UG105: Understanding the Basics of Ultrasound

1. What is Ultrasound? Basic Physics

Ultrasound is the application of sound waves with frequencies greater than 20,000 Hz (20 kHz), which exceeds the upper limit of human hearing (typically 20 Hz to 20 kHz). Medical ultrasound typically uses frequencies in the range of 2–18 MHz (megahertz). Sound waves are mechanical vibrations that travel through tissues and bounce (reflect) when they encounter structures of different acoustic densities. The ultrasound machine measures the time it takes for sound waves to travel to a structure and return, then calculates the distance using the speed of sound in tissue (approximately 1,540 meters per second). This information is processed and displayed as a two-dimensional image showing the location and appearance of internal structures. Ultrasound is non-ionizing (no radiation), real-time (immediate visualization), and safe even with prolonged use, making it ideal for guiding procedures such as vascular access.