Design and use of tailored hard-pulse trains for uniformed saturation of myocardium at 3 Tesla

Abstract

Complete and uniform saturation of myocardium is essential for quantitative myocardial perfusion imaging using the first pass of a contrast agent. At 3 T, inhomogeneities of both the static (B0) and radiofrequency (B 1) magnetic fields have led to the use of adiabatic B 1-insensitive rotation type 4 (BIR-4) pulses, which in practice are constrained by radiofrequency (RF) heating. In this study, we propose the use of trains of weighted hard pulses that are optimized for the measured variation of B0 and B1 fields in the myocardium. These pulses are simple to design, and require substantially lower RF power when compared with BIR-4 pulses. In volunteers, at 3 T, we demonstrated that the proposed saturation pulse with three subpulses results in lower peak and lower average residual longitudinal magnetization over the heart, as compared with 8-msec BIR-4 pulses and conventional hard pulse trains (P < 0.05). © 2008 Wiley-Liss, Inc.