Monitoring oxygen in lungs using GAs in Scattering Media Absorption Spectroscopy - Working towards realistic optical tissue phantoms

Sammanfattning

GASMAS, which stands for Gas in Scattering Media Absorption spectroscopy, is an optical technique for measuring the gas content in porous scattering media. It has shown promise for application in monitoring the gas content of lungs in a non-invasive or minimally invasive way. Monitoring changes in the quantity of oxygen and water vapor in lungs can help to quickly diagnose lung collapse conditions, such as pneumothorax and atelectasis. GASMAS for lung monitoring relies on the scattering properties of the porous lung tissue. The gasses in the lungs are probed by light shining through the tissue of the chest, allowing it to scatter in the lungs, and measuring absorption caused by oxygen and water vapor at specific wavelengths. This technique is already developed for neonatal infants, but further research needs to be conducted to know if the technique is applicable to larger patients, as their larger geometries will attenuate the light more. Before conducting more realistic studies, it is useful to ensure feasibility and safety through studies on optical phantoms. This thesis focuses on the development and examination of simple initial optical phantoms. Within this project, simple optical phantoms of gelatin, titanium dioxide, and India ink were constructed, mimicking the size and optical properties of an adult chest wall.The optical properties of were measured using time-of-flight spectroscopy to be similar to muscle tissue. GASMAS measurements were conducted with light around 764 nm to detect oxygen absorption, with the phantoms and a piece of styrofoam simulating the lung, for multiple setups with various geometries. The results showed the possibility of detecting oxygen absorption through thicker optical phantoms, and gave insights on the effect of the setup geometry and phantom thickness on the GASMAS signal. Gelatin was however shown to not be a viable bulk material for optical phantoms, and future ones should be constructed with another bulk material.