Feasibility of selective exposure radiography
The concept of selective exposure radiography encompasses those techniques which spatially modulate the incident x-ray field to produce a more uniform exit field arising from the patient. The resulting reduction in the dynamic range of the exposure field offers several advantages. In conventional radiography, selective exposure techniques allow all areas of the image to be placed in the linear portion of the film characteristic curve so that local contrast is maximized. With video systems, the reduction in dynamic range minimizes the impact of electronic noise behind the least transmissive regions of the patient. With both electronic and photographic detectors, selective exposure radiography is characterized by uniform quantum statistics and uniform scatter across the image. Several selective exposure techniques currently are being investigated. They include compensating filters placed manually in the x-ray field as well as fan-beam geometries in which the x-ray tube output is modulated with a feedback circuit to maintain constant exposure to the image receptor. At the University of Wisconsin, we have been investigating a digital system which uses an initial low-dose patient image to design an attenuator with transmission complimentary to that of the patient. The attenuator is fabricated for each patient and is positioned automatically in the x-ray beam prior to the acquisition of the final compensated image. The possible applications of this device include chest radiography, coronary angiography, subtraction angiography, and accurate digital videodensitometry. © 1984 SPIE.
