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Abstract

Accurate and early diagnosis of skin diseases will improve clinical outcomes. Visual inspection alone has limited diagnostic accuracy, while biopsy followed by histopathology examination is invasive and time-consuming. The objective is to design and develop a multimodal optical instrument that provides biochemical and morphological information on human skin in vivo. Raman spectroscopy (RS) is capable of providing biochemical information of tissues. Reflectance confocal microscopy (RCM), which generates micron-level resolution images with capability of optical sectioning, can provide refractive-index-based morphological information of the skin. Multiphoton microscopy (MPM) could simultaneously provide biochemistry-based morphological information from two-photon fluorescence (TPF) and second-harmonic-generation (SHG) images. The thesis hypothesis is that a multimodality instrument combining RS, RCM, and MPM could be developed and provide complementary information in real-time for in vivo skin evaluation and aiding non-invasive diagnosis. A confocal Raman spectroscopy system was initially developed and tested in a study on in vivo mouse skin. Spectral biomarkers (899 and 1325-1330 cm-¹) were found to differentiate tumor-bearing skin from normal skin. A RCM system was then integrated with the spectroscopy system to guide spectral measurements. Noninvasive morphological and biochemical analysis was performed on ex vivo and in vivo human skin. The system was further enhanced by adding an MPM module that can image cellular structures with TPF signals from keratin, NADH, and melanin, as well as image elastic and colla ii gen fibers via TPF and SHG signals, respectively. The finalized system was utilized to noninvasively measure a cherry angioma lesion and its surrounding structures on the skin of a volunteer. Confocal Raman spectra from various regions-of-interest acquired under the guidance of MPM and RCM imaging showed different spectral patterns for blood vessels, keratinocytes, and dermal fibers. The system was also successfully used to perform imaging directed two-photon absorption based photothermolysis on ex vivo mouse skin. All the results showed positive evidence, well supporting the overall hypothesis. The developed multimodality system, capable of acquiring co-registered RCM, TPF and SHG images simultaneously at video-rate, and performing image-guided region-of-interest Raman spectral measurements of human skin in vivo, is a powerful tool for non-invasive skin evaluation and diagnosis.