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Inter-echo variance as a weighting factor for multi-channel combination in multi-echo acquisition for local frequency

Junmin Liu1, David A Rudko, Joseph S Gati

  • 1Imaging Research Laboratories, Robarts Research Institute, University of Western Ontario, London, Canada.

Magnetic Resonance in Medicine
|April 23, 2014
PubMed
Summary

A new method improves local frequency shift (LFS) mapping for multi-echo MRI using inter-echo variance (IEV) weighting. This technique reduces artifacts and enhances brain edge contrast, yielding more accurate LFS maps.

Keywords:
channel-combinationinter-echo variancelocal frequency shift mappingmulti-echophase unwrapping error

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Area of Science:

  • Magnetic Resonance Imaging (MRI)

Background:

  • Accurate local frequency shift (LFS) mapping is crucial for quantitative MRI.
  • Existing channel combination methods can introduce artifacts in multi-echo, multi-channel data.

Purpose of the Study:

  • To develop and evaluate a novel inter-echo variance (IEV) weighted local frequency shift (LFS) mapping method.
  • The method is specifically designed for multi-echo acquisitions and multi-channel receive coils.

Main Methods:

  • A pixel-by-pixel inter-echo variance (IEV) weighting was implemented for channel combination.
  • The IEV-weighted method was compared against adaptive and Hermitian product methods.
  • Data was acquired from five healthy volunteers at 7 Tesla.

Main Results:

  • The IEV-weighted method successfully generated LFS maps free from unwrapping artifacts.
  • Quantitative analysis showed the lowest inter-echo frequency variance across the whole brain using the IEV method.
  • Superior contrast at the brain edge was observed with the IEV-weighted approach.

Conclusions:

  • Accurate LFS maps are achievable by processing channel data independently before weighted combination using IEV.
  • The developed IEV-weighted method offers improved performance for LFS mapping in challenging MRI acquisitions.
  • The associated software is publicly available for research use.