Towards development of an intravascular diagnostic catheter based on fluorescence lifetime spectroscopy: Study of an optimized blood flushing system

Fluorescence lifetime spectroscopy has demonstrated potential for characterization and diagnosis of arterial vessels pathologies. However, the intravascular application of such technique is hampered by the presence of blood hemoglobin that affects both the delivery of the excitation light to and the collection of the fluorescence light from the vessel wall. We report here a computational fluid dynamics model that allows for the optimization of blood flushing parameters in a manner that minimizes the amount of saline needed to clear the optical field of view. A 3D turbulence (k - epsilon) model was employed to simulate the flow inside and around a side-viewing fiber-optic catheter. The influence of various infusion rates, blood flow rates and vessel diameters on the flow around the catheter tip and its effects on the wall shear stress (WSS) are studied. Current results suggest that low flushing rates in smaller-diameter vessels (e.g., stenotic vessels) can produce better flushing efficiency by removing the blood cells in the path of the fluorescence light and reducing wall shear stress. The comparison of the results for blood vessels with equal diameter but different flow rates suggests that the effect of systolic and diastolic conditions on the maximum wall shear stress is not substantial. The results from this study can be utilized in determining the optimal flushing rate depending on the diameter of the vessels, blood flow rate, and the maximum wall shear stress that vessel wall can sustain, which can be estimated from the feedback of the fluorescent light from the wall.