Whole-brain 3D FLAIR at 7T using Direct Signal Control

Purpose: Image quality obtained for brain imaging at 7T can be hampered by inhomogeneities in the static magnetic field, B0, and the radiofrequency electromagnetic field, B1. In imaging sequences such as FLAIR, used to assess neurological disorders, these inhomogeneities cause spatial variations in signal which can reduce clinical efficacy. In this work we aim to correct for signal inhomogeneities to ensure whole-brain coverage with 3D FLAIR at 7T.
Methods: The Direct Signal Control (DSC) framework was used to optimise channel weightings applied to the eight transmit channels used in this work on a pulse by pulse basis through the echo train in the FLAIR sequences. 3D FLAIR brain images were acquired on five different subjects and compared with imaging using a quadrature like mode of the transmit array. Pre-computed “universal” DSC solutions calculated from a separate set of five subjects were also explored.
Results: DSC consistently enabled improved imaging across all subjects with no dropouts in signal seen over the entire brain volume, which contrasted with imaging in quadrature mode. Further, the “universal” DSC solutions also consistently improved imaging despite not being optimised specifically for the subject being imaged.
Conclusion: 3D FLAIR brain imaging at 7T is substantially improved using DSC and is able to recover regions of low signal without increasing imaging time or inter-echo spacing.