Dynamic changes of magnetic resonance imaging abnormalities in relation toinflammation and glial responses after photothrombotic cerebral infarctionin the rat brain

This investigation analyzed the potential of high-resolution magnetic reson ance imaging (MRI) at a field strength of 7T to depict leukocyte infiltrati on and glial responses after focal cerebral ischemia induced by photothromb otic occlusion of cerebral microvessels. For this purpose we superimposed m ultiparametric MRI (apparent diffusion coefficient, T2, perfusion-weighted, and gadolinium-DTPA-enhanced T1-weighted imaging) on tissue sections stain ed for phagocytes and astrocytes and, moreover, assessed the regional distr ibution of tissue pH and ATP content by invasive biochemical methods. Compa ring the histological data with the various MRI parameters, high-resolution MRI did not allow a spatial discrimination between distinct areas of phago cyte accumulation or astroglial scar formation, based on image contrast or even quantitative parameter value differences. However, MRI parameters unde rwent characteristic changes and differentiated distinct stages of tissue r emodeling between days 3 and 14 after photothrombosis. Low apparent diffusi on coefficient (ADC) and high T2 values indicated an early stage (3 days) w ith necrosis and beginning glial activation. Normal ADC and reduced T2 elev ation characterized an infarct with advanced glial activation and infiltrat ion of hematogenous cells at 7 days after photothrombosis. Heterogeneous AD C together with T2 elevation reflected a late infarct stage (14 days) when pseudocystic degeneration and scar formation had occurred.