Two-dimensional phase cycled reconstruction for inherent correction of echo-planar imaging Nyquist artifacts

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging
• Image Reconstruction

Background:

• Echo-planar imaging (EPI) is prone to Nyquist artifacts due to inconsistent k-space trajectories.
• Existing one-dimensional correction methods are insufficient, especially for oblique EPI or with eddy currents.
• Current two-dimensional (2D) correction methods often require reference scans and are sensitive to motion-induced errors.

Purpose of the Study:

• To develop an inherent and general 2D phase correction technique for EPI Nyquist artifact removal.
• To overcome limitations of existing methods, including the need for reference scans and susceptibility to motion artifacts.
• To enhance the quality of EPI images across various imaging protocols.

Main Methods:

• A 2D reconstruction framework generates a series of images by iterating through potential phase error values.
• Artifact level is assessed using background energy criteria in sorted and sigmoid-weighted signals.
• The optimal image with minimal artifacts is selected from the generated series.

Main Results:

• The proposed method effectively removes Nyquist ghosts in single-shot, segmented, and parallel EPI.
• No additional reference scans are required, simplifying the imaging protocol.
• The technique avoids error amplification associated with subject motion during reconstruction.

Conclusions:

• This inherent 2D phase correction is a general and effective solution for EPI Nyquist artifact removal.
• The method improves image quality without compromising scan time or introducing motion sensitivity.
• It offers a robust alternative to traditional and existing 2D correction techniques.