Acceleration of slice encoding for metal artifact correction at 0.55 T using hexagonal sampling

Purpose To evaluate a hexagonal sampling approach for accelerated slice encoding for metal artifact correction (SEMAC) at 0.55 T. Contemporary mid‐field systems (0.1 T–1.0 T) show tremendous potential for imaging near metal implants. However, the limited parallel‐imaging options necessitate alternative methods for scan time reduction. Methods We apply retrospective hexagonal undersampling to current state‐of‐the‐art SEMAC with 2‐fold generalized autocalibrating partially parallel acquisitions–based parallel imaging at 0.55 T. The hexagonal sampling approach results in an additional 50% scan time reduction. Feasibility is evaluated with phantom experiments involving spinal fixation and total hip arthroplasty hardware, and in vivo experiments involving patients with spinal fusions with varying compositions and 1 volunteer with a total hip arthroplasty. Results Hexagonal sampling provides an additional 50% scan time reduction with compatible image quality. The two tradeoffs are (i) a small increase in signal void due to the loss of signal from one SEMAC spectral bin during post‐acquisition filtering and (ii) position‐dependent signal‐to‐noise‐ratio reduction at locations close to the edge of the field of view in the phase‐encoding direction. Conclusion We demonstrate that hexagonal sampling can provide 50% scan time reduction in addition to generalized autocalibrating partially parallel acquisitions/parallel imaging for SEMAC at 0.55 T without introducing substantial artifacts. This may be a valuable mechanism for reducing scan time at 0.55 T and other midfield strengths, where parallel‐imaging acceleration is limited.