Two levels of one vascular bed
The blood supply to the brain is provided by four great vessels: two carotid and two vertebral arteries. A study of the neck - the extracranial stage - shows the thickness of the intima-media complex as an early marker of atherosclerosis, atherosclerotic plaques with an assessment of their structure and the percentage of stenosis, tortuosity and course deformity, as well as the condition of the vertebral arteries, including in the bone canal, where they are often compressed in pathology of the cervical spine.
The transcranial stage completes the picture from inside the skull. Through the temporal, occipital and orbital acoustic windows, the sensor reaches the middle, anterior and posterior cerebral arteries, the main and intracranial segments of the vertebral arteries. Their patency, blood flow rates, the presence of stenoses and the functioning of the circle of Willis - a system of connections that allows blood to be redistributed when one of the vessels is turned off - are assessed.
It is the combination of two levels that makes the study truly informative. Stenosis of the carotid artery in the neck can occur without consequences if the circle of Willis is closed and compensation is sufficient, and vice versa, with an open circle, even moderate narrowing can lead to ischemia. Such a comprehensive study is indicated for dizziness, tinnitus, previous transient ischemic attacks and stroke, before cardiac surgery and in preparation for intervention on the carotid arteries.
What does duplex scanning show?
The method combines conventional ultrasound imaging of a vessel with analysis of the blood flow in it. The wall of the artery and vein, the thickness of the intima-media complex, atherosclerotic plaques with an assessment of their structure and the degree of narrowing of the lumen, blood clots, aneurysms, tortuosity and pathological anastomosis are visible.
Spectral analysis translates this into numbers: peak systolic velocity, end-diastolic velocity, resistance indices. They are used to calculate the percentage of stenosis - an indicator that determines whether conservative treatment is sufficient or intervention is required.
Functional tests
Some vascular pathology appears only during exercise. Compression tests detect thrombosis: a healthy vein is completely compressed by the sensor, a thrombosed one is not. The Valsalva maneuver shows the incompetence of the venous valves and reflux underlying varicose veins.
Positional tests are used when compression syndromes are suspected, when a vessel is compressed by muscles, ligaments or an additional rib in a certain position of the limb. At rest the picture is normal.
Advantages over other methods
Duplex scanning does not require contrast or radiation, so it can be repeated as often as necessary, including in cases of renal failure and allergies to iodine-containing drugs, where contrast angiography is contraindicated.
Operator-dependent method: the result depends significantly on the experience of the doctor and the quality of the device. Therefore, when making fundamental decisions, for example, before vascular surgery, the study is often repeated or supplemented with computed angiography.