Doppler brain imaging in children

Currently, neonatology uses duplex Doppler systems that allow visualizing a vessel in an ultrasound section of the brain, installing a control volume in its lumen and obtaining a Dopplerogram reflecting the blood flow in this vessel. Ultrasound devices with color (energy) Doppler mapping (CDM) allow choosing the optimal position for placing the control volume in large cerebral arteries to measure velocity with minimal error, as well as obtaining an image of the venous vessels of the brain. The advantage of color Doppler mapping by energy (CDM) technology is its relative independence from the insonation angle, as well as from the speed and direction of the flow. The three-dimensional reconstruction method has a significant increase in information capabilities, which makes it possible to obtain an idea of the spatial location and shape of the vessels. For a better characteristic of the blood flow, especially at low-speed indicators, the B-flow method is used.

In neonatology, the resistance index is most commonly used, which determines the peripheral vascular resistance. The index is quite informative, since it does not depend on the vessel diameter and the insonation angle. To ensure standard conditions for conducting a Doppler study, the following rules must be followed:

1. The study should be carried out under the condition that the newborn remains at rest, preferably in a state of physiological sleep, 1-1.5 hours after feeding, while maintaining optimal body temperature and ventilation modes.
2. Use a low-pass filter (100 Hz).
3. The dimensions of the control volume are 2-3 mm, which allows for complete occlusion of the vessel lumen and avoids overlapping signals from nearby vessels.
4. The study should be carried out at minimum values of the insonation angle.
5. Select the most straight sections of the vessel, away from bifurcations, to maintain laminar blood flow.

Dopplerographic examination of blood flow is performed in the largest arteries of the brain: internal carotid, anterior, middle, posterior and main, which are defined as pulsating echo-positive structures. The use of the CDC and/or EDC mode significantly simplifies the search and visualization of arteries.

Anterior cerebral artery. The most convenient and simple position for its detection is a sagittal section through the large fontanelle. Usually, the right and left anterior cerebral arteries are located very close to each other, which does not allow them to be distinguished as separate vessels. These arteries can be seen separately using the EDC mode. To obtain blood flow indicators, the control volume is installed in front of the genu of the corpus callosum or in the proximal part of the artery before its bend around this structure, while the angle between the vessel axis and the ultrasound beam is minimal.

Internal carotid artery (distal section). To record blood flow, the vertical part of the vessel is used after it exits the carotid canal at the level of the sella turcica, since further, above the level of the anterior sphenoid process, it divides into the anterior and middle cerebral arteries.

Basilar artery. Examined in the midsagittal section on the anterior surface of the bridge or in the coronary plane a few millimeters beyond the location of the internal carotid artery.

Middle cerebral artery. The main landmark in finding the artery is the lateral groove on the border of the frontal and temporal lobes. The most successful angle of its insonation is achieved with an axial approach.

The examination of all the above-mentioned arteries in a newborn child is often complicated by his/her anxiety, crying and/or severe resuscitation condition of the child. As a screening, it is permissible to use data obtained only from the anterior cerebral artery, since normally the angle-independent parameters differ slightly in the above-mentioned vessels. In newborns, asymmetry of blood flow indicators in the main arteries of the right and left hemispheres of the brain is not normally detected.

Using devices with the EDC function in the coronary plane, it is possible to obtain a complete picture of the arterial circle of the brain, including the middle, posterior communicating, posterior arteries and the proximal parts of both anterior cerebral arteries. When conducting a Doppler examination, it is necessary to remember that there are individual differences in the structure of the vascular system of the brain. Therefore, there are no absolute standards for the linear blood flow velocity (LBFV) in the intracranial arteries, although N. Bode gives a detailed table of these indicators in children from birth to 18 years. The skull and the size of the large fontanelle also have individual characteristics. Therefore, it is recommended to compare absolute velocity indicators in dynamics in one child, obtained by the same researcher, on the same device. More reliable are angle-independent indicators of resistance and pulsation indices (RI, IP).

Cerebral veins. Although it is possible to obtain blood flow signals in large cerebral venous communications of newborns using spectral duplex scanning, color Doppler imaging significantly facilitates their examination. Using the EDC mode, it is possible to visualize through the large fontanelle, in the sagittal plane, under the corpus callosum, along the roof of the third ventricle, two large internal cerebral veins merging into the vein of Galen, which is not always located strictly medially, but is more often deviated to the right. Further along the midline above the cerebellum is the straight sinus; immediately under the bones of the skull and the large fontanelle is the superior sagittal sinus. The inferior sagittal and transverse sinuses are extremely rarely detected. Blood flow assessment is also possible in the veins of the head of the caudate nucleus and the thalamo-striatal veins, which are visualized in the parasagittal scanning plane.

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