Ch.6 Interaction between Sound and Media book flashcards

What is attenuation?

It’s the weakening of a sound wave as it travels through the body.

What unit is attenuation measured in?

Decibels (dB)

What are the three main causes of attenuation?

Absorption, scattering, and reflection

Which cause of attenuation is the biggest in soft tissue?

Absorption (sound turns into heat)

What happens to attenuation when frequency increases?

It increases – higher frequency = more sound loss

What is a decibel (dB)?

A way to compare sound levels using a logarithmic scale.

What does –3 dB mean?

The sound is half as strong as before

What does +3 dB mean?

The sound is twice as strong as before

What is reflection in ultrasound?

It’s when sound bounces back from a tissue boundary, creating echoes used to make images

What is the difference between specular and diffuse reflection?

Specular = smooth surface, clear echo; diffuse = rough surface, scattered echo.

What is acoustic impedance?

A property of tissue that affects how much sound reflects or passes through; it's based on tissue density × speed

What happens when there’s a big difference in acoustic impedance between two tissues?

More sound is reflected back (stronger echo)

What is refraction?

The bending of sound when it crosses a boundary at an angle and the speed changes

What two conditions are needed for refraction to happen?

(1) Oblique angle and (2) different speeds in the two tissues.

What is the attenuation coefficient?

It tells how much sound is lost per centimeter per MHz.

In soft tissue, what is the typical attenuation coefficient?

About 0.5 dB/cm per MHz.

What is the half-value layer (HVL)?

The thickness of tissue that reduces sound strength by half (–3 dB)

Does high-frequency sound have a thin or thick half-value layer?

Thin – it loses strength faster.

Why is lower frequency used for deeper imaging?

Because it has less attenuation and can travel farther into the body.