ABSTRACT
In order to understand the basic principles of echocardiography, it is extremely important to understand the physical principles behind the process and also the definition of the commonly used terms. Ultrasound is sound having frequency of > 20,000 cycles/ sec. It can be directed in a beam and it obeys the laws of reflection and refraction. It is reflected by objects of small size. Ultrasound beam should be extremely narrow so that it can obtain an ice pick view or slice of the heart. Doppler examination is based on the observation that the frequency of sound increases when a source of sound is moving towards the listener and vice versa. The same applies when a reflecting object is moving towards a transducer and other wise. The pulse repetition frequency determines the ability of the Doppler to detect high frequency Doppler shifts. The inability of the Doppler system to detect high frequency Doppler shifts is known as aliasing.
