Abstract: In a medical radiographic apparatus, of the type in which a fan of radiation and detectors receiving the radiation along pencil beams in the fan are traversed laterally in relation to a slice of the patient's body and orbited about an axis intersecting the slice, an angular step between each lateral scan is usually substantially equal to the angle subtended by the radiation at its source. It is proposed to arrange the angular step to be a multiple of the angle subtended by the fan, thus leaving gaps in the range of angular position taken by beams of the fan. The gaps are filled in the course of an extended orbital motion.

Abstract: In computerized tomographic apparatus in which radiation from a source is projected through a body along a plurality of substantially linear beam paths and the source is rotated around the body, interleaving of beam paths is effected by changing the phase of timing pulses, with respect to the rotational movement, at a suitable stage in the scan. A bank of detectors is used to detect the radiation emergent from the body along said paths and a feature of the invention is to change the phase for each detector at a respective time so that no beam paths are duplicated but all sets of interleaved and original beam paths are completed in a single revolution of the scan.