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Magn Reson Med. 2015 Apr;73(4):1654-61. doi: 10.1002/mrm.25247. Epub 2014 Apr 18.

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

Author information

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

Abstract

PURPOSE:

To develop and evaluate a local frequency shift (LFS) mapping method specifically designed for multi-echo acquisitions and multi-channel receive coils.

METHODS:

The proposed method uses the pixel-by-pixel inter-echo variance (IEV) as a weighting factor during channel-combination. Five healthy volunteers were scanned at 7 T. The IEV-weighted method was quantitatively compared to established (adaptive and Hermitian product) channel-combination methods with respect to IEV of LFS over the entire brain.

RESULTS:

In all experiments, the IEV-weighted method generated LFS maps free of artifacts caused by unwrapping errors. Based on measurements of the inter-echo frequency variance throughout the whole brain, the IEV-weighted method produced the lowest variation and the best contrast at the edge of the brain.

CONCLUSION:

The primary finding of the present study is that accurate LFS maps are achievable if the data from each channel is processed independently prior to combination followed by a weighted combination using IEV as the weighting term. The software is freely available to the scientific community.

KEYWORDS:

channel-combination; inter-echo variance; local frequency shift mapping; multi-echo; phase unwrapping error

PMID:
24753032
DOI:
10.1002/mrm.25247
[Indexed for MEDLINE]

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