A Doppler ultrasound test uses reflected sound waves to see how blood flows through a blood vessel. 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 narrow 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 (fetus) to check the health of the fetus.
The three basic types of Doppler ultrasound are:
- Color Doppler. Color Doppler uses standard ultrasound methods to produce a picture of a blood vessel. Also, a computer converts the Doppler sounds into colors that are overlaid on the image of the blood vessel and that represent the speed and direction of blood flow through the vessel. Power Doppler is a special type of color Doppler. Power Doppler can get some images that are hard or impossible to get using standard color Doppler. Power Doppler is most commonly used to evaluate blood flow through vessels within solid organs.
Why It Is Done
Doppler ultrasound is done to:
- Find blood clots and blocked or narrowed blood vessels in almost any part of the body, especially in the neck, arms, and legs.
- Evaluate leg pain that may be caused by intermittent claudication, a condition caused by atherosclerosis of the lower extremities.
- Evaluate blood flow after a stroke or other condition that might be caused by a problem with blood flow. Evaluation of a stroke can be done through a technique called transcranial Doppler (TCD) ultrasound.
- Evaluate varicose veins or other vein problems.
- Map veins that may be used for blood vessel grafts. It also can check the condition of grafts used to bypass blockage in an arm or leg.
- Find out the amount of blood flow to a transplanted kidney or liver.
- Monitor the flow of blood following blood vessel surgery.
- Find out the presence, amount, and location of arterial plaque. Plaque in the carotid arteries can reduce blood flow to the brain and may increase the risk of stroke.
- Guide treatment such as laser or radiofrequency ablation of abnormal veins.
- Check the health of a fetus. Blood flow in the umbilical cord, through the placenta, or in the heart and brain of the fetus may be checked. This test can show if the fetus is getting enough oxygen and nutrients. Doppler ultrasound may be used to guide decisions during pregnancy when:
- The fetus is smaller than normal for his or her gestational age (fetal growth restriction). Blood flow through the large blood vessel in the umbilical cord (the umbilical artery) can be looked at.
- Rh sensitization has occurred. Blood flow through a blood vessel in the brain (the middle cerebral artery, or MCA) can be used to monitor fetal health.
- The mother has other problems, such as preeclampsia or sickle celldisease.
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