Modelling Human Feto-Placental Circulation Based on Imaging

Abstract

The placenta is a vital organ that sustains the baby in utero, providing nutrients and eliminating waste. With 10-15% of pregnancies threatened with complications worldwide there is a need to develop effective therapies. Computational modelling is an established method of studying the placenta, which allows to further our understanding between the structure of the organ and its functioning. While modelling efforts to date have focused on simulations based on an ‘average’ placenta, with advances in imaging techniques it is becoming possible to develop patient specific models, which have the potential to advance both the modelling techniques and our knowledge of the studied organ. The present study developed automated techniques to model a normal placenta delivered at term based on micro-CT images. The diameter and position of larger chorionic vessels was calculated based on images and modelled using a novel method of producing skeleton graphs that accurately represent vessel tortuosity apart from branching. Smaller vessels were grown based on regional vascular density calculated from imaging. The umbilical blood flow for the reconstructed tree was in the normal range, while a confirmation by further studies is needed if the capillary surface area, where the exchange of nutrients and waste occurs, predicted by the model is adequate. The Strahler branching ratio of 2.73 for the chorionic portion of vasculature which was modelled directly from images was similar to the ratio calculated for feto-placental vasculature in mice based on imaging (2.9) and lower than estimated based on a section of first trimester and second trimester placentas (4.2). Modelling individualised placentas in greater numbers will help elucidate the branching characteristics of feto-placental vasculature. Methods presented here can be used to model smaller vessels with increased accuracy given images with high contrast between tissue and vasculature, while generating a small proportion of vessels that cannot be resolved in imaging. The patient specific feto-placental vasculature model developed in this study predicts that only approximately 5% of arterial vasculature is not captured in the images. Improvements in imaging techniques and confocal microscopy studies of capillary surface will help validate this prediction. Methods developed as part of the present study can be used to model feto-placental vasculature of an increased number of subjects, to establish the normal variability in vascular structure as well as determine changes in the structure that are associated with decreased placental efficiency and pregnancy complications.