A Doppler Ultrasound, also called a Colour Doppler Test is a non-invasive test that can be used to estimate the blood flow through blood vessels. It helps doctors evaluate blood flow through major arteries and veins such as those of the arms, legs and neck. It can show blocked or reduced flow of blood through narrowed areas in the major arteries of the neck that could cause a stroke. It also can reveal blood clots in leg veins (deep vein thrombosis or DVT) that could break loose and block blood flow to the lungs (pulmonary embolism). During pregnancy, Doppler Ultrasound may be used to look at blood flow in an unborn baby in order to check the health of the foetus.