MAGNETIC-RESONANCE STUDIES OF THE EFFECTS OF CARDIOVASCULAR-SURGERY ON BRAIN METABOLISM AND FUNCTION

Neurologic and neuropsychologic impairment are important sequelae of c ardiac surgery in general and of coronary artery bypass graft surgery in particular. Although estimates of incidence vary, the numbers affec ted are considerable. Despite the ubiquity of such effects and the gen eral consensus that impairments originate from ischemic injury seconda ry to microemboli produced during surgery, the nature of the underlyin g brain injuries remains poorly understood. Precise, and preferably qu antitative, definition of the localization and nature of the underlyin g injuries is a precondition for the rigorous evaluation of the effica cy of prophylactic measures. The ability of magnetic resonance imaging (MRI) to detect surgically related lesions and the course of brain sw elling is described, as are potential improvements in imaging sensitiv ity. Results of an experimental program studying chemical sequelae of surgery in a pig model are presented. MR spectroscopy can provide noni nvasive information on the biochemical changes in brain and brain meta bolism that permit empirical evaluation of various neuroprotective int erventions. Functional MRI provides a means of studying the neuropsych ologic mechanisms most often affected by cardiac surgery. Experimental data are presented that demonstrate that two such mechanisms, selecti ve attention and working memory, can be imaged successfully. Perfusion mapping, combined with functional imaging, allows for the quantitativ e study of flow and functional activation. Applied to structures such as the cingulate, these techniques permit comparison of surgical seque lae with processes such as normal aging. MRI technology offers the pos sibility of improved anatomic, chemical, and functional definition of the effects of cardiac surgery on the brain. Copyright (C) 1996 Clown in right of Canada.