Laser absorption spectroscopy measurements of different pulmonary oxygen gas concentrations in transmittance and remittance geometry: phantom study

Abstract

Significance: The gas in scattering media absorption spectroscopy (GASMAS) technique has the potential for continuous, clinical monitoring of preterm infant lung function, removing the need for X-ray diagnosis and reliance on indirect and relatively slow measurement of blood oxygenation.

Aim: We aim to determine the optimal source-detector configuration for reliable pathlength calculation and to estimate the oxygen gas concentration inside the lung cavities filled with humidified gas with four different oxygen gas concentrations ranging between 21% and 100%.

Approach: Anthropomorphic optical phantoms of neonatal thorax with two different geometries were used to acquire GASMAS signals, for 30 source-detector configurations in transmittance and remittance geometry of phantoms in two sizes.

Results: The results show that an internal light administration is more likely to provide a high GASMAS signal-to-noise ratio (SNR). In general, better SNRs were obtained with the smaller set of phantoms. The values of pathlength and $O_2$ concentrations calculated with signals from the phantoms with optical properties at 820 nm exhibit higher variations than signals from the phantoms with optical properties at 764 nm.

Conclusion: Our study shows that, by moving the source and detector over the thorax, most of the lung volumes can potentially be assessed using the GASMAS technique.

Keywords: computational model of a thorax; light transport; preterm infants; tuneable diode laser absorption spectroscopy.