Abstract #1840

Measuring inhomogeneous MT (ihMT) in human brain by multi-parameter mapping (MPM)

Gunther Helms^1,2, Lenka Vaculčiaková², Kerrin J. Pine², Harald E. Moeller³, and Nikolaus Weiskopf^2,4

¹Medical Radiation Physics, Clinical Sciences Lund, Lund University, Lund, Sweden, ²Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ³NMR Methods & Development Group, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ⁴Felix Bloch Institute for Solid State Physics, Leipzig University, Leipzig, Germany

Inhomogenous Magnetization Transfer (ihMT), the differential response to irradiation at single and dual frequency offsets, is sensitive to myelination. Quantification of ihMT in terms of MT saturation (MTsat), the percent reduction of Mz, corrects for underlying T₁ and B₁⁺ and allows comparing different implementations to optimize multi-parameter mapping (MPM) protocols. ihMTsat in white matter is roughly one twentieth of MTsat, merely 0.2 p.u. at 5kHz and 100% SAR at 3T. Noise propagation demands acquisition at 1.5mm resolution, large-array coils, and smaller offsets than suggested previously. Inverse MT ratios are highly correlated to ihMTs but obscure the true effect size.

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