Image-Quality Perception as a Function of Dose in Digital Radiography

OBJECTIVE. The purpose of this article is to determine the degree to which the skin entrance dose could be lowered, by adjusting exposure parameters and filtration, and the subsequent effect on readers' confidence levels of digital radiographs. MATERIALS AND METHODS. The study was prospectively performed on a cadaver. Digital radiographs of bones were evaluated and scored on a 9-point scale separately by four radiologists who were blinded to the types of filtration and doses used. The study entailed three phases: phase 1, random dose and filter; phase 2, fixed filter and varying radiation doses (100%, 75%, 50%, and 25% of the standard recommended dose); and phase 3, fixed dose and varying filtration (no filtration, aluminum filter, and aluminum-copper filter). Skin entrance dose was measured using a dosimeter placed on the skin. Differences in scores were tested using a Friedman test. RESULTS. The mean scores given to images with 100%, 75%, 50%, and 25% of the recommended standard dose were 6.18, 6.1, 5.11, and 4.07, respectively. No significant difference was noted between 100%- and 75%-dose images (p = 0.1). A significant difference (p < 0.0001) was noted when we compared the 100%- and 75%-dose images with the 50%- and 25%-dose images. The mean scores given for no filtration, aluminum filtration, and aluminum-copper filtration were 5.67, 5.43, and 5.18, respectively. No significant difference between no filtration and aluminum filtration (p = 0.411) was noted. A significant difference was detected between no filtration and aluminum-copper filtration (p = 0.012). The combination of an aluminum filter and a 75% standard dose achieved a 31.1% reduction in skin entrance dose. CONCLUSION. It is possible to achieve a 31.1% reduction in skin entrance dose for imaging bony structures by using 75% of the standard dose and aluminum filtration without significantly affecting image quality.