Gradient moment smoothing: a new flow compensation technique for multi-shot echo-planar imaging

Area of Science:

• Magnetic Resonance Imaging
• Image Processing
• Biomedical Engineering

Background:

• Multi-shot echo-planar imaging (EPI) is susceptible to phase errors.
• Flow or motion along the phase-encoding direction introduces significant artifacts, including ghosting and signal loss.
• Existing compensation methods may not fully address these phase errors.

Purpose of the Study:

• To identify and correct an additional source of phase error in multi-shot EPI.
• To introduce a velocity-independent flow compensation technique.
• To improve the robustness of multi-shot EPI to in-plane flow and motion.

Main Methods:

• Developed gradient moment smoothing (GMS), a flow compensation technique.
• Implemented GMS by modifying the first moment of a bipolar prephaser pulse shot-by-shot.
• Combined GMS with a flyback echo-planar readout for comprehensive flow compensation.

Main Results:

• Gradient moment smoothing effectively corrects phase errors caused by phase-encoding direction flow.
• Experiments in phantoms and in vivo demonstrated elimination of ghosting and signal loss.
• The combined technique rendered multi-shot EPI relatively insensitive to in-plane flow.

Conclusions:

• Gradient moment smoothing is an effective, time-efficient method for correcting phase errors in multi-shot EPI.
• This technique enhances the viability of multi-shot EPI for accurate in-plane flow imaging.
• The method significantly desensitizes multi-shot EPI to in-plane motion artifacts.