T-1 AND T-2 RELAXATION-TIMES OF THE MAJOR H-1-CONTAINING METABOLITES IN RAT-BRAIN AFTER FOCAL ISCHEMIA

The relaxation properties of water and metabolites were measured in ra t brain following the occlusion of the middle cerebral artery (MCA) wi th localized H-1 MRS. The PRESS sequence was employed to select volume s of 39 mu L in the ischemic and the contralateral hemisphere, T-1 and T-2 relaxation times and peak intensities of water, choline containin g compounds (Cho), creatine and phosphocreatine (Cre) and N-acetyl asp artate (NAA) in both hemispheres were determined at 3-6 h, 1 day and 3 or 4 days after occlusion, Lactate in the ischemic hemisphere was als o quantified, The relaxation properties and peak intensities of NAA, C re and Cho remained unchanged in the ischemic volume during the first 3-6 h of ischemia as compared to the contralateral volume, Water T-2 w as slightly increased in the ischemic volume, After 24 h the T-1 and T -2 of water and Cre and the T-1 of Cho had increased significantly in the ischemic volume, while the peak intensities of Cho, Cre and NAA we re reduced, It appears therefore that tissue changes which occur in th e early phase of ischemia have no significant effects on the relaxatio n behaviour of the metabolites, However, ischemic brain damage affects the relaxation behaviour and concentration of the metabolites and wat er at later stages.