A Chronological Evaluation of Experimental Brain Infarct by Diffusion-Mapping and Magnetization Transfer Contrast Imaging

Abstract

Background and purpose: There is a complex system of evolving physiochemical processes in the ischemic brain. The evaluation of this chain of processes is a major challenge of recent stroke studies. Two magnetic resonance imaging techniques; diffusion-weighted (DW) and magnetization transfer contrast (MTC) imaging were introduced in experimental studies and were shown to have sensitivity for different stages of brain infarct. Materials and methods: We used a reproducible middle cerebral artery (MCA) occlusion model in rat to examine infarcts of different time courses. Magnetic resonance T2-weighted (T2), DW, and MTC imaging were performed 3 h, 1 d, 3 d, 5 d, 7 d, 2 w, 3 w, and 4 w after MCA occlusion. Haematoxylin/eosin (HE) stained sections, which revealed sub regions within infarct lesions, were compared to T2, DW, diffusion-mapping and MTC-mapping images. Results: On DW images 3 hours post occlusion lesions were detected as an area with high signal intensity, while T2 imaging does not raise significant contrast of the lesion at this early stage. Three sub regions of the lesion having different ADCs, are discernible on diffusion-mapping images front 1 day to 7 days. The decrease of MTC effect was measured within the infarct lesion from core to marginal zone, front 7 days to 4 weeks. Conclusions: Diffusion-mapping imaging may help to examine brain infarction from 3 hours to 5 days. MTC imaging recognizes infarcts 7 days after the onset. Following this stage, MTC-mapping images may provide a quantitative method to assess infarct size.