In what units is Specific Absorption Rate (SAR) measured?

Specific Absorption Rate (SAR) is measured in watts per kilogram (W/kg). This unit represents the rate at which energy is absorbed by a unit mass of tissue when exposed to radiofrequency fields, such as those generated by magnetic resonance imaging (MRI) systems. The significance of SAR arises from safety considerations; it helps to quantify the potential thermal effects of exposure to radiofrequency energy, which is particularly important in assessing the safety of MRI procedures.

Using W/kg allows for a direct understanding of how much power is being absorbed by each kilogram of biological tissue, facilitating the establishment of safety guidelines and limits for RF exposure in medical imaging.