Simulation study on the effect of tissue geometries to fluence composition for non-invasive fetal pulse oximetry.

Transabdominal fetal pulse oximetry is a method to estimate the state of oxygenation of a fetus in-utero, utilizing the principle of reflection pulse oximetry. The extraction of fetal related information from a mixed fetal-maternal signal is elementary. Minimizing the ratio of purely maternal components of the signal at the detector side obviously facilitates signal separation. In this paper we analyze the influence of tissue geometries to the fluence composition at the surface of the abdomen. Monte-Carlo method is used to compute photon propagation in spherical layered tissue models. Spatial fluence distributions at the surface of the models are visualized and discussed. Our results show the characteristic effects of the distance between the fetus and the surface and the radius of the abdomen to the fluence composition at the detector. Further, the simulations indicate suitable source-detector configurations considering various anatomical conditions. We conclude that an adoption of the source-detector configuration to the individual tissue geometry at hand is necessary to achieve a proper signal composition and quality. Utilizing simulations for sensor design enhances the understanding of photon distributions in complex tissue geometries and supports a successful implementation of transabdominal fetal pulse oximetry.