Serial proton magnetic resonance spectroscopic imaging, contrast-enhanced magnetic resonance imaging, and quantitative lesion volumetry in multiple sclerosis.

Serial magnetic resonance (MR) studies that included proton MR spectroscopic imaging (MRSI), contrast-enhanced MR imaging (MRI), and lesion volumetric studies were performed on 25 multiple sclerosis (MS) patients with mild to modest clinical deficits. Each patient was scanned at varying intervals for up to 2 years, resulting in a total of 124 usable MR sessions. In these longitudinal studies, metabolic changes were observed on MRSI for some subjects before the appearance of lesions on MRI scanning. Regional changes in metabolite levels were observed to be dynamic and reversible in some patients. Transient changes in N-acetylaspartate (NAA) levels were sometimes found in acute plaques and indicate that a reduced NAA level does not necessarily imply axonal loss. An inverse correlation between the average NAA within the spectroscopic volume and the total lesion volume in the whole brain was observed. This negative correlation implies that NAA can serve as an objective marker of the disease burden. Strong lipid peaks in the absence of gadolinium enhancement and MRI-defined lesions were observed in 4 patients. This observation suggests that demyelination can occur independent of perivenous inflammatory changes and supports the presence of more than one pathophysiological process leading to demyelination in MS.