Publications [#195307] of Nimmi Ramanujam

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1. Vishnoi, Gargi and Hielscher, Andreas H. and Ramanujam, Nirmala and Nioka, Shoko and Chance, Britton, Tissue phantom studies on photon migration through fetal brain in-utero using near infra-red spectroscopy, Proceedings of SPIE - The International Society for Optical Engineering, vol. 3597 (1999), pp. 650 - 660, San Jose, CA, USA [12.356788]
   (last updated on 2011/09/23)

   Abstract:
   We present tissue phantom experimental results and theoretical simulations to study photon migration through the fetal head in-utero. A continuous-wave (CW), dual wavelength (760 & 850 nm) spectrometer was developed and employed for the experiments at a source-detector separation of 10 cm. Theoretical simulations were performed using time-independent, finite-difference, discrete-ordinate, radiative-transport and diffusion equations. Two phantom geometries viz. circular and rectangular were considered. The tissue phantom incorporates a fetal head (absorption coefficient, μa: 0.15 cm^-1 & reduced scattering coefficient, µs': 5.0 cm^-1), an amniotic fluid sac (μa=0.02 cm^-1, µs'= 0.1 cm^-1) and a maternal tissue layer (μa= 0.08 cm^-1, µs'= 5.0 cm^-1). Photon fluence from the tissue phantom was quantified as a function of fetal head depth and its position relative to probe placement. Experimental results obtained with spectrometer were found to be congruent with theoretical results and clinical investigations. The results indicate that photon fluence decreases with increase in fetal head depth for circular geometry, while it increases with increase in fetal head depth for rectangular geometry. This paradoxical result observed may be attributed to the effect of amniotic fluid in the light path. Photon fluence is sensitive for fetal head depths within 40 mm. This is well within the fetal head depths expected in near-term patients (approx. 20 mm).

   Keywords:
   Spectrometers;Brain;Infrared spectroscopy;Photons;Computer simulation;Geometry;Imaging techniques;Numerical methods;