What is Venous Ultrasound Imaging?

Ultrasound or sonography involves sending sound waves into the body. These sound waves are reflected off the internal organs and are recorded by special instruments that create images of anatomic parts. No ionizing radiation (x-ray) is involved in ultrasound imaging. Ultrasound images are captured in real-time so they can show movement of internal tissues and organs, such as the flow of blood in arteries and veins.

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What are some common uses of the procedure?

The most common reason for a venous ultrasound exam is to search for blood clots, especially in the veins of the leg. These clots may break off and pass into the lungs, where they can cause a dangerous condition called pulmonary embolism. If found in time, there are treatments that can prevent this from happening.

Other reasons to do a venous ultrasound study:

• Find the cause of long-standing leg swelling. In people with varicose veins, a common condition, the valves that keep blood flowing in the right direction may not work well, and venous ultrasound can help the surgeon decide how best to deal with this condition.
• Aid placement of a needle or catheter in a large interior vein. Sonography can help locate the exact site of the vein and avoid complications such as bleeding or air in the chest cavity.
• Map out the veins in the leg or arm so that segments may be removed and used to bypass an area of disease. An example is using pieces of vein from the leg to surgically bypass narrowed coronary arteries.
• Examine a blood vessel graft used for dialysis if it is not working as expected; an area of narrowing in the graft may be responsible.

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How should I prepare for the procedure?

You should wear comfortable, loose-fitting clothing for your ultrasound exam. No other preparation is required. You will have to remove clothing and jewellery in the area to be examined.

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What does the equipment look like?

The equipment consists of a transducer and a monitoring system. The transducer is a small, hand-held device that resembles a microphone. The radiologist or Sonographer spreads a lubricating gel on the area being examined and then presses this device firmly against the skin.

The ultrasound image is immediately visible on a nearby screen that looks much like a computer or television monitor. The radiologist or Sonographer watches this screen during an examination and captures representative images for storage. If a Doppler study is done, the image may be in colour and the signal can be heard as an audible sound. Often the patient is able to see and hear it as well.

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How does the procedure work?

The ultrasound transducer generates sound waves that pass through the skin and also serves as a microphone to record the returning sounds—the echoes. When pressed against the skin, the transducer directs high-frequency sound waves toward the veins being studied and records any changes in the pitch and direction of the returning echoes. The bounce-back echoes, or the signature, are automatically measured by the computer and converted electronically to a picture that shows what is happening at that instant—creating a so-called "real-time" image on the monitor screen. These images can be videotaped, or they may be frozen in time to obtain still pictures. If a Doppler study is done, blood flow can be displayed in color on the screen and actually heard.

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How is the procedure performed?

The patient is positioned on an examination table that can tilt and move. A clear gel is applied to the area that will be examined. The gel helps the transducer make a secure contact and eliminates air pockets between the transducer and the skin, since the sound waves cannot penetrate air. The Sonographer then presses the transducer firmly against the skin and sweeps it back and forth to image the area of interest, reviewing the images on the monitor and capturing "snapshots" as required. The entire area of interest will be scanned, obtaining images from different perspectives. Sometimes the examiner may want to obtain images while you are sitting or standing upright. The examination usually takes less than 30 minutes.

When the examination is complete, the patient may be asked to dress and wait while the ultrasound images are reviewed, either on film or on a monitor. Often, though, the Sonographer or radiologist is able to review the ultrasound images in real time as they are acquired, and the patient can be released immediately.

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What will I experience during the procedure?

You will not hear any of the ultrasound emission or the echoes sent back to the screen, although you may hear pulse-like sounds if a Doppler examination is ordered. You probably will lie on your back, and the table may be tilted or moved to provide better access to a particular area. You may be standing for the procedure. Often you will have a chance to watch the screen along with the examiner, though it will not be easy to make sense out of what you see. Most ultrasound studies take no longer than a half-hour. Venous ultrasound is usually a painless examination. If, however, your leg is swollen and tender, the pressure from the ultrasound transducer may add to your discomfort.

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Who interprets the results and how do I get them?

A radiologist, who is a physician experienced in ultrasound and other radiology examinations, will analyze the images and send a signed report with his or her interpretation to the patient's personal physician. The patient receives ultrasound results from the referring physician who ordered the test results. New technology also allows for distribution of diagnostic reports and referral images over the Internet at some facilities.

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What are the benefits vs. risks?

Benefits

• Ultrasound scanning is widely available and less expensive than other imaging methods. It is rapidly completed and no radiation exposure is involved. Furthermore, this procedure is non-invasive, requiring no penetration of the skin or any body cavity.
• Ultrasound scanning gives a clear picture of soft tissues that do not show up well on x-ray images.
• Venous ultrasound helps to detect blood clots in the veins of the legs before they become dislodged and pass to the lungs. It also can show the movement of blood within blood vessels.
• Compared to venography, which requires injecting contrast material into a vein, venous ultrasound is nearly as accurate for detecting blood clots in the calf and almost fully as accurate in finding clots in veins of the thigh.
• Sonography is easily carried out, painless and causes no health problems. It may be repeated as often as is necessary.

Risks

• For standard diagnostic ultrasound there are no known harmful effects to humans.

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What are the limitations of Venous Ultrasound Imaging?

Veins lying deep beneath the skin, especially small veins in the calf may be hard to see clearly.
 

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