Validating the sensitivity of inhomogeneous magnetization transfer (ihMT) MRI to myelin with fluorescence microscopy

G. Duhamel (1) , V.H. Prevost (1) , M. Cayre (2) , A. Hertanu (1) , S. Mchinda (1) , V.N. Carvalho (1) , G. Varma (3, 4) , P. Durbec (2) , D.C. Alsop (3, 4) , Olivier M Girard (1)

1 CRMBM - Centre de résonance magnétique biologique et médicale
2 IBDM - Institut de Biologie du Développement de Marseille
3 HMS - Harvard Medical School [Boston]
4 BIDMC - Beth Israel Deaconess Medical Center [Boston]

Inhomogeneous Magnetization Transfer (ihMT) is a development from the MT MRI technique. IhMT can be considered as a dipolar order relaxation time (T1D) weighted imaging modality whose signal has shown an enhanced selectivity for myelin-rich structures. However, a formal validation of the ihMT sensitivity relative to a gold standard myelin density measurement has not yet been reported. To address this need, we compared ihMT MRI with green fluorescence protein (GFP) microscopy, in a study performed on genetically-modified plp-GFP mice, considered as a reference technique for myelin-content assessment. Various ihMT protocols consisting of variable T1D-filtering and radiofrequency power temporal distributions, were used for comparison with fluores- cence microscopy. Strong and significant linear relationships (r2 (0.87–0.96), p < 0.0001) were found between GFP and ihMT ratio signals across brain regions for all tested protocol variants. Conventional MT ratios showed weaker correlations (r2 (0.24–0.78), p 0.02) and a much larger signal fraction unrelated to myelin, hence corresponding to a much lower specificity for myelin. T1D-filtering reduced the ihMT signal fraction not attributed to myelin by almost twofold relative to zero filtering suggesting that at least half of the unrelated signal has a substantially shorter T1D than myelin. Overall, these results strongly support the sensitivity of ihMT to myelin conten

Mots clés: Inhomogeneous magnetization transfer; ihMT; plp-GFP; Fluorescence microscopy; MRI; Myelin imaging

Domaines: Ingénierie biomédicale; Neurosciences [q-bio.NC]

G. Duhamel, V.H. Prevost, M. Cayre, A. Hertanu, S. Mchinda, et al.. Validating the sensitivity of inhomogeneous magnetization transfer (ihMT) MRI to myelin with fluorescence microscopy. NeuroImage, 2019, 199, pp.289-303. ⟨10.1016/j.neuroimage.2019.05.061⟩. ⟨hal-02156603⟩