Effect of image enhancement for detectability of bone lesions in digitized intraoral radiographs.

Digital image enhancement is concerned with the computer-controlled manipulation of image information. The aim of this study was to evaluate whether diagnostic accuracy would improve in digitally enhanced images of radiographs with impaired density. Each of 83 dry mandibles was divided into four regions. By random assignment it was decided for each region whether or not a hole should be drilled. Three intraoral radiographs (3 x 4 cm) were performed of each region at different exposure times: 2.0 s, 0.60 s, and 0.16 s and interpreted. The radiographs were thereafter recorded by a video camera connected to an IBM-PC. The personal computer held a hardware digitization card defined at a 512 x 512 x 8 matrix resolution on the basis of which a software program with image enhancement facilities was developed. The light and dark radiographs were digitally enhanced by the use of contrast stretching and smoothing filters. The light (0.16 s) original radiographs were less accurate than the ones with optimal density (0.60 s) while no significant differences were found between dark (2.0 s) and optimal density original radiographs. No significant differences were found between original and digitized radiographs of optimal density and digitally enhanced images of light or dark radiographs. The diagnostic accuracy obtained from optimal density radiographs can thus be maintained in digitized dark radiographs and in light radiographs with a four-times dose reduction after digital image enhancement.