Geometries of motion for tomosynthesis image acquisition: (a) Parallel-path motion, (b) partial isocentric motion, and (c) full isocentric motion. Parallel-path motion in (a) illustrates how objects in two planes (circle and triangle) are projected onto different locations in the image plane due to parallax as the tube moves. (Reprinted by permission from Physics in Medicine and Biology, Ref. 20, Copyright © 2003, Institute of Physics (IOP) Publishing Ltd.)