The diagnosis of pulmonary nodules: comparison between standard and inverse digitized images and conventional chest radiographs.

We compared plain chest radiographs, standard (bones white) digitized images, and inverse-intensity (bones black) images to determine their ability to identify pathologically confirmed malignant pulmonary nodules. The images were digitized by using a photo-optical laser scanner and were displayed on a 1024 x 1024 x 8 bit system capable of operator-controlled magnification (2x or 4x) and nonlinear (logarithmic/exponential) contrast transformation in both standard and inverse-intensity modes. Receiver-operator curve analysis was used to study the detection performance of six observers who viewed 40 images obtained in 15 normal subjects and 25 abnormal subjects. There was no statistically significant difference in the area under the ROC curve between the standard digital images and the plain chest radiographs. However, ROC areas were significantly greater (p less than or equal to .05) for inverse-intensity digital images when compared with either standard-intensity digital images or plain chest radiographs. These results suggest that inverse-intensity images may have some advantages in the detection of pulmonary nodules.