Abstract
PurposeDeep brain stimulation (DBS) has proved to be effective in the treatment of movement disorders. However, the direct contact between the metal contacts of the DBS electrode and the brain can cause RF heating in magnetic resonance imaging (MRI) scanning, due to an increase of local specific absorption rate (SAR). Recently, micro coils (μMS) have demonstrated excitation of neuronal tissue through the electromagnetic induction both in vitro and in vivo experiments. In contrast to electrical stimulation, in μMS, there is no direct contact between the metal and the biological tissue.MethodsWe compared the heating of a μMS coil with a control case of a metal wire. The heating was induced by RF fields in a 1.5 T MRI head birdcage coil (often used for imaging patients with implants) at 64 MHz, and normalized results to 3.2 W/kg whole head average SAR.ResultsThe μMS coil or wire implants were placed inside an anatomically accurate head saline-gel filled phantom inserted in the RF coil, and we observed approximately 1°C initial temperature rise at the μMS coil, while the wire exhibited a 10°C temperature rise in the proximity of the exposed end. The numerical simulations showed a 32-times increase of local SAR induced at the tips of the metal wire compared to the μMS.ConclusionIn this work, we show with measurements and electromagnetic numerical simulations that the RF-induced increase in local SAR and induced heating during MRI scanning can be greatly reduced by using magnetic stimulation with the proposed μMS technology.
Highlights
Active implanted medical devices (AIMDs) based on electrical stimulation such as pacemakers (Gold et al, 2017), spinal cord stimulators (Patel et al, 2017), and cardioverter-defibrillators (Proclemer et al, 2001) have become a standard therapeutic choice to restore healthy neural activity in a wide range of medical conditions (D’Haese et al, 2010)
We show with electromagnetic numerical simulations that the RF-induced large local specific absorption rate (SAR) peak during magnetic resonance imaging (MRI) scanning can be reduced by 32 times using magnetic stimulation with a microcoil, which justified the significant reduction observed in tissue heating near the lead tip
This study shows that the antenna effect (Angelone et al, 2010) and, tissue heating during MRI can be reduced by using microscopic magnetic stimulation or μMS instead of traditional electrical stimulation, both with actual thermal measurements and numerical simulations
Summary
Active implanted medical devices (AIMDs) based on electrical stimulation such as pacemakers (Gold et al, 2017), spinal cord stimulators (Patel et al, 2017), and cardioverter-defibrillators (Proclemer et al, 2001) have become a standard therapeutic choice to restore healthy neural activity in a wide range of medical conditions (D’Haese et al, 2010). Deep brain stimulation (DBS) uses electrical stimulation for the treatment of several medically refractory brain disorders, including essential tremor, Parkinson’s disease, major depression, dystonia, Tourette syndrome, MRI-Heating of μMS: An Initial Study chronic pain, and obsessive-compulsive disorder (Lefaucheur et al, 2004; Walter and Vitek, 2004; Montgomery and Gale, 2008; Machado et al, 2009, 2012; Plow et al, 2009; Holtzheimer and Mayberg, 2011; Vitek et al, 2011; Machado and Baker, 2012; Plow et al, 2012; Graat et al, 2017; Clair et al, 2018) Despite their remarkable success, significant limitations are still curtailing the use of AIMDs. For instance, as none of AIMDs’ electrodes are currently completely magnetic resonance imaging (MRI) safe, a full exploration of their clinical utility is limited as there is a lost opportunity to bridge the gap between functional and structural MRI and neurophysiology.
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