EEG-fMRI using z-shimming in patients with temporal lobe epilepsy.
OBJECTIVE
To use z-shimming, a technique that reduces signal loss due to susceptibility artifacts that can result in reduced or absent activation in electroencephalography (EEG) functional MRI (fMRI) sessions in patients with temporal lobe epilepsy (TLE), to determine whether it would result in an increased ability to detect significant regions of blood oxygenation level-dependent (BOLD) signal change.


METHODS
Eight patients with TL EEG spikes underwent an EEG-fMRI scanning session using z-shimming. The signal intensities in the z-shimmed images were compared with those in the standard images. BOLD activation maps were created from the two sets of images using the timings of the spikes observed on the EEG.


RESULTS
The mean signal increase in the TLs as a result of z-shimming was 45.9%+/-4.5%. The percentage of TL voxels above a brain intensity threshold rose from 66.1%+/-7.6% to 77.6%+/-5.7%. This appreciable increase in signal did not lead to any significant differences in the statistical maps created with the two sets of functional images.


CONCLUSIONS
The results suggest that loss of signal is not the limiting factor for the detection of spike-related BOLD signal changes in patients with TLE activity.
Bagshaw
Andrew P
AP
School of Psychology, University of Birmingham, Birmingham, United Kingdom. a.p.bagshaw@bham.ac.uk
Torab
Leili
L
Kobayashi
Eliane
E
Hawco
Colin
C
Dubeau
François
F
Pike
G Bruce
GB
Gotman
Jean
J
D000465:Algorithms; D016477:Artifacts; D001931:Brain Mapping / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D004833:Epilepsy, Temporal Lobe / Q000175:diagnosis*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity