Functional imaging of the brain by MRI

© 1993 SPIE. All rights reserved. Recent developments in Magnetic Resonance Imaging (MRI) enabling imaging of hemodynamics and metabolism hold significant promise in the noninvasive evaluation of normal and abnormal brain function. Among several methods, the most successful approach exploits the sensitivity of MRI to changes in the oxygenation status of hemoglobin (oxy/deoxyhemoglobin) in red blood cells related to local variations in blood flow and oxygen consumption in tissues. In cerebral cortex, such variations may be induced by external stimuli or internal cognitive processes. Typically, MRI signal slightly increases when brain is activated due to increase in oxygen supply (blood flow). These small changes in deoxyhemoglobin content can be detected using conventional MRI systems, although effects are better seen at high magnetic fields. Images are obtained at intervals of a few seconds and with a spatial resolution better than 1 mm. Brain activation maps have been obtained using visual and sensorimotor stimulation. More recent studies have shown brain activation during cognitive processes, such as mental imagery. These studies suggest that MRI may be the method of choice to study mental and cognitive processes underlying the function of the human brain.