Simulation and measurement of RF heating of cardiovascular implantable electronic devices (CIEDs) in adults and pediatric phantoms in OASIS vertical MRI systems

Infants and children with congenital heart defects (CHD), inherited arrhythmia syndromes, and congenital disorders of cardiac conduction often require cardiac implantable electronic devices (CIEDs). Some infants receive a CIED within hours, or even minutes, of birth. The optimal approach to affixing a CIED to the heart of a young patient is to open the chest and sew the cardiac lead directly to the myocardium (“epicardial leads”) as opposed to passing it through veins and affix to the inside of the heart (“endocardial leads”). Unfortunately, however, once epicardial leads have been implanted, the patient is no longer eligible to receive magnetic resonance imaging (MRI) exams. This is because electric fields produced by the MRI machine can interact with implanted leads, causing excessive tissue heating and potential thermal injuries. MR-conditional CIEDs with endocardial leads have been approved by the FDA, but no equivalent system exists for children with epicardial leads. This leaves the most vulnerable patient population unable to receive the standard of care that they need the most, as children with heart disease often require complex clinical decision making which highly benefits from MRI’s sensitivity and accuracy. The problem is exacerbated by the fact that there is no straightforward method to extract epicardial leads, so children who receive these leads are excluded from benefits of MRI for life, even if an FDA-approved endocardial system is later placed when they are older. Our long-term goal is to make MRI technology fully accessible to children with CIEDs. Here we propose to test the hypothesis that vertical MRI scanners with a 90° rotated RF field orientation generate substantially less RF heating around leads of epicardial CIEDs with realistic and clinically relevant configurations. Our hypothesis is based on our simulation studies (unpublished) of a commercially available vertical MRI coil (Oasis, Fujifilm), which generated a 700% less local specific absorption rate (SAR) of energy deposition at the tips of epicardial leads in a pediatric patient model compared to the status-quo quadrature birdcage body coil. Currently, no CIED SAR literature exists for vertical MRI scanners. Our work will be the first assessment of the possibility of safe CIED imaging in children with the new generation of open-bore vertical MRI systems, now available at 1.2 T field-strength and capable of high-resolution structural imaging. We will develop a virtual family of pediatric and adult patient models with both epicardial and endocardial leads, perform numerical simulations to calculate RF heating during MRI in 1.2 T vertical systems (unlabeled) and compare to RF heating of endocardial CIEDs in horizontal systems at 1.5 T (labeled), verify our simulation results in phantom experiments, and use verified computational models to develop lookup tables to select imaging parameters that constraint RF heating to clinically safe levels.