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SAR prediction in adults and children by combining measured B1+ maps and simulations at 7.0 Tesla
Author(s) -
Tiberi Gianluigi,
Costagli Mauro,
Biagi Laura,
Ciantis Alessio De,
Fontaunzia,
Stara Riccardo,
Symms Mark Roger,
Cosottini Mirco,
Guerrini Renzo,
Tosetti Michela
Publication year - 2016
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.25241
Subject(s) - specific absorption rate , fluid attenuated inversion recovery , imaging phantom , nuclear medicine , human head , nuclear magnetic resonance , magnetic resonance imaging , physics , medicine , computer science , radiology , optics , absorption (acoustics) , telecommunications , antenna (radio)
Purpose To predict local and global specific absorption rate (SAR) in individual subjects. Materials and Methods SAR was simulated for a head volume coil for two imaging sequences: axial T1‐weighted “zero” time‐of‐echo (ZTE) sequence, sagittal T2‐weighted fluid attenuated inversion recovery (FLAIR). Two head models (one adult, one child) were simulated inside the coil. For 19 adults and 27 children, measured B 1 + maps were acquired, and global (head) SAR estimated by the system was recorded. We performed t‐test between the B 1 + in models and human subjects. The B 1 + maps of individual subjects were used to scale the SAR simulated on the models, to predict local and global (head) SAR. A phantom experiment was performed to validate SAR prediction, using a fiberoptic temperature probe to measure the temperature rise due to ZTE scanning. Results The normalized B 1 + standard deviation in subjects was not significantly different from that of the models ( P > 0.68 and P > 0.54). The rise in temperature generated in the phantom by ZTE was 0.3°C; from the heat equation it followed that the temperature‐based measured SAR was 2.74 W/kg, while the predicted value was 3.1 W/kg. Conclusion For ZTE and FLAIR, limits on maximum local and global SAR were met in all subjects, both adults and children. To enhance safety in adults and children with 7.0 Tesla MR systems, we suggest the possibility of using SAR prediction. J. MAGN. RESON. IMAGING 2016;44:1048–1055.