MRI of cerebral ischaemia in rats with occlusion of the middle cerebral artery

Abstract

The development of ischaemic brain oedema caused by middle cerebral artery (MCA) occlusion was studied by serial magnetic resonance imaging (MRI) in rats. Multiple spin echo sequences were used with TR = 1500 ms and TE = 30–240 ms (8 echos). Subtraction images were obtained by subtracting the last three echos from the first echo. Fourteen rats were studied 3, 6, and 12 h and 1, 1.5, 3, 4, 6, and 8 days after MCA occlusion, and 2 of them also 3 and 6 weeks later. Two T2 components could be separated, a fast one representing bound water and a slow one representing free bulk water. MR showed T2 prolongation even on the first examination, and the highest values were observed 24h after occlusion. The subsequent examinations showed a slow reduction in oedema. MR studies 3 and 6 weeks after occlusion revealed an area of very long T2, which correlated well with infarction shown by histology. The subtraction images demonstrated both the infarct location and the oedematous changes in the surrounding uninfarcted tissue. MRI imaging employing T2 components and subtraction images appears to be a valuable method for observing the time course of the development and resolution of oedema in cerebral infarction.