The Doppler shift is the change in frequency that occurs when ultrasound waves reflect off moving objects, primarily red blood cells in medical applications. The magnitude of this frequency shift is directly proportional to the velocity of blood flow and depends on the Doppler angle and the transmitted frequency. The ultrasound machine measures this shift and uses the Doppler equation to calculate the speed of blood flow. Higher velocities produce larger frequency shifts. Spectral Doppler displays these shifts as a waveform showing velocity over time, while color Doppler uses the shifts to create a color-coded map of blood flow direction and relative speed across an entire region of the image.
Sonography Term