1. Circuitry for calculating pixel values from detector measurements in a CT scanner and the like in which a plurality of detectors measure attenuated radiation from a fan beam radiation source for consecutive projection views along a plane through an object located between said source and said plurality of detectors, said circuitry comprising means for identifying by calculation a detector for use in back projection through a first pixel in a first view, means for identifying by calculation a detector for use in back projection through said first pixel for a second view, means for identifying through interpolation a detector for use in back projection through said pixel for views intermediate said first and second views based on said calculated detector identifications for said first pixel, means for identifying a detector for use in back projection through a second pixel for said first view, means for identifying a detector for use in back projecting through said second pixel for said second view, means for identifying by interpolation a detector for use in back projecting said second pixel for views intermediate said first and second views based on said calculated detectors for said second pixel, and means for identifying by interpolation detectors for use in back projecting through pixels intermediate said first and second pixels for said first and second views and views therebetween based on said identified detectors for use in back projecting through said first and second pixels.