A vascular ultrasound is a noninvasive imaging study of arteries and veins. The combination of anatomic imaging of blood vessels and hemodynamic information provided by Doppler ultrasound will result in duplex scans. These noninvasive studies can be performed on literally any area of human anatomy. Blood velocity is detected by positioning the Doppler sample gate within the lumen of the desired vessel. The resultant spectral trace also provides information as to the direction, phase, pulsatile rhythm, and resistivity of flow. Antegrade flow is demonstrated above the baseline. Retrograde flow (i.e., flow in the direction opposite that expected) is demonstrated by a spectral trace below the baseline. Flow that is antegrade through all phases (systole as well as diastole) demonstrates a low-resistive profile, which is normally associated with visceral blood vessels (e.g., renal artery, internal carotid artery). High-resistance, or triphasic, flow is typically associated with peripheral arteries (e.g., femoral artery, brachial artery) and shows a forward–backward–forward pattern in each cycle. Spectral broadening occurs when the sample contains blood cells moving at many velocities; this is generally associated with a flow disturbance. Mathematical ratios that contrast peak or mean velocities at various stages in the cycle can give further clues to the integrity of the vascular system examined. Color Doppler ultrasound generally is used to code flow velocities and direction with color and can readily differentiate the patency of vessels. B-flow is a technique that images the blood itself and has an enhanced ability to display plaque margins.
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