Gradient adjustments for improved pcASL exploiting a B1+ shimmed labeling train

Pseudo-continuous arterial spin labeling (pcASL) at 7T suffers from insufficient B₁⁺-amplitudes and specific absorption rate (SAR) constraints. Even with B₁⁺ phase-only or phase/amplitude shimming for the labeling the resulting inversion is suboptimal. In this work, we performed Bloch simulations to examine the impact of thicker pcASL labeling slices by adjusting the slice-selective gradient of a B₁⁺-shimmed labeling train exploiting Variable-Rate Selective Excitation. The findings were evaluated experimentally in 5 healthy volunteers. Using lower slice-selective gradients and subsequently longer exposure of the spins to the pcASL labeling train, the perfusion images improved according to gray matter temporal signal-to-noise ratio by 35%.