An evaluation of rare-earth imaging systems in panoramic radiography.

Panoramic radiographs were made of ninety-nine consenting adult patients who had image-analysis test devices placed within their oral cavities. Quantitative characteristics and perceived image quality of eight screen-film combinations were investigated. The quantitative characteristics of the images evaluated included contrast, resolution (in three regions), and bead detection (a measure of noise). Perceived image quality assessed similar characteristics. In addition, expert observers rated the resultant patient radiographs for both general and specific diagnostic tasks. Calcium tungstate screen-film systems were found to have the highest contrast but with resolution comparable to rare-earth screen-film systems under clinical test conditions. Calcium tungstate systems required up to twice the radiation exposure of the patient. It was found that some rare-earth screen-film combinations may produce clinically acceptable panoramic radiographs while reducing the patient's radiation exposure.