Gas in scattering media absorption spectroscopy shortly called GASMAS, is a tunable diode laser spectroscopic technique developed for the measurement of gas present in turbid media. The technique relies on the sharp and specific absorption lines of gases which enables sensitive measurements of gas concentrations in the presence of a scattering solid medium with much broader absorption features. The Biophotonics laboratory at Tyndall National Institute (Biophotonics@Tyndall) is currently exploring the clinical translation of GASMAS technology into the respiratory healthcare of neonates. In this study, we use computational tools to assess the potential gain in gas absorption signal. One of the challenges in the development of the GASMAS technique is to obtain a sufficiently good signal in the measurements, as the light attenuation is high in tissue and the lungs are interior organs. To have an estimation of the capabilities and limitations in this specific application of gas spectroscopy, we model the transmission of near infrared (NIR) light in tissue when a 760 nm source and a set of 68 detectors are placed in different locations over the thorax. We segmented the main organs of the thorax from anonymized DICOM images of a neonate. This is followed by the creation of 3D computational models to solve light propagation with the diffusion equation, and the modelling of light propagation through the thorax of an infant including optical properties of lung, heart, arteries, bone, muscle, trachea, fat and skin. Finally, we calculate a map of the optimal light source – detector configurations 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 advantages and limitations of the technology is fundamental.
Such simulations enable the recreation of different clinical scenarios and identification of the minimum requirements necessary to further improve the application and develop a bedside clinical device that can potentially be used for continuous monitoring of lung function and control of ventilator settings. The potential capability of measuring non-invasively oxygen, water vapour and carbon dioxide in the lungs, would reduce the need for intubation and extracorporeal membrane oxygenation, as well as lower the incidences of chronic lung disease.
Preterm newborn infants have a high morbidity rate. The most frequently affected organs where free gas is involved are the lungs and intestines. In respiratory distress syndrome, both hyperexpanded and atelectatic (collapsed) areas occur, and in necrotizing enterocolitis, intramural gas may appear in the intestine. Today, these conditions are diagnosed with x-ray radiography. A bed-side, rapid, nonintrusive, and gas-specific technique for in vivo gas sensing would improve diagnosis. We report the use of noninvasive laser spectroscopy, for the first time, to assess gas content in the lungs and intestines of three full-term infants. Water vapor and oxygen were studied with two low-power diode lasers, illuminating the skin and detecting light a few centimeters away. Water vapor was easily detected in the intestines and was also observed in the lungs. The relatively thick chest walls of the infants prevented detection of the weaker oxygen signal in this study. However, results from a previous phantom study, together with scaling of the results presented here to the typical chest-wall thickness of preterm infants, suggest that oxygen also should be detectable in their lungs.
Muscle tissue saturation (StO2) has been measured with two non–invasive optical techniques and the results were compared. One of the techniques is widely used in the hospitals – the CW-NIRS technique. The other is the photon timeof- flight spectrometer (pTOFS) developed in the Group of Biophotonics, Lund University, Sweden. The wavelengths used in both the techniques are 730 nm and 810 nm. A campaign was arranged to perform measurements on 21 (17 were taken for comparison) healthy adult volunteers (8 women and 13 men). Oxygen saturations were measured at the right lower arm of each volunteer. To observe the effects of different provocations on the oxygen saturation a blood pressure cuff was attached in the upper right arm. For CW-NIRS, the tissue saturation values were in the range from 70-90%, while for pTOFS the values were in the range from 55-60%.
Non-invasive diode laser spectroscopy was, for the first time, used to assess gas content in the intestines and the lungs of
a new-born, 4 kg, baby. Two gases, water vapor and oxygen, were studied with two low-power tunable diode lasers,
illuminating the surface skin tissue and detecting the diffusely emerging light a few centimeters away. The light, having
penetrated into the tissue, had experienced absorption by gas located in the lungs and in the intestines. Very distinct
water vapor signals were obtained from the intestines while imprint from oxygen was lacking, as expected. Detectable,
but minor, signals of water vapor were also obtained from the lungs, illuminating the armpit area and detecting below the
collar bone. Water vapor signals were seen but again oxygen signals were lacking, now due to the difficulties of penetration of the oxygen probing light into the lungs of this full-term baby. Ultra-sound images were obtained both from the lungs and from the stomach of the baby. Based on dimensions and our experimental findings, we conclude, that for early pre-term babies, also oxygen should be detectable in the lungs, in addition to intestine and lung detection of water vapor. The present paper focuses on the studies of the intestines while the lung studies will be covered in a forthcoming paper.
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