Pathologic damage in MS assessed by diffusion-weighted and magnetization transfer MRI

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Abstract
Objective: To compare diffusion characteristics of MS lesions, normal-appearing white matter (NAWM) from patients, and normal white matter from control subjects, and to investigate the correlations between the magnetization transfer ratio (MTR) and a directionally averaged tissue water diffusion coefficient (D¯) in patients. Background: MS and other pathologic processes that modify tissue integrity can result in abnormal diffusion of water molecules detectable by diffusion-weighted imaging (DWI). Methods: Conventional dual-echo and DWI scans were obtained from 35 patients with relapsing-remitting MS and 24 healthy control subjects. MT scans were also obtained from the patients. After coregistration of all scans, MTR and D¯ values from MS lesions and NAWM in different regions were marked using the dual-echo scans as a reference. D¯ values from the same brain regions in control subjects were acquired. Histograms of MTR and D¯ were also produced. Results: Patients with MS had significantly higher D¯ values in all the areas studied. Moreover, histogram metrics (peak height, peak site, and average D¯) from patients were substantially different from those of control subjects. In patients, average lesion D¯ and MTR were markedly different from those in the NAWM. There was an inverse correlation between average lesion MTR and D¯ inside lesions, whereas no correlation was found for average MTR and D¯ taken from the histograms. Conclusions: DWI detects severe tissue disruption inside lesions and subtle widespread abnormalities in NAWM in patients with relapsing-remitting MS. MT and DWI may provide information about different aspects of brain pathology in MS.