Abnormal magnetization transfer ratios in normal-appearing white matter onconventional 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 t o assess the usefulness of the magnetization transfer ratio (MTR) for detec ting vasculometabolic abnormalities on positron emission tomography (PET) s tudies in patients with unilateral severe stenosis of the internal carotid artery (ICA). METHODS: MTR maps and PET data-including regional cerebral blood flow (rCBF ), regional cerebral metabolic rate of oxygen (rCMRO(2)), and regional oxyg en extraction fraction (rOEF)-were investigated in 13 patients with unilate ral 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 classifi ed into three groups based on MTR values (group 0, MTR >47.22%; group 1, MT R = 45.77% to 17.22%; group 2, MTR <45.77%), and the relationship bet vc:ee n MTR and PET data was analyzed by means of both absolute values end asymme tric index (AI). RESULTS: Abnormal values could not he detected in the areas classified as g roup 0, The areas classified as group 1 were characterized by absolutely no rmal values of rCMRO(2) and increased rOEF with AI, which was assessed as v iable and reversible on the PET study. The areas classified as group 2 show ed decreased rCMRO(2) with absolute values, which was considered irreversib le in PET. A. significant overall linear correlation was found between MTR and rCMRO(2) values. CONCLUSION: Using the MTR technique to classify ischemic damage into three groups (normal, reversible, and irreversible), we found a significant corre lation between the reduction of MTR and that of rCMRO(2) in white matter wi th ICA stenosis, We believe that the MTR technique may partly replace PET d ata in the assessment of ischemic injury.