Quantification and origin of differential pulmonary blood flow in patients with a Fontan circulation

Methods Patients with a Fontan circulation were prospectively consented to undergo three dimensional phase contrast (4Dflow) imaging during a clinical cardiac MRI evaluation which also included standard two dimensional phase contrast (2D-PC) imaging of all pertinent vessels. Differential pulmonary blood flow was calculated using standard 2D-PC imaging of the right and left pulmonary arteries (RPA and LPA). On the 4Dflow datasets, an expert reader defined cross sections of the RPA, LPA, and the superior and inferior venae cavae (SVC and IVC) within the Fontan circuit using prototype 4Dflow software (Siemens Healthcare, Erlangen, Germany). These defined the analysis and seed planes respectively. Particles were emitted from either the SVC or IVC plane, and quantification was performed at the outlets using the 4Dflow software. The 3D pathlines were then exported for further analysis. Custom software was written in MATLAB (Mathworks, Natick, MA) for flow quantification. The terminal spatial position of each particle was determined. The number of particles that crossed into the RPA and LPA were counted. The differential pulmonary blood flow was calculated for each simulation as the ratio of particles in the RPA to LPA. Internal consistency of the 4Dflow measurements was validated using conservation of mass analysis. Systemic venous flow by origin (IVC or SVC) and total systemic venous flow into each branch PA were calculated. Preferential flow was defined as flow > 70% into one of the branch PAs.