Materials and Methods
inferior vena cava (IVC)/Fontan, PHN, expiratory breath, inspiratory breath
MINOR, PHN
This study is a descriptive design to evaluate the use of CMR in the SVR long-term follow-up cohort using standard CMR methods [As a part of the SVR III cohort study, participants were asked to undergo a non-contrast, non-sedated CMR exam to assess single ventricle function, blood flow in the major venous and arterial vessels including the superior vena cava (SVC), inferior vena cava (IVC)/Fontan conduit, right pulmonary artery (RPA), left pulmonary artery (LPA), neo-ascending aorta, descending aorta, pulmonary veins and tricuspid inflow. Exclusion criteria from CMR exam were the presence of an implantable device, including pacemakers and implantable defibrillators, or the need for anesthesia or sedation. Patients would still be enrolled in the SVR III study regardless of CMR study participation. If the participants underwent a clinically indicated CMR exam requiring contrast or sedation for clinical diagnostic purposes, and it included SVR III protocol components, it was used for analysis. The trial design, methodology, and complete SVR III protocol was published elsewhere. [MRI protocol: The CMR protocol was designed by a small committee of representatives from participating PHN sites. All studies were performed on 1.5 T scanners (Phillips, General Electric, or Siemens). Participants were studied while freely breathing except as otherwise indicated. Scans were acquired with retrospective ECG gating, maximum parallel imaging acceleration factor of 2, and 3 signal averages. The use of a spoiled gradient recalled echo was encouraged in the setting of prominent susceptibility artifact. The CMR protocol was performed in a stepwise fashion, prioritizing SSFP cine data for measurement of RVEF, and included:ECG gated 3 plane localizersECG gated balanced steady-state free precession (SSFP) cines: RV 2-chamber (vertical long axis), RV “4-chamber” (horizontal long axis), short axis stack through entire RV, and 3-chamber (outflow tract). Slice thickness 5–7 mm, pixel dimensions < 1.5 × 1.5 mm^2, TR < 4 ms, and TE ~ 2 ms.Non-contrast MRA: 3D respiratory navigator and ECG gated SSFP acquisition from the mid-liver to top of the aortic arch with acquired resolution 1.5 mm^3. The trigger delay was optimized for the heart rate and the shot duration was maintained < 130 ms.Phase contrast velocity acquisitions: SVC, IVC/Fontan, RPA, LPA, Neo ascending aorta, pulmonary veins, and tricuspid valve inflowIf CMR were performed as a clinically indicated exam and intravenous gadolinium contrast agent were used, additional data could include:Contrast enhanced magnetic resonance angiography (MRA) from the liver to top of the aortic arch during an inspiratory breath hold.Gradient echo inversion recovery late gadolinium enhancement (LGE) in the short axis stack, 2-chamber (VLA), 4-chamber (HLA), and 3-chamber (outflow tract) planes. LGE images were acquired with an expiratory breath hold if possible.Flow analysis in other vessels not included in the standard research protocol above could also be included.The anonymized CMR studies were transferred to the core laboratory via a commercial medical image cloud service (Ambra Health, New York). Before quantitative analysis study image quality was graded by the core laboratory on a 0–4 scale.0-uninterpretable1-poor: major artifacts compromising all data2-fair: major artifacts compromising some data3-good: minor artifacts without data compromise4-excellent: no or minimal artifacts.Study artifacts included missing slices, incomplete anatomical coverage, velocity aliasing, susceptibility effects due to intravascular devices and coils, patient motion, and ineffective cardiac gating. Images were determined to be adequate for analysis by two reviewers, and images had to be of a quality that allowed for endocardial and epicardial border identification over the entire ventricular mass and volume. Images were analyzed with CVI42 (Circle Cardiovascular Imaging, Calgary, Alberta). Image analysis included standard planimetry for ventricular volumes and ejection fraction and phase contrast velocity measurement. RV ejection fraction was the study primary outcome variable. If available, vessel diameter measurements were made on the non-contrast 3D SSFP MRA. DICOM header information was used to calculate the total scan, short axis function, and phase contrast velocity imaging times. Image time could not be calculated for some datasets due to the DICOM header information being removed during anonymization.