RADIATION-DOSE REDUCTION IN COMPUTED SKELETAL RADIOGRAPHY - EFFECT ONIMAGE QUALITY

Purpose: To evaluate the effect of radiation dose reduction on image q uality in computed musculoskeletal radiography and determine optimal e xposure range. Material and Methods: In 11 corpses. 1 hand and 1 hip w ere examined with film-screen radiography, and a series of computed ra diographs 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 num bers used for the film-screen images. The computed hip radiographs wer e processed in 2 different ways, one simulating the film-screen images and one using contrast enhancement. Four radiologists reviewed the im ages regarding the following parameters: cortical bone, trabecular bon e, joint space. and soft tissue, giving each a diagnostic quality rati ng on a scale from 1 to 5. The median and mean values were found for t he pooled results. Results: For the hands, the computed radiographs we re ranked inferior to the film-screen images for all parameters except soft tissue, where the computed radiographs scored higher. The comput ed 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 sl ightly better than the film-screen images. The decline was somewhat fa ster than for the hands. The contrast-enhanced hip images scored less than the nonenhanced images at any given exposure for all parameters e xcept 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-scree n radiography is feasible, especially in the peripheral skeleton. Cont rast enhancement seems to be valuable only in the evaluation of soft-t issue structures.