Centric ordering is superior to gradient moment nulling for motion artifact reduction in EPI

Area of Science:

• Magnetic Resonance Imaging
• Medical Imaging Physics

Background:

• Echo-planar imaging (EPI) offers rapid data acquisition but is highly sensitive to motion.
• Motion in the phase-encode direction causes artifacts like ghosting and misregistration, degrading image quality, especially for dynamic structures.
• Existing EPI techniques struggle with motion artifacts, necessitating artifact reduction methods.

Purpose of the Study:

• To evaluate two artifact reduction methods for phase-encode direction motion in EPI.
• To compare centric versus top-down k-space trajectories.
• To assess velocity gradient moment nulling (GMN) for artifact reduction with each trajectory.

Main Methods:

• Computer simulations were used to model EPI acquisition.
• Flow phantoms were employed to simulate cardiovascular flow.
• In vivo experiments were conducted using rabbit models.
• K-space trajectories (centric vs. top-down) and velocity gradient moment nulling (GMN) were systematically evaluated.

Main Results:

• Uncompensated centric ordering demonstrated superior image quality compared to other tested methods.
• Centric ordering likely improves image quality due to shorter readout duration, reducing T2* relaxation losses and off-resonance effects.
• The linear geometry of phantoms and vessels may help obscure centric blurring artifacts.

Conclusions:

• Uncompensated centric ordering is an effective strategy for reducing motion artifacts in EPI.
• This method enhances image quality for dynamic structures by minimizing phase-encode direction artifacts.
• Further investigation into EPI artifact reduction techniques is warranted for improved clinical applications.