COMPUTED RADIOGRAPHY X-RAY-EXPOSURE TRENDS

Rationale and Objectives. Computed radiography provides correct optica l density on film, independent of the incident radiation exposure, but it can result in under- or overexposure of the imaging plate, In the current study, we evaluated the radiation exposure trends of computed radiography over a 2-year period for portable chest examinations to de termine and compare the radiographic techniques of the computed radiog raphy system relative to conventional screen-film detectors. Methods. A Fuji computed radiography system was interfaced to a digital worksta tion to track system usage and examination demographics, including exa mination type and sensitivity number. Hard-copy films were used for di agnosis. The sensitivity number, a value inversely related to incident exposure on the imaging plate, was used to determine whether the prop er techniques were used by the technologists. Results. The initial use of the computed radiography system revealed a broad distribution of e xposures being used; complaints regarding noisy films (e.g., underexpo sure) resulted in subsequent overexposure for a significant number of films. A quality-control audit indicating excessive exposure resulted in educational feedback and a tighter distribution of exposures within the optimal range as determined by our radiologists. The average tech nique was approximately equivalent to a 200-speed system. Conclusion. Computed radiography provides excellent dynamic range and rescaling ca pabilities for proper film optical density, and thus fewer repeat exam inations. However, underexposure results in suboptimal image quality t hat is related to excessive quantum mottle. Overexposure requires film audits to limit unnecessary radiation exposure. In general, the optim al exposures are achieved with approximately 1.5-2 times the incident detector exposure of a 400-speed rare-earth system. The ability of com puted radiography to reduce radiation exposure is unlikely when compar ed with a typical rare-earth screen-film combination (400 speed) in te rms of adequate image quality for the diagnosis of subtle, low-contras t findings. For certain diagnostic procedures (e.g., nasogastric tube placement verification), lower exposures can be tolerated.