Abstract: In a radiographic apparatus, a source of radiation is arranged to scan a planar spread of radiation in a plane about the body of a patient being examined. A plurality of detector devices is arranged to provide data representing the absorption of the radiation along a plurality of paths within the spread, for different orientations in the plane, for processing to determine a distribution of absorption coefficients for a planar slice of the body. The arrangement is such that a predetermined number of the detector devices are irradiated by the spread of radiation at any time and the actual devices irradiated change progressively as the scan progresses.

Abstract: In a computerized tomographic system in which a fan of radiation effects a rotational scan and the detectors are fixed, collimation is achieved by means of plates hinged adjacent the detectors. The plates are moved by means of a ring, the center of which is caused to execute a circular motion about the center of rotation of the system. The ring carries projections which engage with the ends of the plates remote from the detectors.