Detection of subtle white matter abnormalities in relapsing-remitting MS – Q-space analysis of the slow diffusion component

Background and Purpose: Experimental evidence suggests, that the slow diffusion component depicts intracellular/intraaxonal water molecules rather than the extracellular fraction. We developed and implemented advanced DWI MR sequences and analysis strategies for slow diffusion component analysis along the lines suggested by Assaf and Cohen. High b-value DWI and q-space analysis were performed in patients with chronic subcortical, mainly white matter lesions to study the sensitivity and imaging information when compared to conventional DWI and other MRI contrasts.

Methods: Standardized MRI was performed in 24 patients with relapsing-remitting MS (17w, 7m, age 20–46 years) with EDSS scores from 0–4 and 8 normal controls (4f, 4m, age 24–42 years). a 1.5 T Siemens SONATA system including DW (6 directions, 14 b-values range: b=0–8182s/mm2). Q-space analysis derived quantitative maps of the probability-for-zero-displacement were analyzed.

Results: Low probability for zero displacement maps provide very high contrast of white matter vs. gray matter structures showing prominent slow diffusion components in normal white matter. Chronic subcortical tissue change showed loss of the slow diffusion component even in areas of questionable signal abnormality and in normal appearing white matter on T2-weighted images highlighting the high sensitivity of high b-value diffusion weighted MRI. Histogram analysis demonstrated the high sensitivity of the slow diffusion component, that could not be observed with commonly used b-values up to 1000s/mm2.

Conclusions: This study demonstrates that DWI with high b-values and Q-space analysis provides images is clinically feasible. It provides a strong white matter contrast and higher sensitivity to macroscopically visible lesions and normal appearing white matter in MS than T2-weighted MRI resp. maps of the mean diffusivity.