Evidence of Interictal Evidence of Interictal Epilepctic Activity Using Epilepctic Activity Using

Simultaneous MRI and EEGSimultaneous MRI and EEG

Alberto L. Vazquez, M.S.*Alberto L. Vazquez, M.S.*Steve B. Baumann, Ph.D.Steve B. Baumann, Ph.D.++

Mark L. Scheuer, M.D.Mark L. Scheuer, M.D.++

Douglas C. Noll, Ph.D.*Douglas C. Noll, Ph.D.*

* * Dept. Biomedical EngineeringDept. Biomedical EngineeringUniversity of Michigan, Ann Arbor, MIUniversity of Michigan, Ann Arbor, MI

++ University of Pittsburgh Medical Center, University of Pittsburgh Medical Center, Pittsburgh, PAPittsburgh, PA

BackgroundBackground

• A disadvantage of fMRI responses is its A disadvantage of fMRI responses is its sluggish temporal characteristics while a sluggish temporal characteristics while a disadvantage of EEG is its poor spatial disadvantage of EEG is its poor spatial localizationlocalization

• Combination of EEG and MRI should Combination of EEG and MRI should provide a powerful tool, especially when provide a powerful tool, especially when stimulus cannot be induced, measured, stimulus cannot be induced, measured, and/or controlledand/or controlled

BackgroundBackground

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

BackgroundBackground

• Variety of methods exist to acquire EEG Variety of methods exist to acquire EEG and MRI dataand MRI data– trigger MR with EEG activitytrigger MR with EEG activity– Interleave EEG and MRI (different methods Interleave EEG and MRI (different methods

of interleaving)of interleaving)• Our goal: acquire EEG and MRI tightly Our goal: acquire EEG and MRI tightly

interleaved (with minimal loss of EEG interleaved (with minimal loss of EEG signals) throughout a scansignals) throughout a scan

EEGEEG

• 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 64 channels referentially recorded

(uninterpretable)(uninterpretable)• Bipolar reconstruction (interpretable)Bipolar reconstruction (interpretable)• Data band-pass filtered 0.1-100 HzData band-pass filtered 0.1-100 Hz

EEGEEG

• EEG acquired while RF and gradients are EEG acquired while RF and gradients are quiet quiet

• Data sampled at 256 HzData sampled at 256 Hz• Closely interleaved acquisitionClosely interleaved acquisition

ttMRMR EEGEEGslice 1slice 1

MRMRslice 3slice 3

EEGEEG MRMRslice 2slice 2

…………100ms100ms 650ms650ms 100ms100ms 650ms650ms 100ms100ms

MRIMRI

• GE Signa 1.5 T scannerGE Signa 1.5 T scanner• Single-shot EPI (even slice spacing)Single-shot EPI (even slice spacing)

TR = 3000msTR = 3000msTE = 40msTE = 40msFA = 90degFA = 90deg

• 4 axial slices (7mm, skip 3mm) centered 4 axial slices (7mm, skip 3mm) centered about right temporal lobeabout right temporal lobe

MRIMRI

• Resolution = 3.125mm x 3.125mmResolution = 3.125mm x 3.125mm• Scan duration = 30minsScan duration = 30mins

1 min1 min• Reference used Reference used Gamma function Gamma function

• Delay = 2sDelay = 2s• Data window of Data window of

1min (trends, …)1min (trends, …)

SubjectSubject

• 43 year-old man43 year-old man• Right mesial temporal lobe epilepsyRight mesial temporal lobe epilepsy• Resting EEG contained right anterior Resting EEG contained right anterior

temporal sharp wavestemporal sharp waves• MR images show evidence of right mesial MR images show evidence of right mesial

temporal sclerosis temporal sclerosis • (image???)(image???)

ResultsResults

r > 0.2, p < 0.15r > 0.2, p < 0.15

ROI

ResultsResults

temporal electrodetemporal electrode temporal electrodetemporal electrode

MRIData

Sharp WaveSharp Wave

ResultsResults

ResultsResults

temporal electrodetemporal electrode posterior electrodeposterior electrode posterior electrodeposterior electrode

PresumedPresumedhead movementhead movement

ResultsResults

posterior electrodeposterior electrode

DiscussionDiscussion• EEG data shows neural activity ~300ms in EEG data shows neural activity ~300ms in

durationduration• fMRI response lasted ~12s (delay to onset = fMRI response lasted ~12s (delay to onset =

2s) 2s) • fMRI map agrees with pre-operative diagnosisfMRI map agrees with pre-operative diagnosis• Post-operative findings showed temporal Post-operative findings showed temporal

mesial sclerosis in resected tissue (subject mesial sclerosis in resected tissue (subject has been 8 months seizure-free)has been 8 months seizure-free)

DiscussionDiscussion

• MR temporal course shows large amount MR temporal course shows large amount of variabilityof variability– Subject motion– Little averaging due to small number of Little averaging due to small number of

detected events (n=2)detected events (n=2)– Physiological noise, ...Physiological noise, ...

• No subject motion artifacts were present No subject motion artifacts were present in correlation mapin correlation map

AcknowledgementsAcknowledgements

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

grants NS32756 and DA11469grants NS32756 and DA11469

MRIMRI

• Resolution = 3.125mm x 3.125mmResolution = 3.125mm x 3.125mm• Scan duration = 30minsScan duration = 30mins

• Activation MapsActivation Maps– Correlation analysisCorrelation analysis– Gamma function used as referenceGamma function used as reference– Data window of 1 minData window of 1 min

1 min1 min• Reference used Reference used was Gamma was Gamma function function

• Delay = 2sDelay = 2s• Data window of Data window of

1min (trends, …)1min (trends, …)

MRIMRI

ttMRMR EEGEEGslice 1slice 1

MRMRslice 3slice 3

EEGEEG MRMRslice 2slice 2

…………100ms100ms 650ms650ms 100ms100ms 650ms650ms 100ms100ms