A scanning system for chest radiography with regional exposure control: practical implementation.

Abstract

An experimental scanning apparatus for chest radiography is described which offers good scatter rejection and regional manipulation of film exposure. The apparatus is capable of studying two scanning geometries that uses either a fan of radiation swept laterally over the film in 5s or a spot of radiation scanned over two dimensions in a raster pattern in 8.8s. The manipulation of tube output during the scan is achieved by pulse width modulation with film exposure monitored by a fluorescence detector placed behind the film cassette. Measurement of the scatter rejection properties of the system show that it is superior to that of a 10:1 grid when used with 120-kVp radiation. Phantom images with both geometries demonstrate the capability of the system to improve uniformity of film exposure and soft tissue contrast throughout the mediastinal, diaphragmatic, and retrocardiac areas. The relative characteristics of the one- versus two-dimension scan geometries are given. Clinical raster images formed with the 8.8-s scan time show signs of motion unsharpness which becomes insignificant when the scan time is reduced to 4.5 s.