Changing from Sp-100 calcium tungstate screens to Sp-400 high-rare-earth screens will reduce exposure settings and patient dose by what percent for the same image density?

• A. 25%
• B. 50%
• C. 75%
• D. 90%

Answer: (C)

Higher screen speed means more light is emitted for each absorbed x-ray, so less exposure is needed to achieve the same film density. Switching from Sp-100 calcium tungstate to Sp-400 high-rare-earth increases speed by about a factor of four. To get the same image density, you can reduce the exposure to roughly one-quarter of the original, which corresponds to about a 75% reduction in both exposure settings and patient dose. In practice, the exact dose saving is close to this magnitude, though other factors (filtration, technique, processing) can cause small variations.