Severe Winter Weather Sweeps Across US With Ice and Snow

See the Sweet Holiday Cards Fans Have Sent to TODAY

What is Doppler Ultrasound? Explained by Dr. Tanzeela Rehman | Complete Guide

Basic Principles of Colour Doppler Echocardiography

The Doppler effect refers to the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. It is commonly experienced with sound waves, such as when a car horn passes by: as the car approaches, the sound waves are compressed, causing the pitch to rise, and as it moves away, the waves are stretched, causing the pitch to drop. This effect also occurs with light waves, where the shift towards the blue end of the spectrum (blue shift) occurs wh