Manuel Murbach, Esra Neufeld, Wolfgang Kainz, Klaas P. Pruessmann, and Niels Kuster, Magnetic Resonance in Medicine, Volume 71, Issue 2, pp. 839-845, February 2014, online February 25, 2013
We investigated the correlation between large-scale anatomical features (e.g., height, weight) and radiofrequency (RF) energy deposition during magnetic resonance imaging (MRI). Six anatomical human models (three adults and three children) were evaluated in different MR imaging positions (head to knees) within a 1.5 T body coil. The specific absorption rate (SAR), the pivotal parameter used to quantify absorbed RF, increases with the radial dimension of the patient and, therefore, with the large-scale anatomical properties. For a fixed B1+ incident field, the whole body SAR (wbSAR) can be up to 2.5 times higher (local SAR up to 7 times) in obese adult models compared to child models. When the exposure is normalized to 4 W/kg wbSAR, the local SAR can well exceed safety limits for local transmit coils and shows inter-subject variations of up to a factor of three. The correlations between anatomy and induced local SAR are weak for normalized exposure, but strong for a fixed B1+ field, suggesting that anatomical properties could be valuable for rapid SAR predictions. This study demonstrates that a representative virtual human population is indispensable for the investigation of local SAR levels.
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