Transcranial Doppler


Published in: Today Digital
Author: Dr. Guillermo Jiménez, neurologist Neurology of the General Hospital of the Plaza de la Salud.

Since the beginning of 2007 we are performing transcranial Doppler in the Department of Neurology of the General Hospital Plaza de la Salud (HGPS), both outpatients and inpatients.

The main objective of this article is to make known to the general population, as well as to the medical class, the importance of this diagnostic procedure, still unknown or ignored by most of the ARS.

Transcranial Doppler (DTC) is an ultrasound technique for intracranial vessel exploration, non-invasive, repeatable, relatively inexpensive and can be performed next to the patient's bed. It does not emit radiation, so there are no contraindications to its use, being able to be carried out at any age. It is ideal in severe patients, unstable or difficult to move.

Its use is usual in non-invasive monitoring of cerebral hemodynamics, allowing to know the speed of blood flow in the main intracranial arteries.

To do this, a 2 MHz transducer is used through the skull, over the so-called "acoustic windows", which are the areas of least thickness, and therefore offer less resistance to the passage of ultrasound (transtemporal, transorbital, submandibular and suboccipital). . In the neonatal period, it is done through the fontanelles.

Doppler in 1842. The so-called Doppler effect, described by the Austrian physicist and mathematician Cristian Johan Doppler, consists of the relationship between the speed of an object in motion and the change in frequency of the reflected waves when insonated by a static source of ultrasound.

The sound reflected by a moving target (in this case, the blood) has a frequency different from the sound wave that affects it, and this change in the frequency of the blood's wave is proportional to the speed of the blood flow.

Interestingly, the principle of the Doppler effect was to explain the color of the stars and is from Aaslid and colleagues in 1982 when applied in the study of patients with cerebrovascular diseases.

The DTC emits pulsed ultrasound waves through a transducer, crossing skin and bones to the proximal portion of the cerebral arteries of the polygon of Willis, they are reflected in the erythrocytes, generating an electrical signal.

Between 8 and 13% of the population does not have bony windows with ideal characteristics, which limits the adequate evaluation, especially in the anterior circulation ("deficient bone window").

The technician evaluates with this register, above all, the variation of the average flow velocities, resistance and pulsatility indexes and the wave morphology of the sonogram.

Normal values are established according to internationally accepted protocols with age in children and specific ranges in adults.

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