Design of Non-Selective Refocusing Pulses with Phase-Free Rotation Axis by Gradient Ascent Algorithm in Parallel Transmission at 7 T

Aurlien Massire¹, Martijn A. Cloos², Alexandre Vignaud¹, Denis Le Bihan¹, Alexis Amadon¹, Nicolas Boulant¹

We use gradient ascent pulse engineering combined with the kT-point method to design non-selective refocusing pulses that mitigate severe B1 and ΔB0 inhomogeneities. The novelty of the method lays in the optimization of the relevant rotation matrices themselves rather than magnetization states. Experimental validation was performed on a phantom and using a 7 T scanner equipped with an 8-channel transmit array. The rotation matrix on every voxel was measured using Quantum Process Tomography. In addition, a modified non-selective Spin-Echo sequence was run to evaluate the ability to refocus dephased magnetization. Both experiments confirmed high fidelity of the here-introduced technique.