Meeting Banner
Abstract #2740

The Ultimate Local SAR in MRI

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.

Abstract PDF

Keywords

acceptable accurate achievable achieve achieved allowed allowing although approximated arbitrary array arrays audience averaging away axial basis biomedical bound calculating calculation calculations channel checked coil coils complete compressed computer consortium constrained constrains constraint constraints control convergence convex curve curves cylinder cylinders cylindrical decomposition dept design determine diameter distribution electrical electromagnetic electronics element engineering equations error estimation example excitation expanded expansion explicitly express extend fast fidelity field fields form generated global health improvement institute investigated isotropic know laboratory least length local loop lowest material matrices matrix maxwell merit metric middle mode model modes much noting observation optimization optimum origin orthonormal peak performance phantom phantoms position previously problem process project pulse pulses radiology reasonable reduce required researchers resolution respect room roughly science sciences several simulations smaller solution solutions solved solver solving sought spheres spherical square still subject sufficient supported target technology trade transmit ultimate uniform virtual vision want wave