Temperature and SAR calculations for a human head within volume and surface coils at 64 and 300 MHz
Article first published online: 21 APR 2004
Copyright © 2004 Wiley-Liss, Inc.
Journal of Magnetic Resonance Imaging
Volume 19, Issue 5, pages 650–656, May 2004
How to Cite
Collins, C. M., Liu, W., Wang, J., Gruetter, R., Vaughan, J. T., Ugurbil, K. and Smith, M. B. (2004), Temperature and SAR calculations for a human head within volume and surface coils at 64 and 300 MHz. J. Magn. Reson. Imaging, 19: 650–656. doi: 10.1002/jmri.20041
- Issue published online: 21 APR 2004
- Article first published online: 21 APR 2004
- Manuscript Accepted: 29 JAN 2004
- Manuscript Received: 5 SEP 2003
- NIH. Grant Number: R01 EB000454
To examine relationships between specific energy absorption rate (SAR) and temperature distributions in the human head during radio frequency energy deposition in MRI.
Materials and Methods
A multi-tissue numerical model of the head was developed that considered thermal conductivity, heat capacity, perfusion, heat of metabolism, electrical properties, and density. Calculations of SAR and the resulting temperature increase were performed for different coils at different frequencies.
Because of tissue-dependant perfusion rates and thermal conduction, there is not a good overall spatial correlation between SAR and temperature increase. When a volume coil is driven to induce a head average SAR level of either 3.0 or 3.2 W/kg, it is unlikely that a significant temperature increase in the brain will occur due to its high rate of perfusion, although limits on SAR in any 1 g of tissue in the head may be exceeded.
Attempts to ensure RF safety in MRI often rely on assumptions about local temperature from local SAR levels. The relationship between local SAR and local temperature is not, however, straightforward. In cases where high SAR levels are required due to pulse sequence demands, calculations of temperature may be preferable to calculations of SAR because of the more direct relationship between temperature and safety. J. Magn. Reson. Imaging 2004;19:650–656. © 2004 Wiley-Liss, Inc.