Echocardiography is ultrasound imaging of the heart. It uses an ultrasound beam to scan the heart. The reflected ultrasound waves are analysed by a computer program to give the images of the heart. The device used to transmit and receive the ultrasound beam is known as the transducer. It generates ultrasound waves using piezoelectric crystals which oscillate according to the radiofrequency electrical signals fed into them. Typical ultrasound frequencies ranges from 2.25 – 10 Mhz. Lower frequencies have better penetration, but lower resolution. Higher frequencies have poor penetration, but better resolution.
The simplest mode of echocardiography available now is M-Mode or time-motion mode, which is graphical representation of the movements of various cardiac structures along a single imaging line. It has high temporal resolution and is commonly used to take measurements of cardiac chambers in various phases of the cardiac cycle.
Two dimensional real time imaging gives the live images of the cardiac chambers and valves. This gives excellent anatomic information of the cardiac structures. Opening and closing of the valves can be visualised well. Structural abnormalities and wall motion abnormalities are well studied by two dimensional echocardiography.
Three dimensional echocardiography is coming into vogue in more and more centres. It gives good spatial orientation of the cardiac structures.
Doppler interrogation measures the velocity of blood flow in various regions, especially across the valves and abnormal communications. Doppler information can be mapped on to the two dimensional image using colour flow mapping techniques in a real time fashion. This give excellent information on valve functions.
Tissue Doppler imaging gives information on wall motion abnormalities.
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