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Physics > Chapter 17 > Flashcards

Chapter 17 Flashcards

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1
Q

the creation of an image from sound reflections at twice the frequency of the transmitted sound.

A

Harmonic imaging

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2
Q

Fundamental frequency

A

the frequency of sound created by the transducer and transmitted into the body

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3
Q

twice the fundamental frequency

A

Harmonic frequency

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4
Q

Harmonic frequency sound waves arise from _ behavior

A

Nonlinear

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5
Q

Fundamental image

A

the image created by processing reflections that have the same frequency as the transmitted sound.

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6
Q

the image created by processing reflections that are twice the fundamental frequency.

A

Harmonic image

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7
Q

A portion of clinical studies are suboptimal because of _

A

sound beam distortion.

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8
Q

Harmonic imaging improves poor quality images because _

A

harmonic frequency waves undergo less distortion than fundamental sound waves.

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9
Q

Two forms of harmonics:

A

Tissue harmonics

Contrast harmonics

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10
Q

proportional or symmetrical

A

Linear

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11
Q

_ systems respond in an even manner

A

Linear

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12
Q

irregular or disproportionate, asymmetrical

A

Nonlinear

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13
Q

A system is nonlinear when it behaves _

A

Unevenly

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14
Q

Harmonic frequency sound arises from _ behavior

A

Nonlinear

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15
Q

As a sound wave travels in the body, a miniscule amount of energy is converted from _ to _. This conversion creates tissue harmonics during _

A

the fundamental frequency to the harmonic frequency.

Transmission

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16
Q

Sound travels faster through _ and slower through _

A

Compressions

Rarefactions

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17
Q

_ creates tissue harmonics in the biologic media and alters the shape of the sound beam.

A

Nonlinear variation in speed

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18
Q

The strength of the harmonic wave _ as sound travels in tissue

A

Increases

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19
Q

During fundamental imaging, strong artifacts appear in the first few centimeters of tissue due to:

A

The beam being very strong
Many different superficial anatomical layers distort the
sound beam

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20
Q

Do tissue harmonic signals exist at superficial depths?

A

No

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21
Q

The use of harmonics improves _

A

Signal to noise ratio

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22
Q

The relationship between sound beam strength and harmonic creation is

A

Nonlinear

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23
Q

Do weak sound beams create tissue harmonics?

A

No

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24
Q

Intermediate strength beams create _ amount of tissue harmonics

A

Only a tiny

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25
Q

Strong sound beams create _ tissue harmonic signals

A

Significant

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26
Q

_ are created when sound beams are distorted

A

Side/grating lobes

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27
Q

_ harmonics are created in the side/grating lobes

A

Very few

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28
Q

The main beam is strong and creates _ harmonics. This creates an image with _ distortion

A

Strong

Less

29
Q

Beams that are most likely to create harmonics are _ likely to create artifacts

A

Least

30
Q

Harmonic imaging improves the image quality in 3 primary ways:

A
  1. The harmonic beam is much narrower
  2. Grating lobe artifacts are eliminated
  3. Improves signal-to-noise ratio
31
Q

An imaging technique specifically designed to utilize harmonic reflections while eliminating distorted fundamental reflections

A

Pulse inversion harmonics

32
Q

Disadvantage of pulse inversion

A

Degradation of temporal resolution due to requiring two pulses per scan line

33
Q

Another technique designed to augment harmonic reflections while eliminating fundamental reflections. Two consecutive ultrasound pulses are sent down each scan line. The second pulse is twice the strength as the first pulse.

A

Power modulation harmonics

34
Q

Power modulation reduces

A

Distortion and temporal resolution

35
Q

Contrast agents are designed to _

A

create strong reflections that “light up” blood chambers, vessels, or other anatomic regions

36
Q

Must meet the following 5 requirements:

A
  1. Safe
  2. Metabolically inert
  3. Long lasting
  4. Strong reflector of ultrasound
  5. Small enough to pass through capillaries
37
Q

As an ultrasound pulse interacts with contrast agents, _ are created

A

Much stronger harmonics

38
Q

Contrast harmonics are created because

A

microbubbles act in a nonlinear manner when struck by ultrasound waves

39
Q

Contrast harmonics are created during _ as_

A

Reflection

energy is converted from the fundamental frequency to the harmonic frequency

40
Q

_ harmonics are stronger than _ harmonics

A

Contrast Tissue

41
Q

When a microbubble is within a sound beam, the bubble grows and shrinks in relation to

A

the pressure variations (during compressions and rarefactions)

42
Q

Contrast harmonics are created due to

A

the nonlinear changes in the bubble size.

43
Q

The uneven behavior that causes contrast harmonics is called _

A

Resonance

44
Q

Contrast harmonics: When exposed to high pressure (compressions), the bubble _ and the pressure

A

Shrinks

Increases

45
Q

Contrast harmonics: When exposed to low pressure (rarefactions), the bubble

A

Expands

46
Q

Bubbles _ to a greater extent than they _

A

Expand

Shrink

47
Q

_ pressure is most important with regard to contrast harmonics

A

Peak rarefaction

48
Q

A number related to the likelihood of harmful bioeffects from cavitation (bubble bursting)

A

Mechanical index

49
Q

Mechanical index can estimate _

A

the amount of contrast harmonics produced

50
Q

Mechanical index depends on

A

the frequency of the transmitted sound and the rarefaction pressure of the sound wave

51
Q

MI =

A

peak rarefaction pressure/(square root of freq)

52
Q

MI increases with

A

Lower frequency sound

Stronger sound waves (substantial pressure variation)

53
Q

Lower MI

A

Small pressure variation

Higher frequency

54
Q

Higher MI

A

Large pressure variation

Lower frequency

55
Q

Low MI sound beams do not create harmonics because

A

the microbubbles expand and contract in a linear fashion.

56
Q

If the MI is less than 0.1, bubbles only create

A

Backscatter

57
Q

Intermediate MI’s (0.1 to 1.0) create a _ amount of harmonics

A

Relatively small

58
Q

MI’s greater than 1 create _ harmonic signals. The bubbles may actually

A

Substantial

Expand and break apart

59
Q 
Low MI: <0.1:
_ harmonics 
_
_ behavior
_ frequency sound
_ beam strength
Bubbles expand _
A 
No
Backscatter
Linear
Higher
Low 
Very little
60
Q 
Higher MI: 0.1-1.0
_ harmonics
_
_ behavior
_ frequency sound
_ beam strength
Bubbles expands _
A 
Some
Resonance
Nonlinear
Lower
Higher 
Moderately
61
Q 
Highest MI > 1
_ harmonics 
_
_ behavior
_ frequency sound
_ beam strength
Bubbles expands _
A 
Strongest
Bubble disruption 
Extreme
Lowest
Highest
Greatly
62
Q

Two characteristics of contrast agents are important:

A

The nature of the outer shell

The gas that fills the microbubble

63
Q

_ trap the gas and increase the effective life of a microbubble

A

Shells

64
Q

Shells are designed to be

A

flexible so they can change shape

65
Q

Smaller gas molecules are _ likely to leak through the shell and shrink the bubble.

A

More

66
Q

Larger gas molecules remain _

A

Trapped in the bubble

67
Q 
Tissue harmonics:
Created during_
Occurs as _
Results from_
_ harmonic signal
A

Transmission in tissue
Sound propagates in tissue
Nonlinear behavior of transmitted sound beam
Weaker

68
Q 
Contrast harmonics:
Created during _
Occurs only when_
Results from _
_ harmonic signal
A

Reflection off of microbubble
Contrast agents are present and with MIs greater than 1
Nonlinear behavior of micro bubbles
Stronger

Physics (25 decks)

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