EEG-and MRI-based epilepsy source localization using multivariate empirical mode decomposition and inverse solution method
The only treatment for patients with medical refractory epilepsy is to resect the part of the cortex that is origin of epilepsy by surgery. An extensive pre-surgical evaluation is required to define the Epileptogenic Zone (EZ) accurately. There is a large variation of neuroimaging approaches t...
Saved in:
| Main Author: | |
|---|---|
| Format: | Thesis |
| Language: | English |
| Published: |
2018
|
| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/71441/1/FK%202018%20102%20-%20IR.pdf |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | The only treatment for patients with medical refractory epilepsy is to resect the part of
the cortex that is origin of epilepsy by surgery. An extensive pre-surgical evaluation is
required to define the Epileptogenic Zone (EZ) accurately. There is a large variation
of neuroimaging approaches that are utilized for pre-surgical evaluation depending
on the protocol of each epilepsy surgery center. Although Electroencephalography
(EEG)-based source localization (ESL) estimates the EZ more precisely than other
techniques but, it is used rarely in surgery centers. The reason behind the low usage
of this trustworthy technique is its requirement for technical expertise together with
experts’ supervision and lack of recommended guidelines for this technique. The
accuracy of ESL depends on all the stages of data processing including: head model
reconstruction, signal pre-processing and inverse solution. Therefore, a standardized
algorithm with less supervision is desired to utilize ESL for pre-surgical evaluation.
One of the factors that needs to be considered for the purpose of establishing an
automated and standardized algorithm is eye blink artifact removal due to its morphological
resemblance to epileptic discharges. Few studies considered eye blink artifact
removal for purpose of epilepsy source localization studies and most of them used
either visual inspection or computer-based approaches which still need of experts’
supervision. Besides, non-stationary, non-linear and multivariate characteristics of
EEG needs to be considered for choosing a proper processing method for extracting
epileptic spikes’ features. Nevertheless, patient’s realistic head model is essential to
obtain accurate source localization results. Although many inverse solutions exist
but, the ones which do not require specialists’ involvement with minimal error is
desired. Standardized Low Resolution Tomography (sLORETA) andWeighted Minimum
Norm (WMN) are linear distributed inverse solutions which lead up to zero
localization error using noise-free EEG, state-of-the-art feature extractor and realistic
head model. Therefore, in this study a coupled Multivariate Empirical Mode Decomposition
(MEMD) with embedded automated artifact remover algorithm and inverse solution method is proposed. To remove eye blink artifacts, the mother wavelet of
Bior 3.3 was used due to its high morphological resemblance to eye blink and yet differentiable
characteristic to epileptic spikes. Since MEMD method is a data-driven
method which meets the criteria to be applied for EEG processing, therefore this
method was employed to extract EEG epileptic spike features. In the current study,
clinical dataset of 20 subjects were used to examine sLORETA andWMN fed by raw
EEG signals and MEMD features on each patient’s realistic head model. sLORETA
in combination with MEMD feature after eye blink removal proved to be a reliable
ESL algorithm with 100% accuracy. The results show significantly improved EZ localization
results in comparison with similar works and capability of this algorithm to
not only determine the epilepsy origin lobe, but also the exact focus on the lobe. The
outcomes were validated using MRI references which are verified via post-surgical
results. Therefore proposed algorithm has the advantages to localize EZ using ESL
inexpensively and accurately which promotes usage of this valuable technique for
epilepsy pre-surgical evaluation. |
|---|