What is Doppler ultrasound? Ultrasound imaging involves the use of high-frequency sound waves to produce pictures of the inside of the body. As the sound waves travel through your body, they bounce off tissues in different ways and this contributes to creating an image.
Doppler ultrasound is a special ultrasound technique that evaluates blood as it flows through a blood vessel. It uses the Doppler effect to detect velocity (the speed of flow of blood) inside arteries and veins of the neck, arms, abdomen and legs. There is no ionizing radiation (X-ray) involved. Because ultrasound images are captured in real time, they can show the structure and movement of the body's internal organs, as well as blood flowing through blood vessels. Ultrasound imaging is usually a painless medical test that helps physicians diagnose and treat medical conditions.
What are some common uses of the procedure?The main function is to locate and identify blockages (stenosis) and abnormalities like blood clots, plaque or emboli and help plan for their effective treatment. It is used to monitor the blood flow to organs and tissues throughout the body. It is used in the assessment of tumours and congenital malformations. Sometimes the evaluation of whether a patient is a good candidate for a procedure such as angioplasty is done via this technique and at times it is used to evaluate the success of procedures like grafts or bypass blood vessels.
How should I prepare for the procedure? Comfortable, loose-fitting clothing is preferred as the radiologist or sonographer will need access to the area that needs to be examined. You will need to remove all clothing and jewelry in the area to be examined. You might have to wear a gown during the procedure. If your abdominal vessels are being examined, unless the examination is performed on an urgent basis, you will need to fast for twelve hours before the exam.
How is the procedure performed? For almost all vascular exams, you will lie on your back on a bed. Occasionally the radiologist or sonographer will ask you to lay face-down as they examine your calf vessels.
A clear gel is applied to the area of the body being studied; this is to help the transmission of sound waves and improves the quality of the picture. The sonographer (ultrasound technologist) or radiologist then presses the transducer firmly against your skin and examines the area of interest by pressing the probe to and fro over your body.
They will examine the vessels visually, they may compress them manually from time to time and they will measure flow in them using Doppler. You will recognise the Doppler signal by the sound it makes.
The examination is mostly painless. There may be varying degrees of mild discomfort from pressure as the transducer is pressed against the area being examined, especially if this area is already tender. Do not be alarmed by the measurements they stop and take intermittently; these are essential to determine if there is any disease present. This examination is usually completed within 30 minutes. Once the imaging is complete, the gel will be wiped off your skin. You may be asked to dress and wait while the ultrasound images are reviewed. After an ultrasound exam, you can resume your normal activities.
What are risks? There are no documented risks of this procedure.
What are the limitations? Vessels deep in the body are harder to see than superficial vessels. Specialised equipment may be necessary as these vessels cannot always be well assessed. Smaller vessels are more difficult to image and evaluate than larger vessels, and sometimes one simply cannot comment if the vessel is too small.
It can be very difficult to visualise vessels through a lot of body tissue. Calcifications that occur as a result of atherosclerosis often obstruct the ultrasound beam. Sometimes ultrasound cannot differentiate between a blood vessel that is closed or very nearly closed because the weak volume of blood flow produces a weak signal.