On Intlet Pressure Boundary Conditions for CT-Based Computation of FFRSS: Clinical Measurement of Aortic Pressure

Abstract Background and Objectives: With the development of medical imaging and computational fluid dynamics (CFD), a fast calculation method of steady-state fractional flow reserve (FFRss) based on CTA images has been applied to predict myocardial ischemia. Whilst this is a reliable non-invasive method of calculating FFR, assumptions involved in the analysis still need to be investigated for further improvement in predictive accuracy. In this study, we analyzed the influence of inlet and outlet boundary conditions on FFRSS.Methods: A clinical trial was carried out in Peking University People's Hospital. We enrolled 15 patients with coronary heart disease. All patients underwent coronary CTA examination, aortic pressure measurement and FFR catheter surgery. In order to better reflect the relationship between different entrance boundary conditions and FFRss, we used the invasive measurement of FFR as the standard, and calculated FFRss for 15 patients with coronary heart disease with different degrees of stenosis. The boundary conditions are divided into two groups: (1) pressure calculated based on physiological formula; (2) clinically measured aortic pressure. Based on the boundary conditions calculated by the physiological formula, we further studied the changes of FFRss under different coronary vasodilation responses (12%-48% baseline).Results: The research results show that although the pressure difference between the two pressure boundary conditions is 15mmHg, the FFRss calculation result does not change significantly. With the change of the vasodilation state, the microcirculation resistance of the exit boundary condition gradually increased, and the calculated FFR value increased.Conclusions: We found that changes in the microcirculation resistance of coronary stenoses have a huge impact on FFRss. The changes in FFRss values caused by boundary conditions are due to the overestimation of the vasodilation response. Therefore, individualizing the hyperemia state of the stenotic vessel microcirculation resistance value is an effective method to improve the calculation of FFR.