Overview of Duplex Ultrasound
Duplex ultrasound is a unique type of ultrasound scanning used by doctors to diagnose and treat medical conditions. Combining aspects of both anatomic (which focuses on body structure) and flow (highlighting blood movement) ultrasounds, duplex ultrasonography can provide detailed images for the doctor to analyze.
The term “Doppler ultrasonography” refers to how this type of ultrasound uses the Doppler effect – a physics principle that you might notice when a siren sounds different as it approaches and then passes you. In the case of an ultrasound, it’s used to interpret movement or blood flow within body tissues.
In order to understand a duplex ultrasound image, you need to know a few key principles like the Doppler effect mentioned above, electronic gating (which helps specify what area is being scanned), and the various ways ultrasound waves can be produced.
Anatomy and Physiology of Duplex Ultrasound
The Doppler effect is the change we observe in sound wave frequencies due to movement. This is important for something called duplex ultrasound, a test used by doctors to examine our bodies. Everything happens within the ultrasound machine’s scanning device, which is called a transducer. This transducer has special crystals (piezoelectric crystals) that change electrical energy into ultrasound waves and then back again.
This device sends out sound waves that bounce off the tissues in our bodies and return to the scanner. The change in frequency of these waves, also known as the Doppler shift, is then calculated using a specific equation. One thing to note from this equation is that as the angle of the ultrasound beam increases, the image quality decreases, especially for angles more than 70 degrees.
An important function of ultrasound machines is electronic gating. This function sets the depth level where doctors can examine structures in our bodies using ultrasound. So, if they need to look deeper into the body or make the image clearer, they can adjust this setting.
Ultrasound machines make use of different methods to generate waves, such as continuous wave, pulsed wave, high repetition frequency, color, and power. For instance, continuous wave ultrasound continually sends out waves. As these waves meet moving structures in our bodies, they change and come back to the scanner. Things moving towards the scanner decrease the frequency, while things moving away from it increase the frequency. This information is then changed into an image that shows movement toward the scanner in red and movement away in blue.
However, when there are very high changes in frequency, called “Doppler shifts,” the image can become unclear, and the direction of movement can appear reversed. This is called aliasing artifact or ambiguity. The limit when this happens is determined by a concept called the Nyquist limit.
Another method is pulsed wave ultrasound, which sends out waves in regular intervals, with breaks in between. This technique minimizes the overlap between echoes, allowing for more accurate velocity measurements. Other methods include Color Doppler imaging, which provides information on the rate and direction of blood flow, and Power Doppler imaging, which gives clear pictures of our body structures with less background noise, but less information on the speed of blood flow within vessels.
Why do People Need Duplex Ultrasound
Duplex ultrasound is a type of medical imaging technique that has many benefits compared to other methods. It’s noninvasive, meaning it doesn’t require surgery or any kind of medical procedure. It provides a detailed view of what’s happening inside the body, it’s portable so it can be performed almost anywhere, and is generally well tolerated by patients.
An additional advantage of duplex ultrasound is that it doesn’t expose the patient to potential kidney-damaging contrast substances often used in medical imaging, or to radiation, and it can be used on patients with medical implants.
However, there are some disadvantages to take into account. One significant issue is that duplex ultrasound heavily relies on the person operating the machine, which potentially means that, if not done correctly, it can lead to mistakes or a delayed diagnosis. Also, it might not work as well for individuals with certain body types.
Despite these potential limitations, the duplex ultrasound is often the preferred way of diagnosing certain medical conditions. These include deep vein thrombosis (a blood clot in a deep vein, often in the leg), venous insufficiency (a condition where the veins have trouble sending blood from the legs back to the heart), and issues affecting the brain’s blood vessels, kidneys, the mesenteric region (the part of the abdomen containing the intestines), and the aortoiliac region (the area where the aorta, the main artery of the body, splits into the two main arteries of the legs).
When a Person Should Avoid Duplex Ultrasound
Duplex evaluation, a type of ultrasound test, doesn’t specifically have any conditions in which it shouldn’t be used. However, some factors might make a patient less able to tolerate the test. For example, if a patient has areas of swelling or infection, the test might be harder to tolerate. Also, a patient’s body size and shape can sometimes make this test harder to do.
Equipment used for Duplex Ultrasound
The essential tool for this process is an ultrasound machine with the ability to show two different types of images at the same time. This machine uses a special handheld device filled with tiny components called piezoelectric crystals. These crystals help the machine to adjust and focus the ultrasound waves, which are like sound waves but too high-pitched for our ears to hear. The machine can modify the strength, clarity, and depth of these waves. The depth can be adjusted from less than 1 cm to up to 20 cm deep, depending on what part of the body it’s taking images of.
The ultrasound machine can work with different types of handheld devices, each offering unique benefits. One kind, called a linear array transducer, is especially good for outlining the map of blood vessels in the body. Lower-pitched transducers, which are generally curved or arranged in a pattern known as a phased array, are better for imaging the organs in your belly area or for examining the brain. Some special transducers help to improve image quality and reduce distortion of the image, particularly when imaging deep inside the body. There are even two-dimensional transducers available, capable of creating a three-dimensional image out of ultrasound data.
When this machine is used for duplex ultrasonography – a kind of ultrasound scan that shows both motion and structure in the body – it offers two kinds of display. One is the color-flow Doppler, which gives a picture of how fast the blood is flowing in different parts of the body. The other is the gray-scale B-mode, which provides a black and white anatomical image of the body part being scanned.
Who is needed to perform Duplex Ultrasound?
Having a skilled and certified technician who specializes in examining blood vessels is very important for accurate results. This is because the quality of the test largely depends on the person who is performing it.
Preparing for Duplex Ultrasound
If a patient is going to have a duplex ultrasound examination, the preparation needed depends on what part of the body is being looked at. For instance, if the ultrasound is going to check the blood vessels in the torso (the middle part of your body, where your chest and abdomen are), it might be useful for the patient to not eat or drink anything for 4 to 6 hours before the test. This could help to get better results from the ultrasound exam.
How is Duplex Ultrasound performed
When investigating a deep vein thrombosis (DVT), which is a blood clot in a vein deep in your body, the doctor starts by checking the veins in the middle of your calf. They follow these veins up to the ones behind your knee and in your upper leg. They will push on the veins at different spots to see how the blood is flowing. If the blood flow increases when the doctor pushes further down your leg, but not when the doctor pushes closer to your body, it may suggest that there is a DVT.
For upper body DVTs, the main way to tell if there’s a clot is to check how much the vein squishes when pushed on, as well as looking for signs of a shadow on the ultrasound, which can indicate a blockage. Colour Doppler, a tool used in ultrasound to visualize blood flow, helps increase the accuracy of the test and makes it easier to see any partial blockages.
When it comes to venous insufficiency, a condition where the veins have problems sending blood from the legs back to the heart, the patient is examined while standing or lying down with their body slightly lifted. This change of position increases the pressure gradient, which can help reverse the blood flow in the veins. The doctor will then place an ultrasound probe in the groin and check each vein for compressibility, blood flow, increased flow upon pushing, and visibility. If blood flows backwards for more than half a second when the doctor applies pressure, it points to an issue.
Many different diseases that affect the arteries, such as those that impact the brain, kidneys, intestines, and main central arteries are detected and monitored through duplex ultrasonography – a procedure using ultrasound to see how blood flows through your veins and arteries. However, checking arteries in the body like the central, kidney and intestine arteries can take a lot of time and effort. The quality of these scans heavily depends on the skill of the person performing them. So, this method is not as good as some other imaging techniques, and is usually only used in certain circumstances, like for patients with kidney problems. If there are positive results from an initial screening, further tests will be done.
For arteries that supply blood to the brain, duplex ultrasound is extremely helpful when examining the carotid arteries, found in your neck. This method is excellent for finding plaques – a build-up of fats, cholesterol etc., in your arteries and it’s used to figure out which types are more likely to increase the risk of future strokes. Hypoechoic and heterogeneous plaques are more likely to cause cerebrovascular symptoms than hyperechoic plaques. Plaques that have ulcerations are also considered high risk as they greatly increase the chance of getting a stroke.
Possible Complications of Duplex Ultrasound
Any problems that might come up from using a duplex ultrasound are typically due to the specific medical procedures it’s used in, not because of the ultrasound itself. The ultrasound isn’t generally the cause of complications.
What Else Should I Know About Duplex Ultrasound?
Duplex ultrasound is a valuable tool used in medicine. Because it’s portable, relatively cheap, safe, and well-tolerated by patients, it’s being used more and more for a variety of purposes. This method allows doctors to take images of the inside of your body. Understanding why and how this diagnostic tool is used is beneficial.
