MAGNETIC-RESONANCE-IMAGING OF HUMAN BRAIN-FUNCTION

BACKGROUND Previously the exclusive domain of the technology of positr on emission tomography, functional MRI is now proving capable of mappi ng functional regions of the human cortex in near real time during spe cific task activations or in response to any hemodynamic stress. Of pa rticular interest is the opportunity to observe secondary cortical res ponses, activation due to imagined tasks, memory function, time-resolv ed pathways through cortical regions, and activation in subcortical st ructures. METHODS AND RESULTS One method of functional MRI uses blood oxygenation changes, which can be imaged continuously while functional centers are being stimulated. Image intensity can become darker if th ere is more deoxygenated blood and brighter if more oxygenated blood e nters the brain. This concept works in all perfused tissues in the bod y, and allows use of the blood oxygenation mechanism to image neuronal activation. A second method takes advantage of the fact that the prot ons within the MRI slice are always partially saturated by the rapid r ate of imaging. As blood flow delivers unsaturated blood water protons into an imaged slice, these arterially-delivered protons will appear very bright in the image. Visualization of this effect is accomplished by simple image subtraction or by comparison of intensity changes as a function of the paradigm application frequency. Using either approac h leads directly to a functional map. CONCLUSIONS At present, clinical applications are rapidly moving toward routine non-invasive mapping o f distortions of the functional motor and somatosensory cortex and oth er cortical regions as a result of brain tumors. Other clinical applic ations include the observation of the effect of degenerative diseases such as multiple sclerosis, Alzheimer's disease, stroke, migraine, epi lepsy, and other diseases causing neuronal loss and Parkinsonism. Func tional MRI and its applications will continue to grow exponentially th roughout the decade.