To investigate imaging characteristics of human skin in different sites by using 20-MHz and 50-MHz high-frequency ultrasonography, and to compare the reliability of skin thickness measurement by the above two approaches of ultrasonography.

A total of 39 healthy volunteers aged 18-39 years were enrolled into this study. Then, 20-MHz and 50-MHz ultrasonography were separately performed to image 20 different sites on the body, and the thickness of the epidermis and dermis were measured and evaluated by 3 dermatologists independently. The ultrasonic images were analyzed, and the intraclass correlation coefficient (ICC) was used to assess and compare the reliability of skin thickness measurement by 20-MHz and 50-MHz ultrasound.

The ICC values were less than or close to 0.7 in epidermal thickness measurement at almost all the tested sites between 20-MHz and 50-MHz ultrasono-graphy, suggesting poor reliability. However, 20-MHz and 50-MHz ultrasonography showed excellent reliability in dermal thickness measurement with the ICC greater than 0.75 at almost all the tested smooth and flat body sites. The 20-MHz ultrasound could provide clear images of the dermis and subcutaneous tissue, while 50-MHz ultrasound could only provide clearer images of the dermis in details. In some uneven sites with complex anatomical structures, 20-MHz and 50-MHz ultrasound probes had their own advantages and disadvantages in imaging depth and detail resolution.

The 20-MHz and 50-MHz ultrasono-graphy both can serve as non-invasive imaging techniques to show structures of the epidermis and dermis better. In different parts of human body, ultrasound frequencies should be selected according to their imaging characteristics.

Ultrasonography; Skin structure; Skin thickness; Interclass correlation coefficient