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. 2019 Mar 25;9:5084. doi: 10.1038/s41598-019-41587-2

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Magnetization-transfer MRI provides proton-density contrast in brain while saturating extracellular free water protons. (a) Comparison of M₀ map (M₀), proton-density-weighted MRI with MT (α15MT), R₁ map (R₁), T₁-weighted MRI without (α70) and with MT (α70MT), MT ratio map (α70MTR). (b) Mean MT ratios (α70MTR) and (c) R₂ of various regions in the brain plotted vs. their R₁ as well as (d) R₁ and (e) MT ratios (α15 MTR and α70 MTR) plotted vs. their water content. Functions and correlation coefficients are: (b) y = 0.2936x + 0.1116, r = 0.99b (d) y = −2.3556x + 2.796, r = −0.99, (e) y = −0.8181x + 1.1706, r = −0.97 for α15 and y = −0.6843x + 0.9263, r = −0.99 for α70. (f) Regional signal intensities in α70 MT plotted vs. those in M₀ in a subject. They correlate significantly (r = 0.94, p < 0.0005). (g) Calculated signal intensities for RF-spoiled gradient-echo MRI as a function of the water content in human brain. (TE2) 2D, TR/TE = 250/2.46 ms, α 70°, (TE4 and TE4MT) 2D, TR/TE = 863/4.4 ms, α 70° without and with magnetization transfer, (TE13MT) 2D, TR/TE = 715/13.2 ms, α 70° with magnetization transfer, (3DMT) 3D, TR/TE = 47/7.5 ms, α 22°, (α15TE4MT) 2D, TR/TE = 863/4.4 ms, α 15° with magnetization transfer. Here, for a selected combination of acquisition parameters α, TR, and TE, the variables R₁, R₂*, and MTR used for the calculation of MRI signal can be described as a function of tissue water content as shown in Supplementary Fig. 3. The R₁ and R₂* are obtained from the functions given in the legend of Supplementary Fig. 3a and 3d, respectively. The MTRs for “TE4MT”, “TE13MT”, “3DMT”, and “α15TE4MT” are obtained from the functions given in the legend of Supplementary Fig. 3b, 3c, 3e, and 3f, respectively. ◦ = gray matter structure (prefrontal cortex, caudate nucleus, putamen, thalamus, globus pallidus, and substantia nigra for (d) and (e). In addition, subthalamic nucleus, red nucleus, and locus coeruleus for (b), (c), and (f), × = WM = frontal subcortical white matter, ∙ = CSF = cerebrospinal fluid, error bars = standard deviation.