APPLICATIONS OF NMR-SPECTROSCOPY TO THE STUDY OF EXPERIMENTAL STROKE IN-VIVO

Background and Purpose: Magnetic resonance spectroscopy and imaging en able us to investigate biochemical and pathophysiological changes asso ciated with cerebral ischemia. The specific aims of these studies were to establish the relationships between energy metabolites and regiona l cerebral blood flow and to determine whether diffusion-weighted imag ing is sensitive to the known thresholds for cerebral tissue energy fa ilure and disturbance of transmembrane ionic gradients in gerbils. Met hods: Magnetic resonance spectroscopy measurements of energy metabolit es in the gerbil brain were obtained as a function of cerebral blood f low (measured with the hydrogen clearance technique) before, during, a nd after unilateral or bilateral occlusion of the common carotid arter ies. Diffusion-weighted and T2-weighted images were obtained in a sepa rate series of experiments. Results: Major changes in brain energy met abolites were observed at flow values of 20 ml.100 g-(1) min-(1) and b elow. The cerebral blood flow threshold for maintenance of energy stat us was lowered in hypothermia, consistent with a protective effect. Di ffusion-weighted imaging intensity increased at cerebral blood flow va lues of 15 to 20 ml.100 g-(1).min-(1) and below and increased graduall y following the onset of severe global cerebral ischemia, but with a d elay of about 2.5 minutes. Conclusions: The spectroscopic observations suggest that the flow thresholds for electrical function and edema ar e a direct consequence of energy failure. Comparison of the spectrosco py and imaging data suggests that diffusion-weighted imaging is sensit ive to disruption of tissue energy metabolism or to a consequence of t his disruption. The possibilities arise of visualizing energy failure with the spatial resolution characteristic of magnetic resonance imagi ng and detecting compromised but recoverable tissue.