The Doppler is a medical imaging technique that allows using ultrasound emitted by a probe to study the circulation of the blood vessels. It is sometimes coupled with ultrasound, this is called a Doppler ultrasound. This test is safe and painless and uses a probe and gel which is applied to the skin. A Doppler ultrasound of the neck allows the study of blood flow in the arteries that leave the heart and go to the brain: this is called a Doppler ultrasound of the supra-aortic trunks or SAT. It enables the verification of the condition of the vessels and the identification of any narrowing in the walls and decreased blood flow. Those at risk, such as diabetics, the obese, smokers, or people with heart problems, undergo regular Doppler's of the neck as means of prevention.