The wall filter is designed to exclude Doppler signals with low frequency, and high amplitude (highpass filter) from moving tissue, such as a vessel wall. Wall filter performance is critical for effectiveness of a color Doppler system.

(W) The SI unit of power.
Definition: 1 watt is equal to a power rate of one joule of work per second of time or in electrical terms it is the power produced by a current of one ampere flowing through an electric potential of one volt.
Power is the rate at which work is done, or the rate at which energy is expended and is used both in mechanics and in electricity.
The unit is named for James Watt, a British engineer.

The waveform is the record of a signal that varies over time. A blood flow signal for example, usually varies periodically with the cardiac cycle.

See also Coded Excitation, and Pulse Volume Recording.

The wavelength is a unit of relative distance equal to the length of a wave. This could be a light wave, a radio wave, or even a sound wave. For sound waves the formula is:
l=c/f (wavelength = propagation speed/frequency)
In ultrasound imaging is the wavelength the distance between the onset of peak compression or cycle to the next. The wave propagates as bands of compression and rarefaction. One wavelength is the distance between two bands of compression, or rarefaction. Maximum compression corresponds to maximum pressure. The wavelength (see also Angstrom) is important in image resolution.

See also Spectral Reflector.

Windows are areas where the skull bones are relatively thin or where the naturally occurring forage allows proper penetration of the ultrasound beam. These windows are commonly used for transcranial Doppler (TCD) examinations. However, in the best of cases, only approximately 6% of the intensity of the US used reaches the brain substance.

Different usual windows: