RF-induced Heating Assessment and Heating Reduction Techniques for Partially-In and Partially-Out Medical Implants in MRI
Magnetic Resonance Imaging (MRI) is a non-invasive medical imaging technology that employs strong static, gradient, and radio frequency (RF) fields to produce detailed images of internal body structures. However, patients with partially-in and partially-out (PIPO) medical implants who require MRI scans are continually growing and often excluded from examinations or subjected to scans with extremely cautious RF power restrictions due to potential safety risks. One of the main safety concerns is tissue heating caused by the interaction between the RF field and the metallic PIPO implant. Tissue heating can be very localized, causing permanent damage to human tissue. Therefore, it is crucial to study such cases and develop effective techniques to mitigate RF-induced heating in the presence of PIPO medical implants. This dissertation mainly focuses on the RF-induced heating assessment and heating reduction methods for PIPO implants because the extended portion of the lead is placed outside the body, and it behaves like a long antenna. The process of evaluating RF heating is discussed in detail. Moreover, two methods are proposed to reduce RF-induced heating for PIPO medical implants. Firstly, ferrite material is applied to the external portion of the PIPO lead. A commercial PIPO device is used to demonstrate the effectiveness of the proposed method through experimental measurement and in-vivo simulations. Secondly, a trajectory modification method is proposed by winding the external portion of the PIPO medical leads. The concept is illustrated using two commercial PIPO devices and simplified insulated leads with varying lengths, winding diameters, insertion depths, and applications. Experimental and human body simulation results show a significant reduction in RF heating and the practicality of this proposed method. In addition, RF heating is evaluated for bipolar or dual-lead PIPO devices and compared with unipolar or single-lead PIPO devices. Commercial bipolar and unipolar PIPO devices and simplified solid leads are used for this study. The results of experimental and numerical simulations indicate that the coupling between adjacent leads of the bipolar PIPO system generated significantly lower heating than the unipolar PIPO system and could be comparatively less hazardous to use under MRI.
Magnetic Resonance Imaging (MRI), MRI Safety, Radio Frequency (RF) Heating Assessment and Mitigation, Partially-In and Partially-Out (PIPO) Medical Implants
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