Calculated Confidence Regions of Single Equivalent Current Dipole Fits of Epileptic Spikes in MEG Recordings.
Abstract number :
1.230
Submission category :
Year :
2001
Submission ID :
2758
Source :
www.aesnet.org
Presentation date :
12/1/2001 12:00:00 AM
Published date :
Dec 1, 2001, 06:00 AM
Authors :
G.L. Barkley, M.D., Neurology, Henry Ford Health System, Detroit, MI; S.M. Bowyer, Ph.D., Neurology, Henry Ford Health System, Detroit, MI; K.M. Mason, R.EEG.T., Neurology, Henry Ford Health System, Detroit, MI; N. Tepley, Ph.D., Neurology, Henry Ford Hea
RATIONALE: Several mathematical parameters to describe the features of single equivalent current dipole (ECD) fits of epileptic spikes are part of standard software supplied by manufacturers of MEG devices. For MEG units manufacturered by 4-D Neuroimaging these parameters are: single current dipole moment (Q), correlation coefficient, goodness of fit (GoF), and root mean square (RMS) field value. We felt that the calculated parameter for the confidence region of the single ECD would provide useful information about the robustness of the epileptic spike maps.
METHODS: Six patients with localization-related epilepsy were monitored with a 148 channel whole head MEG. Data were digitized at 508.65 samples per second with a 0.1-100 Hz bandpass and displayed at 3-100 Hz with a 60 Hz notch filter. Epileptic spikes were selected and a single ECD fit was made using 35-40 channels over the area of interest. A short segment of quiet activity was used as baseline noise data for confidence region calculations. The highest correlation coefficient was the parameter given the greatest weight in the choice of the time point selected as the best ECD map for any given spike. As a control, continuous noise data was collected without a subject in the room and sharp transients were selected for spike mapping using similar settings as were used for subjects with epilepsy.
RESULTS: A total of 156 spikes were mapped. the mean average confidence region was 1.08 cm^3 +/- 1.05. The mean average correlation coefficient was 0.99, average GoF was 0.97, average RMS was 823 fT and average Q value was 260 nAm. The smallest confidence region usually occurs at the point of largest amplitude of the spike while the highest correlation coefficient usually occurs earlier in the spike. For noise data, 34 sharp transients were identified and mapped. The average confidence volume was 492 cm^3. The average GoF for this data was 0.91, the average correlation coefficient was 0.92, the average RMS was 10.1 +/- 1.8 fT, and the average Q was 5.9 +/- 1.6 nAm.
CONCLUSIONS: Confidence regions of epileptic spikes can be easily calculated and provides additional information that is useful in distinguishing epileptic spikes from noise in MEG data. It is reasonable to consider that spikes falling within overlapping confidence regions probably arise from the same source.
Support: NIH/NINDS Grant NS30914