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2011-07-07
Field Synthesis in Inhomogeneous Media: Joint Control of Polarization, Uniformity and SAR in MRI b 1-Field
By
Progress In Electromagnetics Research, Vol. 118, 355-377, 2011
Abstract
The homogeneity of the amplitude of one of the polarizations of the RF field B1 is a crucial issue in Magnetic Resonance Imaging (MRI), and several methods have been proposed for enhancing this uniformity (``Shimming''). The existing approaches aim at controlling the homogeneity of B+1 and limiting the Specific Absorption Rate (SAR) of the RF field by independently controlling magnitude and phase of individual excitation currents in MRI scanners, either birdcage or TEM coil system. A novel approach is presented here which allows a joint control of B+1 uniformity, SAR, and purity of polarization of the total RF B1 field. We propose a convex optimization procedure with convex constraints, and special attention has been devoted to the issue of convexity of the proposed functional. The method is applied to MRI brain imaging; numerical tests have been performed on a realistic head model at low, medium, and high RF field in order to assess the effectiveness of the proposed method. We found that maintaining a specific polarization plays an important role also in maintaining the homogeneity of B+1 amplitude.
Citation
Elia Amedeo Attardo Tommaso Isernia Giuseppe Vecchi , "Field Synthesis in Inhomogeneous Media: Joint Control of Polarization, Uniformity and SAR in MRI b 1-Field," Progress In Electromagnetics Research, Vol. 118, 355-377, 2011.
doi:10.2528/PIER11051910
http://www.jpier.org/PIER/pier.php?paper=11051910
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