MRI Compatible Retention System for a Bone Conduction Device: An evaluation of required design changes to Sentio Ti™ Implant for compliance with 3 T MRI scans

Abstract

Magnetic resonance imaging (MRI) compatibility is an important requirement for implantable hearing devices, as increasing numbers of patients are expected to undergo MRI examinations during their lifetime. This study evaluates the mechanical response of the Sentio Ti™ transcutaneous bone conduction implant under magnetic torque corresponding to a 3 T MRI environment, with the aim of assessing whether the current design meets established performance criteria defined at 1.5 T. A computational approach was conducted using an existing, experimentally validated finite element model developed in LS-DYNA. The model was used to simulate implant displacement and contact pressure on surrounding soft tissue under worst-case magnetic torque conditions. The torque at 3 T was estimated based on proportional scaling from 1.5 T. Parametric studies were conducted to investigate the influence of reinforcement wire properties and silicone stiffness on implant behaviour. In addition, alternative retention magnet concepts were explored through a concept generation process. The results show that increasing the magnetic field strength from 1.5 T to 3 T leads to a significant increase in mechanical response, with displacement rising from 3.12 mm to 5.65 mm and average contact pressure increasing by a factor of approximately 2–3. Among the investigated parameters, reinforcement wire diameter was found to have the greatest influence on reducing both displacement and contact pressure. However, achieving equivalent performance to 1.5 T through structural modifications alone requires design changes that may be impractical within current geometric constraints. Combined modifications of wire diameter and silicone stiffness provided more feasible solutions, although they did not fully replicate baseline pressure levels. The findings indicate that while structural optimization can significantly improve performance, it may not be sufficient to ensure MRI compatibility at 3 T without compromising design constraints. Modifications to the retention magnet system, such as enabling rotational alignment or controlled movement, are therefore identified as promising strategies. This work provides quantitative insight into implant behaviour at higher magnetic field strengths and supports the development of next-generation MRI-compatible bone conduction devices.