FUNCTIONAL MRI OF THE BRAIN - PRINCIPLES, APPLICATIONS AND LIMITATIONS

MRI now allows noninvasive monitoring of brain function with a combine d spatial and temporal resolution never achieved by other imaging moda lities. Among several methods proposed to evaluate changes in blood vo lume, flow or oxygenation during mental activity, the most successful is based on the sensitivity of MRI to magnetic effects induced by the modulation of the oxygenation status of hemoglobin (oxy/deoxyhemoglobi n) which results from local variations in blood flow. In the brain cor tex, such variations may be induced by task activation or by cognitive processes, such as language or mental imagery. Typically, MRI signal is increased by a few percents when brain is activated due to sharp in crease in oxygen supply (blood flow). Brain activation maps obtained w ith MRI using various task paradigms agreed well with previous PET res ults. However MRI permits direct correlation of function with underlyi ng anatomy within a single imaging modality and repetitive studies on the same individuals. These studies suggest that MRI may be the method of choice in conjunction with other functional techniques, to study m ental and cognitive processes underlying the function of the human bra in. Clinically, potential applications include presurgical mapping, re covery monitoring of stroke or head injuries, exploration of seizure d isorders or monitoring of the effects of neuropharmaceuticals.