Comprehensive MRI Safety Assessment: Impact of Strain-Relief Loop Position, Lateral Movement, and Varying Field Strengths on RF-Induced Heating of Medical Implants
Magnetic Resonance Imaging (MRI) utilizes strong magnetic fields and radiofrequency (RF) waves to produce detailed images of human organs, tissues, and various anatomical structures. Despite its benefits, individuals with active implantable medical devices (AIMDs) and passive implantable medical devices (PIMDs) are often restricted from undergoing MRI due to potential RF interactions with the metallic components of these implants, which can lead to thermal damage to surrounding tissues. With the increasing prevalence of implants, it is essential to address factors contributing to RF-induced hazards to ensure the safety of patients. This dissertation focuses on three factors critical to the RF-induced heating hazards of implantable medical devices (IMDs). First, the impact of strain relief loop positions on RF heating of AIMDs at 1.5T MRI is studied. The AIMDs are constructed with an implantable pulse generator (IPG) and insulated leads with exposed electrodes. Surgeons often coil the leads into strain relief loops (SRLs) to accommodate extra length and reduce the risk of lead breakage. However, the positioning of these loops can significantly alter RF heating, and this study examines the mechanisms behind SRL positioning and its implications across various AIMDs and human models. The second part of this dissertation examines the impact of lateral patient movement on RF heating in AIMDs and PIMDs within wide-bore 3T MRI machines. Medical devices are typically labeled with the assumption that patients are centered laterally, but wide-bore systems allow lateral movement, which may alter labeling. Lastly, the dissertation examines the RF-induced heating behavior of PIMDs at 5T MRI, an emerging field with the recent FDA clearance for 5T MRI systems. The heating effects of PIMDs at 5T are compared with those at 1.5T and 3T, highlighting the differences in heating behavior across various field strengths. The findings of this dissertation provide valuable insights into the RF-induced heating risks of AIMDs and PIMDs across different MRI field strengths and patient positioning scenarios. By addressing key factors such as strain relief loop positioning, lateral movement in wide-bore MRI, and high-field MRI heating effects, this work contributes to the ongoing efforts to enhance MRI safety guidelines for implanted medical devices.
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