1. A method for creating a volumetric data set containing data representing a three-dimensional distribution of a physical quantity, the method comprising: a) providing a plurality of spaced apart two dimensional analog sensors ( 12 ) in fixed orientations; b) simultaneously creating a plurality of two dimensional analog images by exposing the plurality of sensors to the distribution; c) scanning the two dimensional analog images to yield digitized images; d) before scanning the analog images providing fiducial marks ( 18 ) on each of the plurality of sensors, the fiducial marks identifying an order and sequence of the sensors.