The top echorich band in a 50-MHz ultrasound sonogram reflects epidermal properties

High-frequency ultrasonography is a useful noninvasive tool to measure the acoustic properties of skin. Due to the ambiguity or confusion over the meaning of the skin entry echo, measurements have been limited to the dermis or full skin thickness with little data on epidermal properties. The purpose of this study was to better understand the nature of the skin entry echo and determine whether it is related to epidermal structure. We approached the problem by dampening the sudden change in material density from the coupling medium to the skin surface using facial tissue as a masking material. The thickness and acoustic density of bare and masked skin sites were measured using dermal ultrasound with a 50-MHz transducer. Results showed that the original thickness and acoustic density of the skin entry echo did not change when the skin was masked up to two layers. A comparison between the epidermal thicknesses measured using ultrasound and confocal microscopy also indicated that the two methods yielded about the same results with no statistically significant difference detected. This study demonstrates that the purported skin entry echo is not just a meaningless artifact, and it reflects useful properties of epidermal structure.