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Chapter 1: Basics
Sound and Mediums
Sound needs something to travel through
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Sound Needs a Medium
Sound can only travel through a medium: a material made of molecules, like water, air, or body tissue.
No molecules means no sound. Sound cannot travel through a vacuum (empty space).
Imagine clapping your hands in three different environments:
Room: Sound travels through air
Air and water are mediums. Space is a vacuum with no molecules, so the clap produces no sound at all.
Sound travels by making molecules bump into each other. More molecules nearby means more bumping.
In a medium, molecules pass vibrations along. In a vacuum, there is nothing to vibrate.
The medium is the delivery system. Without it, sound energy has nowhere to go.
The Patient's Body Is the Medium
In ultrasound, the sound wave travels through the patient's tissues: skin, muscle, organs, blood, and fluid. Each tissue type is a different medium, and sound behaves differently in each one.
Why Gel Matters
Air between the transducer and the skin would block sound. Ultrasound gel eliminates that air gap so sound can enter the body. No medium, no image.