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Nguyen H, Makaroff SN, Li CQ, Hoffman S, Yang Y, Lu H. High inductance magnetic-core coils have enhanced efficiency in inducing suprathreshold motor response in rats. Phys Med Biol 2023; 68:10.1088/1361-6560/ad0bde. [PMID: 37949063 PMCID: PMC10990567 DOI: 10.1088/1361-6560/ad0bde] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Accepted: 11/10/2023] [Indexed: 11/12/2023]
Abstract
Objective. Transcranial magnetic stimulation (TMS) coil design involves a tradeoff among multiple parameters, including magnetic flux density (B), inductance (L), induced electric (E) field, focality, penetration depth, coil heating, etc. Magnetic materials with high permeability have been suggested to enhance coil efficiency. However, the introduction of magnetic core invariably increases coil inductance compared to its air-core counterpart, which in turn weakens theEfield. Our lab previously reported a rodent-specific TMS coil with silicon steel magnetic core, achieving 2 mm focality. This study aims to better understand the tradeoffs amongB,L,andEin the presence of magnetic core.Approach. The magnetic core initially operates within the linear range, transitioning to the nonlinear range when it begins to saturate at high current levels and reverts to the linear range as coil current approaches zero; both linear and nonlinear analyses were performed. Linear analysis assumes a weak current condition when magnetic core is not saturated; a monophasic TMS circuit was employed for this purpose. Nonlinear analysis assumes a strong current condition with varying degrees of core saturation.Main results. Results reveal that, the secondaryEfield generated by the silicon steel core substantially changed the dynamics during TMS pulse. Linear and nonlinear analyses revealed that higher inductance coils produced stronger peakEfields and longerEfield waveforms. On a macroscopic scale, the effects of these two factors on neuronal activation could be conceptually explained through a one-time-constant linear membrane model. Four coils with differentB,L,andEcharacteristics were designed and constructed. BothEfield mapping and experiments on awake rats confirmed that inductance could be much higher than previously anticipated, provided that magnetic material possesses a high saturation threshold.Significance. Our results highlight the novel potentials of magnetic core in TMS coil designs, especially for small animals.
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Affiliation(s)
- Hieu Nguyen
- Neuroimaging Research Branch, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Baltimore, MD, United States of America
| | - Sergey N Makaroff
- Department of Electrical & Computer Engineering, Worcester Polytechnic Institute, Worcester, MA, United States of America
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
| | - Charlotte Qiong Li
- Neuroimaging Research Branch, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Baltimore, MD, United States of America
| | - Samantha Hoffman
- Neuroimaging Research Branch, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Baltimore, MD, United States of America
| | - Yihong Yang
- Neuroimaging Research Branch, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Baltimore, MD, United States of America
| | - Hanbing Lu
- Neuroimaging Research Branch, National Institute on Drug Abuse, Intramural Research Program, National Institutes of Health, Baltimore, MD, United States of America
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Scholten K, Xu H, Lu Z, Jiang W, Ortigoza-Diaz J, Petrossians A, Orler S, Gallonio R, Liu X, Song D, Meng E. Polymer Implantable Electrode Foundry: A shared resource for manufacturing polymer-based microelectrodes for neural interfaces. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.05.565048. [PMID: 37986740 PMCID: PMC10659271 DOI: 10.1101/2023.11.05.565048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2023]
Abstract
Large scale monitoring of neural activity at the single unit level can be achieved via electrophysiological recording using implanted microelectrodes. While neuroscience researchers have widely employed chronically implanted electrode-based interfaces for this purpose, a commonly encountered limitation is loss of highly resolved signals arising from immunological response over time. Next generation electrode-based interfaces improve longitudinal signal quality using the strategy of stabilizing the device-tissue interface with microelectrode arrays constructed from soft and flexible polymer materials. The limited availability of such polymer microelectrode arrays has restricted access to a small number of researchers able to build their own custom devices or who have developed specific collaborations with engineering researchers who can produce them. Here, a new technology resource model is introduced that seeks to widely increase access to polymer microelectrode arrays by the neuroscience research community. The Polymer Implantable Electrode (PIE) Foundry provides custom and standardized polymer microelectrode arrays as well as training and guidance on best-practices for implantation and chronic experiments.
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Affiliation(s)
- Kee Scholten
- Alfred E. Mann Department of Biomedical Engineering, University of Southern California, Los Angeles, USA
| | - Huijing Xu
- Alfred E. Mann Department of Biomedical Engineering, University of Southern California, Los Angeles, USA
| | - Zhouxiao Lu
- Alfred E. Mann Department of Biomedical Engineering, University of Southern California, Los Angeles, USA
| | - Wenxuan Jiang
- Alfred E. Mann Department of Biomedical Engineering, University of Southern California, Los Angeles, USA
| | - Jessica Ortigoza-Diaz
- Alfred E. Mann Department of Biomedical Engineering, University of Southern California, Los Angeles, USA
| | - Artin Petrossians
- Alfred E. Mann Department of Biomedical Engineering, University of Southern California, Los Angeles, USA
| | - Steven Orler
- Alfred E. Mann Department of Biomedical Engineering, University of Southern California, Los Angeles, USA
| | - Rachael Gallonio
- Alfred E. Mann Department of Biomedical Engineering, University of Southern California, Los Angeles, USA
| | - Xin Liu
- Alfred E. Mann Department of Biomedical Engineering, University of Southern California, Los Angeles, USA
| | - Dong Song
- Alfred E. Mann Department of Biomedical Engineering, University of Southern California, Los Angeles, USA
- Neuroscience Graduate Program, University of Southern California, Los Angeles, USA
| | - Ellis Meng
- Alfred E. Mann Department of Biomedical Engineering, University of Southern California, Los Angeles, USA
- Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, USA
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Lee KJ, Park B, Jang JW, Kim S. Magnetic stimulation of the sciatic nerve using an implantable high-inductance coil with low-intensity current. J Neural Eng 2023; 20:036035. [PMID: 37290431 DOI: 10.1088/1741-2552/acdcbb] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Accepted: 06/08/2023] [Indexed: 06/10/2023]
Abstract
Objective.Magnetic stimulation using implantable devices may offer a promising alternative to other stimulation methods such as transcranial magnetic stimulation (TMS) or electric stimulation using implantable devices. This alternative may increase the selectivity of stimulation compared to TMS, and eliminate the need to expose tissue to metals in the body, as is required in electric stimulation using implantable devices. However, previous studies of magnetic stimulation of the sciatic nerve used large coils, with a diameter of several tens of mm, and a current intensity in the order of kA.Approach.Since such large coils and high current intensity are not suitable for implantable devices, we investigated the feasibility of using a smaller implantable coil and lower current to elicit neuronal responses. A coil with a diameter of 3 mm and an inductance of 1 mH was used as the implantable stimulator.Main results.Beforein vivoexperiments, we used 3D computational models to estimate the minimum stimulus intensity required to elicit neuronal responses, resulting in a threshold current above 3.5 A. Inin vivoexperiments, we observed successful nerve stimulation via compound muscle action potentials elicited in hind-limb muscles when the applied current was above 3.8 A, a significantly reduced current than that used in conventional magnetic stimulation.Significance.We report the feasibility of magnetic stimulation using an implantable millimeter-sized coil and low current of a few amperes to elicit neural responses in peripheral nerves. The proposed method is expected to be an alternative to TMS, with the merit of improved selectivity in stimulation, and to electrical stimulation based on implantable devices, with the merit of avoiding the exposure of conducting metals to neural tissues.
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Affiliation(s)
- Kyeong Jae Lee
- Department of Robotics and Mechatronics Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, Republic of Korea
| | - Byungwook Park
- Department of Robotics and Mechatronics Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, Republic of Korea
| | - Jae-Won Jang
- Department of Robotics and Mechatronics Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, Republic of Korea
| | - Sohee Kim
- Department of Robotics and Mechatronics Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, Republic of Korea
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