The effect of local background anatomical patterns on the detection of subtle lung nodules in chest radiographs

Anatomical noise in chest radiography, created by the projection of anatomical features in the thorax such as ribs and pulmonary vessels, greatly influences the detection of subtle lung nodules in chest radiographs. Detection may be hindered by 1) the "global" statistical characteristics of the background in relation to the signal associated with the nodule, and/or 2) the interference of the "local" background pattern with the nodule signal. This investigation aimed at assessing the influence of the latter process in the detection of subtle lung nodules. Six 8 × 8 cm images were extracted from the lung regions of six digital chest radiographs of normal patients from our clinic. Simulated nodules emulating the radiographic characteristics of subtle tissue-equivalent lesions ranging in size from 3.2 to 6.4 mm were numerically superimposed on the images. For each of the six lung images, a set of thirty-one processed images were produced, six containing no nodule, and the remaining 25 containing single nodules of five different sizes placed at five different locations within 6 mm of the center. The variation in location allowed different local background patterns to overlay the nodules. An observer detection study was then performed using 14 experienced radiologists. The observer data were analyzed to determine the variation in detectability with nodule location for all five sizes of the nodules. The preliminary results indicate that the variation in detectability of a nodule due to the influence of its local background surroundings is equivalent to that caused by changing its CD product by a factor of 4.45 (∼ 0.28 in Az).

Duke Scholars

Author Ehsan Samei Radiology