Duplex scanning of lower limb arteries

Real localization of lower extremity vascular lesions and assessment of hemodynamic consequences of stenosis based on non-invasive methods became possible with the development of ultrasound technologies. Hopes associated with obtaining a two-dimensional black-and-white image of a vessel in B-mode in real time did not come true. It turned out that some atherosclerotic plaques and intravascular thrombi give the same acoustic reflection as blood, which is why they cannot be detected. Duplex scanning with color Doppler, implemented in modern ultrasound scanners, is a modern and informative diagnostic technology that allows obtaining objective information about the state of the structure of large, medium and small vessels and their functions.

According to the opinion of many authoritative specialists, reflected in the materials of the International Congress on Angiology, held in London in 1995, duplex scanning should become the main method for diagnosing vascular pathology and the “gold standard” for other methods.

The B-mode image allows you to identify the artery under study, evaluate the anatomical features, establish calcification of the vessel wall and direct the Doppler sensor to the center of the flow along the visualized artery to analyze the blood flow characteristics. In color Doppler imaging, red indicates the flow directed toward the sensor, blue - away from it. Since the color image is superimposed on the black and white in real time, the artery can be seen as a pulsating red lumen, a thrombus or atherosclerotic plaque - as a black area protruding into the lumen, and dense stenosis - as a white protrusion. To convert the Doppler frequency shift into velocity, it is necessary to know the angle between the ultrasound beam and the blood vessel. Most modern duplex systems provide measurement of angle values directly from the black and white image of the vessel. The cursor is aligned with the vessel axis, and the device automatically calculates the blood flow velocity.

The diagnostic capabilities of duplex scanning have been expanded by introducing the EDC method. The method is based on the analysis of the amplitude of ultrasonic vibrations reflected from moving objects. Unlike the CDC, the EDC method is little dependent on the angle between the ultrasound beam and the blood flow, is more sensitive, especially to slow flows, and is more noise-resistant.

The duplex sensor contains separate crystals for imaging and Doppler velocity determination. Low-frequency sensors are capable of visualizing structures at a depth of up to 20 cm. Therefore, sensors with a frequency of 2.5 and 3.5 MHz are required for examining the aortoiliac zone. However, such sensors have limited resolution and low sensitivity when blood flow is reduced. When examining superficial vessels of the lower extremities, it is recommended to use linear sensors with a frequency of 5, 7, and 10 MHz.

Duplex scanning of the lower extremity arteries is performed with the patient in a horizontal supine position. Many prefer to begin the examination with a transverse scan to obtain an image of the OBA at the inguinal fold. Usually, the OBA, SBA, and the initial segment of the GBA are well visualized. The popliteal artery is located with the patient in a prone position. The posterior and anterior tibial arteries are well visualized below the popliteal fossa, but these branches are narrow and therefore in many cases difficult to access for good visualization. It is also difficult to obtain adequate Doppler signals in these vessels. Therefore, the value of duplex scanning decreases when located below the popliteal region.

Duplex scanning is most widely used in clinical practice for lesions of the arteries of the lower extremities to assess the aortoiliac, femoropopliteal segments and the deep femoral artery.

Despite a number of limitations in the capabilities of duplex scanning for characterizing peripheral circulatory disorders, non-invasiveness, safety for the patient, the possibility of repeated studies, a large volume and high quality of information on the nature and extent of damage to the vascular bed, and known advantages over X-ray contrast angiography make this method a priority in the clinic of peripheral vascular disorders.

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