Optical effects of vessel walls on inner diameter assessment in indocyanine green fluorescence angiography

Indocyanine Green Fluorescence Angiography (ICG-FA) is commonly used to characterize blood flow dynamics. While determining flow velocity and inner diameter is crucial for this, we investigated whether the latter is affected by the optical properties of the vessel wall. To do so, we captured FA images of ICG-filled silicone and glass tubes with varying wall-to-lumen ratios. The diameter of each tube was determined with Otsu’s edge detection and for each of them, multiple measurements were performed and compared to the ground truth. Based on the paraxial approximation of light refraction at a spherical surface, an optical model was developed. Both experimentally and with our model, we observed an overestimation for most cases, which qualitatively confirms distortions caused by the vessel wall.