Rapid 3D radiofrequency field mapping using catalyzed double-angle method.

A new method is presented for rapid and accurate large volumetric radiofrequency (RF) field (B(1) (+)) mapping. This method is a modification of the double-angle method (DAM), which accelerates imaging speed and applies 3D acquisition to improve B(1) (+) measurement accuracy. It reduces repetition time and scan time by introducing a catalyzation RF pulse chain at the end of each DAM repetition cycle. The catalyzation pulse chain ensures that, after each TR period, the longitudinal magnetizations reach the same state for both measurements at two flip angles for the DAM so that the long TR requirement (TR >or= 5 T(1)) for complete relaxation of longitudinal magnetization of DAM becomes unnecessary. A multi-echo imaging sequence is additionally incorporated to further improve the efficiency of data acquisition. Simulations demonstrate an excellent flip angle measurement accuracy for catalyzed DAM even with TR << T(1). Phantom and in vivo volunteer studies are presented to demonstrate the catalyzation effect upon B(1)(+) mapping and the application of 3D catalyzed DAM for rapid and accurate large volume RF field mapping. (c) 2009 John Wiley & Sons, Ltd.