You have probably wondered what are the red and blue colours you are seeing on the screen during your private ultrasound or what is the Doppler scan your doctor recommended.
What is Doppler Ultrasound?
Doppler ultrasound is a type of medical ultrasound that uses the Doppler effect to generate images of moving fluids mainly blood. These images show the relative velocity of the fluids and movement within the body.
The test is usually part of an ultrasound investigation for example an abdominal scan to check the blood flow of the liver and portal vein.
What is Doppler effect?
Austrian physicist Christian Doppler in 1842 proposed that the Doppler effect is seen in the change in coloured light from stars and the change in the sound of a passing object, as in a passing train. In 1845, he and Buys Ballot proved the Doppler Effect of sound waves: A sound's pitch would change if its source or recipient is in motion.
When sound is emitted as a constant by an object and a recipient is moving towards or away from the source a change in frequency will occur, this is the Doppler effect. As you can imagine this Doppler effect can give useful information when applied to the human body during Doppler ultrasound examination.
Why is Doppler done?
Doppler is used to look for blood clots and blocked or narrowed blood vessels in almost any part of the body but most commonly in the neck, arms, legs and pregnancy.
DVT Scans
Evaluate the veins of mainly legs and arms for any signs of clots. You can find more dvt scans on our private DVT scan page.
Carotid Arteries
Evaluate the blood flow and the health of carotid arteries. and check for signs of plaque that may increase the chances of a stroke.
Transplant Kidneys or Liver
Evaluate the health and blood flow of transplant kidneys or liver.
Plaque in the carotid arteries can reduce blood flow to the brain.
Pregnancy scans
Doppler is commonly used during pregnancy ultrasound scans to check the blood flow in the umbilical cord, through the placenta, or in the heart and brain of the foetus.
Types of Doppler Ultrasound
The most common types of Doppler are:
Continuous Wave Doppler
The transmitter emits a continuous sinusoidal wave, so a receiver can detect the phase shift. An audible sound is recorded and analysed. CW Doppler provides high sensitivity to low velocities and detection of high velocities without aliasing. However, CW Doppler cannot distinguish between the sending and receiving signals or extraneous echoes. CW Doppler ultrasound does not produce images as Pulsed Wave Doppler does.
Pulsed-Wave Doppler Ultrasound
PWD is combined B-mode to produce images of a certain structure. PW uses a pulsed echo system, the PW transducer both sends and receives the signal. It sends in short bursts, on and off, so it can receive when it is not sending.
Colour Doppler
During colour Doppler the movement of blood flow is presented on the ultrasound screen in colours, usually red and blue denoting movement towards and away the probe respectively.
Power Doppler
During Power Doppler the motion signals are presented in colour like Colour Doppler but combined into one. Power Doppler offers better sensitivity when compared to Colour Doppler but the direction of blood is not represented.
Duplex Ultrasound
Duplex ultrasound is a combination of Doppler tests to see how blood moves through your arteries and veins. Duplex means that two types of ultrasonography are employed: regular B-mode ultrasounds, and Doppler ultrasounds. The conventional ultrasound shows the structures of your blood vessels and Doppler shows the movement of your red blood cells through the vessels and the sound of the frequency shifts.
Duplex ultrasound produces images that can be colour-coded to show if the blood vessel is narrow or blocked.
Duplex ultrasound is commonly used in examinations such as DVT scans, pregnancy scans and carotid arteries scans.
Triplex Doppler
During Triplex Doppler examination the sonographer evaluates the region of interest simultaneously using black and white mode, colour doppler and pulse wave modes.
How is the test done?
This test is done by a specialist in ultrasound most commonly a radiologist, sonographer or vascular technician depending on the body part to be imaged. Doppler scans performed in a hospital or private clinic setting.
You may need to expose the area to be imaged and depending on the examination the practitioner will guide you on how to position yourself.
For example, during a pregnancy scan, you will lie on your back or on your left side with your belly exposed.
Gel is applied to the skin to help the sound waves pass through. The transducer is placed in the gel and moved along the skin. You need to lie very still during the test. You may hear sounds from the flow of blood through the blood vessels.
The test usually takes 5 to 30 minutes.
Is a Doppler Test Painful?
A Doppler test is not painful although you might feel some pressure from the ultrasound probe.
How Much Does a Doppler Scan Cost?
The cost of a Doppler scan depends on the organ to be evaluated and varies from clinic to clinic and depends on location.
References
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
- Roman AS (2013). Late pregnancy complications. In AH DeCherney et al., eds., Current Diagnosis and Treatment Obstetrics & Gynecology, 11th ed., pp. 250–266. New York: McGraw-Hill.
