Refraction

Refraction of a sound wave occurs if it travels between tissues with different propagation speeds. As the incident pulse or returning echo strikes an interface of different density or elasticity and therefore a different propagation speed, the direction of the wave changes according to Snell’s law :

• sin θ1/sinθ2 = c1/c2

Where:

• sin θ1 = incident angle of the sound wave at the interface
• sin θ2 = refraction angle of the sound wave in the new medium            
• c1 = propagation speed in the initial medium
• c2 = propagation speed in the new medium

Ultrasound machines assume all pulsed waves and returning echoes travel along a direct path, therefore refraction can cause refraction artifact .