Anticrossover emulsions evaluated by observer performance tests.

Observer performance in the detection of pulmonary nodules and infiltrates was measured using film coated with anticrossover emulsion, a recent innovation in radiographic film that is expected to produce sharper images because of improved resolution. Test radiographs of an anthropomorphic phantom were shown to six experienced observers. Radiographs containing pseudonodule and pseudoinfiltrate images were obtained with the anticrossover film and the same type of film without the anticrossover coating. Test images contained single nodules, single infiltrates, or both; approximately 45% of the test radiographs were normal. Individual receiver operating characteristic (ROC) curves were formed, and sensitivity and specificity values were calculated. The results demonstrated an improvement in observer performance with the anticrossover film as measured by sensitivity and the area under the average ROC curves.

Directed versus free search for nodules in chest radiographs.

Nodule detection in chest radiographs was compared under free-search and directed-search conditions. In directed search, the observer was told which quadrant of the chest to examine. Each of five observers read a test series of 96 radiographs seven times. Results were analyzed in terms of signal detection theory. NOdule detection was found to be significantly more accurate in directed search than in free search. The results were compared with those of previous experiments which found no such effect or an opposite effect. The present results do not support a previously hypothesized preattentive visual mechanism with better detection capabilities than focused visual attention.

Cost-effectiveness of stereoscopic radiographs in detection of lung nodules.

Detection of lung nodules was assessed using a series of radiographs which were either normal or showed only one nodule. Stereoscopic pairs were obtained in 26 cases (10 positive and 16 normal). A "singles" series comprising one radiograph from each pair was presented to each observer on three occasions. The pairs were later presented side by side and finally were viewed stereoscopically. The results indicate that a second shifted radiograph improves detection of lung nodules enough to be cost-effective. The shifted radiographs do not need to be viewed stereoscopically.

Observer Performance as a function of viewing distance.

The performance of observers in detecting solitary lung nodules of 1.0 and 1.5 cm diameter has been measured for viewing distances of 46, 91, 183, and 470 cm. The data indicate that observer accuracy for detection of 1.5-cm nodules as measured by the area under the ROC curves is essentially unchanged for the three closest viewing distances and falls of by about 30% at the largest viewing distance. Observer performance for detection of 1.0 cm nodules, however, improves as the viewing distance is increased from 46 to 91 cm and then decreases at larger viewing distances.