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Quantitative evaluation of skin photoaging mechanisms using multi-wavelength analysis of photoacoustic images

In recent years, skin aging caused by ultraviolet light exposure has garnered attention in the fields of beauty and health care because photoaging accelerates skin aging. Elastin is closely related to photoaging. In conventional methods for evaluating the elastin degeneration of photoaging skin, Elastica van Gieson staining images of skin section were evaluated using Kligman criteria. However, this diagnosis entails some shortcomings. For example, it is invasive and has no metabolic function. Moreover, its mechanism has not been fully clarified. For this study, photoacoustic imaging was used for evaluating skin photoaging mechanisms with acoustic resolution photoacoustic microscopy (AR-PAM). An ultrasonically focused transducer (50 MHz, 6.7 mm focal length) attached to the imaging head detected photoacoustic waves. Photoacoustic signal distributions of various skin aging sections that were a 25-μm-thick human cheek and buttock skin sections of six types were measured at 20 μm intervals using AR-PAM. This study was conducted to ascertain whether elastin parts are distinguishable from collagen parts in photoacoustic images. A difference was found between the photoacoustic spectrum of elastin and that of the collagen at 420–520 nm wavelengths. To examine the distinguishability between elastin and collagen, the signal intensity ratio of 420/450 nm wavelengths was calculated. The signal intensity ratio of the collagen part is higher than that of the elastin part. These results verified the possibility of discriminating elastin from collagen using multi-wavelength analysis of photoacoustic images.