Magnetoencephalography signals are influenced by skull defects

Lau, Stephan; Flemming, Lars; Haueisen, Jens

doi:10.1016/j.clinph.2013.12.099

Cited by 19 publications

(18 citation statements)

References 25 publications

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“…This is in agreement with computational models ( Telenczuk et al, 2015 ) and experimental evidence ( Shimazu et al, 2000 ), which have shown a dampening factor from epidural to scalp level in the range of 10 to 100 in monkeys. In our surgical setting, skull opening could in principle increase the scalp EEG amplitude ( Lau et al, 2014 , von Ellenrieder et al, 2014a ), which was however not observed in our patient group. We may safely assume that the sources of N20 and HFO are strictly co-localized ( Ozaki and Hashimoto, 2011 ).…”

Section: Discussioncontrasting

confidence: 54%

Detectability of the somatosensory evoked high frequency oscillation (HFO) co-recorded by scalp EEG and ECoG under propofol

Burnos

Fedele

Schmid

et al. 2016

NeuroImage: Clinical

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ObjectiveThe somatosensory evoked potential (SEP) elicited by median nerve stimulation consists of the N20 peak together with the concurrent high frequency oscillation (HFO, > 500 Hz). We describe the conditions for HFO detection in ECoG and scalp EEG in intraoperative recordings.MethodsDuring neurosurgical interventions in six patients under propofol anesthesia, the SEP was recorded from subdural electrode strips (15 recordings) and from scalp electrodes (10/15 recordings). We quantified the spatial attenuation of the Signal-to-Noise Ratio (SNR) of N20 and HFO along the contacts of the electrode strip. We then compared the SNR of ECoG and simultaneous scalp EEG in a biophysical framework.ResultsHFO detection under propofol anesthesia was demonstrated. Visual inspection of strip cortical recordings revealed phase reversal for N20 in 14/15 recordings and for HFO in 10/15 recordings. N20 had higher maximal SNR (median 33.5 dB) than HFO (median 23 dB). The SNR of N20 attenuated with a larger spatial extent (median 7.2 dB/cm) than the SNR of HFO (median 12.3 dB/cm). We found significant correlations between the maximum SNR (rho = 0.58, p = 0.025) and the spatial attenuation (rho = 0.86, p < 0.001) of N20 and HFO. In 3/10 recordings we found HFO in scalp EEG. Based on the spatial attenuation and SNR in the ECoG, we estimated the scalp EEG amplitude ratio N20/HFO and found significant correlation with recorded values (rho = 0.65, p = 0.049).ConclusionsWe proved possible the intraoperative SEP HFO detection under propofol anesthesia. The spatial attenuation along ECoG contacts represents a good estimator of the area contributing to scalp EEG. The SNR and the spatial attenuation in ECoG recordings provide further insights for the prediction of HFO detectability in scalp EEG. The results obtained in this context may not be limited to SEP HFO, but could be generalized to biological signatures lying in the same SNR and frequency range.

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Section: Discussioncontrasting

confidence: 54%

Detectability of the somatosensory evoked high frequency oscillation (HFO) co-recorded by scalp EEG and ECoG under propofol

Burnos

Fedele

Schmid

et al. 2016

NeuroImage: Clinical

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“…This was the case in both electric source imaging (Mégevand et al 2014;Rikir et al 2014) and MSI (Jung et al 2013) studies. The influence of the skull is estimated to be much less important on components of MEG signals than on those of EEG signals (Lau et al 2013), resulting in good spatial properties of MSI in terms of source localization results and source separation . It has been demonstrated that MSI increases the chance that the seizure onset zone is sampled when patients undergo intracranial investigations for presurgical assessment (Knowlton et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Magnetic Source Imaging in Posterior Cortex Epilepsies

et al. 2014

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Posterior cortex epilepsies (PCE) are characterized by less satisfying postoperative results than temporal lobe epilepsies and are thus challenging for non-invasive presurgical investigations. The objective of this study was to evaluate the performance of magnetic source imaging (MSI) in PCE, validating the results by the SEEG (stereoelectroencephalography) definition of irritative and epileptogenic zones (IZ and EZ). Fourteen PCE surgery candidates were investigated using MSI and SEEG. LCMV (Linearly Constrained Minimum Variance) and MUSIC algorithms were used. IZ was quantified using a semi-automatic detection of interictal spikes. EZ was quantified using the epileptogenicity index (EI) method that accounts for both the propensity of a brain area to generate rapid discharges and the time for this area to get involved in the seizure. EI values range from 0 (no epileptogenicity) to 1 (maximal epileptogenicity). Levels of concordance between MSI and IZ, MSI and EZ were determined as follows: A = localized on MSI and SEEG for the site of value 1 (IZ and EZ quantification), B = localized on MSI and SEEG for a part of the IZ or a structure involved in the EZ (without the maximal value 1), C = localized on MSI and not SEEG, D = localized on SEEG and not MSI, E = localized on MSI and SEEG, discordant for site. Five PCE cases were characterized by focal IZ, nine by distributed IZ between several distant brain areas. MSI allowed to determinate IZ in 4/5 focal IZ cases. In case of distributed IZ, levels of concordance were A (2 cases), B (4 cases) and D (3 cases). In most distributed cases, MSI allowed to localize only a part of the IZ. Medial temporal involvement in the IZ was frequent (9/12 cases) and not evidenced by MSI. The brain area that demonstrated the maximal value of EI was shown by MSI in four out of five (80 %) focal IZ cases, in two out of nine (22 %) distributed cases. MSI results depend on IZ characteristics. A distributed IZ organization presents difficulties for MSI and highlights the need for further methodological approaches.

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“…Realistic head models are important tools in neuroscience (Pascual-Marqui, 1999; Michel et al, 2004; Grech et al, 2008; Michel and Murray, 2012; Schneider, 1972; Opitz et al, 2011; Datta et al, 2013; Sadleir et al, 2010; Fernández-Corazza et al, 2013; Bayford and Tizzard, 2012; Vonach et al, 2012; Carter et al, 2005; Miller et al, 2010; Voo et al, 1996; Yang et al, 2009; Panzer et al, 2012; Wendel et al, 2009; Lau et al, 2014; Heers et al, 2012; Rampp and Stefan, 2007). The present paper focuses on realistic head models for EEG research that are used as volume conductor head models (VCHMs) for computing the electric fields created by electrical sources in the brain.…”

Section: Introductionmentioning

confidence: 99%

The role of blood vessels in high-resolution volume conductor head modeling of EEG

et al. 2016

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Reconstruction of the electrical sources of human EEG activity at high spatiotemporal accuracy is an important aim in neuroscience and neurological diagnostics. Over the last decades, numerous studies have demonstrated that realistic modeling of head anatomy improves the accuracy of source reconstruction of EEG signals. For example, including a cerebrospinal fluid compartment and the anisotropy of white matter electrical conductivity were both shown to significantly reduce modeling errors. Here, we for the first time quantify the role of detailed reconstructions of the cerebral blood vessels in volume conductor head modeling for EEG. To study the role of the highly arborized cerebral blood vessels, we created a submillimeter head model based on ultra-high-field-strength (7 T) structural MRI datasets. Blood vessels (arteries and emissary/intraosseous veins) were segmented using Frangi multi-scale vesselness filtering. The final head model consisted of a geometry-adapted cubic mesh with over 17 × 106 nodes. We solved the forward model using a finite-element-method (FEM) transfer matrix approach, which allowed reducing computation times substantially and quantified the importance of the blood vessel compartment by computing forward and inverse errors resulting from ignoring the blood vessels. Our results show that ignoring emissary veins piercing the skull leads to focal localization errors of approx. 5 to 15 mm. Large errors (>2 cm) were observed due to the carotid arteries and the dense arterial vasculature in areas such as in the insula or in the medial temporal lobe. Thus, in such predisposed areas, errors caused by neglecting blood vessels can reach similar magnitudes as those previously reported for neglecting white matter anisotropy, the CSF or the dura — structures which are generally considered important components of realistic EEG head models. Our findings thus imply that including a realistic blood vessel compartment in EEG head models will be helpful to improve the accuracy of EEG source analyses particularly when high accuracies in brain areas with dense vasculature are required.

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Magnetoencephalography signals are influenced by skull defects

Cited by 19 publications

References 25 publications

Detectability of the somatosensory evoked high frequency oscillation (HFO) co-recorded by scalp EEG and ECoG under propofol

Detectability of the somatosensory evoked high frequency oscillation (HFO) co-recorded by scalp EEG and ECoG under propofol

Magnetic Source Imaging in Posterior Cortex Epilepsies

The role of blood vessels in high-resolution volume conductor head modeling of EEG

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