Simulations of a birdcage coil B<inf>1</inf>+ field on a human body model for designing a 3T multichannel TMS/MRI head coil array

Abstract

This article considers a new type of integrated multichannel Transcranial Magnetic Stimulator and Magnetic Resonance Imaging (TMS/MRI) system at 3T that is currently being designed. The system will enable unprecedented spatiotemporal control of the TMS-induced electric fields (E-fields) with simultaneous rapid whole-head MRI acquisition to record the brain activity. A critical design question is how TMS coil elements interact with the transmit field (B 1 + ) of the volume coil integrated in 3T MRI systems. In general, the TMS coils are not designed to have any resonant characteristics at the MRI frequency, they may potentially disturb the RF field due to the eddy currents induced. This is especially a concern with a multichannel TMS setup where the subject's head will be largely covered with the stimulation coils. Therefore, we investigated this problem by computational simulations with realistic TMS coil geometries and a birdcage transmit coil in conjunction with a human body model. We compared the B 1 + interaction effects of a commercially available MR-compatible TMS coil with our coil prototype. In both cases, the results show small local changes in the transmit field B 1 + of the birdcage coil. Maximal Average

The effect of simulation strategies on prediction of power deposition in the tissue around electronic implants during magnetic resonance imaging

“…These include, for example, modification of MRI hardware (Golestanirad et al 2016, McElcheran et al 2016, McElcheran et al 2017a, McElcheran et al 2017b, McElcheran et al 2017c, Wei et al 2018, Golestanirad et al 2019b, McElcheran et al 2019, Kazemivalipour et al 2019 or the implant's trajectory (Golestanirad et al 2017a, Golestanirad et al 2017d, Golestanirad et al 2019c to reduce the coupling of electric fields and implanted leads, modification of lead's geometry and/or material to reduce induced RF currents (Bottomley et al 2010, Serano et al 2015, McCabe and Scott 2017, Golestanirad et al 2019a, and protocol optimization (Golestanirad et al 2016, Golestanirad et al 2019d. These and many other MRI safety studies rely on use of numerical simulations to predict the interaction of MRI electric and magnetic fields with human body and the implant (Neufeld et al 2011, Golestanirad et al 2012, Wolf et al 2013, Li et al 2015, Alon et al 2016, Navarro de Lara et al 2018, Liu et al 2018, Liu et al 2019, Navarro de Lara et al 2020. Another possible approach makes use of thermal modeling and MR thermometry together that may help determine the heating and improve patient safety online (Shrivastava et al 2012).…”

Reducing RF-Induced Heating Near Implanted Leads Through High-Dielectric Capacitive Bleeding of Current (CBLOC)

“…In general, the performance of CBLOC leads depends on the interplay between plurality of factors, including frequency and geometry of MRI RF transmitter, thickness and electric properties of HDC coating and insulator, as well as the trajectory of the lead in the phantom. 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][62]. 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.…”

Modeling Primary Fields of TMS Coils with the Fast Multipole Method

“…Figure 2a is a simplified TMS-MEG coil (Tristan Technologies, San Diego); Fig. 2b is a three-axis multichannel TMS coil array ( [22]; Navarro de Lara et al, 2019); Fig. 2c is a simplified MRi-B91 TMS-MRI coil model (MagVenture, Denmark) with elliptical conductors of a rectangular crosssection; Fig.…”