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Removal of EPI Nyquist ghost artifacts with two-dimensional phase correction
Nan-kuei Chen1, Alice M Wyrwicz
1Department of Biomedical Engineering, Northwestern University, Evanston, Illinois, USA.
Magnetic Resonance in Medicine
|June 2, 2004
Summary
This study introduces a novel 2D phase mapping protocol and algorithm to effectively remove Nyquist ghost artifacts in echo-planar imaging (EPI). The new method improves image quality for MRI applications.
Area of Science:
- Magnetic Resonance Imaging (MRI)
- Image Reconstruction
- Medical Physics
Background:
- Nyquist ghost artifacts in echo-planar imaging (EPI) arise from odd-even echo inconsistencies.
- These artifacts degrade image signal-to-noise ratio and hinder accurate interpretation of EPI data.
Purpose of the Study:
- To present a novel 2D phase mapping protocol and postprocessing algorithm for effective Nyquist ghost artifact removal in EPI.
- To enhance the interpretability and diagnostic value of EPI data.
Main Methods:
- A new 2D phase mapping protocol is developed, involving k-space data regrouping.
- A 2D map encoding low- and high-order phase errors is derived from two phase-encoded reference scans.
- A postprocessing algorithm utilizes the measured phase map for ghost artifact removal in subsequent EPI experiments.
Main Results:
- Experimental results from phantom, animal, and human studies demonstrate the effectiveness of the new technique.
- The proposed method shows superior performance compared to previously reported techniques.
- The technique exhibits better tolerance to signal intensity differences between reference and actual EPI scans.
Conclusions:
- The developed 2D phase mapping protocol and postprocessing algorithm effectively remove Nyquist ghost artifacts in EPI.
- This method offers improved accuracy and robustness for EPI data analysis.
- The technique has potential applications in repeated EPI measurements, including functional MRI and diffusion coefficient mapping, without subject motion concerns.