Inter‐echo variance as a weighting factor for multi‐channel combination in multi‐echo acquisition for local frequency shift mapping. Issue 4 (18th April 2014)

• Record Type: Journal Article
• Authors: Liu, Junmin; Rudko, David A.; Gati, Joseph S.; Menon, Ravi S.; Drangova, Maria
• Is Part Of: Magnetic resonance in medicine. Volume 73:Issue 4(2015:Apr.)
• Page Start: 1654
• Page End: 1661
• Publication Date: 2014-04-18
• Subjects: local frequency shift mapping -- inter‐echo variance -- phase unwrapping error -- multi‐echo -- channel‐combination; Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.25247
• Languages: English
• ISSNs: 0740-3194

Abstract

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.Magn Reson Med 73:1654–1661, 2015. © 2014 Wiley Periodicals, Inc.