Nondisplaced fractures: spatial resolution requirements for detection with digital skeletal imaging

Fifty-six radiographs of nondisplaced or minimally displaced fractures of the extremities and an equal number of studies with normal findings were selected and digitized to produce spatial resolution varying from 5.75 to 0.72 line pairs per millimeter (1p/mm), corresponding to pixel sizes ranging from 0.08 to 0.64 mm. The conventional and digitized images were evaluated by 10 radiologists, who gave their decision confidence on a graded scale. Receiver operating characteristic analyses were performed from these data to compare the digital images with the conventional radiographs. There was a progressive improvement in observer performance as the pixel size decreased. A pixel size greater than 0.16 mm (2.88 1p/mm) resulted in a significant loss of diagnostic accuracy in comparison with conventional radiographs. Specific fractures in which a larger pixel size adversely affected the evaluation included torus injuries, corner fractures in child abuse, minimal avulsion injuries, and fractures that demonstrated only trabecular disruption.