Spontaneous migration to a higher dose in computed radiography (CR) imaging

In order to subjectively determine acceptable dose levels for portable CR, two blind experiments were performed while maintaining conventional screen-film radiography as a reference quality. In the first experiment, a team of two technologists and two radiologists were trained to expose and to quality-assure portable CR images obtained with standard screens at conventional exposures (400 speed). After providing them with a new set of cassettes and informing them that these were 'better and faster,: they were allowed to practice clinically, using the system for bedside AP chest radiography. After four weeks, exposure factors used in those cases were reviewed, and the experiment was repeated with two different teams and two CR systems. In the second experiment, portable CR was used for a large number of cases. The number of radiologists who complained about CR image quality was monitored for cased were alternating technologies (CR and conventional) were used and routinely viewed side by side. during a two-month period, radiation dose gradually increased to a level where radiologists' complaints were significantly reduced. In both experiments, exposure levels gradually migrated to and stabilized at 40-60% higher levels than that routinely used with conventional 400-speed film screen techniques. The perceived need for high exposure ratios between Cr and conventional radiography was related to body size. When the reference quality 'gold standard' remains unchanged, Cr requires higher exposures to yield acceptable image quality, particularly in large patients.