MR MICROSCOPY OF PERFUSED BRAIN-SLICES

To study the origins of signal changes in clinical MRI we have previou sly studied isolated single neuronal cells by MR microscopy, To accoun t for the extracellular environment of the cells, we have developed a prototype perfusion chamber for MR microimaging of perfused rat hippoc ampal brain slices. To demonstrate the utility of this model, brain sl ices were initially perfused in isotonic solutions and then subjected to osmotic perturbations via perfusate exchange with 20% hypertonic an d 20% hypotonic solutions. In diffusion weighted images, signal intens ity changes of +16(sigma(n-1) = 11)% (hypotonic) and -26(sigma(n-1) = 10)% (hypertonic) were observed. No significant variation in response was observed across the slice when several subregions were examined. T hese observations are consistent with the view that contrast changes a re driven primarily by changes in the intra-and extracellular compartm entation of water. This is the first report of MR microimaging of the isolated brain slice, The technique will enable the correlation of MR microimaging measurements with microscopic changes using other modalit ies and techniques to provide a better understanding of signals in cli nical MRI.