as initiating a scan, selecting among different types of scans, calibrating the system, and the like are also performed at the control console  16 . 
     With further reference to FIGS. 2 and 3, the x-ray tube B includes a cooling fluid filled housing  22  that has an x-ray permeable window  24  directed toward the patient receiving region  12 . The contoured profile of the x-ray permeable window  24  deviates substantially from the inner walls of the housing  22 . A housing cavity is disposed within the housing  22  for holding an x-ray insert  26 . 
     The x-rays pass through the x-ray permeable window  24  and across the patient receiving region  12 . Appropriate x-ray collimators focus the radiation into one or more planar beams which span the examination region  12  in a fan or cone pattern, as is conventional in the art. Other equipment associated with the x-ray tube B, such as a high voltage power supply  28 , are also mounted on the rotating frame C. 
     With specific reference to FIG. 2, in a first preferred embodiment, the x-ray tube housing  22  defines a cathode side portion  30  and an anode side portion  32  through which electrical leads are passed. Heated cooling fluid is circulated from inside the cathode side portion  30  of the x-ray tube housing  22  through a first cooling fluid duct  34  to a heat exchanger D on the rotatable frame C. Circulation of the cooling fluid is effected by a fluid pump  36 . Cooled cooling oil exiting from the heat exchanger D is returned to the anode side portion  32  via a second cooling fluid duct  38 . The cooling fluid enters the anode side portion  32  through an anode side aperture (not shown) and flows into an anode side cavity  40  which is defined by a portion of the housing cavity. The fluid passes from the anode side cavity  40  through an annularly disposed cooling fluid path  42  to remove heat created during x-ray generation and into a cathode side cavity  44  defined by another portion of the housing cavity. The fluid exits the cathode side portion  30  by flowing from the cathode side cavity  44  through a cathode side aperture (not shown) into the first cooling fluid duct  34  and recirculates back to the heat exchanger D. 
     With specific reference to FIG. 3, the x-ray insert or metal frame  26  defines a vacuum envelope for holding a rotary anode  48  which is rotatably mounted in the metal frame  26  by bearings (not shown). A cathode  50  is mounted adjacent the rotary anode  48 . Electrons from the cathode  50  are propelled by high voltage against the anode  48  causing the emission of x-rays and heat. The metal frame insert  26  includes a beryllium window  52  mounted adjacent the cathode  50  and the x-ray permeable window  24  of the housing  22 . The beryllium window  52  passes x-rays generated by the cathode  50  and the anode  48  out of the metal frame insert  26  through the x-ray permeable window  24  and into the patient receiving area  12 . The beryllium window  52  is attached to the metal frame insert  26  by brazing or by any other suitable manner. Electrical leads for supplying current to the cathode  50  and leads for biasing the cathode  50  to a large, negative potential difference relative to the anode  48  pass through the metal envelope in a cathode well  54 . 
     With continuing reference to FIG.  3  and further reference to FIGS. 4 and 5, a generally cylindrical cooling jacket  56  is mounted around the metal frame insert  26 . The cooling jacket  56  and the metal frame insert  26  together define the annularly cooling fluid flow path  42  between the anode side cavity  40  and the cathode side cavity  44 . The cooling jacket  56  is preferably made of aluminum but can be made of other low-Z metals, plastic coupled with an aluminum piece facing the beryllium window  52 , or the like. The cooling jacket  56  or, alternatively, the aluminum piece attached to a plastic cooling jacket, functions as an x-ray filter plate at or near the beryllium window  52 . Of course, the materials and shape of the cooling jacket  56  can vary and it is to be appreciated that all such varying materials and shapes are to be considered within the scope of the present invention. 
     With specific reference to FIG. 3, the cooling jacket  56  includes a flared opening  58  located at the entrance of the flow path  42  to allow for smooth coolant flow. The jacket  56  conforms to the general shape of the metal frame insert  26  and directs fluid along the metal frame insert  26 . The jacket  56  opens to the cathode side cavity  44  at or near the cathode well  54  of the metal frame insert  46  causing fluid exiting the flow path  42  to cool the pass through on the cathode well  54  before entering the cathode side cavity  44 . An O-ring seal  60  is mounted between the housing  22  and the flared opening  58  of the jacket  56  to prevent fluid from bypassing the flow path  42 . 
     With continuing reference to FIGS. 4 and 5, a principal set of baffles  62 ,  64  and an auxiliary set of baffles  66 ,  68  are mounted to an inside surface of the jacket  56 . The baffles  62 - 68  extend from the jacket  56  to the wall of the metal vacuum envelope  46  adjacent the beryllium window  52 . Further, the baffles  62 - 68  extend axially along the length of the jacket  56  from an axial edge of the jacket  56  nearest the anode side portion  32  to respective positions on either side of the beryllium window  52 . The baffles  62 - 68  converge, preferably at sixty-five degrees from a transverse direction. The axial length, height, and angle of each of the baffles  62 - 68  can vary. 
     The primary baffles  62 ,  64  direct and accelerate cooling fluid toward the beryllium window  52 . The primary baffles  62 ,  64  are located one each on either side of the beryllium window  52  approximately thirty-three degrees around the cooling jacket  56  relative to the beryllium window  52 . The secondary baffles  66 ,  68  direct and accelerate cooling fluid toward hot zone areas  70 ,  72  created by the primary baffles  62 ,  64 . Hot zone areas  70 ,  72  are created behind the primary baffles  62 ,  64  where cooling fluid is directed away toward the beryllium window  52 . All of the baffles  62 - 68  also serve to maintain a preselected fixed space between the metal frame insert  26  and the cooling jacket  56 . For maximizing heat transfer, the spacing of the jacket  56  from the metal frame insert  46  is designed based on the specified coolant flow rate in maximum power of the CT scanner and to maintain a desirable flow pattern. 
     A plurality of guiding standoffs  74 ,  76  are concentrically opposite the baffles  62 - 68  and extend between the metal frame insert  26  and the interior wall of the cooling jacket  56 . Like the baffles  62 - 68 , the guiding standoffs  74 ,  76  are used to maintain an appropriate amount of spacing between the metal insert  26  and the jacket  56 . The standoffs  74 ,  76  engage grooves in the metal frame  26  to assure alignment of the beryllium window  52  and the baffles  62 - 68 . 
     With reference back to FIG. 2, alternatively, the baffles  62 - 68  are mounted on the exterior surface of the metal frame  26  and extend toward the jacket  56 . 
     In a second preferred embodiment, the fluid path  42  is defined between the metal frame insert  26  and the housing  22 . Thus, the housing  22  serves as the cooling jacket. The baffles  62 - 68  extend between the metal frame insert  26  and the housing  22 . Guiding standoffs are eliminated. 
     With reference back to FIG. 2, a second flow line  78  of cooling fluid is introduced at or near the beryllium window  52  to enhance cooling on the window  52  according to a third preferred embodiment. A small flow distributor  80  is mounted at or near the entrance to the second flow line  78  to divide the cooling fluid exiting the heat exchanger D between the flow channel  42  and the second flow line  78 . The fluid flow channel  42  delivers cooling fluid to the baffles  62 - 68  and the area around the beryllium window  52  in the manner described above. The second flow line  78  delivers fluid directly to the beryllium window  52 . The diameter of the second flow line  78  is such that the flow rate in the second flow line  78  is at least ten percent (10%) of the flow rate passing into the flow channel  42 . 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon a reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.