Yigitcan Eryaman1,
2, Bastien Gurin3, Elfar Adalsteinsson4, 5,
Lawrence L. Wald2, 5
1Research
Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge,
MA, United States; 2Martinos Center for Biomedical Imaging, Dept.
of Radiology, MGH, Charlestown, MA, United States; 3Martinos
Center for Biomedical Imaging, Dept. of Radiology, Massachusetts General
Hospital, Charlestown, MA, United States; 4Dept. of Electrical
Engineering and Computer Science, Massachusetts Institute of Technology,
Cambridge, MA, United States; 5Harvard-MIT Health Sciences and
Technology, Cambridge, MA, United States
We calculated a lower bound for peak 10 g local SAR that can be obtained with an arbitrary transmit coil in a uniform cylindrical phantom. For that purpose we used cylindrical basis expansion to express an arbitrary EM field in the phantom. Then the optimum least square RF shimming or pTx pulse solutions are calculated for the cylindrical modes with an explicit constraint to minimize local SAR. To make this optimization computationally possible the local SAR matrices are compressed using the VOP method. The result is the trade-off (L-curve) between the excitation fidelity and the lowest possible local SAR afforded by an arbitrary transmit array. The ultimate L-curves can be used as a figure of merit for the SAR performance of modeled or constructed pTx coils.