Tomographic scanner

A method and apparatus for examining relative movement of two masses of different radiation attenuation characteristics, separated by a boundary and moving relative to one another over a repetitive motion cycle. The masses are examined from a plurality of successive angles about a common center of rotation. The object is scanned over each motion cycle from each of these angles to derive a plurality of attenuation coefficients encompassing the entire motion cycle. A plurality of differential points is calculated between adjacent scans of a single motion cycle, and a single composite image of all of these differential points is reconstructed for each individual time period of each motion cycle for display.