Local SAR management strategies for RF shimming in fetal MRI at 3T
Filiz Yetisir1, Esra Abaci Turk1,2, Elfar Adalsteinsson3,4,5, Patricia Ellen Grant1,2,6, and Lawrence L Wald4,7,8
1Fetal-Neonatal Neuroimaging and Developmental Science Center, Boston Children's Hospital, Boston, MA, United States, 2Department of Pediatrics, Boston Children's Hospital, Boston, MA, United States, 3Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, United States, 4Harvard-MIT Health Sciences and Technology, Cambridge, MA, United States, 5Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Boston, MA, United States, 6Department of Radiology, Boston Children's Hospital, Boston, MA, United States, 7Athinoula A. Martinos Center for Biomedical Imaging, Harvard Medical School, Boston, MA, United States, 8Department of Radiology, Massachusetts General Hospital, Boston, MA, United States
RF shimming (RFS) improves the transmit field for fetal MRI, however, fetal safety is understudied. Previous simulations studied the SARlocal of the standard imaging mode (CP mode) of each subject to inform the safety of RFS. We evaluated two local SAR management strategies which utilize subject-specific models and use either the individual’s CP mode SARlocal as a limit for RFS or the maximum CP mode SARlocal value across 7 subjects. We evaluated the B1+ performance inside the fetus for each strategy. Using the maximum CP mode SARlocal across the population as the SAR limit greatly improves RFS performance.
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