T₁ and T₂ relaxation times of the major ¹H‐containing metabolites in rat brain after focal ischemia

The relaxation properties of water and metabolites were measured in rat brain following the occlusion of the middle cerebral artery (MCA) with localized ¹H MRS. The PRESS sequence was employed to select volumes of 39 m̈L in the ischemic and the contralateral hemisphere. T₁ and T₂ relaxation times and peak intensities of water, choline containing compounds (Cho), creatine and phosphocreatine (Cre) and N‐acetyl aspartate (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 also quantified. The relaxation properties and peak intensities of NAA, Cre and Cho remained unchanged in the ischemic volume during the first 3‐6 h of ischemia as compared to the contralateral volume. Water T₁ was slightly increased in the ischemic volume. After 24 h the T₁ and T₂ of water and Cre and the T₁ of Cho had increased significantly in the ischemic volume, while the peak intensities of Cho, Cre and NAA were reduced. It appears therefore that tissue changes which occur in the early phase of ischemia have no significant effects on the relaxation behaviour of the metabolites. However, ischemic brain damage affects the relaxation behaviour and concentration of the metabolites and water at later stages.