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Vascular II & Physics II > Physics Ch. 17 > Flashcards

Physics Ch. 17 Flashcards

1
Q

Creation of an image from sound reflections at twice the frequency of the transmitted sound

A

harmonic imaging

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2
Q

Sound created by the transducer and transmitted into the body

A

fundamental frequency

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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

A

non-linear behavior

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5
Q

Harmonic imaging is most useful in __________. Why?

A

improving poor quality images. Frequency waves undergo less distortion than fundamental waves

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6
Q

What are the two forms of harmonics

A

tissue, contrast

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7
Q

proportional, symmetrical, even

A

linear behavior

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8
Q

disproportionate, irregular, uneven

A

nonlinear behavior

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9
Q

Harmonic frequency sound arises from ______ behavior

A

nonlinear

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10
Q

As sound waves travel in the body, a minuscule amount of energy is converted from the fundamental frequency to the harmonic frequency

A

tissue harmonics

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11
Q

Tissue harmonics occur during

A

transmission

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12
Q

Sound is a

A

series of compression and rarefactions

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13
Q

Speed travels ____ through compressions and _____ through rarefactions

A

faster, slower

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14
Q

As sound travels into the tissue, a small amount of energy is transferred from the fundamental frequency to

A

the harmonic frequency

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15
Q

The strength of the harmonics wave ______ as sound travels in tissue

A

grows

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16
Q

Significant amount of artifact within the first few centimeters of tissue is due to

A
  1. strong beam 2. superficial anatomic layers distort the beam
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17
Q

Tissue harmonic signals _____ exist at extremely ______ depths, the signal does not distort- the develop in deeper tissue

A

do not, superficial

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18
Q

The use of harmonics ______ the signal-to-noise ratio

A

increase

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19
Q

Weak sound beams _____ create tissue harmonics. Intermediate sound beams create ______ of tissue harmonics. Strong sound beams create ______ tissue harmonics

A

do not, tiny amount, significant

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20
Q

Harmonics are produced along the _____ beam

A

main

21
Q

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

A

create artifacts

22
Q

Tissue harmonics are ____ present as sound leaves the transducer, they are created _____ in the tissues

A

not, deeper

23
Q

Tissue harmonics is created during

A

transmission

24
Q

Tissue harmonics is _____ in the speed of sound

A

nonlinear behavior

25
Q

Imaging technique designed to utilize harmonic reflections, which are distortion free, while eliminating distorted fundamental reflections

A

pulse inversion harmonics

26
Q

This technique separates the harmonics from the fundamental frequencies more successfully

A

pulse inversion harmonics

27
Q

How does pulse inversion harmonics work

A

2 pulses are transmitted down each scan line. First pulse is normal, second is inverted. They interfere destructively and cancel each other out and all that is left is harmonic frequency

28
Q

Pulse inversion harmonics: time frame= / frame rate= / temporal resolution= / spatial resolution=

A

doubled, halved, reduced, improved

29
Q

Achieves the same goals as pulse inversion, but uses a different engineering approach

A

power modulation harmonics

30
Q

How does power modulation harmonics work

A

2 pulses are sent down each scan line, second pulse is twice the strength of the first one. first (weaker) does not contain harmonics and the second (stronger) contains harmonics

31
Q

Power modulation harmonics: frame rate= / temporal resolution=

A

halved, reduced

32
Q

microbubbles, gas bubbles encapsulated in a shell

A

contrast agents

33
Q

contrast agents/microbubbles are designed to

A

create strong reflections that light up blood chambers/vessels

34
Q

What are the two important characteristics of contrast agents

A
  1. nature of the outer shell 2. gas that fills the microbubble
35
Q

An ultrasound pulse interacts with contrast agents, MUCH STRONGER harmonics are generated

A

contrast harmonics

36
Q

contrast harmonics are created because the

A

microbubbles act in a nonlinear manner when struck by sound waves

37
Q

Contrast harmonics are created during

A

reflection

38
Q

What is the nonlinear/uneven behavior in bubble size called

A

resonance

39
Q

the microbubble expands during

A

rarefaction (low pressure)

40
Q

The amount of contrast harmonics produced may be estimated by the number called the

A

mechanical index

41
Q

The MI depends on

A

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

42
Q

The numerical value of the MI and harmonic production increases with

A
  1. lower frequency sound 2. stronger sound waves
43
Q

Lower MI has

A

small pressure variation, higher frequency

44
Q

Higher MI has

A

large pressure variation, lower frequency

45
Q

Low MI (less than 0.1) creates linear behavior so

A

no harmonics

46
Q

Higher MI (0.1-1.0) creates non linear behavior so

A

some harmonics

47
Q

Highest MI (greater than 1.0) creates no linear behavior so

A

bubble disruption and strongest harmonics

48
Q

Contrast harmonics created by microbubbles are

A

much stronger than tissue harmonics

Vascular II & Physics II (21 decks)

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