Evidence of Interictal Epilepctic Activity Using Simultaneous MRI and EEG

1. Evidence of Interictal Epilepctic Activity Using Simultaneous MRI and EEG

2. 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

3. Background • A 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 controlled

4. Background • Problems 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

5. Background • Variety 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 scan

6. EEG • MRI compatible cap (Electrode Cap, Inc.) • Ear used as EEG voltage reference • 64 channels referentially recorded (uninterpretable) • Bipolar reconstruction (interpretable) • Data band-pass filtered 0.1-100 Hz

7. EEG • EEG acquired while RF and gradients are quiet • Data sampled at 256 Hz • Closely interleaved acquisition 100ms 100ms 100ms 650ms 650ms …… t MR EEG MR MR EEG slice 1 slice 3 slice 2

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

9. MRI • Resolution = 3.125mm x 3.125mm • Scan duration = 30mins • Reference used Gamma function • Delay = 2s • Data window of 1min (trends, …) 1 min

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

11. Results ROI r > 0.2, p < 0.15

12. Results MRIData Sharp Wave temporal electrode temporal electrode

13. Results

14. Results Presumedhead movement temporal electrode posterior electrode posterior electrode

15. Results posterior electrode

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

17. Discussion • MR 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 map

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

19. MRI • Resolution = 3.125mm x 3.125mm • Scan duration = 30mins • Activation Maps • Correlation analysis • Gamma function used as reference • Data window of 1 min

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

21. 100ms 100ms 100ms 650ms 650ms …… t MR EEG MR MR EEG slice 1 slice 3 slice 2