Which statement best describes the fundamental components of an ultrasound wave in tissue?

• A. Only compressions
• B. Only rarefactions
• C. Compressions and Rarefactions
• D. Compression and Refraction

Answer: (C)

Ultrasound in tissue is a longitudinal mechanical wave, so particles oscillate parallel to the direction the wave travels. This creates alternating regions of higher pressure (compressions) and lower pressure (rarefactions) as the wave propagates. Those two features are the fundamental components of the wave, since a complete cycle involves both compression and rarefaction. Refraction is a separate phenomenon that describes a change in the wave’s direction at interfaces with different speeds, not a basic component of the wave itself. So the description that emphasizes both compressions and rarefactions best captures the wave’s essential structure.