Source imaging of deep-brain activity using the regional spatiotemporal Kalman filter

Laith Hamid; Nawar Habboush; Philipp Stern; Natia Japaridze; Ümit Aydin; Carsten H Wolters; Jens Christian Claussen; Ulrich Heute; Ulrich Stephani; Andreas Galka; Michael Siniatchkin

doi:10.1016/j.cmpb.2020.105830

Source imaging of deep-brain activity using the regional spatiotemporal Kalman filter

Comput Methods Programs Biomed. 2021 Mar:200:105830. doi: 10.1016/j.cmpb.2020.105830. Epub 2020 Nov 9.

Authors

Affiliations

¹ Department of Medical Psychology and Medical Sociology, University of Kiel, D-24113 Kiel, Germany. Electronic address: laithalajeel@gmail.com.
² Department of Medical Psychology and Medical Sociology, University of Kiel, D-24113 Kiel, Germany.
³ Institute of Theoretical Physics and Astrophysics, University of Kiel, D-24098 Kiel, Germany.
⁴ Department of Neuropediatrics, University of Kiel, D-24098 Kiel, Germany.
⁵ Institute for Biomagnetism and Biosignalanalysis, University of Münster, D-48149 Münster, Germany; Multimodal Functional Imaging Lab, Department of Physics and PERFORM Centre, Concordia University, Montreal, Canada.
⁶ Institute for Biomagnetism and Biosignalanalysis, University of Münster, D-48149 Münster, Germany.
⁷ Institute of Theoretical Physics and Astrophysics, University of Kiel, D-24098 Kiel, Germany; Institute for Neuro- and Bioinformatics, University of Lübeck, D-23562 Lübeck, Germany; Mathematics EAS, Aston University, Aston Triangle, Birmingham B3 7ET, United Kingdom.
⁸ Digital Signal Processing and System Theory Group, Faculty of Engineering, University of Kiel, D-24143 Kiel, Germany.
⁹ Department of Medical Psychology and Medical Sociology, University of Kiel, D-24113 Kiel, Germany; Department of Child and Adolescent Psychiatry and Psychotherapy, Evangelisches Klinikum Bethel gGmbH, D-33617 Bielefeld, Germany.

PMID: 33250282
DOI: 10.1016/j.cmpb.2020.105830

Abstract

Background and objective: The human brain displays rich and complex patterns of interaction within and among brain networks that involve both cortical and subcortical brain regions. Due to the limited spatial resolution of surface electroencephalography (EEG), EEG source imaging is used to reconstruct brain sources and investigate their spatial and temporal dynamics. The majority of EEG source imaging methods fail to detect activity from subcortical brain structures. The reconstruction of subcortical sources is a challenging task because the signal from these sources is weakened and mixed with artifacts and other signals from cortical sources. In this proof-of-principle study we present a novel EEG source imaging method, the regional spatiotemporal Kalman filter (RSTKF), that can detect deep brain activity.

Methods: The regional spatiotemporal Kalman filter (RSTKF) is a generalization of the spatiotemporal Kalman filter (STKF), which allows for the characterization of different regional dynamics in the brain. It is based on state-space modeling with spatially heterogeneous dynamical noise variances, since models with spatial and temporal homogeneity fail to describe the dynamical complexity of brain activity. First, RSTKF is tested using simulated EEG data from sources in the frontal lobe, putamen, and thalamus. After that, it is applied to non-averaged interictal epileptic spikes from a presurgical epilepsy patient with focal epileptic activity in the amygdalo-hippocampal complex. The results of RSTKF are compared to those of low-resolution brain electromagnetic tomography (LORETA) and of standard STKF.

Results: Only RSTKF is successful in consistently and accurately localizing the sources in deep brain regions. Additionally, RSTKF shows improved spatial resolution compared to LORETA and STKF.

Conclusions: RSTKF is a generalization of STKF that allows for accurate, focal, and consistent localization of sources, especially in the deeper brain areas. In contrast to standard source imaging methods, RSTKF may find application in the localization of the epileptogenic zone in deeper brain structures, such as mesial frontal and temporal lobe epilepsies, especially in EEG recordings for which no reliable averaged spike shape can be obtained due to lack of the necessary number of spikes required to reach a certain signal-to-noise ratio level after averaging.

Keywords: Deep sources; Dynamical inverse solution; EEG; EEG inverse problem; EEG source imaging; Electroencephalography; Epilepsy; Epileptiform activity; Kalman filter; LORETA; RSTKF; STKF; Source reconstruction; Spatiotemporal Kalman filter; State space; Subcortical sources.

MeSH terms

Brain / diagnostic imaging
Brain Mapping
Electroencephalography
Epilepsies, Partial*
Epilepsy*
Humans