Standard versus inverted digital luminescence radiography in detecting pulmonary nodules: A ROC analysis

Objective: Observer performance tests were conducted to compare the effect of presenting digital luminescence radiography (DLR) monitor images in positive mode ("bones black") or negative mode ("bones white") in the detectability of subtle lung nodules. Methods: Five radiologists independently reviewed digital radiographs of 55 patients with either (a) a single, small (6-12 mm), non- calcified peripheral nodule confirmed by chest CT (n = 47) or (b) normal finding (n = 8) confirmed by chest CT, respectively. Mean size of pulmonary nodules was 8.3 mm (range 6-12 mm, median 7 mm). Radiographs were displayed either in standard mode (bones white) or inverse intensity (bones black). A total of 550 observations resulted. For the evaluation ROC analysis was performed using a specialized computer algorithm. Results: The standard presentation mode showed a sensitivity of 61.7% and a specificity of 72.5%, the inverse presentation mode a sensitivity of 68.1% and a specificity of 75.0%. ROC- analysis showed that the difference between the standard mode (Az- value 0.694) and the inverse mode (Az- value 0.810) was significant in favour of the inverse presentation mode (p = 0.001). This finding was especially observed in more experienced radiologist (Az- values 0.716 vs. 0.909, P < 0.001). Conclusion: Our study demonstrates a significant advantage of the inverse mode in the detection of small pulmonary nodules compared with the commonly used negative mode when interpreted by more experienced radiologists. Advance in knowledge: Inverse intensity images ("bones black") may have some advantages in the detection of small pulmonary nodules in experienced readers when presented on a stand-alone display.