0800 bagshaw wed ball47

Clinical Applications of
EEG-fMRI: Epilepsy

Andrew Bagshaw
School of Psychology


EEG-fMRI in Epilepsy


Generally, we are NOT looking at
seizures
– Ictal
– Interictal




 seizures
 between seizures (spikes)

Patients undergo 1-2 hour EEG-fMRI
scanning session with no task
Analysis steps:
– Artefact removal, identification of spikes and
event-related fMRI analysis
 Identify voxels whose signal changes reliably
whenever an epileptic event occurs



Long term goals:
– To aid in pre-surgical evaluation
 Placement of intracranial electrodes?
– To provide a better understanding of the
mechanisms producing epilepsy




Pre-surgical
Evaluation



Basic Mechanisms
of Epilepsy



Future Directions


Pre-surgical Evaluation


Temporal Lobe Epilepsy (TLE)
The most common form of focal epilepsy
 Responds well to surgery


Varied EEG-fMRI responses are observed
 What is the significance of the
‘unexpected’ regions?
– Can these responses differentiate
between patients (surgical outcome
etc.)?


Spikes F7T3

Kobayashi et al Epilepsia 47 343-354 (2006)


Localisation Accuracy


How is localisation accuracy assessed?
– Electro-clinical features (e.g. MRI lesions, scalp EEG topography,
seizure symptomatology)


See Al Asmi et al Epilepsia 2003, Salek-Haddadi et al Brain Res 2006, Di
Bonaventura et al Epilepsia 2006

– EEG source localisation




See Lemieux et al Neuroimage 2001, Bagshaw et al Neuroimage 2006, Leal et

al Epilepsia 2006, Boor et al Clin Neurophysiol 2007
Comparison with distributed EEG models is ongoing (Grova et al In press)

– Intracranial or stereotaxic EEG (SEEG)




e.g. Bénar et al 2006, Laufs et al Magn Reson Imag 2006

For clinical use of EEG-fMRI in pre-surgical evaluation this
issue needs to be better addressed


Basic Mechanisms of Epilepsy


Generalised Epilepsy




Idiopathic generalised epilepsy is
characterised interictally by generalised
spike and wave (GSW) discharges in the
EEG
What regions are involved in GSW
discharge generation?

– Positive EEG-fMRI response

 Confirms role of thalamus seen
in animal models

Aghakhani et al Brain 127 1127-1144 (2004)


Generalised Epilepsy






Negative response
– Regions involved in default
attentional network (Raichle et
al PNAS 2001)
– See also Archer et al
Neuroimage 2003, Gotman et
al PNAS 2005, Hamandi et al
Neuroimage 2006
– Recently also seen in TLE
(Laufs et al Hum Brain Mapp
2007)
Suggests that discharges disrupt
ongoing brain processes
The regions identified by EEG-fMRI
relate not only to the generation of
the discharges, but their wider
effect on brain function

Aghakhani et al Brain 127 1127-1144 (2004)


Negative BOLD

Kobayashi et al Hum Brain Mapp 27 488-497
(2006)



Widely seen in interictal EEG-fMRI
– Generally poorer correspondence
with electro-clinical features
– See Kobayashi et al Hum Brain
Mapp 2006, Salek-Haddadi et al
Brain Res 2006



What is the neurophysiological and
clinical significance of negative
responses in epilepsy?


Future Directions


Ongoing Issues (1)


Interpretation and Validation
– Not all regions of activation correspond well with
electro-clinical information
 e.g. extratemporal responses to temporal lobe
spikes
– Is this new and clinically useful information?
 How can a more detailed interpretation of these
regions of activation be achieved?
– SEEG (but not helpful for non-congruent
responses)
– MR spectroscopy (NAA, Cho, Cr changes)
– Post-surgical outcome…


Ongoing Issues (2)


Patient selection
– Patients must have interictal activity but rare seizures
– 30-40% with discharges in the scanner have no EEG-fMRI responses
 Al Asmi et al Epilepsia 2003, Salek-Haddadi et al Brain Res 2006, Di
Bonaventura et al Epilepsia 2006
 This may be in part be related to SNR issues (Kobayashi et al
Neurology 2006) and improve at higher field strengths

– How to predict whether a patient will show EEG-fMRI responses
beforehand based on the EEG?


More spikes, runs of discharges, less head movement and fewer
background abnormalities (Salek-Haddadi et al Brain Res 2006)

– Can properties of the EEG other than spikes be used?




Delta (Laufs et al Magn Reson Imag 2006)
Gamma (Willoughby et al JNNP 2003)
cf. HFO from SEEG?


Conclusions
EEG-fMRI is a robust research tool which can
provide new information about the generation
and consequences of epileptic activity
 It remains a technique with potential in clinical
epilepsy management, rather than a widely
used tool



Acknowledgements
University of Birmingham
– Shoumitro Deb, Imad Soryal, Tracy
Warbrick
 Montreal Neurological Institute
– Jean Gotman, François Dubeau, Eliane
Kobayashi, Christian Bénar, Christophe

Grova, Yingli Lu, Colin Hawco
