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Physics 110 Exam 2 > Attenuation > Flashcards

Attenuation Flashcards

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1
Q

What does attenuate mean?

A

To weaken or reduce in strength.

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2
Q

What is the decrease in intensity, power, and amplitude of sound as it travels through a medium called?

A

Attenuation

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3
Q

Attenuation is determined by what two factors?

A

Path length

Frequency of sound

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4
Q

What are the units of attenuation?

A

Negative dB, since it’s a decrease of intensity.

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5
Q

How are distance and attenuation related?

A

They are directly related.

The farther a sound travels, the greater the attenuation and the weaker the beam becomes.

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6
Q

How are frequency and attenuation related?

A

They are directly related.

Attenuation is greater in higher frequency sound than in lower frequency sound.

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7
Q

Attenuation is measured in decibels and reported as a _____ _____ not an _____ _____.

A

Relative change

Absolute value

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8
Q

What 3 processes contribute to attenuation?

A

Reflection

Scattering

Absorption

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9
Q

There will be more attenuation with:

_____ _____ and _____ _____.

A

Longer distances

Higher frequencies

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10
Q

There will be less attenuation with

_____ _____ and _____ _____.

A

Shorter distances

Lower frequencies

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11
Q

What happens when sound strikes a boundary?

A

A portion of the energy may be redirected, or reflected, back to the sound source.

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12
Q

How does reflection affect the portion of the sound wave that continues in the forward direction?

A

It is weakened

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13
Q

When is reflection more likely to occur?

A

When the dimension of the boundary is large; that is, more than a few wavelengths of the sound.

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14
Q

What two forms of reflection are created in soft tissue?

A

Specular and Diffuse

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15
Q

What determines which form of reflection is created?

A

Which form occurs depends on the nature of the interface that a sound wave strikes. (ex: smooth or flat)

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16
Q

When do you get specular reflections and how are they reflected?

A

Smooth or flat boundaries create specular reflections, reflected in only one direction in an organized manner.

17
Q

If your transducer is off axis, how does that affect specular reflection?

A

The reflection does NOT return to the transducer.

18
Q

What is it called when a wave reflects off an irregular surface in more than one direction?

A

Diffuse reflection, or backscatter

19
Q

What is an advantage of diffuse reflections?

A

Interfaces at suboptimal angles to the sound beam can still produce reflections that will return to the transducer.

20
Q

What is a disadvantage of diffuse reflections?

A

Backscattered signals have a lower strength than specular reflections.

21
Q

What is scattering?

A

The random redirection of sound in many directions.

22
Q

When does sound scatter?

A

When the tissue interface is small.

(Equal to or less than the wavelength of

the incident of sound beam).

23
Q

How is scatter related to frequency?

A

Directly related.

High frequency = more scatter

24
Q

What is Rayleigh scattering?

A

A special form of scattering that occurs when the structure’s dimensions are much smaller than the beam’s wavelength. Ex: RBC’s

25
Q

How does Rayleigh scattering affect the sound wave?

A

It redirects the sound wave equally in all directions.

26
Q

How does increasing frequency affect

Rayleigh scattering?

A

The occurrence of Rayleigh scattering increases dramatically with higher frequencies.

27
Q

Mathematically, Rayleigh scattering is related to frequency how?

A

Frequency raised to the fourth power.

When frequency doubles, Rayleigh scattering is

16 times greater. (2x2x2x2 = 16)

28
Q

What is the most sizable component of attenuation?

A

Absorption

29
Q

When does absorption occur?

A

When ultrasonic energy is converted into another energy form, such as heat.

30
Q

How is absorption related to frequency?

A

Like scattering, absorption is directly related to frequency. As a result of absorption, higher frequency waves attenuate more than lower frequency waves.

31
Q

How are the attenuation coefficient (dB/cm) in soft tissue and frequency (MHz) related?

A

Directly related.

Specifically, the attenuation coefficient is one-half the frequency. 0.5 dB/cm/MHz

32
Q

For each cm depth, there will be: ______

For each MHz of frequency, there will be: ______

A
  1. 5 dB attenuation
  2. 5 dB attenuation
33
Q

How would you choose which probe to use if you are doing an echo on a big person vs. a carotid scan?

A

If you have to go deeper, you choose the probe with the least attenuation (lower frequency).

Ex: 2.5 MHz for echo vs. 7.5 MHz for carotid

34
Q

What is the tradeoff for using a lower frequency probe?

A

Poorer resolution

35
Q

This is an example of what type of reflection?

A

Diffuse reflection, or backscatter

36
Q

This is an example of what type of scatter?

A

Rayleigh scatter

37
Q

These are examples of what types of

ultrasound waves?

A

a) Continuous
b) Gated continuous
c) Pulsed

Physics 110 Exam 2 (6 decks)

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