Optimization of Pulmonary Vasculature Tridimensional Phenotyping in The Rat Fetus

Comparative, functional, developmental, and some morphological studies on animal anatomy require accurate visualization of three-dimensional structures. Nowadays, several widely applicable methods exist for non-destructive whole-mount imaging of animal tissues. The purpose of this study was to optimize specimen preparation and develop a method for quantitative analysis of the total pulmonary vasculature in fetal rats. Tissues were harvested at E21 and fetuses fixed overnight in 4% paraformaldehyde/phosphate buffered saline. They were treated with 25% Lugol solution for 72 hours to ensure perfusion. Four different methods were used for fetal specimen preparation; isolated lung, upper torso, direct right ventricle contrast injection, and whole body with partial thoracic skin excision. The microCT scan was performed, and pulmonary vasculature was segmented. Vessels were analyzed for diameter, length, and branching. Of the four preparation methods, only whole body with partial thoracic skin excision resulted in adequate reconstruction of the pulmonary vasculature. In silico generated 3D images gathered by micro CT showed pulmonary vasculature distributed throughout the lung, which was representative of the shape and structure of the lungs. The mean number of vessels segmented in the pulmonary tree was 900 ± 24 with a mean diameter of 134.13 µm (range 40.72-265.69 µm). While up to the 30^th generation of vessels could be segmented, both for arteries and veins, the majority of branching was between the 21^st and 30^th generations. Passive diffusion of contrast material enables quantitative analysis of the fetal pulmonary vasculature. This technique is a useful tool to analyze the characteristics and quantify the fetal pulmonary vasculature.