Radiation dose reduction in computed skeletal radiography: Effect on image quality

Purpose: To evaluate the effect of radiation dose reduction on image quality in computed musculoskeletal radiography and determine optimal exposure range. Material and Methods: In 11 corpses, 1 hand and 1 hip were examined with film-screen radiography, and a series of computed radiographs was obtained using exactly the same technique except for the exposure, which was 100, 50, 25, 12.5, 6.25, and 1.56% of the mAs numbers used for the film-screen images. The computed hip radiographs were processed in 2 different ways, one simulating the film-screen images and one using contrast enhancement. Four radiologists reviewed the images regarding the following parameters: cortical bone, trabecular bone, joint space, and soft tissue, giving each a diagnostic quality rating on a scale from 1 to 5. The median and mean values were found for the pooled results. Results: For the hands, the computed radiographs were ranked inferior to the film-screen images for all parameters except soft tissue, where the computed radiographs scored higher. The computed images with 50 and 25% exposure were ranked equal to the 100% ones. The quality rating slowly declined with lower exposures. For the hips, the 100 and 50% computed radiographs were generally similar to or slightly better than the film-screen images. The decline was somewhat faster than for the hands. The contrast-enhanced hip images scored less than the nonenhanced images at any given exposure for all parameters except soft tissue, where the contrast-enhanced images scored better at all exposures. The difference between nonenhanced and enhanced images became less at the lower exposures. Conclusion: Lowering the exposure in computed musculoskeletal radiography below the level of film-screen radiography is feasible, especially in the peripheral skeleton. Contrast enhancement seems to be valuable only in the evaluation of soft-tissue structures.