X-ray tube assembly with beam limiting device for reducing off-focus radiation

A beam limiting apparatus is provided for reducing the amount of off-focus radiation in the image-forming beam emitted from an x-ray tube assembly. The x-ray tube assembly has a housing with an x-ray port for the passage of x-rays therethrough, a mounting boss defining the x-ray port, an x-ray tube mounted within the housing and defining a glass envelope, an anode mounted within the glass envelope, and a cathode spaced relative to the anode within the glass envelope. A peripheral flange of the beam limiting apparatus is mountable to the mounting boss of the x-ray tube housing, and a radiation-absorbing body of the beam limiting apparatus projects downwardly from the peripheral flange through the x-ray port. The radiation-absorbing body is formed of an electrically nonconductive, filled epoxy resin material, and defines a base surface, an x-ray entrance aperture formed through the base surface, an x-ray exit aperture spaced relative to the x-ray entrance aperture, and an x-ray transmissive beam conduit formed between the entrance and exit apertures. An x-ray transmissive window is integrally molded with the radiation-absorbing body and extends across the beam conduit. The base surface of the radiation-absorbing body is spaced closely adjacent to the glass envelope of the x-ray tube and defines a predetermined gap therebetween. The x-ray tube housing also is molded of an electrically non-conductive, radiopaque, filled epoxy resin material, and includes a conductive outer surface formed of a conductive coating.