Photon migration through fetal head in utero using continuous wave, near infrared spectroscopy: clinical and experimental model studies

Near infrared (NIR) measurements were made from the maternal abdomen (clini cal studies) and laboratory tissue phantoms (experimental studies) to gain insight into photon migration through the fetal head in utero, Specifically , a continuous wave spectrometer was modified and employed to make NIR meas urements at 760 and 850 nm, at a large (10 cm) and small (2.5/4 cm) source- detector separation, simultaneously, on the maternal abdomen, directly abov e the fetal head. A total of 19 patients were evaluated, whose average gest ational age and fetal head depth, were 37 weeks +/-3 and 2.25 cm +/-0.7, re spectively. At the large source-detector separation, the photons are expect ed to migrate through both the underlying maternal and fetal tissues before being detected at the surface, while at the short source-detector separati on, the photons are expected to migrate primarily through the superficial m aternal tissues before being detected. Second, similar NIR measurements wer e made on laboratory tissue phantoms, with variable optical properties and physical geometries. The variable optical properties were obtained using di fferent concentrations of India ink and Intralipid in water, while the vari able physical geometries were realized by employing glass containers of dif ferent shapes and sizes. Third, the NIR measurements, which were made on th e laboratory tissue phantoms, were compared to the NIR measurements made on the maternal abdomen to determine which tissue phantom best simulates the photon migration path through the fetal head in utero. The results of the c omparison were used to provide insight into the optical properties and phys ical geometry of the maternal and fetal tissues in the photon migration pat h. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S1083-3668 (00)00702-3].