Designer RF field profiles for parallel imaging applications

Abstract

A method for designing specific nonuniform B 1 magnetic field patterns within a given coil volume is presented. This technique is applied to produce field patterns relevant to parallel MRI detector coils but could be applied more generally. Results that are particularly applicable to both SENSE and SMASH imaging are derived. A cylindrical geometry has been used for the application described here, but any geometry could be used in principle. The designer field of interest for the SMASH case is one that varies like sin(x). The basic approach for the SMASH coil derives coefficients for harmonics of the common sin() current distribution. The designer field used for the example SENSE coil is one that has a sharp spatial cutoff. The general technique used for the SENSE coil example is essentially a target field approach similar to that used for gradient coil design. The approach described herein is appropriate at low B 0 field strengths, when one can use quasi-static approximations for the field behavior.