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Quantification of fluorescence in vivo is complicated by the influence of tissue optical properties on the collected fluorescence signal. When tissue optical properties in the measurement volume are quantified, one can obtain the intrinsic fluorescence, which equals the product of fluorophore absorption coefficient and quantum yield. We applied this method to in vivo single-fiber fluorescence spectroscopy measurements on mouse tongue, skin, liver, and oral squamous cell carcinoma, where we detected intrinsic fluorescence spectra of the photosensitizers chlorin e6 and Bremachlorin at t = [3, 4.5, 6, 24, 48] h incubation time. We observed a tissue-dependent maximum of 35% variation in the total correction factor over the visible wavelength range. Significant differences in spectral shape over time between sensitizers were observed. Although the wavelength position of the fluorescence intensity maximum for ce6 shifted to the red, Bremachlorin showed a blue shift. Furthermore, the Bremachlorin peak appeared to be broader than the ce6 fluorescence peak. Intrinsic fluorescence intensity, which can be related to photosensitizer concentration, was decreasing for all time points but showed significantly more Bremachlorin present compared to ce6 at long incubation times. Results from this study can be used to define an optimal treatment protocol for Bremachlorin-based photodynamic therapy. [ABSTRACT FROM AUTHOR]

Background and Objective: In order to understand the mechanisms of photodynamic therapy (PDT) it is important to monitor parameters during illumination that yield information on deposited PDT dose. The aim of this study is to investigate the possibility of monitoring implicit parameters, such as photobleaching, in addition to monitoring explicit parameters (fluence (rate), oxygenation, photosensitizer concentration) directly or indirectly. These parameters are monitored during PDT without interrupting the therapeutic illumination., Materials and Methods: Rats were injected with 0.3 mg kg(-1) m-THPC. Sixteen hours after administration the abdominal muscle in rats was irradiated for 1,500 seconds using clinically relevant fluence rates of 50, 100, and 250 mW cm(-1) of diffuser length at 652 nm. In addition to the linear diffuser for delivering treatment light, isotropic fiber-optic probes and fiber-optic probes for differential path-length spectroscopy (DPS) were placed on both sides of the muscle to monitor tissue physiological parameters, fluence rate, and fluorescence., Results: The m-THPC treatment groups show a decrease in fluence rate throughout PDT of 16%, 19%, and 27% for the 50, 100, and 250 mW cm(-1) groups, respectively. Both during and post-PDT differences in vascular response between treatment groups and animals within the same treatment group are observed. Furthermore we show fluence rate dependent bleaching of m-THPC up to a measured fluence rate of 100 mW cm(-1)., Conclusion: The data presented in this study show the possibility of simultaneously monitoring fluence (rate), fluorescence, hemoglobin oxygen saturation, and blood volume during PDT without interruptions to the therapeutic illumination. Differences in saturation profiles between animals and treatment groups indicate differences in vascular response during illumination. Furthermore, the relationship between fluence rate and m-THPC fluorescence photobleaching is complex in an interstitial environment., (Copyright 2009 Wiley-Liss, Inc.)