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Coil design considerations for deep transcranial magnetic stimulation.

Publication ,  Journal Article
Deng, Z-D; Lisanby, SH; Peterchev, AV
Published in: Clin Neurophysiol
June 2014

OBJECTIVES: To explore the field characteristics and design tradeoffs of coils for deep transcranial magnetic stimulation (dTMS). METHODS: We simulated parametrically two dTMS coil designs on a spherical head model using the finite element method, and compare them with five commercial TMS coils, including two that are FDA approved for the treatment of depression (ferromagnetic-core figure-8 and H1 coil). RESULTS: Smaller coils have a focality advantage over larger coils; however, this advantage diminishes with increasing target depth. Smaller coils have the disadvantage of producing stronger field in the superficial cortex and requiring more energy. When the coil dimensions are large relative to the head size, the electric field decay in depth becomes linear, indicating that, at best, the electric field attenuation is directly proportional to the depth of the target. Ferromagnetic cores improve electrical efficiency for targeting superficial brain areas; however magnetic saturation reduces the effectiveness of the core for deeper targets, especially for highly focal coils. Distancing winding segments from the head, as in the H1 coil, increases the required stimulation energy. CONCLUSIONS: Among standard commercial coils, the double cone coil offers high energy efficiency and balance between stimulated volume and superficial field strength. Direct TMS of targets at depths of ~4 cm or more results in superficial stimulation strength that exceeds the upper limit in current rTMS safety guidelines. Approaching depths of ~6 cm is almost certainly unsafe considering the excessive superficial stimulation strength and activated brain volume. SIGNIFICANCE: Coil design limitations and tradeoffs are important for rational and safe exploration of dTMS.

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Published In

Clin Neurophysiol

DOI

EISSN

1872-8952

Publication Date

June 2014

Volume

125

Issue

6

Start / End Page

1202 / 1212

Location

Netherlands

Related Subject Headings

  • Transcranial Magnetic Stimulation
  • Neurology & Neurosurgery
  • Models, Anatomic
  • Humans
  • Guidelines as Topic
  • Finite Element Analysis
  • Equipment Safety
  • Equipment Design
  • 3209 Neurosciences
  • 17 Psychology and Cognitive Sciences
 

Citation

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Deng, Z.-D., Lisanby, S. H., & Peterchev, A. V. (2014). Coil design considerations for deep transcranial magnetic stimulation. Clin Neurophysiol, 125(6), 1202–1212. https://doi.org/10.1016/j.clinph.2013.11.038
Deng, Zhi-De, Sarah H. Lisanby, and Angel V. Peterchev. “Coil design considerations for deep transcranial magnetic stimulation.Clin Neurophysiol 125, no. 6 (June 2014): 1202–12. https://doi.org/10.1016/j.clinph.2013.11.038.
Deng Z-D, Lisanby SH, Peterchev AV. Coil design considerations for deep transcranial magnetic stimulation. Clin Neurophysiol. 2014 Jun;125(6):1202–12.
Deng, Zhi-De, et al. “Coil design considerations for deep transcranial magnetic stimulation.Clin Neurophysiol, vol. 125, no. 6, June 2014, pp. 1202–12. Pubmed, doi:10.1016/j.clinph.2013.11.038.
Deng Z-D, Lisanby SH, Peterchev AV. Coil design considerations for deep transcranial magnetic stimulation. Clin Neurophysiol. 2014 Jun;125(6):1202–1212.
Journal cover image

Published In

Clin Neurophysiol

DOI

EISSN

1872-8952

Publication Date

June 2014

Volume

125

Issue

6

Start / End Page

1202 / 1212

Location

Netherlands

Related Subject Headings

  • Transcranial Magnetic Stimulation
  • Neurology & Neurosurgery
  • Models, Anatomic
  • Humans
  • Guidelines as Topic
  • Finite Element Analysis
  • Equipment Safety
  • Equipment Design
  • 3209 Neurosciences
  • 17 Psychology and Cognitive Sciences