# Summarizing Ultrasound

## Summary

• The acoustic impedance is defined as:

$$Z=\mathrm{\rho v},$$

$$\rho$$ is the density of a medium through which the sound travels and $$v$$ is the speed of sound through that medium.

• The intensity reflection coefficient $$a$$, a measure of the ratio of the intensity of the wave reflected off a boundary between two media relative to the intensity of the incident wave, is given by

$$a=\cfrac{{({Z}_{2}-{Z}_{1})}^{2}}{{({Z}_{1}+{Z}_{2})}^{2}}.$$

• The intensity reflection coefficient is a unitless quantity.

## Glossary

### acoustic impedance

property of medium that makes the propagation of sound waves more difficult

### intensity reflection coefficient

a measure of the ratio of the intensity of the wave reflected off a boundary between two media relative to the intensity of the incident wave

### Doppler-shifted ultrasound

a medical technique to detect motion and determine velocity through the Doppler shift of an echo