Photon migration through fetal head in utero using continuous wave, near-infrared spectroscopy: development and evaluation of experimental and numerical models

In this work experimental tissue phantoms and numerical models were develop ed to estimate photon migration through the fetal head in utero. The tissue phantoms incorporate a fetal head within an amniotic fluid sac surrounded by a maternal tissue layer. A continuous wave, dual-wavelength (lambda= 760 and 850 nm) spectrometer was employed to make near-infrared measurements o n the tissue phantoms for various source-detector separations, fetal-head p ositions, and fetal-head optical properties, in addition, numerical simulat ions of photon propagation were performed with finite-difference algorithms that provide solutions to the equation of radiative transfer as well as th e diffusion equation. The simulations were compared with measurements on ti ssue phantoms to determine the best numerical model to describe photon migr ation through the fetal head in utero. Evaluation of the results indicates that tissue phantoms in which the contact between fetal head and uterine wa ll is uniform best simulates the fetal head in utero for near-term pregnanc ies. Furthermore, we found that maximum sensitivity to the head can be achi eved if the source of the probe is positioned directly above the fetal head . By optimizing the source-detector separation, the signal originating from photons that have traveled through the fetal head can drastically be incre ased. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S1083-3 6668(00)01402-7].