Ultrasound and water in the stratum corneum

Because the penetration depth of ultrasound waves is inversely related to their frequency, high-frequency ultrasound (20 to 150 MHz) can be employed for the study of the skin, which, thanks to its superficial location, can be explored achieving a high resolution and magnification.1-16 The generation and detection of ultrasound is based on the pulse-echo principle: 17,18 Employing 20 MHz B-scanning, each echo signal is converted into a pixel, which is depicted by one false color out of 256 colors composing a fictional scale, where 0 corresponds to absence of echogenicity and 255 to maximum in echogenicity. Thus, a cross-sectional image of the skin is represented on the monitor. The positioning of each pixel from the surface to the depth is established according to the interval between echo transmission and echo return (assuming a constant velocity throughout the tissue of 1580 m/s)