Simulation of lung nodules for nodule detection studies.

Two techniques for simulating lung nodules in nodule detection studies were evaluated. In one technique, radiographs were obtained with plastic beads placed on the surface of a chest phantom to simulate lung nodules. In the second technique, the same plastic beads were radiographed against a uniform background, and their radiographic images were then superimposed photographically onto a radiograph of the same chest phantom. Nodule detection rates determined by four different film readers were significantly different for films prepared by the two different techniques. The differences in detection rates are explained by differences in nodule contrast due to film sensitometric characteristics and scattered radiation effects. Photographic superpositioning does not mimic these effects accurately, as they affect clinical chest films. For this reason, it is suggested that nodule simulation films prepared by the photographic superpositioning technique cannot be used to predict nodule detection rates for clinical chest radiography. Other aspects of lung nodule simulation techniques also are discussed.