Question

How is a medium characterized?

• A. ( \text{By its thickness} ) \
• B. ( \text{By its acoustic impedance} ) \
• C. ( \text{By its water content} ) \
• D. ( \text{By its density} ) \

Hint:

Acoustic impedance is the key parameter governing reflections in ultrasound. A large difference in acoustic impedance between two tissues results in a strong echo (e.g., bone-soft tissue interface), whereas a small difference results in weak echoes (e.g., within a homogeneous soft tissue).

Answer 1

The Correct Option is B

In the context of ultrasound and sound wave propagation, a medium is primarily characterized by its acoustic impedance.
Acoustic impedance (Z) is a fundamental property of a medium that determines how much sound energy is reflected or transmitted at an interface between two different media.
It is defined as the product of the density (rho) of the medium and the speed of sound (c) within that medium: Z=(rho)×c.
When an ultrasound wave encounters an interface between two media with different acoustic impedances, a portion of the wave is reflected, and a portion is transmitted.
The greater the difference in acoustic impedance, the greater the reflection.
This principle is crucial for forming images in ultrasound, as it allows for the differentiation of various tissues.
While density is a component of acoustic impedance, it alone does not fully characterize how sound interacts with the medium at an interface.
Thickness and water content are also important properties of biological tissues, but they don't serve as the primary characteristic for sound wave interaction in the same way acoustic impedance does.