Optimisation of Flip-Angle Schedules for MR Fingerprinting with inhomogeneous Transmit Fields

Motivation: Unlocking SNR benefits of ultra-high field for high-resolution quantitative MRI is hindered by transmit-field (B1+) inhomogeneities because optimal flip-angles are not realised throughout the field-of-view. Goal(s): We investigate how flip-angle schedules for MR Fingerprinting can be adjusted to enhance robustness towards B1+ inhomogeneity. Approach: We incorporate B1+ into Cramer-Rao bound optimisation, demonstrate that predicted errors are reduced compared with a conventionally optimised flip-angle schedule, and show this in invivo experiments. Results: B1+ informed CRB optimisation reduces predicted peak T2-error by a factor of three, which removes artefacts in invivo experiments. B1+ corrections successfully removed shading in T1-maps. Impact: This work addresses one of the problems of quantitative imaging at ultra-high field to make its benefit more accessible. The larger aim is to achieve high resolution parameter maps which can be useful for diagnosis and research of neurodegenerative diseases.