Important Definitions!

1. Attenuation: When sound waves weaken in intensity, power, and amplitude as they propagate in a medium.

2.  Reflection: When sound strikes a boundary, causing a portion of the waves energy to be redirected.

3.  Specular Reflection: When the boundary is smooth, like with soft tissue, the sound is reflected in only one direction in an organized manner.

4.  Diffuse Reflection: When sound reflects  off an irregular surface, like the liver, it radiates in more than one direction.

5.  Scattering: The random redirection of sound in many directions. This happens particularly in lung tissue because the alveoli are filled with air.

6.  Rayleigh's scattering: A special form of scattering that occurs when the structures dimensions are much smaller than the beams wavelength. It redirects the sound wave equally in all directions. This happens when imaging red blood cells.

7.  Absorption: When ultrasonic energy is converted into another energy form, such as heat. This happens specifically with bone.

8.  Attenuation Coefficient: When sound energy is extracted from a wave by absorption, scattering, and reflection.

9.  Attenuation in media: From lowest to highest attenuation: water, blood, urine, biologic fluids, fat, soft tissue, muscle, bone and lung, air.

10.  Normal incidence: The incident sound beam strikes the boundary at exactly 90 degrees.

11.  Oblique incidence: The incident sound beam strikes the boundary at any angle other than 90 degrees.

12.  Refraction: The change in direction of wave propagation when traveling from one medium to another. This is why a pencil in a glass of water appears bent.

13.  Snells' Law: A fundamental formula in wave physics that predicts exactly how much a wave will bend (refract) when it passes at an angle from one medium into another.