Quantitative multiphoton imaging for guiding basal-cell carcinoma removal

For secure removal of the basal cell carcinoma tissue, the technique of Mohs' micrographic surgery is often used. However, Mohs' micrographic surgery is time-consuming. In this work, we evaluate the ability of multiphoton fluorescence (MF) and second harmonic generation (SHG) imaging to discriminate the borders of human basal cell carcinoma. Morphologically, basal cell carcinomas are featured by clumps of autofluorecent cells with relatively large nuclei and marked peripheral palisading in the dermis. In contrast, SHG from collagen contributes largely to the multiphoton signal in normal dermis. Within the cancer stroma, SHG signals diminish and are replaced by autofluorescent signals. The results suggest that normal collagen structures responsible for SHG have been altered in the cancer stroma and may reflect an up-regulated collagenolytic activity of cancer cells. To better delineate the cancer cells and cancer stroma from normal dermis, a quantitative MF to SHG index (MFSI) is developed. We demonstrate that this index can be used to differentiate cancer cells and adjacent cancer stroma from normal dermis. Our work shows that MF and SHG imaging can be an alternative for the real-time guidance of the secure removal of basal cell carcinoma.