Simultaneous B0- and B1+-Map Acquisition for Fast Localized Shim, Frequency, and RF Power Determination in the Heart at 3 T

High-field (>= 3 T) cardiac MRI is challenged by inhomogeneities of both the static magnetic field (B-0) and the transmit radiofrequency field (B-1+). The inhomogeneous B fields not only demand improved shimming methods but also impede the correct determination of the zero-order terms, i.e., the local resonance frequency f(0) and the radiofrequency power to generate the intended local B-1+ field. In this work, dual echo time B-0-map and dual flip angle B-1+-map acquisition methods are combined to acquire multislice B-0- and B-1+-maps simultaneously covering the entire heart in a single breath hold of 18 heartbeats. A previously proposed excitation pulse shape dependent slice profile correction is tested and applied to reduce systematic errors of the multislice B-1+-map. Localized higher-order shim correction values including the zero-order terms for frequency f(0) and radiofrequency power can be determined based on the acquired B-0- and B-1+-maps. This method has been tested in 7 healthy adult human subjects at 3 T and improved the B-0 field homogeneity (standard deviation) from 60 Hz to 35 Hz and the average B-1+ field from 77% to 100% of the desired B-1+ field when compared to more commonly used preparation methods. Magn Reson Med 63:419-426, 2010. (C) 2010 Wiley-Liss, Inc.