Gas in Scattering Media Absorption Spectroscopy in Large Geometries: Towards Monitoring Oxygen in Adult Lungs

Sammanfattning: GAs in Scattering Media Absorption Spectroscopy (GASMAS) is a technique to study free gas inside strongly scattering bulk-materials. GASMAS is successful in safely measuring oxygen in lungs of neonates, with low-power tuneable diode-laser spectroscopy at 760 nm. Because a similar need of lung monitoring exists in older patients, this work explores how GASMAS can be scaled up for larger geometries. The major problem in large geometries is heavy light attenuation in tissue, making it necessary to increase the incident laser power. First, the performance of a low-power diode-laser GASMAS system was tested on wild boar lung. Next, an optical tapered amplifier (OTPA) was incorporated into the system with the goal of amplifying the light up to about 1 W. Finally, a high-power Titanium-Sapphire (TiSa) laser at 760 nm, not viable for practical GASMAS applications due to slow wavelength tuning, was used to study the level of light detection through tissue slabs, for varying slab thickness and laser powers. The results show a good oxygen signal through 3 − 5 cm of lung tissue at 26 mW diode-laser power. The amplification of the diode laser light through the OTPA has not yet been fully successful, but the different parts of the system have been investigated and suggested optimisations were made for the future. With the high-power TiSa-laser, light of higher powers could penetrate through thicker tissue slabs. At 1 W, a good signal was detected through 14 cm of tissue, as compared to 3 − 5 cm with 26 mW. In conclusion, the low-power diode-laser GASMAS system can detect oxygen in small lung geometries. Amplifying the power with an OTPA has good potential to enable oxygen GASMAS in large geometries. Future work should aim to better incorporate the OTPA into the diode-laser system with updated alignment equipment to amplify the power, in order to further investigate the applicability for GASMAS lung monitoring in larger children and adults.