How is SAR measured?

SAR, or Specific Absorption Rate, is a measure used to quantify the rate at which energy is absorbed per unit mass by a biological tissue in an electromagnetic field. It is expressed in watts per kilogram (W/kg), reflecting the power absorbed relative to the mass of the tissue. This measurement is crucial in the context of MRI as it helps to assess the safety and potential thermal effects of the electromagnetic fields produced during scanning.

Understanding how SAR is measured is vital for ensuring that the exposure levels remain within safe limits to avoid adverse health effects on patients. The other choices involve measurements that are not relevant to SAR; for example, joules per kilogram measures energy absorption but does not account for the rate aspect crucial to SAR. Volts per meter represents electric field strength, while hertz per square meter does not correspond to the quantities involved in SAR measurements.