Echocardiography (echo) is an imaging technique to view the structure of the heart. It uses an ultrasound beam to scan the heart and the echoes received from various structures are analyzed by the computer program to reconstruct the image of the heart. The distance of each point in the heart from the source of the ultrasound beam can be calculated if the time needed for the ultrasound wave to travel to and fro is measured and multiplied by the velocity of sound in the body. The reflection of ultrasound is maximum at the interface between media of different velocities. Hence the inner and outer border of the heart muscle is visualized well. Since blood does not reflect ultrasound well, blood fill regions are seen as echofree spaces.
The common modes of echo are M-Mode, 2 dimensional and Doppler. Doppler information superimposed on 2 dimensional images is known as colour Doppler echocardiography. Most of the echocardiograms done now a days are colour Doppler echo. Recent advances in the technique are 3 dimensional echocardiography and tissue Doppler echocardiography. Conventional Doppler measures the velocity of red blood corpuscles in the blood moving through the heart. Tissue Doppler measures the velocity of movements of various regions of the heart muscle. Doppler echo is based on the Doppler principle which states the pitch of the sound from a moving object will vary with the velocity of the moving object.
Echocardiography is a widely used investigation to view the chambers of the heart, movement of heart valves and assessment of flow blood across various valves. Various defects like a hole in the septa separating the cardiac chambers, obstruction of the valves and abnormal position of valves can be easily seen by echocardiography. Doppler flow information makes assessment of leaks and obstructions in valves easy. One of the earliest uses of echocardiography was the detection of fluid collection within the layers of the pericardium which covers the heart. Fluid collecting in the pericardial sac can compress the heart and impair its filling during diastole. This can be easily seen as echo free space just outside the heart, while conventional x-rays cannot differentiate between fluid and heart muscle.