Which unit defines the total quantity of X-ray exposure?

The total quantity of X-ray exposure is defined by the unit milliamperes-seconds (mAs). This unit measures the product of the current (in milliamperes) flowing through the X-ray tube and the exposure time (in seconds). It directly correlates to the amount of X-ray photons produced during a radiographic exposure; therefore, it reflects the total amount of radiation that reaches the patient during the imaging process.

The other units mentioned do not directly quantify X-ray exposure in the same way. The Gray (Gy) is a measure of absorbed radiation dose, indicating how much energy is deposited in a specific mass of tissue, rather than the quantity of exposure itself. The Sievert (Sv) is a measure of the biological effect of radiation on human tissue and is used to express the health effect of low levels of ionizing radiation. Kilovolt peak (kVp) refers to the peak voltage applied across the X-ray tube and primarily affects the quality, or penetrating power, of the X-rays produced rather than the total quantity of exposure.