Glow with the flow: quantifying blood flow and photoluminescence signal in biological tissue

This thesis contributes to the development of optical techniques to assess microcirculation functionality for the diagnosis, monitoring, therapy guidance and understanding of many diseases ranging from the onset of septic shock to the delivery of drugs to tumours. The first part of this thesis aims to develop a non-invasive technique to quantify microcirculatory blood flow velocity based on laser speckle flowmetry. The key results are the experimental and theoretical investigation of the characteristic decorrelation times of speckle dynamics, and the relationship with the flow velocity and optical propeerties of the scatterers, specifically multiple scattering in blood vessels and the scattering phase function of red blood cells. The second part is devoted to the quantification of optical signals arising from photluminescent upconversion nanoparticles (UCNPs) for sensitive detection in biomedical tissues. The key results demonstrate that the UCNP optical properties enable the detection of small amounts of particles in UCNP-guided imaging applications, ranging from the detection of a single nanoparticle in biological liquid to modelling of a small UCNP-labelled tumour lesion embedded in biological tissue. The combination of these techniques is particularly useful in the context of tumour therapy by providing information on tumour angiogenesis, enabling molecular contrast and delivering nanoparticle-based drugs.