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Local SAR enhancements in anatomically correct children and adult models as a function of position within 1.5 T MR body coil


Murbach, M; Cabot, E; Neufeld, E; Gosselin, M C; Christ, A; Pruessmann, K P; Kuster, N (2011). Local SAR enhancements in anatomically correct children and adult models as a function of position within 1.5 T MR body coil. Progress in Biophysics and Molecular Biology, 107(3):428-433.

Abstract

Usage of magnetic resonance imaging (MRI) is continuously increasing due to its excellent soft-tissue contrast and improving diagnostic values. MRI also has the advantage that it operates without ionizing radiation. The main safety concerns are torque, acceleration by the static field, nerve stimulation by the gradient fields, and tissue heating by the radio-frequency (RF) fields. This paper investigates if children and fetuses are at higher risks than adults when the current RF regulations are applied. We analyzed and compared local absorption hotspots, i.e., the peak spatial specific absorption rate averaged over any 10 g (psSAR10g) for five adults, three children of ages 5, 11 and 14 years, and 1 pregnant female (36 weeks' gestation) in 10 different Z-positions (head to calves). In the First Level Operating Mode (4 W/kg whole-body averaged exposure), the psSAR10g values found for adults were as large as 60 W/kg in the trunk and 104 W/kg in the extremities. The corresponding values for children were 43 and 58 W/kg, respectively, and 14 W/kg for the unborn child. Modeling of worst case anatomical RF loops can substantially increase the psSAR10g values, i.e., by factor >>2. The results suggest that local exposure for children and fetuses is smaller than for adults (15-75%), i.e., no special considerations for children and the unborn child are needed regarding psSAR10g due to RF. However, the local thermal load of the unborn may be significantly increased due to the high exposure average (up to 4 W/kg) of the non-perfused amniotic fluid.

Usage of magnetic resonance imaging (MRI) is continuously increasing due to its excellent soft-tissue contrast and improving diagnostic values. MRI also has the advantage that it operates without ionizing radiation. The main safety concerns are torque, acceleration by the static field, nerve stimulation by the gradient fields, and tissue heating by the radio-frequency (RF) fields. This paper investigates if children and fetuses are at higher risks than adults when the current RF regulations are applied. We analyzed and compared local absorption hotspots, i.e., the peak spatial specific absorption rate averaged over any 10 g (psSAR10g) for five adults, three children of ages 5, 11 and 14 years, and 1 pregnant female (36 weeks' gestation) in 10 different Z-positions (head to calves). In the First Level Operating Mode (4 W/kg whole-body averaged exposure), the psSAR10g values found for adults were as large as 60 W/kg in the trunk and 104 W/kg in the extremities. The corresponding values for children were 43 and 58 W/kg, respectively, and 14 W/kg for the unborn child. Modeling of worst case anatomical RF loops can substantially increase the psSAR10g values, i.e., by factor >>2. The results suggest that local exposure for children and fetuses is smaller than for adults (15-75%), i.e., no special considerations for children and the unborn child are needed regarding psSAR10g due to RF. However, the local thermal load of the unborn may be significantly increased due to the high exposure average (up to 4 W/kg) of the non-perfused amniotic fluid.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Institute of Biomedical Engineering
Dewey Decimal Classification:170 Ethics
610 Medicine & health
Language:English
Date:2011
Deposited On:28 Jan 2012 15:29
Last Modified:05 Apr 2016 15:27
Publisher:Elsevier
ISSN:0079-6107
Publisher DOI:10.1016/j.pbiomolbio.2011.09.017
PubMed ID:21964524
Permanent URL: http://doi.org/10.5167/uzh-56455

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