Localization of subclinical ictal activity by functional magnetic resonance imaging: correlation with invasive monitoring.

Functional magnetic resonance imaging (fMRI) with susceptibility-based contrast was used to detect focal changes in cerebral blood flow and metabolism in a patient with focal epilepsy. The patient presented with frequent partial motor seizures involving his right lower face that spread to produce speech arrest and occasionally right arm jerking. Consciousness was never impaired during these events. A multislice echoplanar technique was used to acquire 16 contiguous axial slices every 4 seconds for 11 minutes. Although no overt seizures were observed or reported by the patient during the scanning, a time series analysis of the functional data revealed focal signal-intensity changes in the posterior left frontal lobe, which correlated well both in duration and spatial localization with ictal activity subsequently recorded by invasive electrophysiological monitoring. The spatial localization of fMRI was more accurate than electroencephalography recorded from a subdural grid in predicting the site of successful surgical therapy. These results illustrate the potential of functional MRI for localizing seizure foci with high spatial and temporal resolution. Such studies can be readily combined with high-resolution anatomical imaging, task-activation studies, and other magnetic resonance techniques.