@misc{9236328,
  abstract     = {{Pulmonary complications such as pneumothorax and atelectasis are common in intensive care patients. Current diagnostic techniques, including computed tomography (CT) and X-ray imaging, are not suitable for continuous monitoring and expose patients to ionizing radiation. This motivates the development of continuous and non-invasive monitoring methods. Gas in Scattering Media Absorption Spectroscopy (GASMAS) is an optical technique that has shown promising results for neonatal lung monitoring. However, extending GASMAS to adult lung monitoring remains challenging because the thicker chest wall causes significant attenuation of the optical signal. This thesis investigates the feasibility of adult lung monitoring using Gas in Scattering Media Absorption Spectroscopy (GASMAS) through numerical simulations, phantom development, and experimental measurements. Monte Carlo simulations of photon transport were performed in voxelized thoracic geometries using the pmcx framework for both external and internal (esophageal) illumination configurations over a range of chest wall thicknesses and source-detector separations. A durable tissue-mimicking phantom was developed using a gelatin matrix containing titanium dioxide and India ink, and its optical properties were characterized by time-of-flight spectroscopy. In addition, the water-vapor-based GASMAS calibration method was evaluated numerically by comparing photon pathlength distributions at the oxygen (764 nm) and water vapor (935 nm) absorption wavelengths. The results show that a detectable GASMAS oxygen signature can be obtained through an adult-equivalent chest wall thickness of 3 cm. For realistic adult geometries, internal esophageal illumination produced consistently stronger relative signals than external illumination. In both simulation and experimental measurements, increasing the source-detector separation enhanced the GASMAS signal, although it also increased the noise level. The simulated and experimental signal trends were in good agreement. In addition, the equal-pathlength assumption underlying the water-vapor-based calibration method was validated, with photon pathlength distribution overlaps of 82 - 94 % across the simulated conditions. These findings support the feasibility of GASMAS for adult lung monitoring and identify internal illumination as a promising approach for clinical translation. At the same time, the results demonstrate that external illumination can also provide measurable GASMAS signals, highlighting its potential for non-invasive lung monitoring in adult thoracic geometries.}},
  author       = {{Mawella Withanawasam, Isuru Chanilka}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Feasibility of Adult Lung Monitoring Using GASMAS: Development and Evaluation of Advanced Large-Geometry Phantoms}},
  year         = {{2026}},
}