Evaluation of Accelerated SEMAC at 0.55T using Hexagonal Sampling and Parallel Imaging

Motivation: Low-field and mid-field MRI systems have tremendous potential for imaging near metal implants with reduced artifacts, but reduced ability to do parallel imaging limits encoding options. Goal(s): To achieve 50% scan time reduction in addition to conventional parallel imaging at 0.55T. Approach: Hexagonal sampling (in ky-kf space) combined with GRAPPA-2 in SEMAC acquisitions was evaluated qualitatively and quantitatively via phantom and in vivo experiments at 0.55T. Results: GRAPPA-2 hexagonal sampling achieved comparable image quality to conventional GRAPPA-2 SEMAC with slight SNR reduction and a modest increase in artifact area, while allowing a 50% decrease in scan time. Impact: We evaluate the performance of hexagonal sampling combined with GRAPPA-2 at 0.55T where high parallel imaging factors are challenging via phantom and in vivo experiments. 50% additional scan time reduction is achieved with a modest increase in artifact area.