Development of a Transfer-Function Measurement Procedure for the Evaluation's of MRI-Conditional Medical Devices at 3T
Canadian Conference on Electrical and Computer Engineering
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Radio frequency (RF) heating of leads on medically implanted devices is a critical patient safety matter in Magnetic Resonance Imaging (MRI). Safety is generally assessed via large-scale computer simulations, which relies on the use of a 'transfer function' (TF) approach in order to make the simulations sufficiently efficient to allow very large numbers of lead trajectories to be considered. In this work, a method to measure the transfer function of a simple stainless-steel wire with insulator was developed, which serves as proof-of-principle for use of the method in more realistic devices. A Finite-difference time-domain (FDTD) method was employed for comparison and to determine the induced electric field near a test wire which was then compared to the measured values. The TF method was applied to 127.6 MHz RF exposure (corresponding to a 3 T MRI system) using a custom developed R F probe in order to improve the accuracy and sensitivity of the measurements. Hydroxyethylcellulose (HEC) gel was used to mimic the lossy tissue environment of the human body. Reasonable agreement between the simulations and measurement were obtained and the method is under development for use at other frequencies of interest.