What is a duplex vascular scan?
Duplex scanning is a type of diagnostic study. This seroscal echography includes color coding and spectral Doppler analysis. Today, duplex scanning of the head and neck is considered the main diagnostic method for detecting various pathologies of the system of blood channels in these zones. Next, we consider in more detail what this procedure is and for what diseases it is prescribed.
Duplex scanning is a procedure that combines the ability to visualize the lumens of the blood channels and surrounding tissues in the mode of 2-dimensional seroscal echography (B-mode) and simultaneous assessment of hemodynamics using Doppler technologies. In accordance with the results, an analysis is made of the elasticity and stiffness of the walls, the functional state of the endothelium, the violation of integrity (dissection), the presence, prevalence and nature of changes in the structure and thickness of the wall.In the course of the study, a specialist can identify intraluminal formations, their localization, echogenicity, extent. Duplex scanning of blood vessels allows you to assess the degree of patency of the lumen, changes in diameter. During the procedure, the geometry of the blood channels is analyzed. In particular, deformations, deviations from the normal anatomical trajectory, abnormalities of discharge, branching and extension are detected. Duplex vascular scanning provides information about intraluminal flows. Information is obtained on the basis of processing the Doppler reflected signal using the Fourier (fast transform) method.
Information Collection Methods
Information during transcranial and conventional scanning may look like Doppler spectra or color cartograms. In the latter case, on the basis of research data, the specialist receives qualitative information about the blood flow, its nature (turbulent, laminar), defects in filling of cartograms and others. The spectral mode allows you to give a quantitative characteristic of the intraluminal flow.In other words, the study makes it possible to objectify the absence or presence of hemodynamic disorders and determine the degree of their severity. The obtained diagnostic information is based on the assessment of speed indicators and various calculated indices that indirectly characterize the degree of peripheral resistance, as well as the tone of the wall of the blood channels.
Extracranial study: indications
Duplex scanning of the vessels of the head is assigned when:
- Clinical signs of chronic or acute cerebrovascular insufficiency. These include the headache.
- Planning operations for different types of cardiac pathology. First of all, it refers to CHD. In particular, duplex scanning of arteries is prescribed before stenting.
- The presence of risk factors for cerebrovascular pathologies. These include smoking, arterial hypertension, obesity, hyperlipidemia, diabetes.
- The presence of signs of damage to the arterial pools against the background of the systemic nature of pathological processes.
- Diseases of surrounding tissues and organs with a potential likelihood of extravasal effects.
Duplex vein scan is performed in the presence of clinical signs of thrombosis.
Duplex scanning is distinguished by high resolution, non-invasiveness and the possibility of multiple repeated procedures. Due to this, the study is considered an indispensable tool in clinical neurology. Duplex scanning allows full prophylactic screening in an asymptomatic population. With the use of this method of research, the possibilities of differential diagnosis are greatly expanded. Duplex scanning of the neck vessels allows detecting medium and small stenosis of carotid canals. Based on this, it can be stated that the study can be used as a basic screening method in individuals without clinical signs of cerebral circulatory disorders.
Transcranial examination: indications
This type of study is assigned if:
- Duplex scanning of the brachiocephalic blood channels revealed occlusive or stenotic pathology - a potential source of cerebral blood flow disorders.
- The signs of chronic or acute cerebral ischemia with unidentified specific causes of its occurrence were revealed.
- Found indirect signs of damage in the intracranial arteries.
- There is a pathology of the brain substance diagnosed by scintigraphy, magnetic resonance and computed tomography and other imaging techniques, accompanied by changes in the structure and cerebral circulation.
- There are clinical manifestations of intracranial hypertension.
- There is a need for dynamic monitoring of cerebral blood supply indicators to analyze the effectiveness of the applied treatment in the acute period of hemorrhagic and ischemic stroke against the background of cerebrovascular insufficiency, as well as to assess the state of the vessels at different stages of surgical revascularization.
Duplex scanning of the vessels of the head not only helps to identify the occlusive and stenotic pathology of the brain, but also makes it possible to evaluate its hemodynamic and pathogenetic significance. The survey allows you to detect:
- Complex disorders caused by systemic diseases of the blood channels.
- Anomalies in the development of blood vessels, aneurysms, malformations, cerebral vasospasm fistula, impaired circulation.
- Early (preclinical) signs of systemic disease.
Duplex head scan allows you to monitor the effectiveness of therapeutic interventions. During the study, it is possible to assess the reserve capacity of the circulatory system of the brain, to establish the likely etiological role of the detected pathological process or symptom complex in the genesis of the manifestation of one or several clinical syndromes for a particular patient. The survey also makes it possible to determine the functions of the central and local mechanisms of regulation of the tone of the blood channels.
Duplex neck scan
The mandatory scope of the survey included several sites. In particular, they include:
- The lower division of the brachial head.
- Segments V1, V2 of vertebral blood channels.
- Internal carotid arteries. Their condition is assessed before entering the skull.
- Common carotid arteries. They are examined throughout the length.
- Proximal sections of the external carotid arteries.
If there are indirect signs of irregularities in the V3 segment, echolocation can also be performed in this area.
Duplex scan of the lower limbs: indications
A survey is appointed when:
- Puffiness in the ankle joint.
- Discomfort and pain in the lower part of the legs when moving and at rest.
- Convulsive twitching, pulling sensations in the fingers.
- Gravity in the lower extremities.
- Blanching or darkening of the skin, redness or seals.
- Vascular stars, pronounced changes in the saphenous veins.
- Trophic ulcers.
Duplex scanning of the lower extremity veins is also recommended in the absence of a pulse in the legs.
Description of the procedure
Duplex scanning of lower extremity veins does not require special training. Clothing should be chosen such that a specialist has access to the surveyed sites. Before a duplex scan of the veins of the lower extremities is performed, the patient lies down on the couch. With the help of special equipment and a sensor with gel applied to it, the doctor conducts through the main blood channels of the legs.Due to the gel, the transfer of information to the device is enhanced. Additionally, duplex scanning of the veins of the lower extremities can be performed while standing.
Features of the study
When conducting duplex scanning of head vessels, a low frequency of radiation is used. This is due to existing obstacles in the path of the rays in the form of bone elements of the skull. When using low frequencies, it becomes impossible to visualize the vascular walls and assess the state of the lumens. The information obtained is indirect. The information is based on the analysis of color cartograms for the streams of the intracranial veins and arteries, as well as Doppler spectra. In this regard, against the background of a transcranial study, it is impossible to assess changes and diagnose processes that are not accompanied by the formation of systemic and local hemodynamic disturbances. Due to the different thickness of the bony elements of the skull, causing the unequal permeability of ultrasonic radiation, echolocation is performed in specific areas. They are called "ultrasonic windows". The quality and amount of information obtained during transcranial scanning depends on their severity.The main limitations can be caused by a significant deterioration of ultrasound imaging against the background of a decrease in the acoustic ability of the bony elements of the skull.
In the process of scanning the extracranial sites of the brachycephral arteries, differential signs are revealed that are characteristic of stenosing atherosclerosis, microemboli, thrombosis, vasculitis, angiopathy. In a transcranial study, it is possible to verify occlusive or stenotic lesions with the determination of their severity without specifying the morphological equivalents. The examination also reveals specific phenomena characteristic of failure of the autoregulation of blood flow in the brain, cerebral angiospasm and others. When an atherosclerotic lesion of the stenosing type is found in the carotid arteries, the echostructure of the plaque and the degree of impaired lumen patency are evaluated for each damaged vessel.
Investigation of vertebral blood channels
Due to the presence of anatomical features of their location, visualization of the arteries is possible only fragmentary.They are available for monoplane research. This significantly limits the ability to scan in the diagnosis of various diseases. So, with high reliability with low quality of visualization, only stenosing lesions with narrowing of the lumens of more than 40-50% in diameter, located in accessible areas, are determined. Echostructural analysis of formations inside the lumen, as a rule, is not performed. This is due to limited opportunities for visualization of the walls of the blood channels. The definition of functional changes in the diameter of blood vessels is carried out using load testing. There are no objective specific ultrasound features for extravasal compression in the vertebral blood channels in the zone of transverse processes of the vertebral elements of the upper part of the column in the zone of craniovertebral articulation.Duplex diagnostic criteria used in everyday practice have an indirect character and necessarily require confirmation by the methods by which visualization becomes possible.These include, in particular, angiographic examinations in the background or with carrying out stress functional tests. Scanning of the jugular veins (external, internal), as well as vessels in the vertebral venous plexus is carried out in cases of suspected thrombosis in them.
The clinical significance of the duplex circulatory indicators obtained in the Doppler spectral mode from the lumens of the vascular collectors listed above, as well as their role in assessing the pathological changes of cerebral hemodynamics in other cases, is considered highly questionable. This takes into account the variability of the blood outflow from the cranial cavity when the patient changes the position of the body, the inconstancy of the structure of the blood channels themselves, the flow synchronization with breathing, as well as the light compressibility of the lumens.
With the help of duplex scanning, it is possible to follow the course of blood flow and determine vascular reactions in the area of damage both on the background of selective and systemic thrombolysis. Stabilization of flow in the affected area or acceleration in the lumen,a decrease in the intensity or disappearance of collateralization is considered to be objective signs of the effectiveness of the applied therapy. In the absence of positive dynamics in assessing the echographic picture, a specialist may conclude that the treatment received by the patient is ineffective. In practice, there are often cases of inconsistency between the clinical effect and the success of revascularization.
Like any other ultrasound, duplex scanning is an operator-dependent method. And - to a certain extent - subjective. The success of the application of complex imaging capabilities in clinical neurology, in addition to the skills and experience of a specialist operator, will largely depend on the quality characteristics of the equipment used in the examination. As a result, in all controversial diagnostic cases during the planning of surgery on the cerebral vessels, the reference method for ultrasound in angiology is the radiopaque method and its varieties recognized in practice as the "gold standard."