Optical spectroscopy in biomedicine - detection of embedded inclusions and in vivo pharmacokinetics

Sammanfattning: The main theme of this thesis is the use of fluorescence spectroscopy in biomedicine. The work presented in the thesis can be divided into three areas of applications. The first area involves the use of fluorescence to find the location of a deeply situated fluorophore within turbid media. Fluorescence emitted from the fluorophore will be attenuated when propagating through the medium, due to the optical properties of the surroundings. The fluorescence light will be more attenuated at some wavelengths as the tissue optical properties are wavelength-dependent, and this difference will be more pronounced the longer the light travels. An intensity ratio of fluorescence at two selected wavelengths can therefore provide information about the depth of the inclusion. This has been investigated with both simulations and experiments with tissue phantoms. A further step has been to incorporate this depth-dependent ratio into a reconstruction algorithm used in fluorescence tomography. Photodynamic therapy (PDT) is a local treatment modality of tumors, requiring light, oxygen and an administered photosensitizer, which preferably accumulates in tumor tissue. The second main area in this thesis has been the study of the pharmacokinetics of a liposomal formulation of the photosensitizer Temoporfin in different animal tumor models. Fluorescence measurements have been performed in order to estimate the quantity of photosensitizer within tumor and normal tissues following either topical or systemical administration of the drug. These quantities were compared to the drug concentrations obtained with chemical extraction. Time intervals of 2-8 hours between administration and measurements were investigated. Absorption spectroscopy was also performed when using topical application of the drug, yielding a good correlation of photosensitizer concentration compared to extraction data. Tumor selectivity of this liposomal Temoporfin formulation was shown at these short time intervals. Fluorescence measurements have also been performed in a first clinical PDT trial using topical application of this new formulation. The final application utilizing fluorescence was to measure temperature optically. Certain crystals change their fluorescence spectrum when the temperature is altered. By attaching a crystal to a fiber tip, the temperature can be monitored at the position of the fiber. An intensity ratio of detected fluorescence in two wavelength bands can provide an estimate of the temperature. The temperature was monitored during a 10 minutes long light illumination on skin of a volunteer, indicating a temperature increase. The technique was also tested interstitially in meat, showing a temperature increase during the entire illumination as no perfusion was present, which normally stabilizes the temperature.