Technique of ultrasound Doppler vascular imaging

No special preparation for ultrasound Dopplerography is required. It is necessary that the patient does not receive treatment affecting the state of the vessels or physiotherapy 2 hours before the examination.

Ultrasound Dopplerography of blood vessels is performed with the patient lying on his back, preferably without a pillow. The doctor sits down next to him and first carefully examines the face and neck area. Particular attention is paid to identifying the presence, localization and severity of increased pulsation in the projection of the carotid arteries and jugular veins. Then the doctor carefully palpates all accessible segments of the carotid arteries: common carotid, bifurcations, branches of the external carotid arteries - facial in the area of the angle of the lower jaw, superficial temporal - at the level of the tragus of the auricles. Preliminary auscultation of the projection of the common carotid artery, bifurcations, subclavian arteries and orbital arteries with the eyelids lowered is advisable. In this case, it is more convenient to use a cone-shaped bell of the stethoscope. The presence of systolic murmur over the projection of the carotid and/or subclavian artery is usually characteristic of stenotic stenosis. A whistling noise in orbit can sometimes be heard with a pronounced narrowing of the siphon of the internal carotid artery. After an indicative palpation and auscultation, the sensor is lubricated with a contact gel, then the location of the extracranial segments of the carotid arteries marked by palpation begins. The most important condition for the adequacy of the diagnostic manipulation is an alternate study of symmetrical sections of the extracranial vessels on the right and left. At first, difficulties may arise in determining the force of pressing the sensor to the skin. It is important that the researcher's hand holding the probe does not hang without support - this position is uncomfortable and prevents obtaining a stable blood flow signal, since there is no uniform and constant contact of the sensor with the skin. The doctor's forearm should lie freely on the patient's chest. This significantly simplifies the movement of the hand when locating vessels and is especially important for adequately performing compression tests. Having accumulated a certain amount of experience, the doctor detects the optimal position and pressure of the sensor to the skin, which allows, through small changes in the angle of the sensor (an angle of 45° is considered optimal), to obtain the most resonant and clear arterial or venous signal.

The examination of the carotid system begins with the location of the common carotid artery at the inner edge of the sternocleidomastoid muscle in its lower third.

The 4 MHz sensor is positioned at an angle of 45° to the blood flow line in the vessel in the cranial direction. The spectrum of the common carotid artery is traced along its entire accessible length up to the bifurcation. It should be noted that before the bifurcation - just below the upper edge of the thyroid cartilage - a slight decrease in the linear blood flow velocity with a moderate expansion of the spectrum is usually noted, which is associated with a slight increase in the diameter of the carotid artery - the so-called bulb of the common carotid artery. In some observations, approximately in the same zone, but slightly more medially, an arterial signal of medium amplitude with the opposite direction can be located. This is the blood flow recorded along the superior thyroid artery - a branch of the homolateral external carotid artery.

Above the bifurcation of the common carotid artery, the origins of the internal and external carotid arteries are located. It is important to emphasize that the place where the carotid artery begins should be called the "origin" and not the "mouth" (an established but incorrect term). Since we are talking about a flow of fluid (in this case, blood), the terms used naturally imply an analogy with a river. But in this case, the initial or proximal segment of the internal carotid artery cannot be called the mouth - it is the source, and the mouth should be called the distal part of the carotid artery, at the place where it branches into the middle and anterior cerebral arteries.

When locating the post-bifurcation area, it should be taken into account that the source of the internal carotid artery is often located posteriorly and lateral to the external carotid artery. Depending on the level of bifurcation, it is sometimes possible to further localize the internal carotid artery up to the angle of the mandible.

The internal carotid artery is characterized by a significantly higher diastolic flow velocity due to the low circulatory resistance of the intracranial vessels and normally has a characteristic “singing” sound.

On the contrary, the external carotid artery as a peripheral vessel with high circulatory resistance has a systolic peak that clearly exceeds diastole and a characteristic abrupt and higher timbre. Depending on the angle of divergence on the branch of the common carotid artery, signals from the internal and external carotid arteries can be located both in isolation and superimposed on each other.

Blood flow localization along the branches of the ophthalmic arteries (supratrochlear and supraorbital) is the most important part of ultrasound Dopplerography. According to some researchers, it is this component of Doppler localization that carries the main information in recognizing hemodynamically significant carotid stenosis. The sensor with contact gel is carefully installed in the inner corner of the orbit. Experience shows that during periorbital insonification, it is more convenient and safer for the patient to hold the wire at its base rather than the sensor body. This allows for more careful dosing of the degree of pressing the sensor head to the orbit and minimization of possible (especially for a novice doctor) pressure on the eyelid when performing compression of the common carotid artery. By slightly changing the degree of pressing and tilt, we achieve the maximum amplitude of the pulsating arterial signal - this is a reflection of the blood flow along the supratrochlear artery. After the spectrographic assessment, the direction of the flow is necessarily recorded: from the cranial cavity - antegrade (orthograde, physiological); into the orbit - retrograde; or bidirectional.

After symmetrical insonation of the opposite supratrochlear branch, the probe is positioned slightly higher and laterally to record the flow on the supraorbital artery.

The vertebral artery is located at a point slightly below and medial to the mastoid process. However, obtaining a pulsating arterial signal in this area does not guarantee the location of the vertebral artery, since the occipital artery (a branch of the external carotid artery) is located in the same area. The differentiation of these vessels is carried out by two signs.

• Normally, the Dopplerogram of the vertebral artery has a more pronounced diastolic component. The values of its systolic-diastolic components are approximately 2 times lower than those of the internal carotid artery, and the pattern of the pulsating curve is more reminiscent of trapezoidal complexes due to lower peripheral resistance. The nature of the spectrogram of the occipital artery is typical for a peripheral vessel - high pointed systole and low diastole.
• A compression test with a 3-second pressing of the homolateral common carotid artery helps to distinguish the vertebral artery from the occipital artery. If the signal from the sensor located in the projection of the supposed vertebral artery stops being registered, it means that the occipital artery, not the vertebral artery, has been located. In this case, a small displacement of the sensor is necessary, and upon receiving a new signal, the pressing of the common carotid artery should be repeated. If the flow from the artery being located continues to be registered, it means that the operator has found the desired vertebral vessel.

To locate the subclavian artery, the sensor is positioned 0.5 cm below the clavicle. By varying the angle of inclination and the degree of pressure, a pulsating arterial complex with a pattern characteristic of a peripheral vessel is usually obtained - a pronounced systole, low diastole and an element of "reverse" flow below the isoline.

After the initial examination of the main arteries of the head, a series of clarifying compression tests are carried out, allowing indirect determination of the functioning of the collateral system of the brain, which are of great importance both in the pathogenesis and in the sanogenesis of stenotic and occlusive lesions. Several types of collaterals are distinguished:

• extra-intracranial flows:
  • anastomosis between the occipital artery (a branch of the external carotid artery) and the cervical arteries (muscular branches of the vertebral artery);
  • connection between the superior thyroid artery (a branch of the external carotid artery) and the inferior thyroid artery (a branch of the subclavian-vertebral artery);
• extra-intracerebral flows - anastomosis between the supratrochlear artery (a branch of the temporal artery, originating from the external carotid artery) and the ophthalmic artery (a branch of the internal carotid artery);
• intra-intracerebral flows - along the connecting arteries of the circle of Willis.

In cases of stenotic and occlusive lesions of the internal carotid artery, more than 70% of the main collaterals are most often the following:

• homolateral external carotid artery (external carotid artery → temporal artery → supratrochlear artery → ophthalmic artery);
• contralateral internal carotid artery → flow via anterior communicating artery into ischemic hemisphere
• flow through the posterior communicating artery from the vertebral artery system.