# Ch 6: Sound and Media Flashcards

What is it called when sound waves weaken as they travel in the body?

attenuation

What is it called when the u/s system strengthens the electrical signal?

amplification

Define ‘decibel notation’.

A standard measurement tool to report changes in the degree of attenuation or the extent of amplification.

Logarithms are…

the mathematical construct on which decibels are based; a novel method of rating numbers.

What is the log of 1,000?

- (10 x 10 x10)

What is the log of 10,000?

- (10 x 10 x 10 x 10)

What is an everyday example of a logarithmic scale?

The Richter scale, which measures the strength of earthquakes.

Decibel notation does not measure absolute numbers; rather decibels report…

relative changes.

What are the two intensities that decibels require?

a starting level and an actual (ending) level

In decibels, the measured level is divided by the starting level, which means that decibels are a…

ratio.

What is a relative measurement, a comparison, a ratio, and logarithmic?

decibel notation

Positive decibels report signals that are…

increasing in strength.

Negative decibels report signals that are…

decreasing in strenth.

Attenuation is determined by which two factors?

path length and frequency of sound

Distance and attenuation are ___ related.

directly. The farther sound travels, the more it attenuates.

Frequency and attenuation are ___ related.

directly. The higher the frequency, the more it attenuates.

What three processes contribute to attenuation?

reflection

scattering

absorption

What is it called when a portion of the wave’s energy is redirected after striking a boundary?

reflection

What two forms of reflection are created in soft tissue?

specular and diffuse/backscatter

Define ‘specular reflection’.

Sound that is reflected in only one direction in an organized manner, as when a boundary is smooth.

Define ‘diffuse/backscatter reflection’.

Sound that is reflected in more than one direction in a disorganized manner, as when a boundary is irregular.

An advantage of diffuse reflections is that…

interfaces at suboptimal angles can still produce reflections that will return to the transducer.

A disadvantage of diffuse reflections is that…

backscattered signals have a lower strength than specular reflections.

What is it called when u/s signals are redirected in many directions?

scattering

Scattering and frequency are ___ related.

directly. The higher the frequency, the more the signal will scatter.

Sound scatters when the tissure interface is ___ the wavelength of the sound beam.

smaller than

This special form of scattering occurs when the structure’s dimensions are much smaller than the beam’s wavelength.

Rayleigh scattering

Rayleigh scattering redirects the sound wave equally in ___ directions.

all

Mathematically, scattering is related frequency raised to the ___ power.

fourth

When frequency doubles, Rayleigh scattering is ___ times greater.

- (2 x 2 x 2 x 2)

What is the significance of attenuation in diagnostic sonography?

More attenuation means less accurate images.

What occurs when u/s energy is converted into another energy form?

absorption