Overview of Sonography Vascular and Lymphatic Assessment, Protocols, and Interpretation
Ultrasonography is a technique that uses sound waves to create pictures of the inside of your body for diagnostic purposes. This technique is portable, affordable, and non-invasive, leading to its increasing popularity in recent years. One type of ultrasonography, called vascular ultrasound, focuses on the blood vessels.
Vascular ultrasound can be used to study various conditions affecting the arteries and veins. This includes diseases affecting the peripheral arteries (arteries outside the heart), arterial aneurysms (unusual bulges in the artery wall), vascular malformations (abnormal formation of blood vessels), as well as venous thrombosis and venous insufficiency (conditions affecting the veins).
Besides blood vessels, sonography can also give us information about the lymphatic system (a part of the immune system) by showing the size and shape of lymph nodes (small glands that filter lymph, the fluid in the lymphatic system). This article will discuss these principles of arterial, venous, and lymph node sonography, as well as their applications to some commonly seen diseases.
Anatomy and Physiology of Sonography Vascular and Lymphatic Assessment, Protocols, and Interpretation
Doppler ultrasonography is a procedure that uses sound waves to create images of the body’s blood vessels. It measures the speed of the blood flow within these vessels. This technology works by using Doppler shift, which helps to identify whether the blood is moving towards or away from the ultrasound machine, also known as the transducer. By directing sound waves at an angle less than 60 degrees, specialists can make sure that they are getting the most accurate measure of blood flow velocity or speed.
Arteries, which are the blood vessels that carry blood away from the heart, can be categorized as either high resistance or low resistance. High resistance arteries typically exhibit a waveform pattern called ‘triphasic waveform’. This type of waveform can usually be observed in arteries located within skeletal muscles. Anything that alters the path of the blood flow in these arteries, such as disease or branching, can potentially change the waveform.
This triphasic waveform consists of a rapid increase and decrease in blood flow speed during systole (heart muscle contraction), reversal of flow during diastole (heart muscle relaxation), and a small amount of forward flow at the end of diastole.
On the other hand, low resistance arteries usually show a ‘monophasic waveform’. These types of waveforms are found in arteries that supply organs with high oxygen demand like the kidneys, intestines, umbilical cord etc. Unlike high resistance arteries, these arteries are continually wide open, allowing for more oxygen absorption. They have two main phases: a slow rise in speed during systole and a gradual decrease during diastole.
There’s been some discussion regarding another type of waveform called ‘biphasic waveform’. It was found that this term was causing confusion so it has recently been replaced by the term ‘multiphasic’ waveform, which includes both triphasic and biphasic waveforms. This new term is more relevant and does not cause any confusion.
Another aspect that’s measured is the resistive index (RI), which can hint at problems if it is extremely high or low. High RI can signify blockage or constriction in the blood vessels, while low RI could represent problems like dampened heartbeats or normal blood flow during diastole. Any changes in the waveform may denote the presence of a blockage, also known as a stenosis.
In comparison to the arterial blood flow, the movement of blood in veins is usually at a lower speed. The blood flow pattern in the veins may change due to breathing or faint heart pulsations. In the portal vein, which carries blood from the gastrointestinal tract and spleen to the liver, there should normally be a forward or ‘hepatopedal’ flow into the liver. If there is a reversal, termed as hepatofugal, it indicates an abnormal condition – portal hypertension, a type of high blood pressure affecting the liver.
Why do People Need Sonography Vascular and Lymphatic Assessment, Protocols, and Interpretation
There are many reasons why a doctor may use a vascular ultrasound, a type of scan that takes pictures of blood vessels in the body. For example, it can be helpful in diagnosing issues with blood flow in the arteries and veins, such as peripheral arterial disease, abnormalities in the blood vessels, bulges in the blood vessels (aneurysms), narrowing of the arteries (stenoses), and blockages (emboli).
This test can check arteries in various parts of the body, including the kidneys, brain, neck, belly, and gut. It can also assess the umbilical arteries in pregnant women.
In addition to checking arteries, a vascular ultrasound is useful for examining veins too. It can be used to diagnose blood clots, check how well dialysis grafts (surgically placed blood vessels for dialysis) are working, identify abnormalities in the veins, and identify chronic illnesses related to veins. The ultrasound can look at veins in different areas of the body, including those in the liver and spleen.
A vascular ultrasound is also a useful tool in observing the effect of specific treatments, like the placement of a shunt (tube) in the liver to improve blood flow, or procedures that open up narrow or blocked blood vessels (angioplasty, venoplasty) or place a mesh tube in a blood vessel to hold it open (stent placement).
One more use of a vascular ultrasound is to check the lymph nodes, which are small glands that filter lymph fluid (part of the body’s immune system). This could be necessary if a physician feels a swelling in the lymph nodes, if a person is concerned about the spread of cancer (for example, in the case of breast cancer), or in the case of certain infections like tuberculosis. Occasionally, a vascular ultrasound can also aid doctors in planning a biopsy, which is a procedure to take a small sample of tissue for testing, in people with widespread illness.
When a Person Should Avoid Sonography Vascular and Lymphatic Assessment, Protocols, and Interpretation
Whether you’re suitable for a certain medical exam can depend on various factors. Generally, if a person is larger in size, it can be harder to get clear results from an ultrasound scan. This is because their body may block some of the sound waves used in the scan, making it less accurate.
Other things, like having a cast, dressing, or surgical material on the body, could also make it harder to perform the exam. Any tremors or movements of the muscles in the arms and legs can also make it difficult to get accurate readings from a Doppler scan, which is a type of ultrasound that looks at blood flow in the veins and arteries.
Equipment used for Sonography Vascular and Lymphatic Assessment, Protocols, and Interpretation
When sound waves become higher pitched (higher frequency) and the wavelength gets shorter, this results in the ultrasound image having a higher level of detail (spatial resolution). However, these types of waves don’t go very far before they lose strength (attenuation). For this reason, when doctors want to look at things deep inside the body like kidneys or iliac arteries, they use transducers that create lower-frequency sound waves (2.5 to 3.5 MHz) because these waves don’t lose strength as easily.
But there’s a downside: while these lower-frequency waves can go deeper, they don’t produce an image with as much detail. On the other hand, higher-frequency transducers (7 to 10 MHz) can’t go as deep, but they provide a more detailed image. So, doctors use these for things close to the surface like blood vessels and soft tissues like finger tendons. The choice of transducer to examine lymph nodes depends on where these nodes are in the body.
The ultrasound machine chosen should be able to work in two modes: B-Mode and Doppler. B-Mode, with ‘B’ standing for ‘Brightness’, helps doctors to assess the anatomy. It provides details like the size of blood vessels and their shape. Doppler mode then helps measure how quickly the blood is flowing, as mentioned earlier.
Preparing for Sonography Vascular and Lymphatic Assessment, Protocols, and Interpretation
Before having a medical exam, it’s important for the doctor and technician to look at any previous images or scans related to your health. This helps them get a better idea of your condition. It’s also beneficial if you can remove any items like casts, bandages, or other materials from the body part being examined, if it’s possible. These items may obstruct the visibility in the exam.
If you can’t remove these items, don’t worry. The technician who’ll do your exam will let the doctor know about it. When you meet the technician, they will ask for your name, date of birth, and other specific details so they can correctly identify you.
If you have questions about what the doctor is looking for, what comes next, or what the results could mean, it’s best to ask your main doctor. The technician can provide technical details about the exam process, but your doctor is the best person to address larger health-related concerns.
How is Sonography Vascular and Lymphatic Assessment, Protocols, and Interpretation performed
Ultrasounds are a type of imaging that doctors use to check the inside of your body. Like a map, they provide a picture of your organs, blood vessels, and tissues. The methods used during an ultrasound depend on what part of your body is being examined.
When an ultrasound is performed on your arm or leg arteries (the vessels that carry blood away from your heart), the doctor first checks the entire length of your arteries, from the top to the bottom. The ultrasound images are taken in two directions – one is a lengthwise view (longitudinal) and the other looks across the vessel (transverse). These are taken in two modes: a normal ultrasound mode (B-mode) and a Doppler mode, which shows blood flow.
The doctor will note how the blood is moving through your arteries. This could be in three, two or one distinct waves: triphasic, biphasic, and monophasic, along with the speed of the blood flow. If there is a narrow or tight spot in your artery (stenosis), the doctor will measure the blood speed just before, at, and just after this spot with ultrasound.
For arm or leg vein ultrasounds (veins carry blood towards your heart), the doctor will also examine the entire length of your veins, from top to bottom. However, the doctor usually doesn’t need to check the veins in your calf (the back part of your lower leg) for blood clots or “deep venous thrombosis”. This is suggested by the American College of Radiology because these smaller veins are less likely to have clots that could cause health problems.
Unlike arteries, veins are checked using a technique called “compression”, in which the ultrasound probe is used to put pressure on the vein. This helps the doctor see if there are any blood clots present, because a vein with a clot will not compress or reduce in size easily. The technologist performing your ultrasound will note this.
They also check each vein for “augmentation”, which is a response when they squeeze (compress) your limb to make your blood flow increase. Additionally, they will record whether there are normal, rhythmic changes in blood flow speed with each breath (phasicity) or not.
Possible Complications of Sonography Vascular and Lymphatic Assessment, Protocols, and Interpretation
Using ultrasound for studying your blood vessels might sometimes lead to confusing results known as artifacts. These discrepancies originate from both the technical limitations of the equipment used, as well as incorrect adjustment of the settings on the ultrasound machine. Familiarity with these artifacts helps in avoiding incorrect diagnosis.
An artifact called ‘aliasing’ can occur when blood velocity is too rapid for the selected measurement range. This generates a visual mistake on the ultrasound display, where the maximum speed appears to be cut off and displayed wrongly on the opposite side of the graph. Another telltale sign of aliasing is a sudden color change in the display, like blue turning to red, without any marker indicating a reversal of blood flow. This can be resolved by setting a higher speed range on the ultrasound machine. Particular attention should be given to aliasing when examining areas with rapid blood flow such as stenosis (narrowed blood vessels).
Low blood flow areas can be overlooked if the velocity setting is set too high. This can lead to incorrect diagnosis, in some cases, such as blood clotting. Therefore, it’s vital always to verify the velocity settings.
The gain control on the ultrasound machine affects how bright the structures look in the display. ‘Blooming’ is an artifact that occurs when a high gain level is chosen and color doppler is used. This effect can distort the ultrasound image by making it appear as if the color overlays the nearby structures, possibly making clots harder to see. Adjusting the color gain to a lower level can prevent this from happening. On the other hand, if the gain is set too low, color images or spectral displays might not show at all. To set the gain accurately, increase it until you see noise, and then reduce it gradually until the noise disappears.
Another artifact, called ‘spectral broadening’, can artificially appear for a variety of reasons. One cause is if the Doppler sample volume is too large for the size of the vessel. This distorts the display, as it includes both the slower blood flow near the vessel wall and the faster flow in the center of the vessel. Given that the smallest Doppler sample volume has a lower limit, smaller vessels are vulnerable to this artifact. Additionally, setting the Doppler sample too close to the edge of the vessel or having a high gain can lead to spectral broadening. This can be avoided by correctly setting the gain, adjusting the size of the Doppler sample volume, and placing it right in the middle of the blood vessel.
What Else Should I Know About Sonography Vascular and Lymphatic Assessment, Protocols, and Interpretation?
Extremity arterial stenosis refers to a narrowing of the arteries in the arms or legs, which can be detected using an ultrasound technique called arterial sonography. The ultrasound findings for this condition could provide the following data:
* Higher peak systolic velocity (PSV), which is the top speed of blood flow in the arteries.
* A PSV ratio greater than 2 suggests a stenosis, or narrowing, over 50%.
* A PSV ratio greater than 3 suggests a stenosis of more than 70%.
* A change from a triphasic (three-phase) to a monophasic (single-phase) blood flow pattern, moving from the beginning to the end of the artery.
* A wider range of speeds (spectral broadening) in the blood flow occurring after the narrowed portion of the artery.
* Slowed and delayed (parvus tardus) blood flow after the narrowed part of the artery.
* A complete absence of blood flow signals a 100% blockage in the artery.
Deep venous thrombosis (DVT) is a common condition where a blood clot forms in the deep veins, usually in the legs. Venous duplex imaging, another type of ultrasound, is frequently used to look at blood clot characteristics, such as:
* The inability to compress the vein segment that contains the blood clot.
* The loss of rhythmic blood flow changes due to breathing (phasicity) after the blood clot, even when forcedly exhaling.
* No colored flow signal on Doppler ultrasound, indicating that blood flow may not be occurring.
* A decrease in blood flow speed when pressing down (augmentation).
Another commonly detected condition using ultrasound imaging is lymphadenopathy, which refers to the abnormal enlargement of lymph nodes, possibly due to cancer or inflammation. Here are some ultrasound features that may suggest a lymph node is malignant (cancerous):
* Absence of the fatty hilum, which is the fatty area inside the lymph node.
* Presence of cystic necrosis, which means there are dead, liquid-filled areas within the lymph node.
* A long-to-short axis ratio less than 2, indicating the lymph node may be more round than usual.
* A larger size of the lymph node; although, size criteria can differ based on the node’s location.
* A resistive index (measure of blood flow resistance) above 0.8.
* High resistance blood flow within the lymph node.
* Presence of calcifications, or hardened areas, within the lymph node.