Robust detection of epileptic seizures based on L1-penalized robust regression of EEG signals☆
Introduction
Epilepsy is a neurological disorder that affects around 70 million people worldwide (Fazel, Wolf, Långström, Newton, & Lichtenstein, 2013). The defining characteristic of epilepsy is recurrent seizures that strike without warning. Symptoms may range from brief suspension of awareness to loss of consciousness and sometimes violent convulsions (Iasemidis et al., 2003). Unlike other neurological disorders, such as stroke or Alzheimer’s disease, which tend to develop later in life, epilepsy often affects people in the prime of their lives, with the majority between 15 and 64 years of age (Hesdorffer, Hauser, Annegers, & Cascino, 2000). Early detection of epileptic seizures is of a high interest from the treatment aspect since it allows more tailored therapies and reduces the side effects of the anti-epileptic medicine (Myint, Staufenberg, & Sabanathan, 2006).
Studies of epilepsy often rely on the electroencephalogram (EEG) as the EEG can indicate the brain’s electrical activities associated with seizures (Smith, 2005). Much research and development in the area of automated seizure detection using EEG signals have been carried and several EEG-based seizure detection systems have been reported in the literature. Feature extraction and feature classification are the two essential modules that are necessary to build an automatic seizure detection system. Around ninety percent of the prior work has focused on developing effective feature extraction techniques that can discover the most discriminative EEG features for seizure diagnosis. Most of these techniques use hand-crafted features extracted from the time-domain (Meier, Dittrich, Schulze-Bonhage, Aertsen, 2008, Minasyan, Chatten, Chatten, Harner, 2010), frequency-domain (Aarabi, Fazel-Rezai, Aghakhani, 2009, Correa, Laciar, Patiño, Valentinuzzi, 2007, Polat, Güneş, 2007), wavelet-domain (Abibullaev, Seo, Kim, 2010, Güler, Übeyli, 2005, Tzallas, Tsipouras, Fotiadis, 2007), and sometimes from multiple domain representations of the EEG (Mitra et al., 2009). However, domain-based schemes experience two major difficulties. First, the non-stationarity nature of EEG makes it difficult to have a single seizure pattern, making the hand-crafted features less practical in clinical settings (Kaplan, Fingelkurts, Fingelkurts, Borisov, & Darkhovsky, 2005). Second, in practice, the EEG data is prone to different sources of artifacts such as muscle activities and eye-blinking as well as white noise. Artifacts and noise interfere with EEG signals, producing serious distortions that negatively affect the seizure detection performance (Abualsaud, Mahmuddin, Saleh, & Mohamed, 2015).
To overcome these challenges, we develop a robust seizure detection system that can accurately recognize epileptic seizures under real-life conditions as well as ideal conditions. A feature extraction method, based on L1-penalized robust regression (L1PRR), is proposed to provide the most informative seizure-associated features. The proposed scheme is applied to the EEG frequency spectra, and the extracted spectral features are used as an input to the random forest (RF) classifier for EEG training and classification. We used the benchmark clinical dataset provided by Bonn University (Andrzejak et al., 2001) to compare the seizure detection performance of our proposed method to those of the state-of-the-art techniques. We first examine how efficiently our proposed method performs under ideal conditions, i.e., when the EEG data is completely free of artifacts and noise. Results demonstrate that our approach achieves superior performance than those in literature; delivering the highest seizure detection rates of 100% sensitivity, 100% specificity, and 100% classification accuracy. More importantly, the performance of our approach is tested in the presence of muscle activities and eye-blinking artifacts as well as white noise. Our approach is proven to be robust against all of these interferences. It maintains high seizure detection performance even at high noise levels, making it more practical and workable in real-life and clinical settings.
Section snippets
Time-series EEG data
In this study, we conduct our seizure detection experiments on the benchmark clinical EEG dataset provided by Bonn University (Andrzejak et al., 2001). This is popular and well-known dataset for epileptic seizure detection. It comprises five different sets denoted A, B, C, D, and E; each set includes 100 single-channel EEG signals of 23.6 s duration each. Sets A and B contain surface EEG signals recorded from 5 healthy volunteers using the standard 10–20 system for EEG electrode placement (
Literature review
In this section, we briefly review the previous work in the context of epileptic seizure detection using EEG signals.
Methodology
This section demonstrates how the L1-penalized robust regression (L1PRR) model is applied to the EEG spectrum to extract the most discriminative EEG features pertinent to epileptic seizures. It also depicts how the L1PRR problem can be solved using a computationally-simple approach named block coordinate descent (BCD). Finally, it describes how the extracted features are used for training and testing random forest (RF) classifier.
Results and discussion
To evaluate the effectiveness of the proposed robust regression-based seizure detection approach, we compare its performance to those of the state-of-the-art detectors that use the same benchmark dataset. The detection performance was evaluated using the standard metrics of sensitivity, specificity, and classification accuracy (Hussein, Ward, Wand, & Mohamed, 2016).
Conclusion
This paper presents a robust method for automatic detection of epileptic seizures using EEG signals. This method relies on a robust feature extraction scheme that we developed based on L1-penalized robust regression (L1PRR). L1PRR can adaptively learn the most informative EEG features pertinent to seizures under ideal and real-life conditions. The performance of the proposed method is first examined under ideal conditions, i.e., when the EEG data is free of noise. Experimental results on a
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The first author is funded by Vanier Canada Graduate Scholarship from the Natural Sciences and Engineering Research Council of Canada (NSERC) http://www.vanier.gc.ca/en/nomination_processprocessus_de_mise_en_candidature_overview.html.