Publications [#195300] of Nimmi Ramanujam

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1. Choe, R. and Durduran, T. and Guoqiang Yu and Nijland, M.J.M. and Nathanielsz, P.W. and Chance, B. and Yodh, A.G. and Ramanujam, N., Noninvasive cerebral hemoglobin oxygenation quantification of fetal sheep under hypoxic stress in-utero using frequency-domain diffuse optical two-layer model, Proc. SPIE - Int. Soc. Opt. Eng. (USA), vol. 4955 no. 1 (2003), pp. 379 - 87, San Jose, CA, USA [12.478175]
   (last updated on 2011/09/23)

   Abstract:
   A study using pregnant sheep was designed to simulate fetal hypoxia in order to investigate the ability of near-infrared spectroscopy (NIRS) to detect and quantify fetal hypoxia in utero. The near-infrared spectroscopic probe consisted of two detectors and six source positions. It was placed on the maternal ewe abdomen above the fetal head. The light sources were modulated at 70 MHz and frequency-encoded so that simultaneous measurements at 675, 786, 830 nm for each source position were possible. After the baseline measurements, fetal hypoxia was induced by blocking the aorta of pregnant ewe and thus compromising the blood supply to the uterus. Blood gas samples were concurrently drawn from the fetal brachial artery and jugular veins. Analysis of the diffuse optical data used a two-layer model to separate the maternal layer from the fetal head. The analysis also employed a priori spectral information about tissue chromophores. This approach provided good quantification of blood oxygenation changes, which correlated well with the blood gas analyses. By contrast the homogeneous model underestimated oxygenation changes during hypoxia

   Keywords:
   bio-optics;biological techniques;blood vessels;frequency-domain analysis;haemodynamics;infrared spectroscopy;oxygen;proteins;veterinary medicine;