Fig. 3
During their propagation, compression or shear waves are modified due to their interaction with the physical medium. Their direction and amplitude may change due to (a) reflection or (b) refraction at the interface of media with different acoustic impedance. The amplitude may also decrease (i.e., attenuation) due to (c) absorption and (d) scattering produced by the insonified medium. e Space between scatterers or within specular reflectors favor the spreading of the wave field due to diffraction. Waves received by the ultrasound transducer to produce an image are attributed to reflection and scattering