Ultrasound

Abstract

Sonography is a section diagram imaging procedure that is based on the propagation of ultrasonic waves (Figs. 7.1, 7.2). The characteristic features of ultrasonography are sound waves that are bound to matter and propagate in a longitudinal direction. The movement of the material particles results in compression and decompression in the tissue. Because the matter particles oscillate transversely to the direction of propagation of the wave, about its rest position, energy is only transported longitudinally in the direction of propagation of the wave. On average, the location of the particles remains constant over time. The characteristics of the sound waves include the wavelength λ, the frequency f and the amplitude A. Here, the speed of propagation of sound waves depends primarily on the density and compressibility of the examined tissue; this speed is at its lowest in air (330 m/s) and at its highest in bone (3,300 m/s), while in soft tissue the speed of sound is approximately 1,500 m/s.

When passing through biological tissue, sound waves are weakened. This is caused by absorption, reflection, refraction, scattering and divergence.