Background

The skin is the largest organ of the human body. The state of the skin is closely related to human health. Imaging technology plays an important role in dermatology. Conventional pure optical dermatoscopes are limited by imaging depth and can only visualize epidermal morphology. Ultrasound imaging can visualize the entire skin structure with deep penetration, but its spatial resolution and ability to visualize microvessels are relatively poor. Photoacoustic imaging (PAI), based on the photoacoustic effect, is a hybrid biomedical imaging technology, which combines high-contrast optical imaging and deep penetration ultrasound imaging (Wang and Hu, 2012). As a meritorious application mode of PAI, photoacoustic dermoscopy (PAD) provides researchers and clinicians with a new way of noninvasively observing deep skin structures (Xu et al., 2016; Ma et al., 2018, 2020, 2021; Wang et al., 2022a, 2022b). PAD overcomes the strong photon scattering caused by the skin tissue’s multilayered structures and complex heterogeneous medium, and achieves full-thickness imaging of human skin with high resolution (Wang et al., 2022b). Differently configured PADs allow spatial resolution to be scaled to the desired skin imaging depth, while maintaining a high depth-to-resolution ratio. By depicting the fine anatomical structures from epidermis to subcutaneous tissue, PAD can be used to diagnose abnormal pigmentation, and vascular malformation. PAD is gradually proposed in clinical dermatology for the diagnosis of melanoma, psoriasis, port-wine stains, dermatitis, skin grafting, and for the assessment of the efficacy of cosmetics (Aguirre et al., 2017; Tsuge et al., 2020; Wang et al., 2022a). In clinical diagnosis and treatment, quantitative information on the distribution, depth, and diameter of the melanin and vessels can be obtained to determine optimum treatment parameters for individual patients. Currently, the limitation of PAD lies in the fact that coupling gel is required to transmit photoacoustic signals, which is not conducive to imaging skin ulcers. In the future, non-contact photoacoustic detection technology could make up for this deficiency. This protocol is dedicated to the design and debugging of PAD for human skin imaging. Overall, this protocol will promote preclinical and clinical applications of PAD in dermatology and plastic surgery.