Long-Term Monitoring in Epilepsy

The goal of long-term monitoring for the epilepsy unit is to localize the onset of seizures to guide neurosurgical resection of the seizure focus.

Accuracy of Dense Array versus Conventional EEG

Research at the University of Geneva (Michel et al., 2004) has compared dEEG (128 channels) with lower channel count (27 channels), as shown in the figure above (a). The results (b) show that MRI-constrained electrical source analysis was accurate with 128 channels, as confimed by seizure elimination with surgical resection, whereas localization was inaccurate by several centimeters with 27 channels. Results from many similar studies have now confirmed that dense-array EEG source localization improves accuracy when compared to presurgical evaluation with conventional medical EEG (Holmes, 2008).

Holmes, M. D. (2008). Dense array EEG: Methodology and new hypothesis on epilepsy syndromes. Epilepsia, 49, 3-14.

Michel, C. M., M. M. Murray, G. Lantz, S. Gonzalez, L. Spinelli, and R. Grave de Peralta (2004).  EEG Source Imaging.  Clinical Neurophysiology, 115, 2195-2222.
 

Registration of dEEG with MRI

Dense array EEG provides greater accuracy in localizing neurophysiological activity to allow careful registration of the EEG results with the anatomical anomalies seen on MRI. Because of the improved sampling of inferior brain areas (orbital frontal and basal temporal), GeoMedica now recommends 256-channel sampling for both children and adults in long-term monitoring for neurosurgical planning.

Although many epilepsy centers have considered it impossible, or at least impractical, to record dEEG continuously over many days, advances in both high-bandwidth network acquisition and in the clinical protocol for the Geodesic Sensor Net are now making it practical for EEG technologists, nurses, and physicians to integrate dEEG into the daily workflow of the epilepsy monitoring unit.

Dense Array EEG in Neurosurgical Planning

As illustrated by GeoSource's software on a recent cover of Epilepsy and Behavior, the precision of dEEG allows the seizure onset to be examined in relation to the specific anatomy shown on the magnetic resonance image (MRI). With this development, dEEG source information can now be integrated with neurosurgical image guidance in treating the pathological brain region.

With these advances, dEEG now represents a fusion of the monitoring and imaging paradigms of medical devices, such that imaging the activity of specific brain regions can be conducted during continuous monitoring around the clock for many days.