milligrays

Milligray (mGy) is the SI unit of absorbed dose, representing the amount of energy deposited by ionizing radiation in a kilogram of matter. By definition, 1 gray equals 1 joule of energy absorbed per kilogram, so 1 milligray is one thousandth of that: 0.001 Gy.

Milligray is commonly used to report absorbed doses in diagnostic radiology, nuclear medicine, and radiobiology. Many medical procedures impart small energy deposits, so doses are typically expressed in milligrays (and sometimes micrograys). In radiotherapy, absorbed doses are usually given in grays or centigrays because the clinical ranges are larger.

Conversions and relationships: 1 Gy = 1000 mGy, and 1 mGy = 1000 µGy. Since 1 Gy equals 100 rad, 1 mGy equals 0.1 rad. For X-rays and gamma rays, the dose equivalent in sieverts is approximately equal to the absorbed dose in milligrays, because the radiation weighting factor is about 1.

Measurement and dosimetry: Absorbed dose in mGy is measured with instruments such as ionization chambers, thermoluminescent dosimeters (TLDs), optically stimulated luminescence (OSL) dosimeters, and semiconductor detectors. In medical contexts, CT dose metrics like CTDIvol and dose-length product (DLP) are reported in mGy to quantify patient exposure; organ and effective doses are often expressed in millisieverts (mSv).

Regulatory and clinical context: Radiation protection guidelines specify exposure limits and diagnostic reference levels in terms of effective dose (mSv) or absorbed dose (mGy) depending on context. The milligray remains a key unit for quantifying localized energy deposition and for ensuring appropriate image quality while minimizing patient and occupational exposure.