Doppler is used to measure blood flow by bouncing high-frequency ultrasound waves off red blood cells. It is used to detect blocked vessels or reduced blood flow.

Because ultrasound machines tend to be split into “black and white” and “colour Doppler” categories, there is a common misconception that in order to have Doppler capability, one must also purchase a colour ultrasound machine. In fact this is not the case; black and white ultrasound machines with Doppler are common and, in many instances, all that is necessary