Effect of exposure variation on the clinical utility of chest radiographs.

Abstract

To study the effects of exposure error on the clinical utility of chest radiographs. Under- and overexposed screen-film images were simulated by adding exposure offsets to the normalized CR log(10) exposure data from a computed radiography (CR) system and printed by using the sensitometric response of a medium-latitude system. The clinical utility of the overall image, lung, and soft tissue in 48 images were independently graded by eight radiologists. Most variability in image scores was due to differences in exposure. About 95% of the lung regions and 75% of the soft-tissue regions were rated as having good or ideal clinical utility at the nominal exposure. About 80% of the overall images were rated as good or better for exposures within 40% [0.15 log(10) exposure] of the nominal. The overall image scores were heavily influenced by the lung region, and reader tolerance for exposure error was greater for soft tissue than for lung. The optimal exposure for soft tissue was about 60% [0.25 log(10) exposure] greater than for lung; therefore, no single exposure was optimal for the entire image. Conventional medium-latitude screen-film systems have intrinsic limitations for capturing and displaying the wide transmittance differences in the thorax. The clinical utility of chest radiographs may be improved by developing better image capture and display techniques.