Perception of simulated lesions in the lung

The detectability of phi 20 mm, disk-shaped objects on a normal chest film was investigated at viewing distances of 0.3, 1.0 and 3.0 m. Objects with a tapered border were found to be best perceived at longer distances. The photpgraphic density difference between object and background yielding a 50% detection probability was found to increase from 0.025 to 0.060 when the outer gradient zone of the object increased from 0.8 to 4.0 mm.