Assessing RF heating of active implantable medical devices in low-field MRI system

There is a steady growth in the use of implantable medical devices in the US and globally. More than 12 million Americans carry a form of orthopedic, cardiac, or neuromodulation device and the number grows by 100,000 annually. At least 75% of these patients will need magnetic resonance imaging (MRI) during their lifetime, with many requiring repeated examinations. Unfortunately, the interaction between MRI’s radiofrequency (RF) fields and conductive implants can lead to thermal injuries due to RF heating, making MRI inaccessible to most patients. Recently, low-field MRI scanners (0.55 T and below) have gained traction due to reduced cost and ease of siting. Because metal artifacts and risk of magnetic forces are reduced at lower fields, this class of scanners are widely publicized as implant-friendly albeit abject lack of evidence on their RF safety. This is concerning, because although SAR tends to be lower at lower field strengths, the scenario can dramatically change in the presence of elongated implants (such as leads) because of the antenna effect. Specifically, our (unpublished) data shows that up to 300% higher RF heating can occur around leads of a cardiac or a neuromodulation device at 0.55 T compared to 1.5 T MRI depending on the lead’s length. Because low-field scanners are now FDA-approved for clinical use, it is imperative to generate evidence-based knowledge as to their RF heating profile to prevent unintended injuries to patients. In direct response to this need, we propose a to leverage our expertise in MRI computational modeling and safety assessment and our access to state-of-the-art deep brain stimulation (DBS) and cardiovascular implantable electronic devices (CIEDs) to perform a rigorous and unbiased evaluation of RF heating of DBS and cardiac devices during MRI at 0.55 T. Specifically, we will augment our existing repository of patient-derived implant models to include models of pediatric and adult patients with CIEDs, and perform electromagnetic and thermal simulations to calculate RF heating of these devices during MRI at 0.55 T (unlabeled) and compare it with RF heating generated by a 1.5 T scanner (labeled). We will then develop age-specific and device-specific lookup tables that allow selection of imaging parameters that constraint RF heating during MRI at 0.55 T. Our team includes experts in MRI physics and safety, clinicians with expertise in pediatric electrophysiology and device implantation, as well as industrial partners in MRI and medical devices. The outcome of our work will generate the first body of knowledge of RF heating of electronic implants at low-field MRI, and provide the basis for evidence-based assessment of risk-benefit ratio of MRI exams. Digital models of pediatric and adults developed in this work will be made publicly available to provide a one-of-a-kind database for simulation and modeling in future applications.