Abnormal Magnetization Transfer Ratios in Normal- appearing White Matter on Conventional MR Images of Patients with Occlusive Cerebrovascular Disease

BACKGROUND AND PURPOSE: Chronic hypoperfusion may cause ischemic insult in the deep white matter. The magnetization transfer phenomenon is associated with the amount and constitution of myelin. The purpose of this study was to assess the usefulness of the magneti-zation transfer ratio (MTR) for detecting vasculometabolic abnormalities on positron emission tomography (PET) studies in patients with unilateral severe stenosis of the internal carotid artery (ICA). METHODS: MTR maps and PET data—including regional cerebral blood flow (rCBF), re-gional cerebral metabolic rate of oxygen (rCMRO2), and regional oxygen extraction fraction (rOEF)—were investigated in 13 patients with unilateral severe stenosis of the ICA. The same regions of interest were selected in the white matter both on MTR maps and PET scans. The areas were classified into three groups based on MTR values (group 0, MTR.47.22%; group 1, MTR 5 45.77 % to 47.22%; group 2, MTR,45.77%), and the relationship between MTR and PET data was analyzed by means of both absolute values and asymmetric index (AI). RESULTS: Abnormal values could not be detected in the areas classified as group 0. The areas classified as group 1 were characterized by absolutely normal values of rCMRO2 an