What is colour Doppler echocardiography? Cardiology Basics

What is colour Doppler echocardiography? Cardiology Basics

Usual colour Doppler echocardiogram is superimposition of colour Doppler images on a two dimensional echocardiogram. Colour M-Mode is superimposition of colour Doppler images on an M-Mode echocardiogram. The principle of Doppler is that the frequency of sound wave coming from an object which is moving towards the ultrasound probe increases while that from an object moving away from the probe decreases. It is similar to the difference in the sound of a train whistle, which is different when the train is moving towards you than when it is moving away from you. In Doppler echocardiography, the target is moving red blood cells.

Colour Doppler echocardiography receives the ultrasound signals reflected from moving red blood cells in the heart. Ultrasound signals are emitted and received by the ultrasound probe used for echocardiography. By notation, flow of blood away from the probe is depicted as blue and flow towards the probe is depicted as red. When the blood flow velocity increases in abnormal situations, the flow becomes turbulent. A turbulent flow will be shown as a mosaic colour which is a mixture of the basic colour of the flow with shades of yellow added to it. All high velocity flows across the diseased valves will be shown as mosaic jets.

Colour Doppler echocardiography is very useful in giving a quick visual assessment of regurgitation and stenosis of heart valves. It will also show abnormal flows as in an atrial or ventricular septal defect. Mosaic coloured jet on colour Doppler echo is easily seen. For example, when the VSD is small, the pressure difference between the right and left ventricles is high. This produces a turbulent high velocity jet which can be easily seen on colour Doppler. But it may be difficult to see a small defect by echocardiography without Doppler.

Stenosis of the valves can be made out by the reduced opening at the time when it is supposed to be open. There will be associated thickening of the valve as well. Doppler echocardiography will show a high velocity mosaic jet across the stenosed valve. But in case of a regurgitant valve, it is often difficult to make out a small regurgitant orifice between the valve leaflets when it is supposed to be fully closed. In that situation, Doppler echocardiography will show a high velocity mosaic jet across it, which is easily seen.

The extent to which the colour Doppler jet extends behind the regurgitant valve is an important indicator of the severity of the regurgitation. The area of the mosaic jet into the chamber preceding the valve is another important indicator of the severity of the regurgitation. The size of the regurgitant orifice can be assessed by the width of the mosaic jet on color Doppler at its origin between the valve leaflets. Sometimes a perforation in the valve leaflet may be causing the regurgitation. This can also be seen as a mosaic jet originating away from the region where the valve leaflets meet, in the belly or base of the valve.