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Improvement of a convulsive seizure detector relying on accelerometer and electrodermal activity collected continuously by a wristband

  • February 2016
  • Conference: Epilepsy Pipeline Conference 2016
  • At: San Francisco (CA)
  • Affiliation: Empatica, Srl
Authors:
Francesco Onorati at Takeda
Francesco Onorati
Giulia Regalia at Empatica Inc.
Giulia Regalia
Chiara Caborni at Eni SpA - San Donato Milanese (MI)
Chiara Caborni
  • Eni SpA - San Donato Milanese (MI)
Rosalind W Picard at Singapore-MIT Alliance
Rosalind W Picard
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Abstract

Wrist acceleration (ACM), measured through a wearable device, has been used to automatically identify the motion of convulsive seizures such as generalized tonic-clonic seizures (GTCSs). ACM-based seizure detectors can trigger with many repetitive movements, and are affected by high false alarm rates, which might prevent daily life use. Recently, EDA and ACM features have been used to improve the classification performance of a seizure detector, reducing the false alarm rate in the detection of 16 GTCSs recorded from 7 patients. Here we present the results of further improvements, better matched to the real-time computational capacity of wearable devices, building a seizure detector from a higher number of patients and GTCSs (i.e., 38 GTCSs from 18 patients).
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Rationale
Acceleration (ACM), measured through a wrist-band, has been used to
automatically identify the motion of convulsive seizures such as generalized
tonic-clonic seizures (GTCSs) [1] [2]. However, ACM-based seizure
detectors have high false alarm rates, which might prevent daily life use.
Electrodermal activity (EDA) is a physiological signal reflecting the activity
of the sweat glands driven by the Sympathetic Nervous System. Direct
stimulation of some subcortical regions [3] elicits ipsilateral EDA responses.
Using both EDA and ACM features improves the classification performance
of a GTCS detector, reducing the false alarm rate [4] (16 GTCSs from 7
patients).
Using a larger feature set further lowers the false alarm rate while
preserving high sensitivity [5] (20 GTCSs from 9 patients).
Here we present the results of further improvements, using a smaller set of
features, better matched to use in patient-friendly wearable devices: 38
GTCSs from 18 patients, obtaining similarly high sensitivity (92-95%) with
low false alarm rates (0.56-2.26 per day).
F Onorati1, G Regalia1, C Caborni1, R Picard1,2*
1. Empatica, Inc, Cambridge, MA and Milan, Italy, www.empatica.com 2. MIT Media Lab, Massachusetts Institute of Technology, Cambridge, MA
*emails: fo@empatica.com or picard@media.mit.edu
References
[1] J Lockman et al., “Detection of seizure-like movements using a wrist accelerometer”,
EpilepsyandBehavior, v. 20, no. 4, pp. 638-641, 2011.
[2] S. Beniczky et al., “Detection of generalized tonic–clonic seizures by a wireless wrist accelerometer: A
prospective, multicenter study”, Epilepsia, v. 54, no. 4, pp. e58–e61, 2013.
[3] C. A. Mangina and J H Beuzeron-Mangina, “Direct electrical stimulation of specific human brain
structures and bilateral electrodermal activity”, IntJofPsychophysiology, v. 22, no. 1–2, pp. 1–8, 1996.
[4] M-Z. Poh et al., “Convulsive seizure detection using a wrist-worn electrodermal activity and
accelerometry biosensor,” Epilepsia, v. 53, no. 5, pp. e93–e97, 2012.
[5] G. Regalia et al., “An improved wrist-worn convulsive seizure detector based on accelerometry and
electrodermal activity sensors”, AmericanEpilepsySocietyannualmeeting 2015, abs no. 3096, 2015.
Methods
Labeled seizure data were collected during clinical video
EEG (v-EEG) monitoring.
Data: 44 recordings from 18 patients wearing a wrist-band
able to record EDA and 3-axes ACM (Figure 1(a)).
EDA and ACM signals were analyzed off-line using
proprietary software to clean the data and extract signal
features over a 10 sec. window every 2.5 sec (overlap: 75%).
Support Vector Machine (SVM) classifiers were trained: one
with 46 features (SVM_46), one with 30 features (SVM_30).
A leave-one-patient-out cross-validation approach was used
to test classifier sensitivity (Se) and false alarm rate (FAR),
defined as number of false alarms per day.
The optimal decision threshold was selected by receiver
operating characteristic (ROC) curve analysis.
Results
Recordings included 38 GTCSs from 18 patients over a total
of 1027 hours (42.7 days). Both classifiers show acceptable
FAR while keeping Se higher than 90% (Figure 2).
SVM_46 at Se=92% (i.e., 35 seizures detected out of 38)
showed FAR=0.56 and at Se=95% (i.e., 36 out of 38) FAR=2.26.
SVM_30 achieved similar performance (Se=92% and FAR=0.74,
Se=95% and FAR=2.02), using fewer features.
Conclusions
A seizure detection system based on ACM and EDA features was
developed using clinical data collected from a larger number of patients and
seizures with respect to previous work, capturing greater subject variability of
GTCS expression. The classifier we obtained allows a higher seizure
detection rate while maintaining an acceptable false alarm rate.
Furthermore, it is efficiently integrated into a wearable wristband to provide
real-time alarms of ongoing seizures.
WithgratitudetoDrs.DanFriedman,TobiasLoddenkemper,ClausReinsberger,RaniSarkis,andtheirteams
atNYU,BostonChildrensHospital,andBrigham&WomensHospital,BostonandtoJonathanBidwellandhis
teams at Emory and Childrens Healthcare of Atlanta Hospital,Atlanta, for their generous support collecting
sensordataandprovidinggoldstandardv-EEGlabeleddata.
Figure 1. (a) EDA and 3-axes ACM signals of two patients recorded
during a generalized tonic-clonic seizure (GTCS) with a wrist-worn
device. (b) Schematic workflow of the GTCSs detector.
Figure 2. Performance of the SVM classifier based on 46 EDA and ACM
features (SVM_46, blue line) and re-trained by using 30 features (SVM_30,
red line).
Figure 3. Distribution of FAR (top) and Sensitivity (bottom) of the new
SVM_30 GTCS detector across data from 18 patients (38 GTCSs, 1027
hours of recordings).
When using SVM_30 with a threshold set to provide Se 95%,
most of the patients (10/18 = 55%) had less than 1 false
alarm every 2 days and most (16/18 = 88%) had ALL of their
GTCSs detected (Figure 3).
Improvement of a convulsive seizure detector relying on
accelerometer and electrodermal activity collected continuously by a wristband
FEATURE
EXTRACTION GTCS DETECTOR
ACM
EDA
FEATURE
SET
NO GTCS
GTCS (ALARM)
(a)
(b)
PATIENT 1 PATIENT 2
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