Doppler echography

The echography Doppler is an echographic examination in two dimensions noninvasive which makes it possible to explore intracardiac and intravascular blood flows. It is based on a physical phenomenon of the Ultrason S, the Doppler effect.

It is often called echo Doppler .

Technique

The Doppler echograph consists of a traditional echograph coupled to a Doppler probe. When a beam of Ultrason S crosses the cardiac cavities or the vessels, the echo returned by the illustrated elements of blood (which become transmitters) will have a longer length (its most serious) if they move away from the sensor; and a shorter wavelength (its acutest) if they move towards the sensor.

The Doppler probe will thus collect an echo from which the frequency (wavelength) will be different from the frequency of emission.

The difference of the frequencies of emission and reception: F - F' or F' - F makes it possible to calculate the speed and the direction of the red Globules.

There exist 2 modes of Doppler:

the continuous Doppler :

The probe emits Ultrason S permanently and the frequencies reflected by the red globules are analyzed continuously. One collects a spectrum speeds thus corresponding to all the zones crossed by the beam. It makes it possible to record flows of very high swiftness, without measurable speed limit, it thus makes it possible to analyze maximum speed with a high degree of accuracy. Its disadvantage is a less good localization of analyzed flow.

the Doppler pulsated :

The probe functions alternatively like transmitter and receiver. It is possible to regulate the period of the pulsation what makes it possible to select the depth of the explored zone. Recorded flow is thus located better on the image. On the other hand, very fast flows, beyond a measurable maximum speed, cannot be recorded in pulsated Doppler.

The current Doppler echographs allow a coding color blood flows. By convention, positive flows which approach the probe are coded in red, flows which move away from there are coded in blue. It thus allows a visualization direct of blood flows which are superimposed on the image in two-dimensional echography in grey scale.

It is practiced in general while going up since the veins of the lower extremities to the iliaques and hollow veins lower.

Diagnosis

The echography Doppler is used in the diagnosis of pathologies of the vessels and the heart.

Heart: congenital cardiopathies, valvulopathies, Péricardite S.
Arteries: Sténose S, Thrombosis S (Athérosclérose), Aneurism S, intermittent limping, acute Ischaemia.
Veins: major venous thromboses, Varix S.

The echography Doppler is often an examination of first intention. Indeed, it is relatively inexpensive and it has large a sensitivity, in particular for the diagnosis of major venous thromboses.

However it is sometimes necessary to carry out thorough examinations to specify the diagnosis like Angiographie S.

Risks

The echography Doppler is a noninvasive Examen, i.e. which does not require effraction of the barrier that the Peau constitutes. That makes it possible to avoid the risks of Infection S.

Moreover, this examination is painless and atraumatic, the Ultrason S being without danger to the fabrics. It can thus be repeated as much once than necessary.

Finally there does not exist any counter-indication with this examination, it can be practiced on women enclosure or infants.

Limits

The quality of the imagery obtained is very variable from one patient to another. The thoracic Obesity and deformations make sometimes the examination not easily interpretable.

The probe being handled manually, the plan of cut of the image obtained can vary. The quality of the results thus remains very dependant on the skill and the experiment of the operator.

External bonds

Site of the CHU of Rouen
Course of the medical college of Paris 6
Course of the university Lyon 1 on the indications of echography Doppler
Course of the medical college of Besancon on the echocardiography Doppler

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