Study of the effect of boundary conditions on fractional flow reserve using patient specific coronary phantoms

Purpose: 3D printing has become an accepted radiological tool which allow accurate physical renderings of organs for diagnosis and treatment planning. Use of 3D printed phantoms to replicate blood flow conditions have been reported, however, comprehensive studies comparing in-patients and in-vitro measurements are scarce. We propose to study whether 3D-printed patient specific coronary benchtop models, can be used to study how variations in outflow boundary conditions influence benchtop fractional flow reserve (FFR) measurements and how these compare with a research CT-FFR software. Materials and Methods: Fifty-two CT-derived patient-specific 3D-printed coronary phantoms were used for comprehensive flow experiments and a benchtop-FFR (B-FFR) was evaluated along the diseased arteries. A programmable cardiac pulsatile pump provided six coronary outflow rates equally distributed between normal and hyperemic blood flow conditions (250-500 mL/min). B-FFR results were compared to catheter lab Invasive-FFR (I-FFR) measurements and a CT-FFR research software. The effect of coronary outflow changes was compared with catheter lab diagnosis using operator characteristics (ROC) and Area Under ROC (AUROC). Results: The highest AUROC was for B-FFR-500, 0.82 (95% CI: 0.65-0.92,), and gradually decreased as the flow rate decreased to B-FFR-250, 0.79 (95% CI: 0.70-0.87). The CT-FFR AUROC was 0.80 (95% CI: 0.69-0.86). Conclusion: 3D-printed patient specific coronary phantoms and controlled flow experiments demonstrated significant agreement between hyperemic simulated flow B-FFR-500 and I-FFR. We also observed not negligible variations of the B-FFR for small coronary outflow rates changes, implying that slight changes in outflow conditions may results in diagnosis change, especially in the 0.75-0.85 FFR range.