Ultrasonic dopplerography in neurology

UZDG (ultrasound dopplerography) refers to special apparatus methods of investigation and is widely used by neurologists. It allows in real time to assess the blood flow through the main shallow arteries and veins. In neurology, ultrasound of the main vessels of the neck and transcranial ultrasound are used.

Principle of USDG

The method is based on the Doppler effect. This is the name of the change in frequency or wavelength that is perceived by the observer (receiver) when the source of radiation or receiver moves. As a moving object with UZDG appear uniform elements of blood. The ultrasonic waves reflected from them are captured by the sensor. The sensor remains stationary at the time of measurement and serves simultaneously as a source of radiation and a receiver due to two piezoelectric crystals.

There is a special formula for calculating the Doppler frequency shift, which can determine the velocity of blood flow. In this case, not only the frequencies of the emitted and captured signals are taken into account, but also the angle between the direction of the ultrasonic beam and the velocity vector of the blood elements. But at present, the doctor of ultrasound diagnostics does not need to use the formula himself. The dynamically changing difference in the frequencies of the outgoing and perceived (reflected) signal is evaluated by the apparatus and converted into sound and image on the screen. The doctor receives information in the form of a spectrogram or an "envelope" of the curve.

UZDG allows for a qualitative (audiovisual) and quantitative assessment of blood flow. During the study, the speed, direction, and nature of the movement of blood through the vessels of a large and the average caliber, its symmetry is estimated, areas with pathological blood flow are identified. But the UZDG does not allow to clarify the position of the vessels, the structure of their walls and the causes of existing functional disorders.

Which vessels are examined

Directing the patient to the USDG, the neurologist determines the necessary amount of research. Most often, a functional assessment of the patency of the main arteries of the neck (anterior and posterior group). But it is also possible to include transcranial and periorbital ultrasound in the protocol of examination, as well as the determination of blood flow through the main veins.

In adults with UZDG vessels of the head and neck, the following are available for research:

• vertebral arteries;
• arteries of the carotid basin (subclavian, common carotid, external and internal carotid);
• suprapubic arteries;
• intracranial vessels (anterior, middle and posterior cerebral arteries, anterior and posterior connective arteries, main artery and part of vertebral arteries);
• ocular arteries;
• jugular and subclavian veins;
• ocular vein;
• vertebral venous plexus.

In young children with transcranial ultrasound, blood flow in the deep veins of the brain can be further assessed: the middle cerebral veins, the Venus Galen, the basal veins of Rosenthal.

UZDG technique

Dopplerography of the vessels of the neck is percutaneous, the patient lies on the couch with the headboard lowered to the horizontal level. The sensor of the device is placed in the projection of the investigated vessel, to improve the conductivity of the signal, a contact gel is used. The optimum angle of inclination of the sensor to the surface of the skin is 45 °, the doctor, if necessary, adjusts his position in small movements to obtain the clearest and brightest signal.

During the basic UZDG of the neck vessels, it is very important to observe a uniform pressure on the patient's skin by the sensor. The applied force should be sufficient for a good signal, but at the same time, do not lead to a change in the diameter of the vessel under study. When conducting UZDG in dynamics it is desirable that repeated studies be performed by the same doctor. This minimizes the errors associated with the peculiarities of the technique of applying the sensor to different specialists.

During UZDG, deviations from the standard average statistical parameters of blood flow in individual vessels and the symmetry of blood filling are assessed. Functional tests can also be used in the study to identify violations regulatory-compensatory mechanism and indirect signs of the state of the collateral vascular network. They are carried out after determining the parameters of the base blood flow along the main extracranial vessels. Functional tests can include short-term compression (compression)
certain arteries, clamping of the brachial artery with the help of the cuff of the tonometer, intense head turns, coughing, changes in the depth and frequency of breathing. The most commonly used compression test.

Transcranial ultrasound in an adult is possible only when the sensor is applied to certain areas of the head - the so-called acoustic windows. This is the zone of the smallest thickness and density of the bones of the skull or the area of ​​the location of natural openings. These are temporal bones, orbits and the suboccipital region, where the atlanto-occipital articulation is located. In children of the first year of life, transcranial ultrasound is also performed through large and small fontanelles and seams between the bones of the skull, which significantly increases the informative value of the study.

To assess autoregulation of cerebral circulation, orthostatic and antiorthostatic functional tests are performed, short-term compression of the common carotid artery. For transcranial ultrasound, respiratory tests and certain drugs (eg, nitroglycerin) may also be used.

Indications

One of the indications for the study are signs of widespread atherosclerosis of the vessels.

UZDG vessels of the head and neck can be used for screening individuals at risk for developing vascular pathology. This study also reveals a shortage of blood flow along the main vessels, which is often the cause of progressive cerebrovascular diseases and vascular accidents. And when assessing venous blood flow, you can identify signs of volume formation and the degree of compensation for existing hydrocephalus.

Indications for ultrasound in neurology:

• clinical signs of acute and chronic disorders of cerebral circulation, transient ischemic attacks with various symptoms;
• persistent or recurrent cephalgic syndrome;
• increasing cognitive deficits;
• fainting and syncopal conditions;
• dizziness and ataxia of a different nature;
• suspicion of impaired blood supply in the vertebrobasilar basin, vertebral artery syndrome;
• ischemic heart disease, signs of systemic atherosclerosis;
• hypertonic disease;
• the revealed asymmetry of arterial pressure and pulse on hands;
• sharp deterioration of vision, not associated with ophthalmic pathology;
• suspected aneurysm;
• persistent, not amenable to medical correction of sleep disorders;
• expressed degenerative-dystrophic changes in the cervical spine;
• condition after head and neck injuries, neurosurgical interventions;
• diabetes mellitus, vasculitis and other diseases with systemic changes in the vascular wall.

UZDG is also widely used as a screening study of newborns after complicated births, children with deviations in the neurological status and having signs of hydrocephalic syndrome.

How do the results

The registration of the Doppler frequency shift can be performed in several ways. The sound method is the simplest. It is used in portable devices and allows the doctor to quickly assess the nature of the blood flow. During UZDG arteries, vibration, whistling, sharp notes of different tonality, "mur-moor phenomenon", quiet blowing noise can be heard. The sound of normal arteries is a clear, spontaneous, pulsating signal in accordance with the rhythm of the heart. And the venous blood flow resembles surf or gives a low-modulated noise depending on respiratory movements.

The main way to register the data obtained at UZDG is a dopplerogram. This is the name for the graphic representation of frequency shifts, which consists of the envelope curve and the Doppler spectrogram. The analysis of these components can be carried out in a complex or separately.

The abnormalities detected at UZDG may include a change in the Doppler pattern with a drop in its amplitude, asymmetry in the linear velocity of the blood flow, the presence of turbulent or retrograde blood flow. The increase of the indexes of circular resistance and spectral expansion is also determined.

When describing the results of the USDG, the doctor indicates a blood flow deficit in certain arteries, expressed as a percentage, its symmetry and the expected level of occlusion.

Advantages and disadvantages

UZDG does not carry a radiation load, is painless, does not require special training and has no age restrictions. This study refers to non-invasive, because it does not require the introduction of any drugs and contrast agents, only an external sensor is used. UZDG allows in real time to assess the nature of blood flow, the level of occlusion of extracranial vessels and determine the degree of deficiency of blood supply to the brain. It can be carried out in the severe condition of the patient, if there is a clinical indication for this.

At the same time, the UZDG does not allow visualizing the causes of vascular stenoses, assess the condition of the vascular wall and surrounding tissues. It can not replace angiography, MRI or CT. But now the USDG is often one of the components of duplex and triplex vascular scanning, which expands the diagnostic possibilities of using ultrasound.

The specialist conducts dopplerography of the brain and tells about this method of diagnosis: