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Sonography > Ch. 17 Physics: Harmonics and Contrast Agents > Flashcards

Ch. 17 Physics: Harmonics and Contrast Agents Flashcards

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

Where does harmonic imaging come from?

A

nonlinear behavior

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3
Q

What are the Two forms of harmonics are important in diagnostic sonography?

A

Tissue Harmonics

Contrast Harmonics

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4
Q

Why is harmonic imaging important to poor quality images?

A

harmonic frequency waves undergo less distortion than fundamental waves, therefore improving poor quality images.

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5
Q

What are the Two types of sound beam behavior?

A

Linear

Nonlinear

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6
Q

What is a linear sound beam behavior?

A

Proportional or symmetrical, responding in an even manner

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7
Q

What is nonlinear sound beam behavior?

A

Irregular or disproportionate, behaves unevenly

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8
Q

Harmonic frequency is _____

A

Nonlinear

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9
Q

Energy is transferred from fundamental to harmonic frequency as sound travels through tissue speeding up (compression) and slowing down (rarefaction).

A

Tissue harmonics

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10
Q

A sound wave is a series of ____________ and ___________.

A

Compressions

rarefactions

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11
Q

Sound travels faster during what?

A

Compressions

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12
Q

sound travels slower during what?

A

Rarefactions

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13
Q

In fundamental imaging, artifacts will be present for what two reasons?

A

The beam is very strong

Many different superficial anatomic
layers distort the sound beam

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14
Q

True or false:
Tissue harmonic signals do exist at extremely superficial depths.

A

False
They do not. They develop deeper in the tissue

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15
Q

Harmonics increases the ____________ ratio.

A

signal-to-noise

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16
Q

Where in the sound beam does max harmonics occur?

A

Mid-field

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17
Q

Where in the sound beam do no harmonics occur?

A

Near and far field

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18
Q

The relationship between the sound beam strength and harmonic creation is ________.

A

nonlinear

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19
Q

Weak beams =

A

no harmonics

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20
Q

intermediate beams =

A

miniscule amount of harmonics

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21
Q

Strong beams =

A

intense harmonics

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22
Q

A tiny amount of energy is converted into harmonics from ……

A

fundamental energy.

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23
Q

True or false:
Only the strong central part of the beam will make harmonics.

A

True

24
Q

Beams that are most likely to create harmonics are least likely to create ______.

A

artifacts.

25
Q

What are the Two imaging techniques that are designed to enhance harmonic reflections?

A

Pulse inversion harmonics (most common)

Power modulation harmonics

26
Q

What separates the fundamental frequency from the harmonic with greater success than filters achieved?

A

Pulse inversion harmonics

27
Q

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

A

Pulse inversion harmonics

28
Q

In pulse inversion harmonics, what is the second pulse sent down the scan line?

A

an inverted copy of the original.

29
Q

What happens when Fundamental signals destructively interfere?

A

cancel each other out

30
Q

How do Harmonic signals interfere with pulse inversion harmonics?

A

constructively

31
Q

What is the disadvantage of pulse inversion harmonics?

A

decreased temporal resolution and frame rate

32
Q

another technique to isolate the harmonic sound beam.

A

Power modulation harmonics

33
Q

What are the two beams that are sent out for power modulation harmonics?

A

A weak beam

A beam 2x as strong

34
Q

During reception of the power modulation harmonic, reflections from the strong pulse are ________________________ from the second reflection

A

doubled and subtracted

35
Q

Power modulation harmonics ___________ frame rate and temporal resolution.

A

decreases

36
Q

also known as microbubbles (encapsulated air)

A

Contrast agents

37
Q

Because of their different acoustic properties they create strong reflections that “light up” the structure being imaged.

A

contrast agents

38
Q

How are contrast agents taken?

A

injected or swallowed

39
Q

What are the 5 requirements of contrast agents?

A

Safe

Metabolically inert

Long lasting

Strong reflector of ultrasound

Small enough to pass through capillaries

40
Q

When sound interacts with contrast agents, much __________ harmonics are created.

A

stronger

41
Q

How do microbubbles act when struck by a sound wave?

A

non linear

42
Q

Contrast harmonics are created during ……

A

reflection

43
Q

True or false :
Contrast harmonic signals are weaker than tissue harmonics

A

False
They are stronger

44
Q

a number that allows for the estimation of contrast harmonics that will be created by a sound beam.

A

Mechanical index (MI)

45
Q

What two factors does mechanical index rely on?

A

Frequency

Peak rarefaction pressure

46
Q

MI and harmonic production increases with:

A

Lower frequency sound

Stronger sound waves (substantial pressure variation)

47
Q

The contrast agents need either_________ or _________to create high Mechanical Indices.

A

Time or strength

48
Q

MI and frequency are __________ related.

A

inversely

49
Q

MI and Peak Negative Pressure are _____________ related.

A

Directly

50
Q

represents the potential amount of contrast harmonics produced.

A

MI

51
Q

Low mechanical index sound beams means

A

no harmonics
MI less than 0.1

52
Q

Intermediate mechanical index means

A

relatively small amount of harmonics
MI 0.1 to 1.0

53
Q

High mechanical index means

A

substantial harmonic signals
MI greater than 1.0

Very strong harmonic reflections from bubble disruption

54
Q

determines the behavior of the bubbles (linear or nonlinear)

A

MI

55
Q

A low MI creates what kind of behavior?

A

Linear

Sonography (39 decks)

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