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

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) over bar) 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) over bar values from MS lesions and NAWM in different regions were marked using the dual-echo scans as a reference. (D) over bar values from the same brain regions in control subjects were acquired. Histograms of MTR and (D) over bar were also produced. Results: Patients with MS had significantly higher (D) over bar values in all the areas studied. Moreover, histogram metrics (peak height, peak site, and average (D) over bar) from patients were substantially different from those of control subjects. In patients, average lesion (D) over bar and MTR were markedly different from those in the NAS;VM. There was an inverse correlation between average lesion MTR and (D) over bar inside lesions, whereas no correlation was found for average MTR and (D) over bar 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.