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Magnetic resonance studies of the effects of cardiovascular surgery on brain metabolism and function
R Deslauriers1, J K Saunders, M C McIntyre
1Institute for Biodiagnostics, National Research Council, Canada.
Insights
Cardiac surgery can cause brain injury, but magnetic resonance imaging (MRI) techniques offer new ways to understand and potentially prevent these neurologic and neuropsychologic impairments.
Area of Science:
- Neuroscience
- Radiology
- Cardiovascular Surgery
Background:
- Cardiac surgery, particularly coronary artery bypass graft surgery, is associated with significant neurologic and neuropsychologic impairments.
- The precise nature and localization of brain injuries resulting from cardiac surgery remain poorly understood, hindering the evaluation of preventative strategies.
Purpose of the Study:
- To explore the utility of advanced magnetic resonance imaging (MRI) techniques for defining the anatomic, chemical, and functional effects of cardiac surgery on the brain.
- To investigate neuroprotective interventions using noninvasive brain imaging methods.
Main Methods:
- Utilized magnetic resonance imaging (MRI) to detect surgically related brain lesions and swelling.
- Employed MR spectroscopy to assess biochemical changes and brain metabolism in a pig model.
- Applied functional MRI and perfusion mapping to study mechanisms like selective attention and working memory, and their relation to cerebral blood flow.
Main Results:
- Demonstrated MRI's capability to detect surgically induced brain lesions and swelling.
- Showcased MR spectroscopy's potential for evaluating neuroprotective interventions by providing biochemical data.
- Confirmed functional MRI's ability to image cognitive mechanisms affected by surgery, such as attention and working memory.
Conclusions:
- Advanced MRI techniques, including spectroscopy and functional imaging, offer improved anatomic, chemical, and functional definition of cardiac surgery's effects on the brain.
- These imaging modalities provide a foundation for rigorously evaluating neuroprotective measures against post-cardiac surgery cognitive deficits.
Abstract:
Neurologic and neuropsychologic impairment are important sequelae of cardiac surgery in general and of coronary artery bypass graft surgery in particular. Although estimates of incidence vary, the numbers affected are considerable. Despite the ubiquity of such effects and the general consensus that impairments originate from ischemic injury secondary to microemboli produced during surgery, the nature of the underlying brain injuries remains poorly understood. Precise, and preferably quantitative, definition of the localization and nature of the underlying injuries is a precondition for the rigorous evaluation of the efficacy of prophylactic measures. The ability of magnetic resonance imaging (MRI) to detect surgically related lesions and the course of brain swelling is described, as are potential improvements in imaging sensitivity. Results of an experimental program studying chemical sequelae of surgery in a pig model are presented. MR spectroscopy can provide noninvasive information on the biochemical changes in brain and brain metabolism that permit empirical evaluation of various neuroprotective interventions. Functional MRI provides a means of studying the neuropsychologic mechanisms most often affected by cardiac surgery. Experimental data are presented that demonstrate that two such mechanisms, selective attention and working memory, can be imaged successfully. Perfusion mapping, combined with functional imaging, allows for the quantitative study of flow and functional activation. Applied to structures such as the cingulate, these techniques permit comparison of surgical sequelae with processes such as normal aging. MRI technology offers the possibility of improved anatomic, chemical, and functional definition of the effects of cardiac surgery on the brain.