Detection of subtle lung nodules: Relative influence of quantum and anatomic noise on chest radiographs

PURPOSE: To assess the relative influence of quantum mottle and structured lung patterns (anatomic noise) on the detection of subtle lung nodules on chest radiographs. MATERIALS AND METHODS: Sixty 8 x 8-cm lung pattern images were extracted from digital chest radiographs in healthy individuals. Sixty quantum mottle images of the same size and quantum noise level were extracted from uniformly exposed digital radiographs. Simulated nodules with various peak contrast-diameter products (CD) that emulated subtle tissue-equivalent lung nodules were numerically superimposed at the center on three-fourths of the images. Printouts were independently viewed and scored by five experienced radiologists. The area under the receiver operating characteristic curve (A(z)) was estimated as a measure of the detectability of the nodules. RESULTS: At a fixed observer performance level (eg, A(z) = 0.8), much smaller and lower-contrast nodules were detected on quantum mottle images (1-mm diameter, CD = 0.01 mm), compared with those on anatomic images (4.5-mm diameter, CD = 0.20 mm). The findings generally agreed with the signal-to-noise ratio calculations based on statistical observer models. CONCLUSION: The detection of subtle lung nodules on chest radiographs is limited by anatomic noise.