milligray

Milligray (mGy) is a unit of absorbed dose of ionizing radiation in the International System of Units (SI). It is defined as one thousandth of a gray (1 mGy = 0.001 Gy). A gray corresponds to the deposition of one joule of energy in one kilogram of matter, so a milligray represents one-thousandth of that energy per kilogram.

Milligray is commonly used to quantify the absorbed dose received by tissue during medical imaging, radiographic procedures, and radiation protection planning. In diagnostic radiology, patient skin and organ doses are typically measured in milligrays, while therapeutic applications such as external beam radiotherapy use doses on the order of grays, with milligray-level changes relevant for dosimetry calibrations and accumulated dose tracking.

Relationship to other dose quantities: Absorbed dose measured in grays is related to biological risk through the equivalent dose (sieverts) and effective dose, which multiply by radiation and tissue weighting factors. For photons like x-rays and gamma rays, and with a radiation weighting factor of 1, 1 Gy roughly corresponds to 1 Sv for risk assessment, though precise calculations use tissue-specific factors and radiation type.

Measurement and standards: Doses in milligrays are reported by dosimeters and dosimetry protocols in clinical settings, calibration laboratories, and radiation protection guidelines. The unit is part of the SI system, with the gray and the sievert serving as the larger units for absorbed dose and radiation risk, respectively.