The duplex ultrasound is a diagnostic test administered to assess blood circulation. It combines the techniques of traditional ultrasound with those of Doppler ultrasound. Traditional ultrasound uses sound waves to create black-and-white images of the veins and arteries. Doppler technology, on the other hand, uses sound waves to track circulating blood, generating color images of blood as it flows through the body. Using this combination of techniques, duplex ultrasound helps to distinguish several important characteristics of the blood vessels, including speed and direction of blood flow and diameter of the vessels themselves. Duplex ultrasound can also detect the presence and extent of any obstruction in the blood vessels, such as atherosclerosis or blood clots.
Types of Duplex Ultrasound
There are several different types of duplex ultrasounds that may be administered, depending on the patients symptoms and the region of concern. These types include:
- Duplex ultrasound of the abdomen
- Duplex ultrasound of the carotid artery in the neck
- Duplex ultrasound of the extremities
- Duplex ultrasound of the kidneys
For most types of duplex ultrasound examinations, no preparation is necessary, but patients undergoing an abdominal exam are typically instructed to fast after midnight prior to the test. It also is important for patients to inform their doctors if they are taking any prescribed anticoagulants or certain other medications since these can affect test results.
Reasons for a Duplex Ultrasound
A duplex ultrasound helps the doctor visualize and measure blood flow to many regions of the body. It is useful in assessing the width of specific blood vessels and detecting any blockages, and it has the advantage of being less invasive than an arteriogram or venogram. Duplex ultrasounds can be used to diagnose or evaluate such diseases as:
- Abdominal aortic aneurysm
- Arterial occlusion
- Carotid occlusive disease
- Deep vein thrombosis
- Renal function after transplant
- Peripheral arterial disease
- Renal vascular disease
- Varicose veins
- Venous insufficiency
Patients considered to be at high risk for circulatory problems are more likely candidates for a duplex ultrasound. This category includes smokers, diabetics, and patients with high blood pressure or high cholesterol.
The Duplex Ultrasound Procedure
During the examination, the patient wears a hospital gown and lies on a table. A gel that assists in conduction is spread over the part of the body to be examined. The medical professional administering the test moves a transducer (wand) over the region being evaluated. The transducer emits sound waves; an attached computer measures the sound waves as they echo, creating images. The patient hears a swishing sound during the exam; this is the sound of the blood moving as it circulates through the blood vessels. The patient may experience slight pressure during the procedure, but there is not usually much discomfort.
Throughout most of the procedure, the patient lies still, but may to asked to change positions from time to time and to take and hold a deep breath. During a duplex ultrasound of the extremities, an ankle-brachial index (ABI) may need to be calculated. For this purpose, blood pressure cuffs will be placed on the patient's arms and legs. The ABI result is the number resulting from dividing the ankle blood pressure by the blood pressure in the arm.
Results of a Duplex Ultrasound
The results of a duplex ultrasound are evaluated carefully to detect any abnormalities in the affected blood vessels, such as plaque buildup or blood clots. There are no risks associated with the procedure. Depending upon the medical findings, other treatments, including possible surgery, may be necessary.