Analysis of Metallic Shielding for Reduction of RF Induced Heating of Electrode During MRI for Active Implants
Abstract
The options available to patients with implantable devices are limited. It is because there are multiple interactions between the MRI environment and the implantable medical devices. The three main components of MRI systems- static magnet, RF coil, and a gradient coil- interact with the implantable medical devices. These interactions can cause force, torque, device vibrations and RF-induced heating. Among all these potential hazards is the heating caused by the RF electromagnetic field. The lead wires of the implants can act as antennas and pick up the electric field generated by the RF coil. This results in the induced current traveling along the length of the device that will dissipate as heat where it is coupled to tissue. The combination of critically sensitive tissues and high heat makes this interaction the most significant risk for patient safety. Hence, there arises a need to design effective techniques that can minimize RF heating induced during an MRI. The technique of shielding has been proven to reduce RF-induced heating. The focus of current research is to provide analysis of shielding technique for reduction of RF-induced heating of electrodes during MRI. Shielded leads have been developed as a method to reduce RF-heating responsible for temperature rise at the electrodes. The purpose of this work is to provide a quantitative understanding of how a conducting metallic shield over a lead will reduce RF heating at the electrode during MRI scans. A physical model and equations for reduction of RF heating by a shielded lead are presented. Temperature rises are calculated for different lengths of shielded and unshielded leads. Confirming measurements are made for a quarter-wavelength coaxial cable model of the lead. Measured temperature rise and transfer function depended on terminations conditions, with the shorted lead exhibiting the temperature rise sixteen times less than an open-ended lead. The information provided by this work is expected to facilitate the development of lead wires with reduced RF-induced heating. The availability of lead wires with reduced heating will allow expanded access to MRI by patients with implantable devices.
Degree
Ph.D.
Advisors
Nyenhuis, Purdue University.
Subject Area
Electrical engineering|Medical imaging|Electromagnetics
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