Multi­-Scattering: Computational light transport in turbid media

Abstract: This thesis presents and describes the development of an online freely accessible software called Multi-Scattering for the computational modeling of light propagation in scattering and absorbing media. The model is based on the use of the Monte Carlo method, where billions of photon packets are being launched and tracked through simulated cubic volumes. The software also includes features for modeling image formation by inserting a virtual collecting lens and a detection matrix which simulate a camera objective and a sensor array respectively. In addition, the Lorenz-Mie theory is integrated to generate the scattering phase functions from spherical particles. The model has been accelerated by means of general-purpose computing on graphics processing units, reducing the computation time by a factor up to 200x in comparison with a single CPU thread. By using four graphic cards on a single computer, the simulation speed increases by a factor of 800x. With an anisotropy factor g= 0.86, the transport path of one billion photons can be computed in 10 seconds for optical depth OD=10 and in 20 minutes for OD=500.The simulations are running from a computer server at Lund University, allowing researchers to login and use it freely without any need for programming skills or specific software/hardware installations. There are countless types of scattering media in which this model can be used to predict photon transport, including medical tissues, blood samples, clouds, smoke, fog, turbid liquids, spray systems, etc. In this thesis, the software has been used for a variety of scattering situations and to simulate photon transport: 1) inside a portion of a human head, 2) within atomizing spray systems, 3) in controlled aqueous dispersion of polystyren spheres, 4) for time-of-flight measurements in intralipid solutions and 5) for Diffuse Correlation Spectroscopy applications.Finally, the numerical results have been validated by rigorously comparing the simulated results with experimental data. The user interface for both setting-up a simulation and displaying the corresponding results is found at: https://multi-scattering.com