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Compression and Rarefaction
When a sound wave moves through a medium, it creates two alternating zones:
Compression
Particles squeezed together High pressure High density
Rarefaction
Particles stretched apart Low pressure Low density
These zones alternate back and forth as the wave travels.
Think of a slinky. Push one end and watch the coils bunch up, then spread apart.
Push and Release
Watch the coils compress and stretch
Where coils bunch together: compression. Where they spread apart: rarefaction. The pattern repeats over and over.
Now imagine the same thing happening to molecules in a medium. Dense zones alternate with sparse zones.
The red zones are compressions (high density). The blue zones are rarefactions (low density). Together they form one complete wave cycle.
[Image: Ultrasound transducer sending waves into tissue]
Sound Waves in Tissue▸
When the transducer sends a pulse into the body, it creates alternating compressions and rarefactions in the tissue. These pressure changes are what carry the sound energy through the patient.
Why This Matters▸
The pattern of compressions and rarefactions is how ultrasound carries information. When the wave hits a boundary between tissues, part of it bounces back. The machine reads those returning compressions to build the image.