Two quantities (x, y) are called proportional if they vary in such a way that one of the quantities is a constant multiple of the other, or equivalently if they have a constant ratio (k = y/x). This constant ratio (k) is called the proportionality constant or constant of proportionality of the proportionality relation.

See also Amplitude, Acoustic Power, and Attenuation Coefficient.

(FFT) The fast Fourier transformation is a particularly fast and efficient computational method of performing a Fourier transformation, which is the mathematical process by which raw data is processed into a usable image.
The fast Fourier transform analyzer is a common device that performs spectral analysis in ultrasound instruments. In this case, it displays different quadrature Doppler frequencies or reflector velocities when a sample volume cursor is used along time. The Doppler frequency is proportional to the spectral reflector velocity.

See also Proportionality Constant, and Sampling Rate.

Poiseulles law states that the flow rate in a long, straight tube with laminar flow is proportional to its length and viscosity and inversely proportional to the fourth power of its radius.

See also Proportionality Constant.

The scattering strength is proportional to the sixth power of the radius of the point scatterer, and furthermore inversely proportional to the fourth power of the ultrasound wavelength (i.e., proportional to the fourth power of the ultrasound frequency).
The scattering strength of a point scatterer is measured by cross-section scattering.

See also Proportionality Constant, Backscattering.