Duplex sonography is a non-invasive evaluation of blood flow through your arteries and veins. It is an advanced specialized interpretation of ultrasound waves combining the principles of anatomic and flow ultrasonography to generate images. These images are produced by utilization of the Doppler effect. The Doppler effect measures the frequency shift for example, the flow in an artery and their relative velocity in direction towards and reverse the probe.
A common physical demonstration of the Doppler effect is when an ambulance passes with its siren blaring you can hear the pitch of the siren change: as it approaches the siren’s pitch sounds higher than when it is moving away.
Why It's Done
In stroke, headaches or neck pain an ultrasound study of the brain suppling arteries extracranial (at the neck) and intracranial (inside the brain) identifies the hemodynamic status of the vessels. Investigations include extracranial mainly the common carotid artery and it branches and the vertebral arteries and intracranial the middle, anterior and posterior cerebral arteries and the basilar artery. The presence of pathology as stenosis, occlusions, dissections or inflammations known as vasculitis can be identified fast and easily.
How the Test is Performed
Ultrasound examinations are painless and easy for the patient. The examination can be done in comfortable clothing or a disposable gown to protect your clothes because ultrasound gel will be applicated over the area of interest. The gel helps the sound waves get into your tissues.
A probe is moving by the hand of the examiner over the area being tested. The Doppler mode creates a "swishing" sound, which is the sound of your blood moving through the arteries and veins. You need to stay still during the exam. You may be asked to lie in different body positions, or to take a deep breath and hold it. It usually takes about 30 minutes.
Common indications for performance of this examination include, but are not limited to:
- Transient ischemic attacks
- Amaurosis fugax
- Carotid bruit
- Stroke (Cerebrovascular Accident)
- Follow-up of known carotid stenosis
- Post intervention follow-up (carotid endarterectomy, stent, etc)
- Trauma in the distribution of the carotid artery