Assessment of Blood Flow Mixing with Probabilistic 3D Flow Connectivity Mapping in Post-Fontan Patients.

In severe cases, infants can be born with only one functioning ventricle. Separately-timed surgical modifications are required to deliver blood to the heart and lungs in a functional manner. After the final surgical step, a so called 'Fontan circulation' results in the systemic venous return being supplied directly to the lungs through the pulmonary arteries. Surgical techniques have evolved such that these patients live into adulthood; however, some will develop serious complications. Outcome differences between patients with Fontan circulation are not fully understood but there is growing evidence that the hemodynamics of the Fontan connection may play an important role. It is suspected that patients with poor outcome have an uneven blood distribution at their Fontan connection, causing non-uniform delivery of protein-rich venous return. The goal of this research proposal is to develop new 4D MR imaging tools that measure blood mixing within the Fontan circulation and integrate uncertainties due to measurement noise with probabilistic 3D flow connectivity mapping. We will enable the evaluation of blood mixing in the Fontan connection as a potential biomarker for patients at risk for complications. To assess 3D blood flow in Fontan patients, this project includes the methods development of new 4D MR imaging tools that quantify blood mixing based on pathline connectivity. Reported mixing values will integrate measurement noise uncertainties by probabilistic 3D flow connectivity mapping. 3D CINE bSSFP imaging will be combined with 4D flow to improve phase contrast MR angiography (PC-MRA) calculations for the extraction of the Fontan vessel geometry. The 3D CINE-optimized PC-MRA will be compared to the contrast-enhanced MRA reference standard. We will test mixing quantification using CFD models of idealized Fontan geometries. MR compatible flow phantoms will be constructed to validate the data analysis tools (mixing, probabilistic flow connectivity mapping) using in-vitro 4D flow MRI. Combined 3D CINE bSSFP and 4D flow MRI to assess blood mixing and probabilistic 3D flow connectivity mapping will be applied in a cohort of post-Fontan patients. We will test the hypotheses that 1) quantitative measures of distribution to the left and right lung correlate with the symptom severity of failing Fontan and 2) geometry of the surgically achieved Fontan circulation is an independent predictor of changes in flow distributions in the pulmonary arteries.