5.3.3 Applications of two-photon confocal laser sc...
Minimally invasive diagnosis of skin tumors is a major reason for developing multiphoton skin imaging.Ranked by levels of incidence from the highest to the lowest the major types of skin are as follows：basal cell carcinoma（originating from cells that make up the stratum basale of the epidermis），squamous cell carcinoma（originating from squamous cells that make up the major part of the epidermis），and melanoma（originating from melanocytes）.Despite the comparatively low proportion of melanoma cases，it has the highest mortality rate.Early examples of multiphoton imaging for skin tumors include Teuchner et al.，who measured the two-photon fluorescence of melanin in excised skin tissue.Subsequently，Skala et al.studied a hamster cheek pouch cancer model where tumors were biopsied and imaged in 3D.From these images，five features were identified for distinguishing normal，precancerous，and cancerous（squamous cell carcinoma）tissues.Skala and coworkers extended this work to include fluorescence lifetime metabolic imaging based on NADPH and flavin adenine dinucleotide（FAD）emission，noting that metabolism was different in tumors when compared with normal tissue.
Although the use of animal models is helpful，the study of human tissues is an important step towards eventual clinical applications.Most of these studies are based on two-photon fluorescence of endogenous fluorophores.In a proof-of-concept study on basal cell carcinoma by Cicchi et al.，an increase in fluorescence intensity was observed in cancerous tissue taken from a single patient.In another early study，melanoma was imaged based on fluorescence emissions from NADPH and elastin，and SHG signal from collagen.Melanoma cells were observed to fluoresce much brighter than the surrounding cells.A much larger trial，with 250 patients，was also performed for imaging melanoma.The increased fluorescence from cancerous melanocytes was confirmed，and morphological differences could also be seen.In another large study，115 patients were recruited to study the sensitivity and specificity of two-photon fluorescence for the diagnosis of melanoma；values of up to 95％sensitivity and up to 97％specificity were reported（Figure 5-6）.The overarching message of these reports seems to be that multiphoton fluorescence imaging may be a promising non-invasive approach providing morphological and molecular information that appears to be diagnostic and provides similar information as excisional biopsy.(https://www.daowen.com)