Duplex scanning of arteries of lower extremities
Last reviewed: 23.04.2024
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The actual localization of the lesion of the vessels of the lower limbs and evaluation of the hemodynamic consequences of stenosis on the basis of non-invasive techniques became possible with the development of ultrasound technology. Hopes associated with obtaining a two-dimensional black and white image of a vessel in the B-mode in real time, did not materialize. It turned out that some atherosclerotic plaques and intravascular thrombi produce the same acoustic reflection as blood, because of which they can not be detected. Duplex scanning with CDC, realized in modern ultrasonic 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.
In the opinion of many authoritative experts, reflected in the materials of the International Congress on Angiology, held in London in 1995, duplex scanning should become the main method of diagnosing vascular pathology and the "gold standard" for other techniques.
The image in the B-mode allows to reveal the examined artery, to evaluate the anatomical features, to establish the calcification of the vessel wall and to direct the Doppler sensor to the center of the flow along the visualized artery to analyze the characteristics of the blood flow. At the CDC, the red color indicates the flow directed to the sensor, the blue one from it. Since the color image is superimposed on black and white in real time, the artery can be seen as a pulsing red gleam, a thrombus or an atherosclerotic plaque - in the form of a black patch that protrudes into the lumen, and dense stenosis as a white protrusion. To recalculate the Doppler frequency shift in velocity, it is necessary to know the angle between the ultrasound beam and the blood vessel. Most modern duplex systems provide the measurement of the angle values directly from the black-and-white image of the vessel. The cursor is aligned along the axis of the vessel, and the device automatically calculates the blood flow velocity.
The diagnostic capabilities of duplex scanning are extended due to the introduction of the EHD method. The method is based on an analysis of the amplitude of ultrasonic vibrations reflected from moving objects. Unlike the CDC, the EHD method is not very dependent on the angle between the ultrasonic beam and the blood stream, it is more sensitive, especially to slow flows, and is more noiseproof.
The duplex sensor contains separate crystals for imaging and Doppler velocity determination. Low-frequency sensors are able to visualize structures at a depth of up to 20 cm. Therefore, sensors with a frequency of 2.5 and 3.5 MHz are necessary for the investigation of the aorto-ileal zone. However, such sensors have limited resolution and low sensitivity when reducing blood flow. In the study of superficial vessels of the lower limbs, the use of linear sensors with a frequency of 5, 7 and 10 MHz is recommended.
Duplex scanning of the arteries of the lower extremities is performed in the horizontal position of the patient on the back. Many people prefer to begin the study with a transverse scan to obtain a BIA image near the inguinal fold. OBA, PBA and the initial segment of the GBA are usually well visualized. The popliteal artery is losated when the patient lies on his stomach. 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 the location is below the popliteal level.
The most common in the clinic with lesions of the arteries of the lower extremities was duplex scanning for assessing the aorto-iliac, femoropopliteal segments and the deep thigh artery.
Despite a number of limitations of the duplex scanning capabilities for the characterization of peripheral circulation disorders, non-invasiveness, safety for the patient, the possibility of repeated studies, large volume and high quality of information on the nature and extent of vascular lesions, known advantages over radiocontrast angiography make this method a priority in Clinic of peripheral vascular disorders.
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