Sonography Principles & Instrumentation (SPI) Ultrasound Registry Practice Test 2026 - Free SPI Practice Questions and Study Guide

The order of propagation speed from lowest to highest is represented by air, fat, muscle, and bone. This arrangement is based on the acoustic properties of these tissues and substances, particularly their densities and elasticities.

Air has the lowest propagation speed due to its low density and high compressibility, meaning sound travels very slowly in this medium. Fat, while still relatively low, allows sound to travel faster than air because it is denser and less compressible. Muscle has a higher propagation speed than fat, primarily due to its increased density and structure, which allows sound waves to travel more efficiently. Lastly, bone has the highest propagation speed among these materials. This is attributed to its high density and rigidity, allowing for very rapid transmission of sound waves.

Understanding this order is crucial in ultrasound practices, as it influences how sound waves interact with different tissues, which in turn affects image quality and diagnostic accuracy. This knowledge aids sonographers in interpreting images and understanding how sound waves behave in various environments within the body.