Development of an Absorbing Radio Frequency Shield for Safe Magnetic Resonance Imaging



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In this dissertation, we propose a design for an absorbing radio frequency shield (ARFS) that helps to reduce the RF-induced heating effects at the tip of a deep brain stimulation (DBS) lead. We first review the transfer function method used to evaluate RF-induced temperature rise at a DBS lead tip, including both theory and measurements. Next, an ARFS shell is designed for a generic head-trunk human model for basic electromagnetic full-wave and thermal validations. A multi-layered ARFS shell structure is proposed, which consists of a highly conducting layer (HCL) embedded in a thick absorbing conductive layer (ACL) and an insulating layer. Furthermore, a similar ARFS shell is applied to an anatomically-correct human model with implanted DBS leads. The temperature rise at the lead tip is calculated and the shielding effectiveness of the proposed ARFS is analyzed. A total number of 297 lead-pathways are investigated. A head-only ARFS is also discussed for higher flexibility. Finally, the lead-tip temperature rise is measured inside a phantom for seven typical lead trajectories, in order to validate the methodology and the effectiveness of the proposed ARFS.

The proposed ARFS structure is demonstrated to effectively reduce the temperature rise at the DBS lead tip for the trajectories studied in this dissertation. The average percentage reduction is 49.0% from the experimental results and 55.6% from the corresponding simulation results.



ARFS, RF-induced heating, Transfer function method, DBS lead