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

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging (MRI)
• Biomedical Engineering

Background:

• Mid-field MRI systems (0.1T-1.0T) offer potential for imaging near metal implants.
• Limited parallel imaging options on these systems necessitate scan time reduction strategies.
• Slice Encoding for Metal Artifact Correction (SEMAC) is a key technique for metal artifact reduction.

Purpose of the Study:

• To evaluate a hexagonal sampling approach for accelerated SEMAC at 0.55T.
• To assess the feasibility of hexagonal undersampling for reducing scan times in SEMAC.
• To determine if hexagonal sampling impacts image quality or introduces artifacts.

Main Methods:

• Retrospective hexagonal undersampling was applied to SEMAC with 2-fold generalized autocalibrating partially parallel acquisitions (GPAA) at 0.55T.
• Phantom experiments with spinal fixation and hip arthroplasty hardware were conducted.
• In vivo experiments included patients with spinal fusions and a volunteer with a hip arthroplasty.

Main Results:

• Hexagonal sampling achieved an additional 50% scan time reduction.
• Image quality remained compatible with existing methods.
• Tradeoffs included minor signal void and position-dependent signal-to-noise ratio reduction at field-of-view edges.

Conclusions:

• Hexagonal sampling provides a 50% scan time reduction for SEMAC at 0.55T when combined with GPAA/parallel imaging.
• This method does not introduce substantial artifacts.
• Hexagonal sampling is a valuable tool for reducing scan times on mid-field MRI systems where parallel imaging is limited.