Single-shot echo-planar imaging with Nyquist ghost compensation: interleaved dual echo with acceleration (IDEA)...

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Neuroimaging
• Biophysics

Background:

• Echo planar imaging (EPI) is crucial for blood oxygen level-dependent functional MRI (fMRI) due to its speed and sensitivity.
• Nyquist (N/2) ghosting is a significant artifact in EPI, particularly at high magnetic field strengths.
• Gradient imperfections like eddy currents and off-resonance effects cause k-space inconsistencies, leading to ghosting.

Purpose of the Study:

• To introduce a novel EPI method, Interleaved Dual Echo with Acceleration (IDEA) EPI, to mitigate Nyquist ghosting.
• To enable the acquisition of ghost-free EPI images without requiring phase correction.
• To demonstrate the effectiveness of IDEA EPI at both 3 T and 7 T.

Main Methods:

• Acquired two k-spaces (echoes) using positive and negative readout lobes by applying phase encoding blips to alternate readout gradients.
• Constructed two nearly ghost-free images per shot from the acquired k-spaces.
• Utilized parallel imaging and/or partial Fourier acquisition to compensate for the increased echo train length.
• Reconstructed images via complex averaging for residual phase error cancellation or separate image reconstruction.

Main Results:

• IDEA EPI successfully generated two ghost-free images per shot.
• The method demonstrated efficacy in phantom and in vivo imaging at 3 T and 7 T.
• Residual phase errors were effectively cancelled through complex averaging.

Conclusions:

• IDEA EPI provides a straightforward and pragmatic solution to Nyquist ghosting in EPI.
• The technique enhances image quality for fMRI, especially at high field strengths.
• IDEA EPI offers a valuable advancement for high-resolution and artifact-free neuroimaging.