Presence of intralesional melanocytes as a histopathological feature of actinic keratosis based on in vivo harmonic generation microscopy in Asians

Characterization of picosecond laser-induced optical breakdown using harmonic generation microscopy

BACKGROUND AND OBJECTIVES

By creating microinjuries usually confined to the epidermis, a fractional picosecond 1064-nm Nd:YAG laser that delivers an array of highly focused beamlets can be effectively used for facial rejuvenation or resurfacing. However, the mechanism of dermal remodeling underlying this nonablative treatment remains unclear.

METHODS

Five participants having skin phototype III-IV were recruited for intervention using a fractional picosecond 1064-nm Nd:YAG laser system equipped with a holographic diffractive beam-splitting optic. The laser-induced histopathological changes on human skin were examined in vivo using a harmonic generation microscopy (HGM), visualizing second harmonic generation (SHG), and third harmonic generation (THG) contrasts dichromatically. SHG refers for collagen distribution, while THG represents for epidermal components in the HGM signal.

RESULTS

Histological hematoxylin and eosin staining and in vivo HGM imaging studies revealed the presence of epidermal vacuoles below the stratum granulosum along with keratinocyte degeneration or cytolysis. In addition to the epidermal vacuoles, HGM imaging exclusively demonstrated laser-induced shock wave propagation arranged as a THG-bright concentric pattern in the epidermis and loss of SHG signals in the papillary dermis immediately beneath the epidermal vacuoles.

CONCLUSIONS

Alongside generating epidermal vacuoles, the fractional picosecond 1064-nm Nd:YAG laser induced collagen changes. These collagen changes may lead to dermal remodeling and neocollagenesis underlying the fractional picosecond laser treatment.

In vivo harmonic generation microscopy for monitoring the height of basal keratinocytes in solar lentigines after laser depigmentation treatment

The development of solar lentigines (SLs) is related to chronic ultraviolet exposure-induced cell senescence. We have previously demonstrated that basal keratinocyte enlargement is a morphological hallmark of skin senescence correlated to the process of skin aging, while clinical studies on the long-term monitoring of the cellular morphological changes in SLs after laser treatment are lacking. In this study, we have developed the harmonic generation microscopy (HGM) for in vivo monitoring the height of basal keratinocytes (HBK) and had administered Q-switched ruby laser or picosecond 532-nm Nd:YAG laser treatment on each side of the face of 25 Asian patients with facial SLs, respectively. In vivo HGM imaging was conducted to longitudinally analyze HBK and the horizontal cell size (HCS). Before treatment, the HBK was significantly higher in the SLs lesional area than that in the adjacent normal region, whereas there was no significant difference in the HCS. After treatment, the lesional HBK remained significantly higher than normal skin regardless of the laser treatment used. Our study indicates that the basal keratinocytes remain abnormal after laser treatment and demonstrates the capability of in vivo HGM for longitudinal, quantitative monitoring of cell senescence and therapeutic effect in SLs.

Investigating the optical clearing effects of 50% glycerol in ex vivo human skin by harmonic generation microscopy

Imaging depth and quality of optical microscopy can be enhanced by optical clearing. Here we investigate the optical clearing of the ex vivo human skin by 50% glycerol topical application, which is allowed for cosmetic usage. Harmonic generation microscopy, by combining second and third harmonic generation (THG) modalities, was utilized to examine the clearing effect. The THG image intensity is sensitive to the improved optical homogeneity after optical clearing, and the second harmonic generation (SHG) image intensity in the dermis could serve as a beacon to confirm the reduction of the scattering in the epidermis layer. As a result, our study supports the OC effect through 50% glycerol topical application. Our study further indicates the critical role of stratum corneum shrinkage for the observed SHG and THG signal recovery.