Ultrasound Physics - 6\sound & Media Interaction

Front 1

The decrease in intensity, power, and amplitude as sound travels

Back 1

Attenuation

Front 2

After a sound wave is received by a transducer, converted into electricity and returned to the system, it is strengthened or ___

Back 2

Amplified

Front 3

A method of rating numbers. Specifically this represents the number of 10's that are multiplied to create the original number

Back 3

Logarithm
100 = 10x10 = Log is 2
1000 = 10x10x10 = Log is 3
10000 = 10x10x10x10 = Log is 4

Front 4

Changes to a returning sound wave are reported as a ratio: the returning beam's intensity level divided by its starting intensity level

Back 4

Decibel (+/- dB)

Front 5

Decibel notation measures ___ changes, not absolute numbers

Back 5

Relative

Front 6

This kind of decibel indicates an increased signal strength

Back 6

+ Decibel

Front 7

This kind of decibel indicates a decreased signal strength

Back 7

- Decibel

Front 8

If an intensity doubles express this in decibels

Back 8

+3 dB

Front 9

If an intensity is reduced by half express this in decibels

Back 9

-3 dB

Front 10

If an intensity is 10x larger express this in decibels

Back 10

+10 dB

Front 11

If an intensity is 1/10 as large express this in decibels

Back 11

-10 dB

Front 12

Attenuation is determined by what two factors?

Back 12

Distance & Frequency

Front 13

How are distance and attenuation related?

Back 13

Directly Related

Front 14

How are frequency and attenuation related?

Back 14

Directly Related

Front 15

Which has less attenuation: shorter distances & lower frequencies? longer distances & higher frequencies?

Back 15

Shorter distances & lower frequencies

Front 16

How is attenuation measured?

Back 16

Decibels

Front 17

Is attenuation reported as a relative change or an absolute change?

Back 17

Relative change

Front 18

Name the three processes that contribute to attenuation

Back 18

Reflection
Scattering
Absorption

Front 19

This happens when sound strikes a boundary and a portion of the wave's energy is redirected back to the sound source

Back 19

Reflection

Front 20

Soft tissue creates what two types of reflection?

Back 20

Specular & Diffuse

Front 21

This happens when a boundary is smooth and a portion of the sound wave's energy is reflected in one direction and in an organized manner

Back 21

Specular Reflection

Front 22

Explain a limitation of Specular Reflection

Back 22

If the wave is slightly off-axis, the reflection does not return to the transducer

Front 23

This happens when a sound wave reflects off an irregular surface and it radiates in more than one direction

Back 23

Diffuse Reflection (Backscatter)

Front 24

Explain one advantage of Diffuse Reflection

Back 24

Even if the wave is off-axis or at suboptimal angle, some reflections will still return to the transducer

Front 25

Explain one disadvantage of Diffuse Reflection

Back 25

Backscattered signals have a lower strength

Front 26

Random redirection of sound waves in many directions

Back 26

Scattering

Front 27

How is frequency and scattering related?

Back 27

Directly Related

Front 28

Sound scatters when the tissue interface is ___ (equal to or less than the ___ of the sound beam)

Back 28

Small / Wavelength
(Lung tissue scatters sound because the alveoli are filled with air)

Front 29

A reduction in the intensity of a sound beam to 1/2 its original value is ___ dB

Back 29

-3 dB

Front 30

A reduction in the intensity of a sound beam to 1/4 of its original value is ___ db

Back 30

-6 db

Front 31

-10 db means that the intensity is reduced to ___ of its original value

Back 31

1/10

Front 32

dB is a mathematical representation with a ___ scale:
A. logarithmic and relative
B. division and relative
C longitudinal and relative
D. logarithmic and absolute

Back 32

A

Front 33

T/F: we need one intensity to calculate dB

Back 33

F

Front 34

Every 3 dB change means that the intensity will ___

Back 34

Increase 2x (or double)

Front 35

Every 10 dB change means that the intensity will ___

Back 35

Increase 10x

Front 36

A wave's intensity is 2 mW/cm(2). There is a change of 9 dB. What is the final intensity?
A. 6 mW/cm(3)
B. 2 mW/cm(2)
C. 16 mW/cm(2)
D. 16 microW/cm(2)

Back 36

C

Front 37

This is a special form of scattering that occurs when the structure's dimensions are much smaller than the beam's wavelength (frequently with RBCs)

Back 37

Rayleigh Scattering

Front 38

This occurs when ultrasonic energy is converted into another form of energy such as heat

Back 38

Absorption

Front 39

What is the relationship between absorption and frequency?

Back 39

Directly Related

Front 40

This is the number of decibels of attenuation that occurs when sound travels one centimeter

Back 40

Attenuation Coefficient

Front 41

Attenuation Coefficient: Units?

Back 41

dB/cm

Front 42

In soft tissue, what is the relationship between the attenuation coefficient and frequency?

Back 42

Directly Related

Front 43

Which has the highest attenuation:
A. air, bone, lung
B. water, blood, urine

Back 43

A
(B is the least)

Front 44

The distance that sound travels in a tissue that reduces the intensity of sound to 1/2 its original value

Back 44

Half-Value Layer Thickness
Penetration Depth
Half-Boundry Layer

Front 45

Half-Value Layer Thickness: Units?

Back 45

cm

Front 46

What effect would the following have on the half-value layer thickness?
- high frequency sound
- media with high attenuation rate

Back 46

Thin Half-Value Layer

Front 47

What effect would the following have on the half-value layer thickness?
- low frequency sound
- media with low attenuation rate

Back 47

Thick Half-Value Layer

Front 48

The half-value layer thickness depends on what two factors?

Back 48

1. Medium
2. Frequency

Front 49

The acoustic resistance to sound traveling in a medium

Back 49

Impedance

Front 50

Reflection of an ultrasound wave depends upon the difference in ___ of the two media at a boundary

Back 50

Impedance

Front 51

Is impedance calculated or measured?

Back 51

Calculated
(density x propagation speed)

Front 52

Impedance: Units?

Back 52

Rayls (Z)

Front 53

As the path length increases, the attenuation of ultrasound in soft tissue ___

Back 53

Increases

Front 54

Attenuation in lung tissue is <, >, = attenuation in soft tissue

Back 54

>

Front 55

Attenuation in bone is <, >, = attenuation in soft tissue

Back 55

>

Front 56

Attenuation in air is <, >, = attenuation in soft tissue

Back 56

>

Front 57

T/F: in a given medium, attenuation is unrelated to speed of sound

Back 57

T

Front 58

What is the numeric relationship between frequency and attenuation coefficient in soft tissue?

Back 58

Attenuation Coefficient (dB/cm) = Half the Frequency

Front 59

As frequency decreases, depth of penetration ___

Back 59

Increases

Front 60

As path length increases, the half boundary layer ___

Back 60

Remains the same

Front 61

Impedance is a characteristic of what?

Back 61

Medium

Front 62

As the path length increases, the attenuation coefficient of ultrasound in soft tissue ___

Back 62

Remains the same

Front 63

Medium A and B have the same densities. The speed of sound in medium A is 10% higher than in B. Which medium has the higher acoustic impedance?

Back 63

A

Front 64

An angle less than 90 degrees is called a/an ___ angle

Back 64

Acute

Front 65

An angle exactly 90 degrees is called a/an ___ angle

Back 65

Right

Front 66

An angle more than 90 degrees is called a/an ___ angle

Back 66

Obtuse

Front 67

When the sound beam strikes a boundary at exactly 90 degrees, this is called what?

Back 67

Normal Incidence
Perpendicular

Front 68

When the sound beam strikes a boundary at any angle other than 90 degrees, this is called what?

Back 68

Oblique Incidence
Non-Perpendicular

Front 69

An angle that is not 90 degrees is called a/an ___ angle

Back 69

Oblique

Front 70

What type of incidence should be avoided when using doppler?

Back 70

Oblique Incidence

Front 71

When a beam strikes a soft tissue boundary, one part of it is ___ and the other moves ___

Back 71

Reflected (backwards)
Forward

Front 72

The intensity of the beam immediately before it strikes a boundary is called what?

Back 72

Incident Intensity

Front 73

The intensity of the portion of the beam that returns back in the direction from which it came, is called what?

Back 73

Reflected Intensity

Front 74

The intensity of the portion of the beam that continues forward, is called what?

Back 74

Transmitted Intensity

Front 75

The percentage of the intensity that bounces back when a beam strikes a boundary is called what?

Back 75

Intensity Reflection Coefficient (IRC, <1%)

Front 76

The percentage of the intensity that continues forward after the beam strikes a boundary is called what?

Back 76

Intensity Transmission Coefficient (ITC, >99%)

Front 77

At the boundary between two media, what principle applies?

Back 77

Conservation of Energy

Front 78

At the boundary between two media, if the reflected and transmitted intensities are added, what is the result?

Back 78

Incident Intensity

Front 79

At the boundary between two media, if the IRC and ITC are added, what is the result?

Back 79

100%

Front 80

A sound wave with intensity of 50 W/cm(2) strikes a boundary and is totally reflected. What is the intensity reflection coefficient (IRC)?
A. 50 W/cm(2)
B. 25 W/cm(2)
C. 0 W/cm(2)
D. 100%
E. 0

Back 80

D

Front 81

A sound wave with intensity of 50 W/cm(2) strikes a boundary and is totally reflected. What is the reflected intensity?
A. 50 W/cm(2)
B. 25 W/cm(2)
C. 0 W/cm(2)
D. 100%
E. 0

Back 81

A

Front 82

With normal incidence, what is the relationship between the size of the reflection and the impedance difference?

Back 82

Directly Related

Front 83

With normal incidence, ___ depends upon a/an ___ difference between the two ___ on either side of a ___

Back 83

Reflection
Impedance
Media
Boundary

Front 84

With oblique incidence, what two laws apply?

Back 84

1. Conservation of Energy
2. Reflection Angle = Incident Angle

Front 85

The sum of reflected and transmitted coefficients must always equal 100%. The sum of reflected and transmitted intensities must always equal the incident intensity. This is called what?

Back 85

Conservation of Energy

Front 86

With oblique incidence, in what direction are reflection sent?

Back 86

Away from the transducer (equal, but opposite to the direction of the incident beam)

Front 87

With oblique incidence, what may occur to the transmitted beam that continues forward?

Back 87

Refraction (it may bend, or change direction, slightly)

Front 88

A change in direction of wave propagation when traveling from one medium to another is called what?

Back 88

Refraction

Front 89

What two conditions must be present for refraction to occur?

Back 89

1. oblique incidence
2. two media with different propagation speeds

Front 90

What law defines the physics of refraction?

Back 90

Snell's Law

Front 91

Under what conditions will the transmission angle equal the incident angle (no refraction)?

Back 91

Speed 1 = Speed 2

Front 92

Under what conditions will the transmission angle be greater than the incident angle (refraction)?

Back 92

Speed 1 < Speed 2

Front 93

Under what conditions will the transmission angle be less than the incident angle (refraction)?

Back 93

Speed 1 > Speed 2

Front 94

A pulse of ultrasound propagates in soft tissue, such as liver. The pulse strikes a soft tissue-soft tissue interface with oblique incidence. Some of the sound energy is transmitted. To what extent is the transmitted beam refracted?

Back 94

Little to no refraction

Front 95

A sound pulse travels in medium 1 and strikes an interface with medium 2 at 30 degrees. The angle of transmission is 10 degrees. From these facts alone, what can be said about the difference between the speeds of media 1 and 2?

Back 95

Large Difference

Front 96

A sound pulse travels in medium 1 and strikes an interface with medium 2 at 30 degrees. The angle of transmission is 10 degrees. In which medium does sound travel the slowest?
A. medium 1
B. medium 2
C. cannot be determined

Back 96

B

Front 97

A sound pulse travels in medium 1 and strikes an interface with medium 2 at 30 degrees. The angle of transmission is 10 degrees. In which medium is the impedance higher?
A. medium 1
B. medium 2
C. cannot be determined

Back 97

C

Front 98

Sound travels in a medium and orthogonally strikes a boundary with a different medium. Although sound waves traveling in the media have vastly different speeds, there is no refraction. How can this be?

Back 98

Refraction cannot occur with normal incidence

Front 99

A sound wave strikes a boundary at normal incidence. The impedances of the two media are identical. What percentage of the sound wave is refracted?
A. 100%
B. 75%
C. 0%
D. 25%
E. 90%

Back 99

C