ABSTRACT
Ultrasound imaging uses sound waves to determine the mechanical characteristics of tissue. Sound waves are longitudinal waves that travel through matter using the medium as a carrier for the wave energy. is means that sound cannot travel in a vacuum. In lo ngitudinal w aves, t he d irection o f w ave p ropagation i s parallel to t he mot ion of t he me chanism t hat forms t he w ave: particles, mole cules, a nd s o o n. I n c ontrast, ele ctromagnetic waves (e.g., l ight, x -ray, a nd r adiowaves) a re t ransverse w aves where the electric eld and the magnetic eld are perpendicular to each other, and the direction of propagation is perpendicular to the wave mechanism itself. Ultrasound waves are represented by medium compression and expansion, which form the crests and valleys, respectively, in t he wave description, t hat i s, pressure waves. Figure 32.1 illustrates the compression at the crest of the wave and the expansion at the valley.
