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Abstract #0332

Observation of Frequency Shifts Induced by Chemical Exchange in Brain Tissue

Karin Shmueli1, Steve Dodd2, T-Q Li3, Jeff H. Duyn1

1Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States; 2Functional and Molecular Metabolism Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States; 3Department of Medical Physics, Karolinska Huddinge, Stockholm, Sweden


Water-macromolecular exchange has been proposed to explain brain gray and white matter frequency (phase) contrast. We extended previous observations of exchange-induced frequency shifts (fexch) in protein solutions by performing chemical shift imaging experiments using reference chemicals (TSP and dioxane) to observe positive fexch in fixed human and fresh pig brain tissue. Substantial negative GM-WM δfexch was observed which was similar for all tissues and references but opposite to in-vivo GM-WM frequency contrast, implying that tissue magnetic susceptibility may have a greater contribution. Exchange should therefore be included in frequency contrast models but is insufficient to explain in-vivo GM-WM phase contrast.

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