Echocardiography Utilizes principle of ultrasound for visualization of heart and great vessels. It uses sound in the frequency of 1-10 MHz. As the frequency of probe increases resolution improves at the cost of reduction of penetration. Due to thichchest wall in adults, probes with frequency range of 2-5 MHz are used and for paediatric application higher frequency of 7.5-10 MHz probes are used because of thin chest wall.
The underlying principle of cardiac ultrasonography is that speed of sound through tissue is equal to that in water. The transducer which has a Peizoelectric crystal emits a seriels of burst at a given frequency which is reflected from cardiac and other slmctures and is returned to the transducer. These received ultrasound waves ade then displayed as images of cardiac structures on monitor screen and can be stored in videotape, hard disc or optical disc.
The distance of the i-eflective object from the transducers can be calculated by determining the time required for round trip transit.
Distance (meters) = Velocity (meterslsecond) / Time (second)
Velocity = Velocity of sound
The returning strength of ultrasound signal is directly proportional to the reflective intensity of the object and is in integrated into displayed image. Echocardiography provides valuable information regarding diagnosis, valvular morphology, etiology, identification and quantification of lesions, cardiac size and function, intracardiac hemodynamics and disorders of pericardium and great vessels.
There are various echocardiographic techniques available:
1) Transthoracic echocardiography
2) Transesophageal echocardiography
3) Stress echocardiography:
a) Exercise
b) Pharmacological
4) Fetal echocardiography
5) Contrast echocardiography
6) 3-D echocardiography
7) Intravascular ultrasound
Most commonly used technique is transthoracic echocardiography (TTE). Others require further skill and expertise, once the physician has acquired the skills of TTE.