How Much Detail is Needed in Modeling a Transcranial Magnetic Stimulation Figure-8 Coil: Measurements and Brain Simulations




Curated By TMS Solutions on Sep 14, 2017 2:14:00 AM
Curated By TMS Solutions

TITLE
How Much Detail is Needed in Modeling a Transcranial Magnetic Stimulation Figure-8 Coil: Measurements and Brain Simulations

AUTHORS
Petrov PI; Mandija S; Sommer IEC; van den Berg CAT; Neggers SFW. Institution Petrov, Petar I. Dept of Psychiatry, Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, the Netherlands. Mandija, Stefano. Center for Image Sciences, University Medical Center Utrecht, Utrecht, the Netherlands. Sommer, Iris E C. Dept of Psychiatry, Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, the Netherlands. van den Berg, Cornelis A T. Center for Image Sciences, University Medical Center Utrecht, Utrecht, the Netherlands. van den Berg, Cornelis A T. Department of radiotherapy, University Medical Center Utrecht, Utrecht, the Netherlands. Neggers, Sebastiaan F W. Dept of Psychiatry, Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, the Netherlands.

SOURCE
PLoS ONE [Electronic Resource]. 12(6):e0178952, 2017.

ABSTRACT
Despite TMS wide adoption, its spatial and temporal patterns of neuronal effects are not well understood. Although progress has been made in predicting induced currents in the brain using realistic finite element models (FEM), there is little consensus on how a magnetic field of a typical TMS coil should be modeled. Empirical validation of such models is limited and subject to several limitations.

METHODS
We evaluate and empirically validate models of a figure-of-eight TMS coil that are commonly used in published modeling studies, of increasing complexity: simple circular coil model; coil with in-plane spiral winding turns; and finally one with stacked spiral winding turns. We will assess the electric fields induced by all 3 coil models in the motor cortex using a computer FEM model. Biot-Savart models of discretized wires were used to approximate the 3 coil models of increasing complexity. We use a tailored MR based phase mapping technique to get a full 3D validation of the incident magnetic field induced in a cylindrical phantom by our TMS coil. FEM based simulations on a meshed 3D brain model consisting of five tissues types were performed, using two orthogonal coil orientations.

RESULTS
Substantial differences in the induced currents are observed, both theoretically and empirically, between highly idealized coils and coils with correctly modeled spiral winding turns. Thickness of the coil winding turns affect minimally the induced electric field, and it does not influence the predicted activation.

CONCLUSION
TMS coil models used in FEM simulations should include in-plane coil geometry in order to make reliable predictions of the incident field. Modeling the in-plane coil geometry is important to correctly simulate the induced electric field and to correctly make reliable predictions of neuronal activation.

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Topics: Mechanism of Action


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