Whole-brain B1 -mapping using three-dimensional DREAM

Abstract

Purpose: Demonstration of a 3D version of the DREAM sequence (3DREAM) for rapid 3D flip angle and $B_1^{+}$ mapping of the human brain.

Methods: A rectangular non-selective STE preparation is followed by a 3D readout with a Cartesian center-out spiral phase encoding order. This enables parallel imaging acceleration in both phase encoding dimensions as well as early capture of the prepared magnetization.

Results: $B_1^{+}$ mapping of the whole human head is demonstrated on a 7T system at a nominal resolution of 5 mm with and without parallel imaging acceleration. Artifacts caused by the different signal decay of the FID and STE signal during the long imaging train is suppressed by appropriate filtering of the FID image. Remaining blurring can be controlled by adjusting the echo train length and readout flip angle.

Conclusions: 3DREAM provides a whole-brain flip angle map in a few seconds or individual maps for an 8-channel array in about a minute.

Keywords: $B_1$ mapping; flip angle; high-field MRI; parallel transmission.