Localization Accuracy of Electric and Magnetic Source Imaging in Epilepsy with a 3D Printed Human Head Phantom
Abstract number :
1.19
Submission category :
3. Neurophysiology / 3G. Computational Analysis & Modeling of EEG
Year :
2022
Submission ID :
2204023
Source :
www.aesnet.org
Presentation date :
12/3/2022 12:00:00 PM
Published date :
Nov 22, 2022, 05:23 AM
Authors :
Saeed Jahromi, MS – the University of Texas at Arlington; Rupesh Chikara, PhD – Post doctoral, Department of Bioengineering, the University of Texas at Arlington; Steven Stufflebeam, MD – Athinoula A. Martinos Center for Biomedical Imaging – Massachusetts General Hospital & Harvard Medical School; Mark Ottensmeyer, PhD – Department of Radiology – Massachusetts General Hospital; Gianluca De Novi, PhD – Department of Radiology – Massachusetts General Hospital; Christos Papadelis, PhD – Jane and John Justin Neurosciences Center – Cook Children’s Health Care System
Rationale: Electric and magnetic source imaging (ESI/MSI) play a critical role in the presurgical evaluation of patients with focal drug-resistant epilepsy (DRE). A growing body of in-vivo studies has investigated ESI/MSI in the presurgical evaluation of patients with DRE by evaluating their clinical utility and localization accuracy. Yet, in-vivo studies lack a solid ground truth for the exact location of the epileptic focus since scalp EEG and magnetoencephalography (MEG) recordings are rarely performed simultaneously with intracranial EEG (iEEG), and thus may capture different sources. An effective way to validate the localization accuracy of ESI/MSI is through head-shaped phantoms that resemble the electromagnetic properties of the human head. Here, we report the design, fabrication, and testing of a three-layer human head phantom that can produce realistic interictal epileptiform discharges (IEDs) and assess the ability of ESI/MSI to localize cortical and deep brain sources.
Methods: We simulated materials having electromagnetic properties of human head tissues (i.e., brain, skull, and scalp) by mixing chopped carbon fibers with liquid silicone in different mixing ratios. The produced materials were initially tested in terms of static resistance. The concept behind the phantom’s design was to pour these materials inside molds, which had the shape of the brain, skull, and scalp (Figure 1A). Based on segmented surfaces extracted from the normal MRI of a 3-year-old child with DRE (Figure 1B), we 3D printed molds of the scalp, skull, and brain (Figure 1C). We inserted into the innermost layer (brain) 20 dipolar sources representing conditions of varying source localization difficulty (e.g., cortical, subcortical, and deep brain sources) (Figure 1C). We recorded simultaneous MEG and HD-EEG (1 kHz sampling rate) while dipolar sources were activated through a waveform generator (Figure 1D). Using computed tomography, we marked the locations of the implanted sources. Finally, we performed source localization at the peak of each spike using equivalent current dipole (ECD) (Goodness of Fit > 90%) using Brainstorm.
Results: Realistic IEDs in terms of amplitude, duration, and morphology were obtained in both MEG and HD-EEG recordings (Figure 2A,B). For MEG data, two dipolar sources placed close to the left insula and right brainstem had a localization error of 8.6 ± 0 mm and 8.6 ± 2.9 mm, respectively (Figure 2C). For HD-EEG data, the dipolar source placed close to the right brainstem had a localization error of 11.4 ± 0 mm (Figure 2C).
Conclusions: Based on advances in 3D printed technology and bioengineering concepts, we present here for the first time the fabrication and testing of a phantom that resembles the electromagnetic properties of the human head. The phantom is able to generate signals that have the characteristics of actual IEDs. Such technology can allow the reliable assessment of the localization abilities of MEG and HD-EEG in different clinical scenarios and further serve as a tool for educational purposes.
Funding: RO1NS104116-01A1 by NINDS
Neurophysiology