Abstracts

Rationale: Vagus nerve stimulation (VNS) has been widely used as an adjunctive treatment for some epilepsy. Direct exposure of any part of the VNS System to MR system radio-frequency (RF) transmitting coil can cause the RF heating near lead electrodes. This may cause pain, temporary injury, necrosis, or even permanent tissue damage. The analysis of RF heating effect is a complicated process, and it is function of patient size, coil type and its operating frequency, and patient s relative location within the coil. This work mainly focuses on the study of MRI-related heating of VNS residual leads when head coils are used as the transmitting coil.Methods: In this work, three members of the virtual family, adult male, adult female and boy namely, which represent different head sizes, are loaded under different RF transmitting head coils. These coils are commercially-used highpass and lowpass types and are designed for 1.5 Tesla and 3 Tesla systems. Commercial FDTD-based software, SEMCAD is used to evaluate the electric field distribution inside human body models. An approach calculating average electric field along the potential lead pathway is proposed to conservatively assess the RF induced heating.Results: The position variation in axial plane is not very sensitive compared to the distance variation along the bore direction of an MRI system. For different human models, boy model has possible higher heating compared to those from adult male and adult female models. Between highpass and lowpass coil type comparison, a lowpass coil seems to give a higher heating than that from a highpass coil. From the electric field data analysis, it appears for head coils studied here, 3T system lead to higher RF heating. Conclusions: Although the analysis of in-vivo MRI-related heating in this scenario is a complicated process due to the interaction of RF coil, human body and VNS lead, our preliminary estimation provides an effective reference to understand RF induced heating risks. According to our analysis, in most cases the electric field along VNS lead pathway is quite small under head transmitting coil. The worst case of maximum average electric field with all factors considered is under 125 V/m. Experimental will be conducted in the future to obtain the exact temperature rises.