Assessment of myelination in hypomyelinating disorders by quantitative MRI.

PURPOSE: To apply myelin-sensitive quantitative magnetic resonance imaging (MRI) techniques in defined hypomyelinating conditions and to identify spatial patterns of myelination as criteria for characterization of undefined disorders. MATERIALS AND METHODS: Seven patients were included, based on the diagnosis of mitochondrial cytopathy, Pelizaeus-Merzbacher disease, GJA12/GJC2-related Pelizaeus-Merzbacher-like disease, hypomyelination with atrophy of the basal ganglia and cerebellum, and leukoencephalopathy with ataxia, delayed dentition, and hypomyelination. The control group comprised 23 children and adolescents (age range 2.6-22.4 years). The 3T MRI protocol consisted of high-resolution T1- and T2-weighted 3D MRI, diffusion tensor (DTI), and magnetization transfer (MT) imaging. Parameter maps of mean diffusivity, fractional anisotropy, and MT saturation were displayed as pseudocolor overlays and assessed by region-of-interest and histogram analysis. RESULTS: Structural MRI revealed widespread signal alterations in white matter, but were hampered by signal heterogeneity. Quantitative DTI and MT reflected the degree of hypomyelination and discriminative patterns of myelination emerged on MT saturation maps. CONCLUSION: The quantitative parameters in the defined hypomyelination conditions provide additional criteria to further classify undefined white matter disorders.