Extended Multi-Flip-Angle B1 Mapping: A 3D Mapping Method for Inhomogeneous B1 Fields

Quantitative, three-dimensional mapping of the B-1 field per unit current is necessary for comprehensive characterization of the performance of radiofrequency coils. A mapping method with high dynamic range is required, particularly for surface and array coils with inhomogeneous B-1 fields. For many applications, the main magnetic field cannot be assumed to be uniform across the sensitive volume of the RE coil. B-1 mapping methods relying on on-resonance conditions thus yield erroneous results. We have, therefore, developed an extension of the multi-flip-angle approach (ExMFA) for B-1 mapping in inhomogeneous B-0 and B-1 fields with high dynamic range. Based on simulations and experimental data, ExMFA is compared to the commonly used double-angle and the standard multi-flip-angle approaches with special focus on applications in inhomogeneous excitation fields. Comparative evaluation reveals the improved performance of the ExMFA approach. (C) 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 37B: 203-214, 2010