Multiphoton tomography of skin tumors after ALA application

In skin, the most common form of cancer is the basal cell carcinoma, affecting about 800.000 people in US each year. One of the treatments is photodynamic therapy (PDT) with a topical application of 5-aminolevulinic acid (ALA) derivates. These photosensitizers accumulate mainly in cancerous cells and can be activated by light resulting in a destruction of the cells. We performed multiphoton tomography based on near-infrared (NIR) femtosecond laser pulses on skin biopsies in order to study the biosynthesis of protoporphyrine IX and the effect of treatment with submicron resolution. The fluorescence of the photosensitizer was excited using two-photon processes and monitored through the epidermis towards the basal layer. In comparison with normal skin the cancerous cells showed different morphology and fluorescence behavior. Multiphoton tomography might become a useful tool for high resolution imaging of cancerous tissue and to evaluate the therapeutical effects.