Final answer:
The effects of tissue on sound waves or the effects of a medium on an ultrasound wave are called acoustic impedance, which reflects and transmits sound waves at the boundary between media of different impedances.
Step-by-step explanation:
The effects of tissue on sound waves or the effects of a medium on an ultrasound wave are called acoustic impedance. This is a property of a medium that impacts the propagation of sound waves through it, making their transmission more difficult. When an ultrasound wave encounters the boundary between two media of different acoustic impedances, there is a reflection and transmission of the wave's energy. The formula for acoustic impedance (Z) is Z = ρu, where ρ is the density of the medium (in kg/m³) and u is the speed of sound through the medium (in m/s). The greater the difference in the acoustic impedances of the two media, the more wave energy is reflected and the less is transmitted. It means that, when comparing the acoustic properties of various media, including soft tissue, bone, and air, the variance in their impedances will affect how sound waves behave at the boundaries between them.