What is the unit of measurement for exposure in radiology?

• A. Sv
• B. C/kg
• C. mAs
• D. Gy

Answer: (B)

Exposure in radiology refers to the amount of ionization an X-ray or gamma-ray beam produces in air. It is defined as the electric charge liberated per kilogram of air, and in SI units this is coulombs per kilogram (C/kg). That’s why this unit is the best fit for exposure.

Think of the other quantities as different ideas: absorbed dose, measured in gray (Gy), tells you how much energy is deposited per kilogram of material; equivalent dose, in sieverts (Sv), adjusts that dose for radiation type and biological impact; and mAs is simply a technique setting (tube current times exposure time) used to control how much radiation is produced, not a measurement of exposure itself.