EFFECT OF EXPOSURE VARIATION ON THE CLINICAL UTILITY OF CHEST RADIOGRAPHS

PURPOSE: To study the effects of exposure error on the clinical utilit y of chest radiographs. MATERIALS AND METHODS: Under- and overexposed screen-film images were simulated by adding exposure offsets to the no rmalized CR log(10) exposure data from a computed radiography (CR) sys tem and printed by using the sensitometric response of a medium-latitu de system. The clinical utility of the overall image, lung, and soft t issue in 48 images were independently graded by eight radiologists. RE SULTS: Most variability in image scores was due to differences in expo sure. 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 ex posure. About 80% of the overall images were rated as good or better f or exposures within 40% (0.15 log(10) exposure) of the nominal. The ov erall image scores were heavily influenced by the lung region, and rea der 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 op timal for the entire image. CONCLUSION: Conventional medium-latitude s creen-film systems have intrinsic limitations for capturing and displa ying the wide transmittance differences in the thorax. The clinical ut ility of chest radiographs may be improved by developing better image capture and display techniques.