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ultrasound physics > Ch 17: Harmonics & Contrast Agents > Flashcards

Ch 17: Harmonics & Contrast Agents Flashcards

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1
Q

This is 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

The transmitted frequency is called the __ frequency.

A

fundamental

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3
Q

The __ frequency is twice the transmitted frequency.

A

harmonic

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4
Q

Harmonic frequency sound waves arise from __ behavior.

A

nonlinear

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5
Q

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

A

harmonic image

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6
Q

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

A

fundamental image

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7
Q

What two forms of harmonics are important in diagnostic sonography?

A
  1. tissue harmonics

2. contrast harmonics

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8
Q

This kind of behavior is proportional and symmetrical.

A

linear

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9
Q

This kind of behavior is irregular and disproportionate.

A

nonlinear

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10
Q

T/F? Tissue harmonics happens during transmission.

A

true

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11
Q

The __ of the harmonic wave grows as sound travels in tissue.

A

strength

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12
Q

Tissue harmonic signals do not exist at __ depths.

A

extremely superficial

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13
Q

The use of harmonics __ the signal-to-noise ratio.

A

increases

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14
Q

T/F? The relationship between sound beam strength and harmonic creation is linear.

A

FALSE, nonlinear

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15
Q

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

A

artifacts.

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16
Q

T/F? Tissue harmonics are primarily created along the beam’s side lobes.

A

FALSE, along the beam’s main axis

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17
Q

This is an imaging technique specifically designed to utilize harmonic reflections while eliminating distorted fundamental reflections.

A

pulse inversion harmonics

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18
Q

With pulse inversion harmonics, a __ pulse is followed by a __ pulse.

A

typical, inverted

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19
Q

In pulse inversion harmonics, the typical and inverted pulse reflections are combined in the…

A

receiver.

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20
Q

The disadvantage of pulse inversion harmonics is that…

A

the frame rate is halved and the temporal resolution is reduced.

21
Q

This is an imaging technique specifically designed to augment harmonic reflections.

A

power modulation harmonics

22
Q

With power modulation harmonics, a __ pulse is followed by a __ pulse.

A

typical, 2x as strong

23
Q

The disadvantage of power modulation harmonics is that…

A

the frame rate is halved and the temporal resolution is reduced.

24
Q

These are gas bubbles encapsulated in a shell.

A

contrast agents aka microbubbles

25
Q

Contrast agents must be…

A
  1. safe
  2. metabolically inert
  3. long lasting
  4. strong reflector
  5. capillary small
26
Q

T/F? Contrast harmonics are created during transmission.

A

FALSE, reflection

27
Q

The uneven behavior of microbubbles in a sound beam is called…

A

resonance.

28
Q

When exposed to the high pressure component of a sound wave (compression), the microbubble __.

A

shrinks

29
Q

When exposed to the low pressure component of a sound wave (rarefaction), the microbubble __.

A

expands

30
Q

What keeps the microbubble from shrinking very much?

A

internal pressure

31
Q

What keeps the microbubble from expanding very much?

A

nothing!

32
Q

T/F? Bubbles shrink to a greater extent than they expand.

A

FALSE, the opposite

33
Q

This is number that estimates the amount of contrast harmonics produced.

A

mechanical index aka MI

34
Q

The MI depends on the…

A
  1. transmission frequency

2. rarefaction pressure

35
Q

The MI increases with…

A
  1. lower frequency sound

2. stronger sound waves

36
Q

Why are microbubbles strong scatterers of sound waves?

A

Because they resonate when exposed to sound in the 2 to 4 MHz range.

37
Q

Low MI does not create harmonics because…

A

the microbubbles expand and contract evenly in a linear fashion.

38
Q

When the MI is less than __, bubbles create only backscatter.

A

0.1

39
Q

When the MI is __, bubbles create relatively small amounts of harmonics.

A

0.1 to 1.0

40
Q

When the MI is __, bubbles create substantial harmonics.

A

greater than 1.0

41
Q

What are the important characteristics of contrast agents when used with harmonic imaging?

A
  1. the nature of the outer shell

2. the gas that fills the bubble

42
Q

The relationship between the bubble’s shell and internal gas determines its…

A

stability and longevity.

43
Q

Which is stronger: tissue or contrast harmonics?

A

contrast harmonics by a lot

44
Q

Contrast harmonics are created during…

A

reflection.

45
Q

Contrast harmonics are created by __ behavior.

A

nonlinear

46
Q

Contrast harmonics are related to the __ index.

A

mechanical

47
Q

Low MI creates linear behavior and…

A

no harmonics.

48
Q

Higher MI creates nonlinear behavior and…

A

some harmonics.

49
Q

Very high MI creates bubble disruption and…

A

very strong harmonics.

ultrasound physics (23 decks)

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