Vertical MRI for safe imaging of children with cardiac devices

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hypothesis is based on our simulation studies (unpublished) of a commercially available vertical MRI coil (Oasis,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.

Grant Number: 1R03EB037729-01
NIH Institute/Center: NIH
Principal Investigator: Bhumi Bhusal