FIGURE 16.

Using parallel transmit to simultaneously improve transmit B₁ and constrain total RF energy of multiband pulses. (A) L curves quantifying tradeoffs between total RF power and excitation errors (i.e., root mean square error (RMSE)) in the human brain at 7T for Full pTx MB (○) and MB B1 shim (×), along with Circularly polarized (CP) mode (□) located at the crossing between the horizontal and vertical lines, labeled “Same fidelity” and “ Same Power”, respectively. Calculations were performed for a 7T coil described previously (Adriany et al., 2008) with azimuthally distributed 16 transmit and receive microstrip elements (B) MB2 RF excitation in the human brain at 7T for CP mode conventional MB, MB B1 shim and Full pTx MB pulses with the same total RF power. The pulses were designed for the coil described in (A) using subject dependent B₁ calibration maps. The pulses were based on a single spoke design, with the base pulse being a filtered SINC pulse of BWTP = 10. Pulse duration = 1 ms, nominal flip angle = 6°, and inter-slice distance = 56 mm.