What type of waves are ultrasound in tissue?

• A. Electromagnetic, transverse
• B. Mechanical, longitudinal
• C. Mechanical, transverse
• D. Electromagnetic, longitudinal

Answer: (B)

Ultrasound waves in tissue are mechanical, longitudinal waves. A wave’s type is defined by how particles in the medium move relative to the direction the wave travels. In soft tissues, the particles oscillate back and forth along the direction of travel, creating compressions and rarefactions as the wave moves forward. This requires a material medium to carry the oscillations, unlike electromagnetic waves which can propagate without a medium and are typically transverse. While solids can support both longitudinal and transverse waves, diagnostic ultrasound relies on longitudinal waves because they propagate efficiently through tissue and produce the echoes used to form images.