Saturated double-angle method for rapid B1 plus mapping

For in vivo magnetic resonance imaging at high field (>= 3 T) it is essential to consider the homogeneity of the active B, field (B-1+), particularly if surface coils are used for RF transmission. A new method is presented for highly rapid B-1+ magnitude mapping. It combines the double angle method with a B-1-insensitive magnetization-reset sequence such that the choice of repetition time (TR) is independent of T, and with a multislice segmented (spiral) acquisition to achieve volumetric coverage with adequate spatial resolution in a few seconds. Phantom experiments confirmed the accuracy of this technique even when TR << T-1, with the side effect being lowered SNR. The speed of this method enabled B-1+ mapping in the chest and abdomen within a single breath-hold. In human cardiac imaging, the method enabled whole-heart coverage within a single 16-s breath-hold. Results from phantoms and healthy volunteers at 1.5 T and 3 T are presented.