Abstract

As an application of near-infrared spectroscopy, pulse oximetry is widely used to non-invasively measure the arterial oxygen saturation (SpO₂). To improve the maternal and fetal outcome during delivery, transabdominal fetal pulse oximetry can be used to measure the fetal SpO₂. The layered tissue structure above the fetus, however, is complex and thick. In order to understand the feasibility of transabdominal pulse oximetry, we simulated light propagation through the maternal abdomen. For realistic geometry, we segmented a magnetic resonance imaging (MRI) scan of a pregnant women to create a 3D anatomical model, from which a 3D tetrahedron mesh was generated. Using this mesh, we then simulated photon propagation for 5 wavelengths and a grid of 70 sources and detectors (35 each) on the maternal abdomen above the fetal head with NIRFAST. Finally, depth sensitives were examined with Jacobian (J) and flat field. For a fetal head at ~4 cm depth, we found the normalized J at this depth is ~0.1-1% for source-detector distances within 9-10 cm. We also observed that at the same depth, the normalized flat field sensitivity is ~5-10%, which is 1-2 orders of magnitude higher than the normalized J. These results indicate that enough light can reach the fetus when considering ~9 cm source detector distances.

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