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Physics > Harmonics And Contrast Agents > Flashcards

Harmonics And Contrast Agents Flashcards

1
Q

What is the Fundamental Frequency?

A

Frequency of sound transmitted into the body by the transducer; main frequency of the transducer.

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2
Q

What is the Harmonic Frequency?

A

Twice the fundamental frequency; resonant frequency.

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3
Q

What is the Fundamental Image?

A

Image created by main frequency.

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4
Q

What is Harmonic Imaging?

A

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

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5
Q

Define Nonlinear Behavior.

A

Means irregular or disproportionate, asymmetrical; difference of speed between compression (fast) and rarefaction (slow); creates a ‘spilling’ of energy.

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6
Q

Define Linear Behavior.

A

Means proportional or symmetrical; responds in an even manner.

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7
Q

What are Tissue Harmonics?

A

Resonance of tissue created by the conversion of a miniscule amount of energy from the fundamental frequency to the harmonic frequency as it travels through the body.

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8
Q

What are Pulse Inversion Harmonics?

A

Most commonly used technique that separates fundamental frequency from harmonic frequency by transmitting 2 inverted pulses down each scan line.

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9
Q

True or False: Harmonic frequencies undergo more distortion than fundamental frequencies.

A

False.

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10
Q

Fill in the blank: The 1st Harmonic is _______.

A

Twice the fundamental frequency.

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11
Q

What happens to harmonics in superficial layers?

A

Do not develop in very superficial layers.

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12
Q

Where do harmonics develop?

A

In deeper/intermediate layers.

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13
Q

What is an advantage of harmonic imaging?

A

Increases S/N ratio and is distortion free.

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14
Q

What types of artifacts do harmonic frequencies avoid?

A

Do not create lobe artifacts.

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15
Q

What is the significance of the main axis in harmonic imaging?

A

Arise from main axis, strongest part of the sound beam.

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16
Q

What occurs when fundamental signals exhibit linear behavior?

A

Destructively interfere and completely cancel each other out, leaving only the harmonic portion.

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17
Q

What is the effect of harmonic imaging on image quality?

A

Improves image quality because harmonic frequencies undergo less distortion.

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18
Q

What is Power Modulation?

A

A technique used to augment harmonic reflections while eliminating distorted fundamental reflections.

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19
Q

What is the disadvantage of using Power Modulation?

A

Temporal Resolution is reduced.

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20
Q

How does the Power Modulation technique work?

A

It sends 2 consecutive pulses down each scan line, with the second pulse being 2x the strength of the first.

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21
Q

What does the first, weaker pulse in Power Modulation contain?

A

No harmonics.

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22
Q

What happens during reception in Power Modulation?

A

Reflections from the first pulse are amplified to DOUBLE, cancelling out the fundamental frequency of the second pulse’s reflections.

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23
Q

What do microbubbles do in medical imaging?

A

Create strong reflections that ‘light up’ blood chambers, vessels, or other anatomic regions.

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24
Q

What are the requirements for microbubbles?

A
  • Safe
  • Metabolically inert (inactive)
  • Long lasting
  • Strong reflector of ultrasound
  • Small enough to pass through capillaries
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25
Q

What are microbubbles strong scatterers of?

A

Sound.

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26
Q

Why do microbubbles resonate when exposed to frequencies of 2-4 MHz?

A

Because they are the same size as RBCs.

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27
Q

What are the two characteristics of microbubbles?

A
  • The outer shell should be flexible
  • The gas molecule that fills the microbubble should be large enough to remain trapped within the bubble.
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28
Q

Fill in the blank: Microbubbles are gas bubbles encapsulated in a _______.

A

[shell].

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29
Q

What is the Mechanical Index (MI)?

A

A number that estimates the amount of contrast harmonics produced; depends on the frequency and peak rarefaction pressure.

30
Q

What are the three classifications of beam strength?

A
  • Weak
  • Intermediate
  • Strong
31
Q

What is a summary of tissue harmonics?

A

Not present as sound leaves the transducer.

32
Q

How are contrast harmonics created?

A
  • Created deeper in the tissues
  • Created in the tissues during transmission
33
Q

What phenomenon occurs during sound in rarefactions?

A

Much stronger than tissue harmonics; created during reflection as energy is converted from the fundamental frequency to the harmonic frequency.

34
Q

What nonlinear behavior affects microbubbles when struck by sound waves?

A

Nonlinear changes in size of microbubbles or resonance: bubbles expand to a greater extent than they shrink.

35
Q

What is the importance of peak rarefaction pressure in relation to contrast harmonics?

A

It expands the bubble and is most important with regard to contrast harmonics.

36
Q

List the advantages of using contrast harmonics.

A
  • Small pressure variation
  • Higher frequency
  • Less bioeffects
  • Increased spatial resolution
  • Increased contrast resolution
  • Reduces artifact
37
Q

What is the relationship between frequency and Mechanical Index?

A

Inversely related.

38
Q

What is the relationship between peak rarefaction pressure and Mechanical Index?

A

Directly related.

39
Q

What is the amount of tissue harmonics created primarily influenced by?

A

Nonlinear behavior in the speed of sound: sound in compressions travels faster than in rarefactions.

40
Q

What are the characteristics of beams that create harmonics?

A

Primarily created along the beam’s main axis; least likely to create artifacts.

41
Q

What is the effect of higher Mechanical Index?

A
  • Large pressure variation
  • Lower frequency
  • More bioeffects
42
Q

Fill in the blank: _______ refers to the strength of the beam in ultrasound.

A

[Beam Strength]

43
Q

What is the Mechanical Index (MI)?

A

A number that estimates the amount of contrast harmonics produced; depends on the frequency and peak rarefaction pressure.

44
Q

What are the three classifications of beam strength?

A
  • Weak
  • Intermediate
  • Strong
45
Q

What is a summary of tissue harmonics?

A

Not present as sound leaves the transducer.

46
Q

How are contrast harmonics created?

A
  • Created deeper in the tissues
  • Created in the tissues during transmission
47
Q

What phenomenon occurs during sound in rarefactions?

A

Much stronger than tissue harmonics; created during reflection as energy is converted from the fundamental frequency to the harmonic frequency.

48
Q

What nonlinear behavior affects microbubbles when struck by sound waves?

A

Nonlinear changes in size of microbubbles or resonance: bubbles expand to a greater extent than they shrink.

49
Q

What is the importance of peak rarefaction pressure in relation to contrast harmonics?

A

It expands the bubble and is most important with regard to contrast harmonics.

50
Q

List the advantages of using contrast harmonics.

A
  • Small pressure variation
  • Higher frequency
  • Less bioeffects
  • Increased spatial resolution
  • Increased contrast resolution
  • Reduces artifact
51
Q

What is the relationship between frequency and Mechanical Index?

A

Inversely related.

52
Q

What is the relationship between peak rarefaction pressure and Mechanical Index?

A

Directly related.

53
Q

What is the amount of tissue harmonics created primarily influenced by?

A

Nonlinear behavior in the speed of sound: sound in compressions travels faster than in rarefactions.

54
Q

What are the characteristics of beams that create harmonics?

A

Primarily created along the beam’s main axis; least likely to create artifacts.

55
Q

What is the effect of higher Mechanical Index?

A
  • Large pressure variation
  • Lower frequency
  • More bioeffects
56
Q

Fill in the blank: _______ refers to the strength of the beam in ultrasound.

A

[Beam Strength]

57
Q

What is the term for the behavior exhibited by sound at lower frequencies and higher beam strength?

A

Nonlinear behavior

Nonlinear behavior occurs when transmitted sound propagates through tissue.

58
Q

What is the range of Mechanical Index (MI) for higher harmonics?

A

0.1 to 1.0

Higher harmonics are associated with some resonance and nonlinear behavior.

59
Q

Fill in the blank: The _______ is the strongest type of harmonics created during reflection off of microbubbles.

A

Contrast Harmonics

60
Q

What happens to bubbles during extreme nonlinear behavior?

A

Bubbles expand greatly

This behavior is observed when contrast agents are present and with MIs greater than 0.1.

61
Q

True or False: Higher MI values indicate weaker harmonic signals.

A

False

62
Q

What type of sound is created during transmission in tissue?

A

Tissue Harmonics

Tissue harmonics result from the nonlinear behavior of transmitted sound beams.

63
Q

What is the Mechanical Index (MI) threshold for the highest harmonics?

A

> 1.0

64
Q

Fill in the blank: Lower frequency sound is associated with _______ beam strength.

A

Lower

65
Q

What is affected by the microbubble’s shell and the gas within it?

A

Stronger harmonic signal

66
Q

What phenomenon occurs when sound propagates in tissue?

A

Resonance

Resonance can occur as sound waves interact with tissues, especially at certain frequencies.

67
Q

What characterizes the behavior of bubbles during transmission?

A

Bubble expands moderately

68
Q

What is the relationship between beam strength and harmonic signal strength?

A

Higher beam strength leads to stronger harmonic signals.

69
Q

What type of behavior is characterized by the creation of harmonics during microbubble disruption?

A

Extreme nonlinear behavior

70
Q

Fill in the blank: The _______ signal is weaker when lower frequency sound is present.

A

Tharmonic

71
Q

What occurs only when contrast agents are present?

A

Creation of contrast harmonics

Physics (24 decks)

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