Which option best describes a sound beam in ultrasound?

• A. Electrical impulses
• B. A collection of mechanical vibrations in the form of compressions and rarefactions
• C. A wave that man can hear
• D. Ionic vibrations

Answer: (B)

The essence here is that an ultrasound sound beam is a mechanical wave traveling through tissue, made up of alternating compressions and rarefactions. This pressure variation is what carries energy and allows echoes to form when tissues reflect some of that energy back to the transducer. The beam isn’t electrical impulses—that drive the transducer but are not the wave itself. It isn’t something humans can hear, since ultrasound operates at frequencies above the audible range. And it isn’t ionic vibrations, since sound in tissues is a mechanical phenomenon. So the description that best fits is a collection of mechanical vibrations in the form of compressions and rarefactions.