Abstract:
A system and method for collecting backscattered electrons within a substantially evacuated vessel containing both an electron-emitting cathode assembly and an electron-attracting anode assembly. The system and method comprises an electron collector assembly including a first plate, a second plate, an internal member, a fluid inlet, and a fluid outlet. The first plate is mounted within the vessel closest to the anode assembly. The second plate is mounted within the vessel closest to the cathode assembly. The internal member is positioned between the first plate and the second plate, and includes an internal conduit for conveying a heat absorbing cooling fluid therethrough.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of and claims priority to U.S. patent application Ser. No. 11/306,233, filed on Dec. 20, 2005, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present disclosure relates generally to electron collectors, and more particularly to a system and method for collecting backscattered electrons within, for example, a substantially evacuated vessel, such as an x-ray tube. 
         [0003]    An x-ray tube generally includes a cathode assembly and an anode assembly disposed within a vacuum vessel. The anode assembly includes an anode. The anode commonly includes a stationary or a rotating target with a target track or impact zone fabricated on an outer surface thereof. The target track or impact zone is generally fabricated from a refractory metal with a high atomic number, such as tungsten or a tungsten alloy. The cathode assembly is positioned at some distance from the anode assembly, and a high voltage differential is maintained therebetween in order to accelerate electrons toward the anode. This high voltage differential generates an electric field having a strength defined as the voltage differential between the anode and cathode divided by the distance therebetween. The cathode assembly emits electrons in the form of an electron beam that are accelerated across the high voltage differential and impact the target track at a focal spot at a high velocity. As the electrons impact the target track, the kinetic energy of the electrons is converted to high-energy electromagnetic radiation, or x-rays. The x-rays are then transmitted through an object and intercepted by a detector that forms an image of the object&#39;s internal structure and contents. 
         [0004]    Many of the electrons incident on the anode target are backscattered from the anode&#39;s target track in random directions and scattered throughout the vacuum vessel to strike internal components of the x-ray tube. As these backscattered electrons impact internal components of the x-ray tube, their kinetic energies are transferred to these internal components in the form of thermal energy or heat. Excess heat generation adversely affects the durability of the x-ray tube. Furthermore, in addition to transferring thermal energy to the x-ray tube&#39;s internal components, the impact of backscattered electrons also produces off-focus x-ray radiation that may increase undesirable exposure to x-ray radiation and diminish x-ray image quality. 
         [0005]    Therefore, there is a need for a system and method of improving the collection of backscattered electrons in an x-ray tube. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    In an exemplary embodiment, an electron collector assembly for collecting backscattered electrons within a substantially evacuated vessel that contains an electron-emitting cathode and an electron-attracting anode spaced apart therein, said electron collector assembly comprising a first plate mounted proximate to said anode within said vessel, said first plate having a first side at least partially facing said anode and a second side facing opposite said first side; a second plate mounted proximate to said cathode within said vessel, said second plate having a first side and a second side at least partially facing said cathode; an inner member positioned between said first plate and said second plate, said inner member having an internal conduit for conveying a heat absorbing cooling fluid therethrough; an inlet in fluid communication with said internal conduit; and an outlet in fluid communication with said internal conduit. 
         [0007]    In an exemplary embodiment, an electron collector assembly for collecting backscattered electrons within a substantially evacuated vessel that contains an electron-emitting cathode and an electron-attracting anode spaced apart therein, said electron collector assembly comprising a first plate mounted proximate to said anode within said vessel, said first plate having a first side at least partially facing said anode and a second side facing opposite said first side; an inner member integral with said first plate, said inner member having an internal conduit for conveying a heat absorbing cooling fluid therethrough; a second plate mounted proximate to said cathode within said vessel, said second plate having a first side and a second side at least partially facing said cathode; an inlet in fluid communication with said internal conduit; and an outlet in fluid communication with said internal conduit. 
         [0008]    In an exemplary embodiment, an electron collector assembly for collecting backscattered electrons within a substantially evacuated vessel that contains an electron-emitting cathode and an electron-attracting anode spaced apart therein, said electron collector assembly comprising a first plate mounted proximate to said anode within said vessel, said first plate having a first side at least partially facing said anode and a second side facing opposite said first side; a second plate mounted proximate to said cathode within said vessel, said second plate having a first side and a second side at least partially facing said cathode; an inner member integral with said second plate, said inner member having an internal conduit for conveying heat absorbing cooling fluid therethrough; an inlet in fluid communication with said internal conduit; and an outlet in fluid communication with said internal conduit. 
         [0009]    In an exemplary embodiment, a system for collecting backscattered electrons within a substantially evacuated vessel containing both an electron-emitting cathode assembly and an electron-attracting anode assembly spaced apart therein, said system comprising a first plate mounted proximate to said anode assembly within said vessel, said first plate having a first side at least partially facing said anode assembly and a second side facing opposite said first side; a second plate mounted proximate to said cathode assembly within said vessel, said second plate having a first side and a second side at least partially facing said cathode assembly; and an inner member positioned between said first plate and said second plate, said inner member having an internal conduit for conveying heat absorbing cooling fluid therethrough. 
         [0010]    In an exemplary embodiment, a method for collecting backscattered electrons within a substantially evacuated vessel containing both an electron-emitting cathode assembly and an electron-attracting anode assembly spaced apart therein, said system comprising mounting a first plate proximate to said anode assembly within said vessel, said first plate having a first side at least partially facing said anode assembly and a second side facing opposite said first side; mounting a second plate proximate to said cathode assembly within said vessel, said second plate having a first side and a second side at least partially facing said cathode assembly; and positioning an inner member between said first plate and said second plate, said inner member having an internal conduit for conveying heat absorbing cooling fluid therethrough. 
         [0011]    Various other features, aspects, embodiments and advantages will be made apparent to those skilled in the art from the accompanying drawings and detailed description thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]      FIG. 1  is a cross-sectional view of an exemplary embodiment of an x-ray tube assembly; 
           [0013]      FIG. 2  is a schematic diagram of an exemplary embodiment of an x-ray tube; 
           [0014]      FIG. 3  is a schematic diagram of an exemplary embodiment of an x-ray tube; 
           [0015]      FIG. 4  is a plan view of an exemplary embodiment of an electron collector assembly; 
           [0016]      FIG. 5  is a cross-sectional view of an exemplary embodiment of the electron collector assembly of  FIG. 4  mounted within a substantially evacuated vessel; 
           [0017]      FIG. 6  is a cross-sectional view of the electron collector assembly of  FIG. 5  mounted within the vacuum vessel of an x-ray tube; and 
           [0018]      FIG. 7  is an enlarged cross-sectional view of the electron collector assembly of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]      FIG. 1  is a cross-sectional view of an exemplary embodiment of an x-ray tube assembly  10 . The x-ray tube assembly  10  includes a substantially evacuated vacuum vessel  12  that is situated in a chamber  14  defined within a casing  16 . The vacuum vessel  12  is constructed to endure very high temperatures and includes an anode assembly  22 , a cathode assembly  24 , and an electron collector assembly  20  positioned between the anode assembly  22  and the cathode assembly  24 . The casing  16  may be lined with lead to shield and prevent any extraneous x-ray radiation from straying from the x-ray tube assembly  10 . The chamber  14  within the casing  16  may be filled with a heat absorbing cooling fluid  18  such as, for example, a dielectric oil. The x-ray tube assembly  10  further includes a high voltage anode receptacle  26  and a high voltage cathode receptacle  28  that serve as connection points for an electrical power supply (not shown) for powering the x-ray tube assembly  10 . The anode assembly  22  is in electrical communication with the high voltage anode receptacle  26  and the cathode assembly  24  in electrical communication with the high voltage cathode receptacle  28 . 
         [0020]    During operation of the x-ray tube assembly  10 , the cooling fluid  18  is circulated through the chamber  14  by a pump (not shown). The circulating cooling fluid  18  absorbs heat from the vacuum vessel  12  and other components of the x-ray tube assembly  10 , preventing damage thereto. In addition to absorbing heat from the vacuum vessel  12  and other components of the x-ray tube assembly  10 , the cooling fluid  18  also provides electrical insulation between the high voltage anode receptacle  26  and the high voltage cathode receptacle  28 , the casing  16  and the vacuum vessel  12 . 
         [0021]    The anode assembly  22  includes a rotating anode target  32  mounted to one end of a rotatable shaft  34 . The opposite end of the rotatable shaft  34  is coupled to a motor  36  that rotates the rotatable shaft  34  and anode target  32  at a very high angular velocity. The rotatable shaft  34  extends from the motor  36  into the vacuum vessel  12  with the anode target  32  attached to the end thereof. The cathode assembly  24  includes a cathode filament  38  situated opposite the anode target  32  within the vacuum vessel  12 . 
         [0022]    During operation, when the x-ray assembly  10  is energized by the electrical power supply (not shown) electrically connected between the anode assembly  22  and the cathode assembly  24 , a focused beam of electrons  40  is emitted from the cathode filament  38  of the cathode assembly  24  and directed toward the anode target  32  of the anode assembly  22 . As the electron beam  40  strikes the target track of the rotating anode target  32 , x-rays  33  are generated. The generated x-rays  33  then pass through a first x-ray transmissive window  42  in the wall  44  of the vacuum vessel  12 , and through a second x-ray transmissive window  46  in the casing  16  of the x-ray tube assembly  10 . 
         [0023]    The electron collector assembly  20  is attached to the wall  44  of the vacuum vessel  12 . The electron collector assembly  20  may include an opening  48  extending therethrough allowing one end of the rotatable shaft  34  to extend through the electron collector assembly  20  and allowing the rotatable shaft  34  to rotate, and an aperture  30  extending therethrough for allowing an electron beam  40  from the cathode filament  38  to pass therethrough to the anode target  32 . 
         [0024]    Any backscattered electrons and off-focus x-ray radiation from the anode target  32  are collected by the electron collector assembly  20  positioned between the anode assembly  22  and cathode assembly  24 . The electron collector assembly  20  further prevents any backscattered electrons from re-impacting the anode target  32  and producing additional off-focus x-ray radiation, which may cause undesirable x-ray radiation exposure and negatively affect the quality of an x-ray image. 
         [0025]      FIG. 2  is a schematic diagram of an exemplary embodiment of an x-ray tube  50 . The x-ray tube  50  includes a substantially evacuated vacuum vessel  52 , an electrical power supply  54 , and a motor  56 . The vacuum vessel  52  includes an anode assembly  62 , a cathode assembly  64 , and an electron collector assembly  70  positioned between the anode assembly  62  and the cathode assembly  64 . 
         [0026]    The electrical power supply  54  is connected between the anode assembly  62  and the cathode assembly  64 . An x-ray tube may typically be of a bi-polar configuration or a monopolar configuration. The x-ray tube  50  shown in  FIG. 2  most closely resembles that of a bi-polar configuration. In a bi-polar configuration, for example, the cathode is maintained at a negative voltage and the anode is maintained at a positive voltage.  FIG. 3  illustrates a schematic diagram of an x-ray tube  80  in a monopolar configuration. 
         [0027]    The anode assembly  62  includes an anode target  72  mounted to one end of a rotatable shaft  74 . The opposite end of the rotatable shaft  74  is coupled to the motor  56  that rotates the rotatable shaft  74  and anode target  72  at a very high angular velocity. The rotatable shaft  74  extends from the motor  56  into the vacuum vessel  52  with the anode target  72  attached to the end thereof. A seal and bearing assembly  68  is coupled to the rotatable shaft  74  at the vacuum vessel  52  to substantially keep the vacuum vessel  52  hermetically sealed and allowing the rotatable shaft  74  to rotate. The cathode assembly  64  includes a cathode filament  78  situated opposite the anode target  72  within the vacuum vessel  52 . 
         [0028]    The electron collector assembly  70  is attached to the wall  66  of the vacuum vessel  52 . The electron collector assembly  70  may include an opening  58  extending therethrough allowing one end of the rotatable shaft  74  to extend through the electron collector assembly  70  and allowing the rotatable shaft  74  to rotate, and an aperture  60  extending therethrough for allowing an electron beam  76  from the cathode filament  78  to pass therethrough to the anode target  72  for producing x-rays  77 . 
         [0029]    The electron collector assembly  70  is designed to collect any backscattered electrons and off-focus a-ray radiation from the anode target  72 . The electron collector assembly  70  further prevents any backscattered electrons from re-impacting the anode target  72  and producing additional off-focus x-ray radiation, which may cause undesirable x-ray radiation exposure and negatively affect the quality of an x-ray image. 
         [0030]      FIG. 3  is a schematic diagram of an exemplary embodiment of an x-ray tube  80 . The x-ray tube  80  includes a substantially evacuated vacuum vessel  82 , an electrical power supply  84 , and a motor  86 . The vacuum vessel  82  includes an anode assembly  92 , a cathode assembly  94 , and an electron collector assembly  100  positioned between the anode assembly  92  and the cathode assembly  94 . 
         [0031]    The electrical power supply  84  is connected between the anode assembly  92  and the cathode assembly  94 . The x-ray tube  80  shown in  FIG. 3  most closely resembles that of a monopolar configuration. In a monopolar configuration, for example, the cathode is maintained at a negative high voltage and both the anode and vacuum vessel are electrically grounded. 
         [0032]    The anode assembly  92  includes an anode target  102  mounted to one end of a rotatable shaft  104 . The opposite end of the rotatable shaft  104  is coupled to the motor  86  that rotates the rotatable shaft  104  and anode target  102  at a very high angular velocity. The rotatable shaft  104  extends from the motor  86  into the vacuum vessel  82  with the anode target  102  attached to the end thereof. A seal and bearing assembly  98  is coupled to the rotatable shaft  104  at the vacuum vessel  82  to substantially keep the vacuum vessel  82  hermetically sealed and allowing the rotatable shaft  104  to rotate. The cathode assembly  94  includes a cathode filament  108  situated opposite the anode target  102  within the vacuum vessel  82 . 
         [0033]    The electron collector assembly  100  is attached to the wall  96  of the vacuum vessel  82 . The electron collector assembly  100  may include an opening  88  extending therethrough allowing one end of the rotatable shaft  104  to extend through the electron collector assembly  100  and allowing the rotatable shaft  104  to rotate, and an aperture  90  extending therethrough for allowing an electron beam  106  from the cathode filament  108  to pass therethrough to the anode target  102  for producing x-rays  107 . 
         [0034]    The electron collector assembly  100  is designed to collect any backscattered electrons and off-focus a-ray radiation from the anode target  102 . The electron collector assembly  100  further prevents any backscattered electrons from re-impacting the anode target  102  and producing additional off-focus x-ray radiation, which may cause undesirable x-ray radiation exposure and negatively affect the quality of an x-ray image. 
         [0035]      FIG. 4  is a plan view of an exemplary embodiment of an electron collector assembly  110 . The electron collector assembly  110  may include an opening  120  in the center thereof that extends therethrough for fitting around a shaft assembly from an anode assembly of an x-ray tube, an aperture  122  extending therethrough for allowing an electron beam from a cathode assembly of an x-ray tube to pass therethrough, and an outer periphery  124 . Though the opening  120  is substantially circular and the aperture  122  is substantially square or rectangular as shown, the opening  120  and aperture  122  may have other shapes in alternative embodiments. Furthermore, though the electron collector assembly  120  as shown has a circular outer periphery  124  and is thus generally shaped as a disk, the electron collector assembly  120  may take on other shapes in alternative embodiments. 
         [0036]    To facilitate the introduction of a heat absorbing cooling fluid into an internal conduit of the electron collector assembly  110 , a fluid inlet  140  is mounted to one side  136  of the electron collector assembly  110  and is in fluid communication with the internal conduit within the electron collector assembly  110 . In this way, cooling fluid may be circulated into the electron collector assembly&#39;s internal conduit via the fluid inlet  140 . In addition, to facilitate the removal of the heat absorbing cooling fluid from the internal conduit of the electron collector assembly  110 , a fluid outlet  142  is similarly mounted to one side  136  of the electron collector assembly  110  and is in fluid communication with the internal conduit within the electron collector assembly  110 . In this way, cooling fluid may be circulated out of the electron collector assembly&#39;s internal conduit via the fluid outlet  142 . Furthermore, to ensure that cooling fluid is fully circulated throughout the internal conduit of the electron collector assembly  110 , a septum  150  extends through the electron collector assembly  110  from the opening  120  to the outer periphery  124 . The septum  150  ensures the flow of cooling fluid into the fluid inlet  140  and the out of the fluid outlet  142 . 
         [0037]      FIG. 5  is a cross-sectional view of the electron collector assembly  110  of  FIG. 4  mounted within a substantially evacuated vessel, such as a vacuum vessel  112 . The electron collector assembly  110  is generally centrally mounted within the vacuum vessel  112  that is suitable for incorporation within an x-ray tube. The vacuum vessel  112  includes an anode end  114  for acceptance of an anode assembly therein, a cathode end  116  for acceptance of a cathode assembly therein, and wall  118  enclosing the vacuum vessel  112 . 
         [0038]    The electron collector assembly  110  may include an opening  120  in the center thereof that extends therethrough for fitting around a shaft assembly from an anode assembly of an x-ray tube, an aperture  122  extending therethrough for allowing an electron beam from a cathode assembly of an x-ray tube to pass therethrough, and an outer periphery  124 . The outer periphery  124  of the electron collector assembly  110  may be brazed, soldered, welded or otherwise attached to the wall  118  of the vacuum vessel  112  by any other type of physical attachment as well. 
         [0039]    The electron collector assembly  110  is comprised of a first plate  126  having a first side  128  and a second side  130 , a second plate  132  having a first side  134  and a second side  136 , an inner member  138  positioned between the first plate  126  and the second plate  132 , a fluid inlet  140 , and a fluid outlet  142 . The first plate  126  is generally both electrically conductive and thermally emissive, and is centrally mounted within the vacuum vessel  112 . Though other constituent materials are possible, the first plate  126  may comprise an electrically conductive metal such as, for example, copper. The first plate  126  may also be coated with a thermally emissive outer coating such as, for example, an iron oxide coating. Furthermore, as illustrated in  FIG. 4 , the first plate  126  may include a plurality of thermally emissive protrusions  144  extending outwardly from its first side  128 . As shown, the protrusions  144  generally extend outwardly toward the anode end  114  of the vacuum vessel  112 . Though other constituent materials are possible, the protrusions  144  may comprise an electrically conductive metal such as, for example, copper. The protrusions  144  may also be coated with a thermally emissive outer coating such as, for example, an iron oxide coating. The second plate  132  is generally thermally emissive. Though other constituent materials are possible, the second plate  132  may comprise stainless steel and may be “greened” with a thermally emissive outer coating such as, for example, a chromic oxide coating. 
         [0040]    The inner member  138  is sandwiched in between the second side  130  of the first plate  126  and the first side  134  of the second plate  132 . The second side  130  of the first plate  126  is substantially conterminous with one side of the inner member  138 , and the first side  134  of the second plate  132  is substantially conterminous with the opposite side of the inner member  138 . The inner member  138  is in thermal conductive contact with the second side  130  of the first plate  126  and the first side  134  of the second plate  132 . 
         [0041]    In an exemplary embodiment, the inner member  138  may comprise an internal conduit having a plurality of thermally conductive projections protruding into the internal conduit and allowing a heat absorbing cooling fluid to flow therethrough. In an exemplary embodiment, the internal conduit may be in the form of a latticed structure. In an exemplary embodiment, the inner member  138  may comprise an internal conduit having a material with a plurality of recesses or openings extending therethrough in a sponge-like manner protruding into the internal conduit and allowing a heat absorbing cooling fluid to flow therethrough. In an exemplary embodiment, the internal conduit may be in the form of a sponge-like structure. Situated as such, the projections or sponge-like material are able to physically interact with the heat absorbing cooling fluid flowing through the internal conduit. The heat absorbing cooling fluid may be a liquid such as, for example, an oil, a dielectric oil, a mineral oil, or even a water-based coolant. 
         [0042]    In an exemplary embodiment, the inner member  138  may be brazed, soldered, welded or otherwise attached to the second side  130  of the first plate  126  by any other type of physical attachment, and may be brazed, soldered, welded or otherwise attached to the first side  134  of the second plate  132  by any other type of physical attachment as well. 
         [0043]    In an exemplary embodiment, the inner member  138  may be integral with the second side  130  of the first plate  126 , and may be brazed, soldered, welded or otherwise attached to the first side  134  of the second plate  132  by any other type of physical attachment as well. 
         [0044]    In an exemplary embodiment, the inner member  138  may be integral with the first side  134  of the second plate  132 , and may be brazed, soldered, welded or otherwise attached to the second side  130  of a first plate  126  by any other type of physical attachment as well. 
         [0045]    To facilitate introduction of a heat absorbing cooling fluid into the inner member&#39;s  138  internal conduit, the aforementioned fluid inlet  140  is mounted on the second side  136  of the second plate  132  to be in fluid communication with the inner member&#39;s  138  internal conduit. In this way, cooling fluid may be circulated into the inner member&#39;s  138  internal conduit via fluid inlet  140  in a direction indicated by arrow  146 . In addition, to help facilitate removal of the heat absorbing cooling fluid from the inner member&#39;s  138  internal conduit, the fluid outlet  142  is similarly mounted on the second side  136  of the second plate  132  to also be in fluid communication with the inner member&#39;s  138  internal conduit. In this way, cooling fluid may be circulated out of the internal conduit and away from the second plate  132  via fluid outlet  142  in a direction indicated by arrow  148 . Furthermore, to ensure that cooling fluid is fully circulated throughout the internal conduit of the inner member  138 , the inner member  138  includes a septum  150  within the internal conduit. The septum  150  ensures the flow of cooling fluid into the fluid inlet  140  and the out of the fluid outlet  142 . 
         [0046]      FIG. 6  is a cross-sectional view of the electron collector assembly  110  of  FIG. 5 , mounted within the vacuum vessel  112  of an x-ray tube. In  FIG. 6 , an anode assembly  154  is mounted and installed in the anode end  114  of the vacuum vessel  112 , and a cathode assembly  156  is installed in a cathode end  116  of the vacuum vessel  112 . In such a configuration, the electron collector assembly  110  is thereby interposed and mounted between the anode assembly  154  and the cathode assembly  156 . 
         [0047]    As shown in  FIG. 6 , the anode assembly  154  generally includes an anode assembly mount  158 , a seal and bearing assembly  160 , a rotatable shaft  162 , and an anode target  164 . The mount  158  is generally installed and welded within the vacuum vessel&#39;s anode end  114  to keep the vacuum vessel  112  hermetically sealed. The seal and bearing assembly  160 , is disposed within the mount  158  to support an extension of the shaft  162 . The seal and bearing assembly  160  also facilitates rotation of the shaft  162  while at the same time maintaining the vacuum vessel&#39;s hermetic seal. As further shown in  FIG. 5 , the anode target  164  is fixedly mounted on the end of the shaft  162  with fasteners  166  and  168 . The opening  120  in the electron collector assembly  110  physically accommodates the shaft  162  by permitting the shaft  162  to freely protrude through the opening  120 . 
         [0048]    As additionally shown in  FIG. 6 , the cathode assembly  156  generally includes a cathode assembly mount  170  and an electron emitter  172 . The mount  170  is generally installed and welded within the vacuum vessel&#39;s cathode end  116  to keep the vacuum vessel  112  hermetically sealed. The mount  170  includes electrical connectors  176  and  178  for connecting the cathode assembly  156  to an electrical power supply. The electron emitter  172 , includes an energizable cathode filament  174  mounted to the end of the electron emitter  172  and extending toward the aperture  122  extending through the electron collector assembly  110 . 
         [0049]    The thermally emissive coating on the first plate  126  and on the protrusions  144  allow the first plate  126  and protrusions  144  to absorb radiant heat from the anode target  164 , resulting in decreased temperature of critical components of the x-ray tube. In addition, the thermally emissive coating on the second plate  132  allows the second plate  132  to absorb radiant heat from the cathode assembly  156 , resulting in decreased temperature of critical components of the x-ray tube. 
         [0050]      FIG. 7  is an enlarged cross-sectional view of the electron collector assembly  110  of  FIG. 6 . During operation of the x-ray tube, a focused electron beam  180  is emitted from the cathode filament  174  and accelerated through the aperture  122  toward the anode target  164 . As the electron beam  180  strikes the anode target  164 , x-rays  184  are produced in all directions. A portion of the x-rays  184  are directed out of an x-ray transmissive window  182 . The portion of the x-rays that are not directed out of the x-ray transmissive window  182 , so called off-focus x-ray radiation, are collected or absorbed by the electron collector assembly  110 . 
         [0051]    Many of the electrons striking the anode target  164  are backscattered from the target surface in many different directions. Since the first plate  126  of the electron collector assembly  110  is electrically charged by the electrical power supply  54 ,  84  illustrated in  FIGS. 2 and 3 , many of these backscattered electrons are electrostatically attracted to the first plate  116 . As the backscattered electrons are attracted to the first plate  116 , the electrons ultimately impinge on the first plate  116  and transfer their respective kinetic energies to the first plate  116  in the form of thermal energy or heat. Since the first plate  126  is in thermally conductive contact with the inner member  138 , the thermal energy attributable to impinging electrons in the first plate  126  is thereby transferred to the heat absorbing cooling fluid that is flowing through the internal conduit of the inner member  138 . In this way, the thermal energy attributable to backscattered electrons is effectively removed from the electron collector assembly  110  and the vacuum vessel  112 . 
         [0052]    Furthermore, in addition to producing x-rays  184  and backscattered electrons, the anode target  164  radiates large amounts of heat. By design, much of this radiant heat is effectively absorbed by the plurality of protrusions  144  extending from the first side  128  of the first plate  126 . As the radiant heat is absorbed, thermal energy attributable thereto is transferred from the first plate  126  and to the heat absorbing cooling fluid circulating through the inner member&#39;s  138  internal conduit so that the thermal energy attributable to the anode target  164  is effectively removed from the electron collector assembly  110  and the vacuum vessel  112 . 
         [0053]    In addition to the embodiments discussed above, it is to be understood that the electron collector assembly may take on various alternative embodiments as well. For example, in addition to the first plate having a plurality of protrusions protruding from its first side, the second plate may similarly have a plurality of thermally emissive protrusions protruding from its second side. Furthermore, though the electron collector assembly described hereinabove largely comprises two separate plates and an inner member that are joined together, it is to be understood that the electron collector assembly may alternatively comprise two plates and an inner member that are substantially integral with each other or even a single substantially monolithic plate. In an exemplary embodiment comprising a single monolithic plate, for example, the plate itself may comprise an electrically conductive metal and be thermally emissive. Such a monolithic plate may have a plurality of thermally emissive protrusions protruding from a first side, a second side, or both the first and second sides, and an internal conduit sandwiched between the first and second sides of the plate, the internal conduit allowing a heat absorbing cooling fluid to flow therethrough. In an exemplary embodiment comprising a single monolithic plate, for example, the plate itself may comprise an electrically conductive metal and be thermally emissive. Such a monolithic plate may have a plurality of thermally emissive protrusions protruding from a first side, and a conduit on the second side allowing a heat absorbing cooling fluid to flow therethrough. 
         [0054]    While the disclosure has been described with reference to various embodiments, those skilled in the art will appreciate that certain substitutions, alterations and omissions may be made to the embodiments without departing from the spirit of the disclosure. Accordingly, the foregoing description is meant to be exemplary only, and should not limit the scope of the disclosure as set forth in the following claims.