Investigating the effects of external fields polarization on the coupling of pure magnetic waves in the human body in very low frequencies

Golestanirad, Laleh; Elahi, Behzad; Rashed-Mohassel, J.

doi:10.1186/1477-044x-5-3

Cited by 10 publications

(7 citation statements)

References 12 publications

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“…Examples include use of electrostatic finite element modeling to predict the volume of activated tissue in electrical brain stimulation ( McIntyre and Grill, 2001 ; Butson and McIntyre, 2006 ; Golestanirad et al, 2012b ), eddy current modeling to assess the distribution of cortical currents in magnetic brain stimulation ( Wagner T. et al, 2004 ; Wagner T.A. et al, 2004 ; Golestanirad et al, 2010 , 2012c ), and analysis of body exposure to low frequency magnetic fields and safety hazards due to motion of medical implants in magnetic fields ( Condon and Hadley, 2000 ; Golestani-Rad et al, 2007 ; Golestanirad et al, 2012a ). Recently, the role of numerical modeling has also been emphasized in safety assessment of MRI in patients with conductive implants ( Clare McElcheran and Graham, 2014 ; Golestanirad et al, 2017a , b ; McElcheran et al, 2017 ).…”

Section: Methodsmentioning

confidence: 99%

Solenoidal Micromagnetic Stimulation Enables Activation of Axons With Specific Orientation

et al. 2018

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Electrical stimulation of the central and peripheral nervous systems - such as deep brain stimulation, spinal cord stimulation, and epidural cortical stimulation are common therapeutic options increasingly used to treat a large variety of neurological and psychiatric conditions. Despite their remarkable success, there are limitations which if overcome, could enhance outcomes and potentially reduce common side-effects. Micromagnetic stimulation (μMS) was introduced to address some of these limitations. One of the most remarkable properties is that μMS is theoretically capable of activating neurons with specific axonal orientations. Here, we used computational electromagnetic models of the μMS coils adjacent to neuronal tissue combined with axon cable models to investigate μMS orientation-specific properties. We found a 20-fold reduction in the stimulation threshold of the preferred axonal orientation compared to the orthogonal direction. We also studied the directional specificity of μMS coils by recording the responses evoked in the inferior colliculus of rodents when a pulsed magnetic stimulus was applied to the surface of the dorsal cochlear nucleus. The results confirmed that the neuronal responses were highly sensitive to changes in the μMS coil orientation. Accordingly, our results suggest that μMS has the potential of stimulating target nuclei in the brain without affecting the surrounding white matter tracts.

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Section: Methodsmentioning

confidence: 99%

Solenoidal Micromagnetic Stimulation Enables Activation of Axons With Specific Orientation

et al. 2018

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“…Full-wave methods have been extensively used to address the interaction of electromagnetic waves and living tissues (Golestani-Rad et al, 2007; Golestanirad et al, 2010, 2012a,b). To investigate the performance of the proposed modified fractal electrodes, three-dimensional (3D) finite element models of fractal electrodes were developed inside a 3D homogenous conducting medium (Figure 4).…”

Section: Methodsmentioning

confidence: 99%

Analysis of fractal electrodes for efficient neural stimulation

Golestanirad¹,

Elahi²,

Molina³

et al. 2013

Front. Neuroeng.

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Planar electrodes are increasingly used in therapeutic neural stimulation techniques such as functional electrical stimulation, epidural spinal cord stimulation (ESCS), and cortical stimulation. Recently, optimized electrode geometries have been shown to increase the efficiency of neural stimulation by increasing the variation of current density on the electrode surface. In the present work, a new family of modified fractal electrode geometries is developed to enhance the efficiency of neural stimulation. It is shown that a promising approach in increasing the neural activation function is to increase the “edginess” of the electrode surface, a concept that is explained and quantified by fractal mathematics. Rigorous finite element simulations were performed to compute electric potential produced by proposed modified fractal geometries. The activation of 256 model axons positioned around the electrodes was then quantified, showing that modified fractal geometries required a 22% less input power while maintaining the same level of neural activation. Preliminary in vivo experiments investigating muscle evoked potentials due to median nerve stimulation showed encouraging results, supporting the feasibility of increasing neural stimulation efficiency using modified fractal geometries.

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“…The complexity of RF heating phenomenon and its large parameter space has been emphasized in experimental studies [43,47]. The application of electromagnetic simulations to better understand the phenomenology of electric and magnetic field interaction with the tissue has proven to be indispensable [32,[48][49][50][51][52][53][54][55][56][57][58][59][60][61]. One exquisite advantage of computational models is that they allow for a controlled and systematic change of design parameters and enable the assessment of multitude of design scenarios in a reasonable time.…”

Section: Simulationsmentioning

confidence: 99%

Reducing RF-induced Heating near Implanted Leads through High-Dielectric Capacitive Bleeding of Current (CBLOC)

Golestanirad

Angelone

Kirsch

et al. 2018

Preprint

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Patients with implanted medical devices such as deep brain stimulation or spinal cord stimulation are often unable to receive magnetic resonance imaging (MRI). This is because once the device is within the radiofrequency (RF) field of the MRI scanner, electrically conductive leads act as antenna, amplifying the RF energy deposition in the tissue and causing possible excessive tissue heating. Here we propose a novel concept in lead design in which 40cm lead wires are coated with a ~1.2mm layer of high dielectric constant material (155 < εr < 250) embedded in a weakly conductive insulation (σ = 20 S/m). The technique called High-Dielectric Capacitive Bleeding of Current, or CBLOC, works by forming a distributed capacitance along the lengths of the lead, efficiently dissipating RF energy before it reaches the exposed tip. Measurements during RF exposure at 64 MHz and 123 MHz demonstrated that CBLOC leads generated 20-fold less heating at 1.5 T, and 40-fold less heating at 3 T compared to control leads. Numerical simulations of RF exposure at 297 MHz (7T) predicted a 15-fold reduction in specific absorption rate (SAR) of RF energy around the tip of CBLOC leads compared to control leads.

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Investigating the effects of external fields polarization on the coupling of pure magnetic waves in the human body in very low frequencies

Cited by 10 publications

References 12 publications

Solenoidal Micromagnetic Stimulation Enables Activation of Axons With Specific Orientation

Solenoidal Micromagnetic Stimulation Enables Activation of Axons With Specific Orientation

Analysis of fractal electrodes for efficient neural stimulation

Reducing RF-induced Heating near Implanted Leads through High-Dielectric Capacitive Bleeding of Current (CBLOC)

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