On the development of equivalent medium for active implantable device radiofrequency safety assessment

PURPOSE: To develop the equivalent medium theorem that can be used to perform accurate evaluation of implantable device safety under MRI exposure. METHODS: Numerical methods were used to determine the equivalent medium parameters along clinically relevant trajectories inside a human body model. Additionally, numerical and experimental investigations were performed using both a computational human body model and an inhomogeneous phantom to demonstrate the effectiveness of the method. RESULTS: The equivalent medium parameters, which are determined from a simplified lead configuration, are independent of the lead types and lead design parameters and only depend on the lead trajectories. Experimental investigations using an inhomogeneous phantom showed excellent agreement between the computational predicted values and the direct measured temperature rises indicating the effectiveness and accuracy of this method. CONCLUSION: For the models based on multiple patient trajectories studied, it demonstrates that the equivalent medium theorem is valid for leads of different types and designs, as long as the lead trajectories are determined.