specific absorption rate

Specific absorption rate (SAR) is the rate that electromagnetic energy in the radiofrequency is absorbed by tissues during MR image acquisition represented as watts per kilogram (W/kg).  Both the International Electrotechnical Commission and the USA's Food and Drug Administration limit the amount of energy absorbed during the body over the course of a single examination to 1°C/kg . For a 1°C rise in body temperature, the body can be exposed to 4 W/kg.

For example high SAR sequences of a 3 T MRI deposits approximately between 1.9-2.5 W/kg.

Considerations for increases in body temperature should be made for patients with :

• cardiovascular disease
• hypertension
• diabetes
• increased age
• obesity
• fever
• impaired ability to perspire
• pregnancy (risk for fetal heating)
• drug regimes that may affect thermoregulatory capabilities (e.g. diuretics, tranquillizers, vasodilators)
• extensive tattoos
• plaster or fibreglass casts
• implanted organ devices

Precautions to reduce the SAR to patients can include:

• taking breaks between high SAR sequences
• alternating between low SAR and high SAR sequences
• reducing the flip angle
• reducing slice numbers
• reducing pulse number and duration
• reducing pulse frequency
• ensuring the patient is lightly dressed
• ensure scanner ventilation system is turned on

Siehe auch:

• MRT Sicherheit