Simulations and modeling of light propagation in biological tissue

Sammanfattning: The GASMAS technique has previously proven useful for examining and measuring the oxygen concentration in the lungs of preterm infants. GASMAS can distinguish absorption by one gas from the bulk absorption of the surrounding media, and can provide an instant, non-invasive and non-destructive way of examining lungs, and diagnosing dangerous conditions such as pneumothorax. Pneumothorax can be life-threatening if not caught and treated in time, and for patients suffering from lung diseases such as pneumonia or most recently, SARS-COV-2, a monitoring system would be able to alert medical personnel quickly if a lung collapse would occur while patient is treated with mechanical ventilation. One large obstacle to overcome when scaling up the process, i.e from an infant to an adult, is the amount of light that can be detected, as tissue is a highly scattering media that will distribute the photons over a very large volume, as well as the bulk absorption, which together attenuate the light. This thesis focuses on examining which limits exists for tissue thickness in regards to where the GASMAS technique can be used and to determine the size of body that can be examined using the current best light source and detector placement. This was examined both through simulations of light scattering in tissue using the open-access application Multi-Scattering, and through measurements on pork gammon, used as tissue phantoms, using both a tunable diode laser and a Ti:Sa laser. For laser with the output power of 1W, 1.5W and 2W a thickness limit of the phantoms was found, in regards to light-transmission, to be 14 cm (with the presented setup and equipment). This was however not tested using a sweeping tunable laser needed for GASMAS measurements, and must therefore be further investigated to determine the future usability.