Evidence of Interictal Epilepctic Activity Using Simultaneous MRI and EEG

Alberto L. Vazquez, M.S.* Steve B. Baumann, Ph.D. + Mark L. Scheuer, M.D. + Douglas C. Noll, Ph.D.* * Dept. Biomedical Engineering University of Michigan, Ann Arbor, MI + University of Pittsburgh Medical Center, Pittsburgh, PA

Background A disadvantage of fMRI responses is its sluggish temporal characteristics while a disadvantage of EEG is its poor spatial localizationA disadvantage of fMRI responses is its sluggish temporal characteristics while a disadvantage of EEG is its poor spatial localization Combination of EEG and MRI should provide a powerful tool, especially when stimulus cannot be induced, measured, and/or controlledCombination of EEG and MRI should provide a powerful tool, especially when stimulus cannot be induced, measured, and/or controlled

Background Problems of integrationProblems of integration –gradient-induced currents –saturation of pre-amplifier/electronics –movement and pulsatile flow induced currents –RF artifact due to shielding effects of conductors –susceptibility artifacts from electrodes –safety issues

Background Variety of methods exist to acquire EEG and MRI dataVariety of methods exist to acquire EEG and MRI data –trigger MR with EEG activity –Interleave EEG and MRI (different methods of interleaving) Our goal: acquire EEG and MRI tightly interleaved (with minimal loss of EEG signals) throughout a scanOur goal: acquire EEG and MRI tightly interleaved (with minimal loss of EEG signals) throughout a scan

EEG MRI compatible cap (Electrode Cap, Inc.)MRI compatible cap (Electrode Cap, Inc.) Ear used as EEG voltage referenceEar used as EEG voltage reference 64 channels referentially recorded (uninterpretable)64 channels referentially recorded (uninterpretable) Bipolar reconstruction (interpretable)Bipolar reconstruction (interpretable) Data band-pass filtered HzData band-pass filtered Hz

EEG EEG acquired while RF and gradients are quietEEG acquired while RF and gradients are quiet Data sampled at 256 HzData sampled at 256 Hz Closely interleaved acquisitionClosely interleaved acquisition t MREEG slice 1 MR slice 3 EEG MR slice 2 …… 100ms 650ms 100ms 650ms 100ms

MRI GE Signa 1.5 T scannerGE Signa 1.5 T scanner Single-shot EPI (even slice spacing)Single-shot EPI (even slice spacing) TR = 3000ms TE = 40ms FA = 90deg 4 axial slices (7mm, skip 3mm) centered about right temporal lobe4 axial slices (7mm, skip 3mm) centered about right temporal lobe

MRI Resolution = 3.125mm x 3.125mmResolution = 3.125mm x 3.125mm Scan duration = 30minsScan duration = 30mins 1 min Reference used Gamma functionReference used Gamma function Delay = 2sDelay = 2s Data window of 1min (trends, …)Data window of 1min (trends, …)

Subject 43 year-old man43 year-old man Right mesial temporal lobe epilepsyRight mesial temporal lobe epilepsy Resting EEG contained right anterior temporal sharp wavesResting EEG contained right anterior temporal sharp waves MR images show evidence of right mesial temporal sclerosisMR images show evidence of right mesial temporal sclerosis (image???)(image???)

Results r > 0.2, p 0.2, p < 0.15 ROI

Results temporal electrode MRI Data Sharp Wave

Results

Results temporal electrode posterior electrode Presumed head movement

Results posterior electrode

Discussion EEG data shows neural activity ~300ms in durationEEG data shows neural activity ~300ms in duration fMRI response lasted ~12s (delay to onset = 2s)fMRI response lasted ~12s (delay to onset = 2s) fMRI map agrees with pre-operative diagnosisfMRI map agrees with pre-operative diagnosis Post-operative findings showed temporal mesial sclerosis in resected tissue (subject has been 8 months seizure-free)Post-operative findings showed temporal mesial sclerosis in resected tissue (subject has been 8 months seizure-free)

Discussion MR temporal course shows large amount of variabilityMR temporal course shows large amount of variability –Subject motion –Little averaging due to small number of detected events (n=2) –Physiological noise,... No subject motion artifacts were present in correlation mapNo subject motion artifacts were present in correlation map

Acknowledgements Electrode Cap, Inc. (???)Electrode Cap, Inc. (???) This work was possible thanks to NIH grants NS32756 and DA11469This work was possible thanks to NIH grants NS32756 and DA11469

MRI Resolution = 3.125mm x 3.125mmResolution = 3.125mm x 3.125mm Scan duration = 30minsScan duration = 30mins Activation MapsActivation Maps –Correlation analysis –Gamma function used as reference –Data window of 1 min

1 min Reference used was Gamma functionReference used was Gamma function Delay = 2sDelay = 2s Data window of 1min (trends, …)Data window of 1min (trends, …) MRI

t MREEG slice 1 MR slice 3 EEG MR slice 2 …… 100ms 650ms 100ms 650ms 100ms