When reviewing the radiographic exposure indicator, when does an 'S' (sensitivity) number significantly above 200 indicate?

• A. Insufficient image contrast
• B. Excessive image contrast
• C. Insufficient receptor exposure
• D. Excessive receptor exposure

Answer: (C)

The expose indicator S-number tells you how much radiation actually reached the imaging receptor, and it is inversely related to receptor exposure. A target around 200 is typical for a balanced exposure. If the S-number is significantly above 200, that means the receptor received less exposure than desired, leading to underexposure. In other words, the image would be too light and may lack sufficient diagnostic detail because not enough photons hit the receptor.

Contrast is influenced mainly by the chosen kVp, filtration, and processing, not directly by the S-number. An excessively high S-number signals insufficient receptor exposure rather than excessive exposure.