Spezifische Absorptionsrate
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:
Assoziationen und Differentialdiagnosen zu specific absorption rate: