Purpose: Phase imaging provides additional information on multiple sclerosis (MS) lesions and may in combination with mean diffusivity (MD) and magnetization transfer ratio (MTR) help differentiating heterogeneity of MS lesion pathology.
Methods: Magnetic resonance imaging (MRI) was performed in 23 MS patients including diffusion tensor imaging (DTI), magnetization transfer imaging (MTI), and SWI. Mean values (MTR, MD, and homodyne filtered phase) from 138 chronic MS lesions and normal appearing white matter (NAWM) were obtained and correlations examined. For explorative analysis, a divisive hierarchical clustering algorithm was applied.
Results: Phase characteristics were an independent characteristic of chronic T2 lesions, as MTR and MD were not correlated with phase values (R = - 0.23, R = - 0.18). Dependent on MTR, MD, and phase, cluster analysis led to five lesion groups. Of the two groups with phase values close to NAWM, one presented with highest MD and most severe MTR decrease (p = 0.01), the other with slight MD increase and MTR decrease. Two lesion groups with highest phase values (p = 0.01) displayed slightly increased MD and moderate decrease in MTR. Clinical data including EDSS, disease duration, and age did not differ significantly between groups.
Conclusions: Increased phase is predominantly detectable in lesions with clear MTR decrease but only moderate MD increase. Phase images seem to represent an independent parameter for MS lesion characterization and may provide additional information on MS lesion heterogeneity.
Keywords: Diffusion tensor imaging; Magnetic resonance imaging; Magnetization transfer contrast imaging; Multiple sclerosis; Susceptibility weighted imaging.