On the Point of Gradient Moment Expansion for Multi-Spoke RF Pulses

In this work we investigated the influence of the point of gradient moment expansion (t_exp) for multi-spoke RF pulses. The results demonstrate that t_exp=t_ISO is ideal if no flow in the RO direction is present, but severe displacement artifacts occur if this is the case. t_exp=TE induces shifts that are directed along the vessel orientation and are independent of the encoding orientation. The presented techniques are the basis for correct velocity quantification with controlled displacement for multi-spoke RF pulses allowing in-plane B₁⁺ homogenization using parallel transmission at UHF.