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Robins PL, Makaroff SN, Dib M, Lisanby SH, Deng ZD. Electric Field Characteristics of Rotating Permanent Magnet Stimulation. Bioengineering (Basel) 2024; 11:258. [PMID: 38534532 PMCID: PMC10968657 DOI: 10.3390/bioengineering11030258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2024] [Revised: 02/26/2024] [Accepted: 03/03/2024] [Indexed: 03/28/2024] Open
Abstract
Neurostimulation devices that use rotating permanent magnets are being explored for their potential therapeutic benefits in patients with psychiatric and neurological disorders. This study aims to characterize the electric field (E-field) for ten configurations of rotating magnets using finite element analysis and phantom measurements. Various configurations were modeled, including single or multiple magnets, and bipolar or multipolar magnets, rotated at 10, 13.3, and 350 revolutions per second (rps). E-field strengths were also measured using a hollow sphere (r=9.2 cm) filled with a 0.9% sodium chloride solution and with a dipole probe. The E-field spatial distribution is determined by the magnets' dimensions, number of poles, direction of the magnetization, and axis of rotation, while the E-field strength is determined by the magnets' rotational frequency and magnetic field strength. The induced E-field strength on the surface of the head ranged between 0.0092 and 0.52 V/m. In the range of rotational frequencies applied, the induced E-field strengths were approximately an order or two of magnitude lower than those delivered by conventional transcranial magnetic stimulation. The impact of rotational frequency on E-field strength represents a confound in clinical trials that seek to tailor rotational frequency to individual neural oscillations. This factor could explain some of the variability observed in clinical trial outcomes.
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Affiliation(s)
- Pei L. Robins
- Computational Neurostimulation Research Program, Noninvasive Neuromodulation Unit, Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, Bethesda, MD 20892, USA; (P.L.R.); (S.H.L.)
| | - Sergey N. Makaroff
- Department of Electrical and Computer Engineering, Worcester Polytechnic Institute, Worcester, MA 01609, USA;
| | - Michael Dib
- Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742, USA;
| | - Sarah H. Lisanby
- Computational Neurostimulation Research Program, Noninvasive Neuromodulation Unit, Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, Bethesda, MD 20892, USA; (P.L.R.); (S.H.L.)
| | - Zhi-De Deng
- Computational Neurostimulation Research Program, Noninvasive Neuromodulation Unit, Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, Bethesda, MD 20892, USA; (P.L.R.); (S.H.L.)
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Robins PL, Makaroff SN, Dib M, Lisanby SH, Deng ZD. Electric field characteristics of rotating permanent magnet stimulation. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2024:2024.02.06.24302359. [PMID: 38370769 PMCID: PMC10871468 DOI: 10.1101/2024.02.06.24302359] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2024]
Abstract
Neurostimulation devices that use rotating permanent magnets are being explored for their potential therapeutic benefits in patients with psychiatric and neurological disorders. This study aims to characterize the electric field (E-field) for ten configurations of rotating magnets using finite element analysis and phantom measurements. Various configurations were modeled, including single or multiple magnets, bipolar or multipolar magnets, rotated at 10, 13.3, and 400 Hz. E-field strengths were also measured using a hollow sphere ( r = 9.2 cm) filled with a 0.9% sodium chloride solution and with a dipole probe. The E-field spatial distribution is determined by the magnets' dimensions, number of poles, direction of the magnetization, and axis of rotation, while the E-field strength is determined by the magnets' rotational frequency and magnetic field strength. The induced E-field strength on the surface of the head ranged between 0.0092 and 0.59 V/m. At the range of rotational frequencies applied, the induced E-field strengths were approximately an order or two of magnitude lower than those delivered by conventional transcranial magnetic stimulation. The impact of rotational frequency on E-field strength represents a previously unrecognized confound in clinical trials that seek to personalize stimulation frequency to individual neural oscillations and may represent a mechanism to explain some clinical trial results.
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Helekar SA, Thonhoff J, John BS, Nguyen L, Rosenfield DB, Appel SH. Modulation of spontaneous motor unit potentials by a new motor cortical magnetic stimulation method in amyotrophic lateral sclerosis. J Neurol 2022; 269:5487-5496. [PMID: 35704101 DOI: 10.1007/s00415-022-11214-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2022] [Revised: 05/28/2022] [Accepted: 06/03/2022] [Indexed: 12/01/2022]
Abstract
BACKGROUND Patients with amyotrophic lateral sclerosis (ALS) show altered cortical excitability. In this study, we measure modulation of spontaneous motor unit potentials (sMUPs) in hand muscles by multifocal cortical stimulation with a newly developed wearable transcranial rotating permanent magnet stimulator (TRPMS). METHODS We conducted cross-sectional and longitudinal electromyographic assessments in 40 and 20 ALS patients, respectively, of the stimulation-induced peak increase in the count of sMUPs in two hand muscles modulated by unilateral TRPMS stimulation of the primary motor cortex. We measured peak sMUP counts during several short sessions consisting of 10 stimuli over 60 s and 30 s post-stimulation periods. The longitudinal component involved an initial assessment at an early stage of the disease and up to five follow-up assessments at least 3 months apart. RESULTS TRPMS stimulation produced no device-related adverse effects. It showed an inverted V-shaped modulation of the peak sMUP counts as a function of ALS functional rating scale revised scores. The ratios of ALS subjects showing peak sMUP count increases between early and intermediate stages (χ2 = 4.086, df = 1, p = 0.043) and intermediate and late stages (χ2 = 4.29, df = 1, p = 0.038) in cross-sectional data were significantly different. Longitudinal assessment also produced a significant (z = 2.31, p = 0.021) result, with all subjects showing a post-initial visit increase in peak sMUP counts. CONCLUSIONS These results are consistent with delayed onset of upper motor neuronal dysfunction with respect to onset of clinical features. However, the above results need to be confirmed in a larger sample of patients and with multiple lines of evidence.
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Affiliation(s)
- Santosh A Helekar
- Stanley H. Appel Department of Neurology, Houston Methodist Neurological Institute, Houston Methodist Hospital, Houston, TX, 77030, USA. .,Weill Cornell Medical College, New York, NY, 10065, USA.
| | - Jason Thonhoff
- Stanley H. Appel Department of Neurology, Houston Methodist Neurological Institute, Houston Methodist Hospital, Houston, TX, 77030, USA
| | - Blessy S John
- Stanley H. Appel Department of Neurology, Houston Methodist Neurological Institute, Houston Methodist Hospital, Houston, TX, 77030, USA
| | - Lisa Nguyen
- Stanley H. Appel Department of Neurology, Houston Methodist Neurological Institute, Houston Methodist Hospital, Houston, TX, 77030, USA
| | - David B Rosenfield
- Stanley H. Appel Department of Neurology, Houston Methodist Neurological Institute, Houston Methodist Hospital, Houston, TX, 77030, USA.,Weill Cornell Medical College, New York, NY, 10065, USA
| | - Stanley H Appel
- Stanley H. Appel Department of Neurology, Houston Methodist Neurological Institute, Houston Methodist Hospital, Houston, TX, 77030, USA.,Weill Cornell Medical College, New York, NY, 10065, USA
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