Variable aperture z-axis tracking collimator for a computed tomograph system

A system for reducing x-ray exposure in a computed tomography system, the computed tomography system including an x-ray source emitting an x-ray fan beam, a pre-patient collimator comprising a plurality of eccentric cams and a plurality of filters and a detector array comprising a plurality of detector cells extending in a z-axis, said system configured to:

• combine a number of detector cells to form at least one slice;
• position the pre-patient collimator to define an x-ray thickness, location and exposure by rotating the eccentric cams of said collimator;
• and
• independently alter positions of said eccentric cams to compensate for z-axis motion of the x-ray fan beam in response to a determined focal spot position of the x-ray fan beam.

A pre-patient collimator for altering the x-ray exposure in a computed tomography system, the computed tomography system comprising an x-ray source and a detector array, said collimator comprising:

• a plurality of eccentric cams fabricated from an x-ray absorbing material, at least a first cam and a second cam positioned on opposing sides of a fan beam radiated from the x-ray source, said cams configured to block a portion of the x-ray fan beam;
• a cam drive for adjusting the fan beam, said cam drive coupled to said cams;
• a filtration device;
• a housing;
• and
• a filter drive for altering position of said filtration device, said filter drive coupled to said housing and said filtration device;
• said collimator configured to independently alter positions of said eccentric cams to compensate for z-axis motion of the x-ray fan beam in response to a determined focal spot position of the x-ray fan beam.