Influence of rib structure on detection of subtle lung nodules

To access the influence of anatomic noise on the detectability of subtle lung nodules depicted on chest radiographs.

From normal chest radiography images, 132 square regions were extracted, of which the centers were on the upper margin of a rib, the inside of a rib, the lower margin of a rib, and the central region between two adjoining ribs. Simulated nodules were digitally superimposed at the centers of these extracted square images. Twelve radiologists viewed 50 soft-copy images consisting of these 792 processed images, including the noise-added images. The observer's confidence level for the square images containing single nodules was used as an index of observer performance.

Results indicated statistically reliable effects of the relationship between rib structures and nodule positions on the detection performance (P < 0.001). The nodule detectability on the images with a center located between two adjoining ribs was significantly the best, whereas it was significantly the worst on the noise-added images with a center located between two adjoining ribs.

The rib structures overlying a subtle lung nodule on chest X-ray images have a detrimental effect on nodule detection performance as anatomic noise, regardless of the nodule location on ribs.