Noninvasive determination of optical energy distribution in live biological tissues is an important aspect of any laser treatment or diagnostic procedure. It is particularly important for optical dosimetry in tissue, tissue diagnostics based on optical properties, quantitative molecular and functional imaging in the human body based on optical contrast, laser therapeutic procedures (such as photodynamic therapy, photothermal therapy, and laser treatment of various skin lesions and hair removal), and laser microsurgery. Monitoring of changes in tissue optical properties can also be utilized for monitoring of laser–tissue interactions, noninvasive optical biopsy, the effects of laser ablation or denaturation of tissue, and ablation by high-intensity focused ultrasound (HIFU). The precision of these procedures would improve significantly if laser irradiation conditions could be adjusted in accordance with initial optical properties and with changes in optical properties during the course of the treatment. Therefore, there is a definite need for noninvasive measurement and visualization of the light distribution profile in the laser-irradiated tissue in vivo. Such feedback information helps predict the optimal laser wavelength, pulse duration, laser intensity, and light dose to be delivered so as to obtain diagnostic information or to cause a sufficient effect during treatment with minimal damage to adjacent tissue layers.
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