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SPI 1 > Attenuation, Interaction of Sound and Media > Flashcards

Attenuation, Interaction of Sound and Media Flashcards

1
Q

How can you determine the log of an even number that is a power of 10?

A

For even powers of 10 (100, 10,000) you can count the zeroes

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2
Q

Do decibels measure absolute or relative changes?

A

Relative changes

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3
Q

What does 3dB indicate?

A

Intensity is doubled

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4
Q

What does 10 dB indicate?

A

Intensity is increased ten-fold

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5
Q

What does -3 dB indicate?

A

Intensity is halved

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6
Q

What does -10 dB indicate?

A

Intensity is reduced to 1/10 the original value

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7
Q

What is attenuation?

A

Sound waves weakening as they propagate through a medium

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8
Q

What units are used to measure attenuation?

A

Decibels

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9
Q

Will attenuation be negative or positive?

A

Negative

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10
Q

How is distance related to attenuation?

A

Directly

The farther sound travels, the greater the attenuation

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11
Q

How is frequency related to attenuation?

A

Directly

The higher the frequency, the greater the attenuation

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12
Q

What are the three processes that contribute to attenuation?

A

Reflection
Scattering
Absorption

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13
Q

What is reflection?

A

When a portion of a sound wave is reflected back to the sound source after striking a boundary

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14
Q

What is specular reflection?

A

When sound is reflected off a smooth surface in only one direction in an organized manner

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15
Q

What is diffuse reflection?

A

When a wave reflects off an irregular surface in more than one direction

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16
Q

What is another term used to describe diffuse reflection?

A

Backscatter

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17
Q

What is the advantage of diffuse reflections?

A

The reflections at suboptimal angles will still produce reflections that come back to the transducer

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18
Q

What is the disadvantage of diffuse reflections?

A

The backscattered signals have a lower strength than specular

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19
Q

What is scattering?

A

The redirection of sound in many directions

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20
Q

What is a tissue that creates scattering?

A

Lung tissue

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21
Q

What is Rayleigh scattering?

A

Scattering that occurs when the dimensions of the structure are smaller than that of the wavelength

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22
Q

What is a structure that produces Rayleigh scattering?

A

Red blood cells

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23
Q

How is scattering related to frequency?

A

Scattering is proportional to frequency raised to the 4th power

24
Q

What is absorption?

A

When ultrasonic energy is converted to a different type of energy, especially heat

25
Q

How is absorption related to frequency?

26
Q

What is the conflict between image accuracy and attenuation with regard to frequency?

A

Higher frequency sound creates accurate images, but has greater attenuation as it travels

27
Q

What is the attenuation coefficient?

A

Number of decibels of attenuation that occurs when sound travels one cm
Unit is dB

28
Q

What is the formula for calculating attenuation?

A

Total Atten (dB) = Atten Coefficient (dB/cm) x distance (cm)

29
Q

What is the formula used to calculate the attenuation coefficient in soft tissue?

A

Atten Coefficient = frequency (MHz) / 2

30
Q

Rank in order from highest to lowest attenuation

muscle, soft tissue, blood, air, bone, fat, water

A

Water, blood, fat, soft tissue, muscle, bone, air

31
Q

What is the half-value layer thickness?

A

The distance sound travels in a tissue that reduces the intensity of sound to half its original value

32
Q

What is impedance?

A

Acoustic resistance to sound traveling in a medium

33
Q

How is impedance calculated?

A

impedance (rayls) = density (kg/m3) x prop. speed (m/s)

34
Q

What is normal incidence?

A

When the incident sound beam strikes the sound beam at 90 degrees

35
Q

What are other terms used to describe normal incidence?

A

Perpendicular, orthogonal, right angle, 90 degrees

36
Q

What is oblique incidence?

A

When the incident sound beam strikes the boundary at any angle other than 90 degrees

37
Q

What is incident intensity?

A

The sound wave intensity before it strikes a boundary

38
Q

What is reflected intensity?

A

The sound wave intensity as it returns back from striking a boundary

39
Q

What is transmitted intensity?

A

Intensity of the portion of the wave after it strikes a boundary and continues forward in the same direction

40
Q

What are units used to describe intensity?

41
Q

What is the intensity reflection coefficient?

A

The percentage of intensity that bounces back when a sound beam strikes a boundary

42
Q

What percentage of a wave is typically reflected at a soft tissue boundary?

A

Less than 1%

43
Q

What is the intensity transmission coefficient?

A

Percentage of intensity that passes in the forward direction after striking an interface

44
Q

How are IRC and ITC reported?

A

As percentages

45
Q

IRC + ITC = ?

A

IRC + ITC = 100%

46
Q

What must happen for there to be a reflection when sound strikes a boundary with normal incidence?

A

Different impedances on either side of the boundary

47
Q

What equation is used to determine the IRC?

A

IRC% = [Z2-Z1/Z2+Z1]^2 x 100

48
Q

How can we determine what % of intensity is transmitted?

A

Whatever sound is not reflected must be transmitted

IRC + ITC = 100%

49
Q

Can we predict if and how much reflection or transmission will occur with oblique incidence?

50
Q

What two physical principles will apply to reflectin with oblique incidence?

A

Conservation of energy

Reflection angle=incidence angle

51
Q

What is refraction?

A

A change in direction of wave propagation when traveling from one medium to another

52
Q

What two conditions must be met for refraction to occur?

A

If there is oblique incidence

If there are different propagation speeds of two media

53
Q

What is Snell’s Law?

A

sin (transmission)/sin (incident) = speed of medium 2/speed of medium 1

54
Q

What does Snell’s Law describe?

A

The physics of refraction

55
Q

What happens to angle of transmission if Speed 2 = Speed 1?

A

no refraction

transmission angle = incident angle

56
Q

What happens to angle of transmission if Speed 2 > Speed 1?

A

transmission angle greater than incident angle

57
Q

What happens to angle of transmission if Speed 2 < Speed 1?

A

transmission angle less than incident angle

SPI 1 (13 decks)

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