Abstract
Purpose: Multichannel Transcranial Magnetic Stimulation (mTMS) arrays enable multiple sites to be stimulated simultaneously or sequentially under electronic control without moving the system's stimulation coils. Here, we build and characterize the performance of a novel modular 3-axis TMS coil that can be utilized as a unit element in large-scale multichannel TMS arrays. Methods: We determined the basic physical characteristics of the 3-axis TMS coil x-, y- and z-elements using a custom 2-channel programmable stimulator prototype. We mapped the temporal rate-of-change of the induced magnetic field (dB/dt) on a 2D plane parallel to the coil surface (including an extended line for full spatial coverage) and compared those values with predictions from magnetic field simulations. Temperature measurements were carried out to assess the incorporated air-cooling method. We measured the mutual and self-inductances of the x/y/z-elements to assess coupling between them. Additionally, we measured and calculated the coupling between z-elements in the array configuration. Finally, we performed electric field simulations to evaluate the stimulation intensity and focality of the coil and compared the results to conventional TMS coils as well as demonstrated suitability of the 3-axis coil for a multichannel array configuration. Results: The experimentally obtained dB/dt values validated the computational model of the 3-axis coil and therefore confirmed that both the coil and stimulator system are operating as intended. The air-cooling system was effective for brief high-frequency pulse trains and extended single- and paired-pulse TMS protocols. The electromagnetic simulations suggested that an array of the 3-axis coils would have comparable stimulation intensity to conventional TMS coils, therefore enabling clearly suprathreshold stimulation of the human brain. The recorded coil coupling between the x/y/z-elements was < 1% and the maximal coupling between z-elements in the array configuration was 1.8% and 3.4% for the measured and calculated values, respectively. Conclusion: We presented a 3-axis coil intended for multichannel TMS arrays. The electromagnetic measurements and simulations verified that the coil fabrication met the desired specifications and that the inductive coupling between the elements was negligible. The air-cooled 3-axis TMS coil appears suitable to be used as an element in multichannel TMS arrays.
| Original language | English (US) |
|---|---|
| Article number | 117355 |
| Journal | Neuroimage |
| Volume | 224 |
| DOIs | |
| State | Published - Jan 1 2021 |
Funding
L.N.L. is a named inventor in a TMS-related patent (US9924889). A.M., K.P. and D.P. are employed by Tristan Technologies, Inc., San Diego, that is a for-profit company with commercial interests in TMS device development. Y.O. is the owner of Moment Technologies, LLC, Boston, MA, that is a for-profit company with commercial interest in TMS device development. Both Tristan Technologies and Moment Technologies are recipients of subawards from the NIH-funded grant R01MH111829 supporting this work. S.N.M is partially employed by NEVA (Bio)electromagnetics, LLC, Yarmouth Port, MA, that is a for-profit company with commercial interest in electromagnetic human modeling and neuromodulation device development. A.N. and T.R. are named inventors in TMS-related patent applications. M.D. declares no competing interests. We want to thank Henrik Corfitzen, Jesper Bruus-Jensen and Yordan Todorov (MagVenture, Farum, Denmark) for providing information about dimensions of the TMS coils (H.C. and Y.T.) as well as continuing support during the tests with the custom-built 2-channel stimulator (H.C. and J.B.-J.). We also thank Tori Turpin (MGH Martinos Center) for helpful comments on the manuscript. Research supported by NIH R00EB015445 , R01MH111829 and the Ralph and Mariam Falk Medical Research Trust.
Keywords
- 3-axis coil
- E-field simulations
- Multichannel TMS
- TMS array
ASJC Scopus subject areas
- Neurology
- Cognitive Neuroscience