Dataset Information

Comparison of spherical and realistically shaped boundary element head models for transcranial magnetic stimulation navigation.

ABSTRACT: MRI-guided real-time transcranial magnetic stimulation (TMS) navigators that apply electromagnetic modeling have improved the utility of TMS. However, their accuracy and speed depends on the assumed volume conductor geometry. Spherical models found in present navigators are computationally fast but may be inaccurate in some areas. Realistically shaped boundary-element models (BEMs) could increase accuracy at a moderate computational cost, but it is unknown which model features have the largest influence on accuracy. Thus, we compared different types of spherical models and BEMs.Globally and locally fitted spherical models and different BEMs with either one or three compartments and with different skull-to-brain conductivity ratios (1/1-1/80) were compared against a reference BEM.The one-compartment BEM at inner skull surface was almost as accurate as the reference BEM. Skull/brain conductivity ratio in the range 1/10-1/80 had only a minor influence. BEMs were superior to spherical models especially in frontal and temporal areas (up to 20mm localization and 40% intensity improvement); in motor cortex all models provided similar results.One-compartment BEMs offer a good balance between accuracy and computational cost.Realistically shaped BEMs may increase TMS navigation accuracy in several brain areas, such as in prefrontal regions often targeted in clinical applications.

SUBMITTER: Nummenmaa A

PROVIDER: S-EPMC3790855 | biostudies-literature | 2013 Oct

REPOSITORIES: biostudies-literature

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Comparison of spherical and realistically shaped boundary element head models for transcranial magnetic stimulation navigation.

Nummenmaa Aapo A Stenroos Matti M Ilmoniemi Risto J RJ Okada Yoshio C YC Hämäläinen Matti S MS Raij Tommi T

Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology 20130725 10

<h4>Objective</h4>MRI-guided real-time transcranial magnetic stimulation (TMS) navigators that apply electromagnetic modeling have improved the utility of TMS. However, their accuracy and speed depends on the assumed volume conductor geometry. Spherical models found in present navigators are computationally fast but may be inaccurate in some areas. Realistically shaped boundary-element models (BEMs) could increase accuracy at a moderate computational cost, but it is unknown which model features ...[more]

PMID: 23890512

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Project description:Objective.Transcranial magnetic stimulation (TMS) is a non-invasive technique widely used for neuromodulation. Animal models are essential for investigating the underlying mechanisms of TMS. However, the lack of miniaturized coils hinders the TMS studies in small animals, since most commercial coils are designed for humans and thus incapable of focal stimulation in small animals. Furthermore, it is difficult to perform electrophysiological recordings at the TMS focal point using conventional coils.Approach.We designed, fabricated, and tested a novel miniaturized TMS coil (4-by-7 mm) that consisted of a C-shaped iron powder core and insulated copper wires (30 turns). The resulting magnetic and electric fields were characterized with experimental measurements and finite element modeling. The efficacy of this coil in neuromodulation was validated with electrophysiological recordings of single-unit activities (SUAs), somatosensory evoked potentials (SSEPs), and motor evoked potentials (MEPs) in rats (n= 32) following repetitive TMS (rTMS; 3 min, 10 Hz).Main results.This coil could generate a maximum magnetic field of 460 mT and an electric field of 7.2 V m-1in the rat brain according to our simulations. With subthreshold rTMS focally delivered over the sensorimotor cortex, mean firing rates of primary somatosensory and motor cortical neurons significantly increased (154±5% and 160±9% from the baseline level, respectively); MEP and SSEP amplitude significantly increased (136±9%) and decreased (74±4%), respectively.Significance.This miniaturized C-shaped coil enabled focal TMS and concurrent electrophysiological recording/stimulation at the TMS focal point. It provided a useful tool to investigate the neural responses and underlying mechanisms of TMS in small animal models. Using this paradigm, we for the first time observed distinct modulatory effects on SUAs, SSEPs, and MEPs with the same rTMS protocol in anesthetized rats. These results suggested that multiple neurobiological mechanisms in the sensorimotor pathways were differentially modulated by rTMS.

Dataset Information

Comparison of spherical and realistically shaped boundary element head models for transcranial magnetic stimulation navigation.

Publications

Comparison of spherical and realistically shaped boundary element head models for transcranial magnetic stimulation navigation.

Similar Datasets

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