ABSTRACT
Photodynamic therapy (PDT) is a technique for treating a variety of malignant and nonmalignant conditions based on the use of light-activated drugs. For the PDT efficiency to be as high as possible, a high triplet state quantum yield is desirable, which competes with the fluorescence quantum yield. Most of the current photosensitizers have some fluorescence emission. The simplest approach is to measure the photosensitizer fluorescence and then compare the signal with the fluorescence signal from tissue samples with known photosensitizer concentration and similar escape function. To avoid the need for tissue-dependent calibration, assumptions can be made about the fluorescence escape function and excitation fluence distribution, based on a priori knowledge of the tissue optical properties. Diffuse reflectance measurements have been used to measure in vivo concentrations, with the advantage that they can be used for photosensitizers with little or no fluorescence. For nonfluorescent photosensitizers, absorption spectroscopy may be used as an optical assay method on the extracted or solubilized samples.
