To provide a worst-case estimate of thermal effects of magnetic resonance imaging by subjecting anesthetized unshorn sheep to power deposition at specific absorption rates well above approved standards for periods of time in excess of normal clinical imaging protocols.
|Setup||aminals laid in the MR scanner|
In head exposure experiments, skin and eye temperatures rose about 1.5°C. Jugular vein temperature increased a maximum of 0.4°C after an average exposure of 75 min.
In whole body exposures, elevation of rectal temperature was correlated with energy input. Deep-body temperature rises in excess of 2.0°C were attained for 4 W/kg whole-body exposure periods greater than 82 min. Sheeps irradiated for 40 min to 4 W/kg in either body coil or head coil were recovered and observed to be in good health for 10 weeks; no cataracts were revealed. Magnetic resonance power deposition at SAR levels well above typical clinical imaging protocols caused body temperature to rise. For exposure periods in excess of standard clinical imaging protocols the temperature increase was insufficient to cause adverse thermal effects.