ABSTRACT
The fundamental physical principle of a dermatological ultrasound scanner is the emission of high-frequency ultrasound (>10 MHz) from a transducer. The sound emission is not continuous, but pulsed; i.e., the equipment automatically and very rapidly switches between emission of sound and registration of the sound returning to the same transducer (echo) from objects being studied. Using different modes of scanning tissue parameters such as in vivo distance, in vivo cross-sectional area, and in vivo volume can be calculated on a purely noninvasive basis. The velocity of longitudinal sound waves in tissue is determined by its elasticity and density. The acoustic characteristic impedance of a tissue is defined as the product of its density and the velocity of sound in the tissue. Measurement using laser-Doppler equipment is in general strongly dependent on the laboratory and the experimental conditions, as skin perfusion is a physiological parameter.
