Impact of tear location on hemodynamics in a type B aortic dissection investigated with computational fluid dynamics

Stanford type B aortic dissections (TB-AD), which split the descending aorta in a true and false lumen, have better in-hospital survival than type A dissections affecting the ascending aorta. However, short-term and long-term prognosis for the individual patient remains challenging, with one in four patients not surviving after 3 years. Towards a better understanding of the influence of tear location on TB-AD hemodynamics, we performed computational fluid dynamics (CFD) with aortic geometry extracted from magnetic resonance angiographic (MRA) images and inflow conditions modeled using the aortic flow waveform measured with 2D phase contrast magnetic resonance imaging (2D pcMRI). Three configurations were investigated. Configuration 1 had both entrance and re-entrance tear (as imaged), in configuration 2 the re-entrance tear was virtually occluded to simulate disease progression (thrombus formation) and in configuration 3, the entrance tear was virtually occluded, simulating endovascular treatment (EVAR) i.e. placing a stent-graft to eliminate inflow into the false lumen. For incorporation of the simulation results into the clinical workflow, a Siemens Leonardo software plugin prototype was developed to visualize and quantify hemodynamic parameters as 4D (3D plus time) volumes. Pressure in the true lumen for all three configurations was similar and varied about 3.4 % (largest variation between configuration 1 and 3). Pressure in the false lumen increased by 7.4 % for configuration 2 compared to configuration 1 and dropped by 97 % for configuration 3 compared to configuration 1. Pressure difference curves (true lumen value subtracted from false lumen value) showed similar behavior for configuration 1 and 2 with largest differences occurring during systole. For configuration 3, largest decrease in pressure difference occurred during systole. Higher pressure in the false lumen compared to the true lumen was found at end systole, indicating reversal of sign of pressure - ifference in configuration 3 (virtually treated TB-AD by EVAR). Velocity patterns did not show pronounced differences between configuration 1 and 2 but revealed reduced flow in the false lumen for configuration 3.