FIGURE 13.

Dynamically applied RF shimming was used to improve performance of CMRA and 4D-flow imaging at 7T. In these sequences, high transmit efficiency was needed for the navigator to ensure a robust signal and sharp lung-liver interface for gating and tracking. Single breath-hold coronal calibration data were acquired for optimization in a target region located in the liver (white box). The fractional available B₁⁺ (A) before and (B) after RF shimming show the high efficiency of phase-only static B₁⁺ shimming for a small localized region. After RF shimming, a robust navigator signal can be obtained (C).