Evaluation of calcification in pulmonary nodules using bone images obtained with single exposure energy subtraction

Bone images obtained by single exposure dual energy subtraction with computed radiography, a new image processing method, were evaluated for the detectability of calcification in lung nodules in both phantom and clinical studies. In the phantom study, five simulated nodules containing known and uniformly distributed amounts of calcium hydroxide were placed in a human chest phantom and images were obtained the following five techniques: 1) conventional radiography (CXR), 2) low kV conventional radiography (Low), 3) Fuji computed radiography (FCR), 4) bone images with conventional singles exposure energy subtraction (ES) and 5) bone image with fine single exposure energy subtraction (FES). The detectability of calcification in the simulated nodules was evaluated by six radiologists using ROC analysis and two-way analysis of variance. In the clinical study, images of 42 lung nodules (21 calcified lung nodules and 21 non-calcified nodules), in which calcification was diagnosed by computed tomography, were obtained with the following four techniques : 1) CXR, 2) FCR, 3) ES and 4) FES and the detectability of calcification in the lung nodules was evaluated by nine radiologists using ROC analysis. In the phantom study, FES was significantly superior to CXR, Low and ES, and equal to FCR in the detectability of calcification in the simulated nodules. Compared with ES, FES was especially superior in the underexposed portion of the chest radiograph. In terms of calcium content in the simulated nodules, FES and FCR were superior to CXR in detecting calcification when a lower calcium hydroxide content was present. In the clinical study, FES was significantly superior to CXR, FCR and ES in the diagnosis of calcification in lung nodules. These findings indicate the usefulness of FES in the detection of calcification in lung nodules, and suggests that it is promising for the diagnostic screening of lung nodules. (author)