Study type: Medical/biological study (experimental study)

Thermal effects of MR imaging: worst-case studies on sheep. med./bio.

Published in: AJR Am J Roentgenol 1990; 155 (5): 1105-1110

Aim of study (acc. to author)

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.



Exposure Parameters
Exposure 1: 64 MHz
Exposure duration: 20-105 min

Exposure 1

Main characteristics
Frequency 64 MHz
Exposure duration 20-105 min
Exposure setup
Exposure source
  • MR scaning device, 1.5 T magnet
Setup aminals laid in the MR scanner
Measurand Value Type Method Mass Remarks
SAR 4 mW/g unspecified calculated - whole-body exposure
SAR 4 mW/g unspecified calculated - head exposed
SAR 1.5 mW/g unspecified calculated - 2 W/kg; body exposure.
magnetic flux density 1.5 T - - - -

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • before exposure
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

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.

Study character:

Study funded by