Simulation of near-infrared light propagation through the thorax of a neonate: addressing the optimization of source and detector positions for measuring lung oxygen content in preterm infants

摘要

Gas in scattering media absorption spectroscopy shortly called GASMAS, is a tunable diode laser spectroscopic techniquedeveloped for the measurement of gas present in turbid media. The technique relies on the sharp and specific absorption linesof gases which enables sensitive measurements of gas concentrations in the presence of a scattering solid medium with muchbroader absorption features. The Biophotonics laboratory at Tyndall National Institute (Biophotonics@Tyndall) is currentlyexploring the clinical translation of GASMAS technology into the respiratory healthcare of neonates. In this study, we usecomputational tools to assess the potential gain in gas absorption signal. One of the challenges in the development of theGASMAS technique is to obtain a sufficiently good signal in the measurements, as the light attenuation is high in tissue andthe lungs are interior organs. To have an estimation of the capabilities and limitations in this specific application of gasspectroscopy, we model the transmission of near infrared (NIR) light in tissue when a 760 nm source and a set of 68detectors are placed in different locations over the thorax. We segmented the main organs of the thorax from anonymizedDICOM images of a neonate. This is followed by the creation of 3D computational models to solve light propagation withthe diffusion equation, and the modelling of light propagation through the thorax of an infant including optical properties oflung, heart, arteries, bone, muscle, trachea, fat and skin. Finally, we calculate a map of the optimal light source – detectorconfigurations to obtain the highest signal from oxygen gas imprint in the lungs.The use of computational tools such as NIRFAST Slicer 2.0 for investigation and further understanding of the advantagesand limitations of the technology is fundamental. Such simulations enable the recreation of different clinical scenarios andidentification of the minimum requirements necessary to further improve the application and develop a bedside clinicaldevice that can potentially be used for continuous monitoring of lung function and control of ventilator settings. Thepotential capability of measuring non-invasively oxygen, water vapour and carbon dioxide in the lungs, would reduce theneed for intubation and extracorporeal membrane oxygenation, as well as lower the incidences of chronic lung disease.