Background: Serial analysis of cellular dynamics over time offers new insights into human skin responses to solar radiation. However, most of the previous studies are based on biopsy ex vivo analysis approaches that preclude the monitoring of the same cells and sites over time. Optical in vivo microscopy enables the possibility of real-time live cell imaging. Here we report a robust non-invasive method to achieve repeated access to the same micro-location over a long period with unprecedented precision.
Methods: The technique is based on a temporary “surface marker” as landmark to help locate the same cells or microstructures between imaging sessions. At baseline, the region-of-interest (ROI) is determined and imaged. At follow up sessions, the ROI can be automatically located. Using this method, we precisely revisited the same cells in human skin after UVB radiation over two weeks. Skin microscopic responses was studied with a multimodality in vivo microscopy system capable of co-registered video rate reflectance confocal microscopy (RCM) imaging, two-photon fluorescence (TPF) imaging and second harmonic generation (SHG) imaging.
Results: The quantitative analysis of TPF signal revealed that melanin distribution pattern changed with time after UVB exposure, suggesting that melanin migrates towards the skin surface. Blood flow was monitored in the same capillary over two weeks. Multimodal analyses enabled accurate calculation of viable epidermis, stratum corneum thickness and cell density variations over time, demonstrating the time points of tissue edema and cell proliferation.
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