Adjustable off-focal aperture for x-ray tubes

A radiographic scanner comprising:

• a source of penetrating radiation for projecting a generally fan shaped beam of radiation;
• an off-focal radiation absorbing plate defining first and second differently dimensioned radiation passing portions which cross at the axis of rotation;
• a moveable mounting means for movably mounting the off-focal radiation absorbing plate adjacent the radiation source such that each of the radiation passing portions is selectively moveably into alignment with the radiation beam, the moveable mounting means mounting the off-focal radiation absorbing plate for rotation about an axis which is generally parallel to a central axis of the radiation beam;
• a shutter means disposed between the off-focal radiation absorbing plate and a patient receiving region for selectively gating the radiation beam therepast to irradiate a selected region of the patient;
• a beam collimating means disposed between the off-focal radiation absorbing plate and the patient receiving region for collimating the radiation beam;
• and,
• a radiation detecting means for receiving radiation from the radiation source which has traversed the patient.

A radiographic scanner comprising:

• a source of penetrating radiation for projecting a generally fan shaped beam of radiation;
• an off-focal radiation absorbing means including a radiation attenuating member which has at least first and second differently dimensioned radiation passing portions;
• a moveable mounting means for movably mounting the radiation attenuating member adjacent the radiation source for rotation about an axis which is generally parallel to a central axis of the radiation beam such that one of the radiation passing portions is selectively moveable into alignment with the radiation beam;
• a shutter means disposed between the moveable radiation attenuating member and a patient receiving region for selectively gating the radiation beam therepast to irradiate a selected region of the patient;
• a beam collimating means disposed between the moveable radiation attenuating member and the patient receiving region for collimating the radiation beam;
• radiation detecting means for receiving radiation from the radiation source which has traversed the patient;
• a stationary radiation absorbing member mounted adjacent the moveable radiation attenuating member and having a radiation passing slot therein for passing the radiation therethrough, the first radiation passing portion of the moveable radiation attenuating member being aligned with the stationary slot in a first position and the second radiation passing portion being aligned with the stationary slot in a second position;
• and
• a flexible cable interconnecting the moveable radiation attenuating member with a source of motive power for selectively moving the moveable radiation attenuating member between the first and second positions.

An x-ray tube assembly for radiographic scanners, the tube assembly comprising:

• an evacuated envelope;
• an anode rotatably mounted within the envelope;
• a housing surrounding the envelope to define a cooling fluid reservoir therebetween, the housing defining an aperture therein and having a collar mounted thereto surrounding the aperture;
• an x-ray permeable, fluid impermeable window mounted to the housing extending into and sealing the housing aperture;
• an x-ray beam defining means including a first radiation attenuating member with a first radiation passing region therein, the first member being mounted within the collar extending within the housing aperture immediately contiguous to the window;
• an off-focal radiation attenuating means including a second radiation attenuating member which defines first and second radiation passing portions, the second member being moveably mounted within the collar and extending within the housing aperture immediately contiguous to the beam defining means for movement at least between a first position in which the first radiation passing portion is aligned with the radiation passing region and a second position in which the second radiation passing portion is aligned with the radiation passing region, such that the off-focal radiation attenuating means is disposed as close to the anode as the window permits;
• and,
• means for moving the second member at least between the first and second positions.

A radiographic apparatus comprising:

• an evacuated x-ray tube envelope;
• an anode disposed in the envelope for emitting radiation from a focal spot thereon, off-focal radiation being emitted from areas of the anode adjacent the focal spot;
• a housing surrounding the envelope;
• an aperture defined in the housing adjacent the focal spot and closed by an x-ray permeable window such that a beam of emitted x-rays pass therethrough;
• a near end plate mounted inside the housing aperture immediately contiguous to the window, the near end plate being constructed of a radiation attenuating material and defining an elongated radiation passing portion therethrough;
• a distal end plate of radiation attenuating material mounted inside the housing aperture contiguous to the window opposite the near end plate from the focal spot and defining an elongated x-ray passing region;
• a means for moving at least one of the near and distal plates for selectively moving the radiation passing region and portion thereof selectively into and out of alignment;
• and,
• a patient supporting means for supporting a portion of a patient to be irradiated generally in alignment with the focal spot and the near and distal plates.

A radiographic apparatus comprising:

• an evacuated x-ray tube envelope;
• an anode disposed in the envelope for emitting radiation from a focal spot thereon, off-focal radiation being emitted from areas of the anode adjacent the focal spot;
• an x-ray port mounted adjacent the envelope and the focal spot such that a beam of emitted x-rays pass therethrough;
• a near end plate constructed of a radiation attenuating material and defining a plurality of crossed elongated radiation passing portions that cross at an axis extending between the focal spot and a patient support means;
• a means for mounting the near end plate for rotation around the axis extending between the focal spot and the patient support means;
• a distal end plate of radiation attenuating material disposed opposite the near end plate from the focal spot and defining an elongated x-ray passing region;
• and,
• a means for moving at least one of the near and distal plates for selectively moving the elongated radiation passing region of the distal end plate and each of the elongated radiation passing portions of the near end plate selectively into and out of alignment.

A method of radiography comprising:

• rotatably mounting a generally planar radiation blocking member which has at least a larger radiation passing portion and a smaller radiation passing portion recessed inside an aperture in a housing of an x-ray tube immediately contiguous of a radiation passing window;
• mounting the x-ray tube within a radiographic apparatus for irradiating a patient with radiation emitted through the x-ray tube port along a central axis;
• positioning a larger portion of a patient within the radiographic apparatus in alignment with the x-ray port, moving the radiation blocking member within a plane perpendicular to the emitted radiation until the larger dimension radiation passing portion is in alignment with the patient, and irradiating the aligned larger patient portion with x-rays from the x-ray tube port;
• disposing a smaller portion of a patient in the radiographic apparatus in alignment with the x-ray port, moving the radiation blocking member within the perpendicular plane until the smaller dimension x-ray passing portion is in alignment with the portion of the patient to be irradiated, and irradiating the patient with x-rays from the x-ray tube port.