Silicon Carbide and MRI: Towards Developing a MRI Safe Neural Interface

Mohammad Beygi; William Dominguez-Viqueira; Chenyin Feng; Gokhan Mumcu; Christopher L Frewin; Francesco La Via; Stephen E Saddow

doi:10.3390/mi12020126

Silicon Carbide and MRI: Towards Developing a MRI Safe Neural Interface

Micromachines (Basel). 2021 Jan 26;12(2):126. doi: 10.3390/mi12020126.

Authors

Mohammad Beygi¹, William Dominguez-Viqueira², Chenyin Feng³, Gokhan Mumcu¹, Christopher L Frewin⁴, Francesco La Via⁵, Stephen E Saddow^{1

6}

Affiliations

¹ Electrical Engineering Department, University of South Florida, Tampa, FL 33620, USA.
² Moffitt Cancer Center, Tampa, FL 33620, USA.
³ Department of Mechanical Engineering, University of South Florida, Tampa, FL 33620, USA.
⁴ NeuroNexus, LLC, Ann Arbor, MI 48108, USA.
⁵ IMM-CNR, Catania, I-95121 Sicily, Italy.
⁶ Department of Medical Engineering, University of South Florida, Tampa, FL 33620, USA.

Abstract

An essential method to investigate neuromodulation effects of an invasive neural interface (INI) is magnetic resonance imaging (MRI). Presently, MRI imaging of patients with neural implants is highly restricted in high field MRI (e.g., 3 T and higher) due to patient safety concerns. This results in lower resolution MRI images and, consequently, degrades the efficacy of MRI imaging for diagnostic purposes in these patients. Cubic silicon carbide (3C-SiC) is a biocompatible wide-band-gap semiconductor with a high thermal conductivity and magnetic susceptibility compatible with brain tissue. It also has modifiable electrical conductivity through doping level control. These properties can improve the MRI compliance of 3C-SiC INIs, specifically in high field MRI scanning. In this work, the MRI compliance of epitaxial SiC films grown on various Si wafers, used to implement a monolithic neural implant (all-SiC), was studied. Via finite element method (FEM) and Fourier-based simulations, the specific absorption rate (SAR), induced heating, and image artifacts caused by the portion of the implant within a brain tissue phantom located in a 7 T small animal MRI machine were estimated and measured. The specific goal was to compare implant materials; thus, the effect of leads outside the tissue was not considered. The results of the simulations were validated via phantom experiments in the same 7 T MRI system. The simulation and experimental results revealed that free-standing 3C-SiC films had little to no image artifacts compared to silicon and platinum reference materials inside the MRI at 7 T. In addition, FEM simulations predicted an ~30% SAR reduction for 3C-SiC compared to Pt. These initial simulations and experiments indicate an all-SiC INI may effectively reduce MRI induced heating and image artifacts in high field MRI. In order to evaluate the MRI safety of a closed-loop, fully functional all-SiC INI as per ISO/TS 10974:2018 standard, additional research and development is being conducted and will be reported at a later date.

Keywords: MRI compatibility; MRI image artifacts; SAR; finite element simulation; neural interface; silicon carbide.