Vertical MRI for safe imaging of children with cardiac devices

Northwestern University At Chicago, Evanston IL

Investigators

Abstract

Abstract 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. Since intravenous access to heart in young patients is limited by the small vein size, the optimal approach to affixing a CIED to the heart of such patients 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, 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. This forces clinicians to resort to CT and X-ray imaging, which not only produce sub-optimal images but also expose the young children to significant doses of ionizing radiation, increasing their lifetime risk of cancer. 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 Our hypothesis is based on our simulation studies (unpublished) of a commercially available vertical MRI coil (Oasis, Fujifilm), which generated a 700% less local specific absorption rate (SAR) of energy deposition at the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. At present, there is highly limited literature available on CIED SAR specifically for vertical MRI scanners. We will develop a virtual family of pediatric patient models with trajectories of both epicardial and endocardial leads. We will also develop and experimentally validate ISO/TS 10974 standard compliant active implantable medical device (AIMD) model of the implants based on transfer function methods and use the model to predict 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). Based on the results, we will develop lookup tables to select imaging parameters that constrain RF heating to clinically safe levels.