1Radiology, A. A. Martinos Center for Biomedical Imaging, MGH, Charlestown, MA, United States; 2Harvard Medical School, Boston, MA, United States; 3Harvard-MIT Division of Health Sciences & Technology, MIT, Cambridge, MA, United States
We propose a strategy which employs the dark modes of excitation coil array to cancel local E-fields that produce SAR hotspots. The method is based on the observation that some modes of an array coil (e.g. birdcage with the wrong circular polarization) produce E-fields but not useful excitation of MR magnetization (i.e. no B1+). We can therefore energize these dark modes exclusively with the goal of cancelling local SAR hot-spots. While this will not lower SARglobal (since more power will be used), our goal is local SAR reduction at a few hot spots where local SAR is the limiting factor.