Multiphoton microscopy in dermatological imaging

A minimally invasive imaging modality that provides both cellular and extracellular structural information with subcellular resolution is helpful for clinical diagnosis as well as basic laboratory research in dermatology. Multiphoton microscopy (MPM), using femtosecond laser as the light source, is efficient in non-linear excitation of endogenous fluorophores and induction of second harmonic generation signals from non-centrosymmetric biomolecules such as collagen. This imaging modality is minimally invasive in the sense that much of the traditional histological procedures can be bypassed en route to obtain morphological and structural information of high scattering skin tissues. This unique feature has allowed clinical dermatological diagnosis, both ex vivo and in vivo. In addition to discussing the basic principles of multiphoton microscopy, this review is aimed at emphasizing its specific applications to dermatological imaging, including characterizing stratum corneum structures, visualizing and quantifying transcutaneous drug delivery, detecting skin cancers, exploring collagen structural transitions, and monitoring laser-skin interactions.