Accuracy in detecting bone lesions in vitro with conventional and subtracted direct digital imaging

Objective: To implement direct digital imaging (DDI) in subtraction radiography and compare the accuracy of conventional and subtracted DD images in detecting small bone lesions in vitro. Method: Alveolar bone defects were produced in a section of a pig mandible, with slow-speed burs 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.4 mm in diameter. Standardized DD images were subtracted and displayed in black and white, contrast-enhanced and pseudo-colour transformed formats. 370 pairs of slides taken directly from the computer monitor were evaluated by eight observers. Results: The area P(A) under the ROC curve with DDI was 0.67±0.1. This was significantly lower (p<0.001) than any of the three modes of subtraction radiography (mean P(A) = 0.88±0.09). The detection of small lesions (bur diameter 0.6 mm) was significantly better (p<0.001) with contrast enhancement. Observer agreement was smaller for DDI (n = 0.22±0.09) compared with the subtraction images (mean n = 0.64±0.13) (p