Techniques for non-invasive Breslow determination use either mechanical or electromagnetic waves. A wave is the propagation of a perturbation inducing reversible variations of local physical properties. It transports energy but no matter. Ultrasounds and optical waves are used mainly because of their innocuousness. In the next paragraphs, ultrasonography then several optical techniques will be developed. Basic physical principles of each type of wave interaction with skin will be described then accuracy of Breslow index determination by such techniques will be given. One paragraph will talk about techniques that have already given promising results in a clinical environment in vivo, namely ultrasonography and dermoscopy
