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

Objective: To compare diffusion characteristics of MS lesions, normal-appea ring white matter (NAWM) from patients, and normal white matter from contro l subjects, and to investigate the correlations between the magnetization t ransfer ratio (MTR) and a directionally averaged tissue water diffusion coe fficient ((D) over bar) in patients. Background: MS and other pathologic pr ocesses that modify tissue integrity can result in abnormal diffusion of wa ter molecules detectable by diffusion-weighted imaging (DWI). Methods: Conv entional dual-echo and DWI scans were obtained from 35 patients with relaps ing-remitting MS and 24 healthy control subjects. MT scans were also obtain ed from the patients. After coregistration of all scans, MTR and (D) over b ar values from MS lesions and NAWM in different regions were marked using t he 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 b ar were also produced. Results: Patients with MS had significantly higher ( D) over bar values in all the areas studied. Moreover, histogram metrics (p eak height, peak site, and average (D) over bar) from patients were substan tially different from those of control subjects. In patients, average lesio n (D) over bar and MTR were markedly different from those in the NAS;VM. Th ere was an inverse correlation between average lesion MTR and (D) over bar inside lesions, whereas no correlation was found for average MTR and (D) ov er bar taken from the histograms. Conclusions: DWI detects severe tissue di sruption inside lesions and subtle widespread abnormalities in NAWM in pati ents with relapsing-remitting MS. MT and DWI may provide information about different aspects of brain pathology in MS.