Evidence of Interictal Epilepctic Activity Using Simultaneous MRI and EEG

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Evidence of Interictal Epilepctic Activity Using
Simultaneous MRI and EEG
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• 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

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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

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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

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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

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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

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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
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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

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MRI

• Resolution 3.125mm x 3.125mm
• Scan duration 30mins

1 min

• Reference used Gamma function
• Delay 2s
• Data window of 1min (trends, )

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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???)

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Results
ROI
r gt 0.2, p lt 0.15
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Results
MRIData
Sharp Wave
temporal electrode
temporal electrode
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Results
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Results
Presumedhead movement
temporal electrode
posterior electrode
posterior electrode
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Results
posterior electrode
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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)

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Discussion

• MR temporal course shows large amount of
  variability
• Subject motion
• Little averaging due to small number of detected
  events (n2)
• Physiological noise, ...
• No subject motion artifacts were present in
  correlation map

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Acknowledgements

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

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MRI

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

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MRI
1 min

• Reference used was Gamma function
• Delay 2s
• Data window of 1min (trends, )

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100ms
100ms
100ms
650ms
650ms

t
MR
EEG
MR
MR
EEG
slice 1
slice 3
slice 2