Doppler effect
Eco-doppler and Eco-color-doppler are ultrasounds that exploit the Doppler effect.
This effect is based on the measurement of frequency variations between the incident beam and the beam reflected by a moving body (in medical applications, moving bodies are represented by erythrocytes (red blood cells), or rather by erythrocyte clusters, and then by blood). The frequency variation of the reflected echoes is related to the speed and direction of the reflecting element. In the clinic, this allows to calculate the speed of the movement of the structure under examination.
There are two basic systems of Doppler acquisition:
- continuous wave (CW), in which the transducer consists of 2 crystals mounted on the same support, one continuously emitting and the other continuously receiving, and emitting a constant oscillation. It allows a morphodynamic study (ie of morphology and movement) of the flows.
- pulsed (PW), in which the emission is phased, in relation to the alternate transmitter / receiver function of a single crystal; this system allows to obtain information also on the distance reflecting surface / transducer. Pulsed emission devices can be of two different types: Color Doppler and Eco-Color Doppler (also called duplex).
The Doppler effect is therefore the principle on which many ultrasound techniques are based in which biological tissues in motion are explored. it is that physical phenomenon whereby the frequency of a sound wave that encounters a moving structure undergoes a variation that is directly proportional to the speed of the movement itself. Doppler devices work by comparing the emitted and reflected frequencies and measuring the difference; from this measurement it is possible to go back to the blood speed and to the direction of travel of the same.
The color-doppler is based on the same principle as the pulsed doppler: this system, in fact, integrates the information relating to the flows and the two-dimensional image in real time where, by convention, the approaching flows have a red color and those in the distance have blue color. In the case of the presence of a turbulence, for example in the bifurcation of the vessel, there will be an alternation of blue and red spots. it is thus possible to differentiate the flow direction in relation to the probe; moreover, these systems help to evaluate the speed and the laminar (projectile) or turbulent flow of the flow.
The frequency of the two waves, incident and reflected, is of the ultrasonic type, in the order of Mega Hertz, inaudible to the human ear. On the contrary, their difference is in the order of Kilo Hertz (KHz = a thousand Hertz), therefore in the area of audibility if properly amplified. Thus, during the execution of the examination, sounds can be heard whose frequency is directly related to the speed of the red blood cells inside the vessel under examination and, interpreting them, diagnostic information can be drawn on the characteristics of the flow.
When are they used?
Eco doppler and Eco-color doppler allow to identify the presence of:
- Arterial narrowing and occlusion, mainly due to atherosclerosis plaques;
- Deep venous thrombosis, especially of the lower limbs;
- Varices (varicose veins) and venous refluxes.
The Eco-color doppler devices allow to obtain, simultaneously and in real time, information on the morphology and structure of the examined organs and on the flow characteristics in the vessels inside them, representing them in the form of variously colored points. Each color doppler image, therefore, is the result of different processes, occurring in successive moments.
The echocolordoppler therefore adds color to the flow signal; in this way the flow variations are more easily identifiable.
