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Ultrasound Physics > Quiz 7 Ch 17 > Flashcards

Quiz 7 Ch 17 Flashcards

(77 cards)

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1
Q

What is fundamental frequency?

A

Sound created by the transducer and transmitted into the body

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2
Q

Harmonic frequency is ______ the fundamental frequency. (Hint: a number)

A

Twice the fundamental frequency

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3
Q

What type of behavior do harmonic frequency sound waves arise from?

A

Nonlinear

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4
Q

What is a fundamental image?

A

An image created by processing reflections that have the same frequency as the transmitted sound. 2 MHz

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5
Q

What is harmonic image?

A

An image created by processing reflections that are twice the fundamental frequency. 4 MHz

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6
Q

Why is harmonic imaging most useful in improving poor quality images?

They undergo more or less distortion than fundamental waves?

A

less distortion

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7
Q

What are the 2 forms of harmonics?

A

Tissue and contrast

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8
Q

What is a linear behavior?

A

Proportional / symmetrical

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9
Q

What is nonlinear behavior?

A

Irregular or uneven

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10
Q

Harmonic frequency sound arises from what kind of behavior?

A

Nonlinear

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11
Q

What is tissue harmonics ?

A

A small amount of energy is converted from fundamental frequency to harmonic frequency

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12
Q

When does tissue harmonics occur?

A

During transmission

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13
Q

Sound waves are a series of ______ and ______.

A

Compressions and rarefactions

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14
Q

Sound travels faster through what?

A

Compressions

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15
Q

Sound travels slower through what?

A

Rarefactions

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16
Q

Nonlinear variations in speed create what?

A

Tissue harmonics

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17
Q

Changes in the speed through soft tissue changes the shape of what?

A

The sound beam

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18
Q

Does the harmonic wave get stronger or weaker as sound travels through tissue?

A

Stronger

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19
Q

Lots of artifacts arise superficially in what type of imaging? Fundamental or harmonics?

A

Fundamental imaging

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20
Q

What are 2 causes of artifacts developing from fundamental imaging?

A

Strong beam

Beam is distorted from the several superficial layers of anatomy

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21
Q

What does NOT exist at superficial depths?

A

Tissue harmonics

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22
Q

Harmonic signals remain _____free with _____ noise.

A

Distortion

Less

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23
Q

What does harmonics increase? What type of ratio?

A

Signal-to-noise ratio

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24
Q

What is the relationship between sound beam strength and harmonic creation?

A

Nonlinear

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25
Tissue harmonics can not be created by _____ sound beams.
Weak
26
What happens when the sound beams are distorted ?
Small amount of energy is directed away from the beams main axis created side lobes and grating lobes
27
Harmonics are produced on what part of the beam?
The beams main axis
28
Sound beams that are less likely to create artifacts are most likely to create what?
Harmonics
29
Harmonics only arise on a _______ main beam.
Non-distorted
30
Tissue harmonics are created at deeper or shallow depths?
Deeper
31
What is pulse inversion harmonics?
Technique that utilizes harmonic reflections
32
What does pulse inversion harmonics eliminate?
Fundamental reflections
33
Reflections contain what 2 things?
Fundamental and harmonic frequencies
34
Fundamental frequencies contain the (same or different) frequencies as the transmitted wave?
Same
35
How many pulses are transmitted down each scan line in pulse inversion harmonics?
2
36
In pulse inversion harmonics, the first pulse is normal but the second pulse is _________ with the first pulse?
Out of phase
37
Is the first pulse compression or rarefaction?
Compression
38
Is the second pulse compression or rarefaction?
Rarefaction
39
In pulse inversion harmonics, reflections of the 2 pulses are combined where?
In the receiver
40
What happens to the 2 fundamental signals in pulse inversion harmonics?
They cancel each other out (destructively interfere)
41
Does constructive interference make a stronger or weaker wave?
Stronger
42
In pulse inversion harmonics, the harmonic portions of the reflections ______ while the fundamental portions ______.
Stay Disappear
43
Do the remaining harmonic reflections cause less distortion or more distortion on an image?
Less distortion
44
What are disadvantages of pulse inversion harmonics?
-2 pulses required for transmission down each scan line - requires twice the number of pulses to create an image -time per frame is doubled -frame rate is halved -temporal resolution is reduced
45
What is power modulation harmonic imaging?
A technique designed to increase harmonic reflections
46
What does power modulation harmonic imaging eliminate?
Distorted fundamental reflections
47
How is power modulation similar to pulse inversion harmonic imaging?
They both use 2 pulses down each scan line
48
In power modulation harmonic imaging, the second pulse is _____the strength of the first pulse.
Twice
49
The first, weak reflection (does or does not) contain harmonics? The second, stronger reflection (does or does not) contain harmonics?
First reflection does not Second reflection does
50
What happens during reception in power modulation harmonic imaging?
Reflections from first pulse are doubled and then subtracted from second reflection (Cancel each other out), leaving only the harmonic portion of the second reflection
51
What happens to the remaining harmonics that aren’t used in power modulation harmonics?
They form an image with less distortion than the fundamental image
52
What happens to the frame rate and temporal resolution in power modulation harmonics?
Frame rate is halved and temporal resolution is reduced
53
What is contrast agents?
Microbubbles
54
What are microbubbles?
Gas bubbles encapsulated in a shell
55
What are microbubbles created for?
They create strong reflectors that light up blood chambers and vessels
56
Are weak or strong harmonics made when a pulse interacts with a contrast agent?
Strong
57
Do microbubbles act as linear or non linear?
Non linear
58
When are contrast harmonics created?
During reflection
59
What happens to the micro bubble when the pressure changes?
The bubble grows and shrinks
60
What are the 5 requirements of contrast agents?
-safe -metabolically inert -long lasting -strong reflector -small enough to pass through capillaries
61
What is resonance?
Uneven behavior of nonlinear changes in bubble size
62
What happens to the microbubble under high pressure?
Bubble will shrink -Pressure inside the bubble increases -Bubble resists compression -Limits how small bubble will become
63
What happens to the microbubble under low pressure?
Bubble expands to a greater extent than when it shrinks (non linear)
64
What type of pressure is most important in regards to contrast harmonics?
Rarefaction(low) pressure at its peak
65
What is the mechanical index in contrast harmonics?
The amount of contrast harmonics that is produced
66
What does the mechanical index depend on?
Frequency of transmitted sound Rarefaction pressure of sound wave
67
What does low mechanical index depend on?
Small pressure variation High frequency
68
What does high mechanical index depend on?
Large pressure variation Low frequency
69
Why are microbubbles strong scatterers?
They have uneven behavior when exposed to sound between 2-4 MHz
70
What is the relationship between the MI and harmonic creation?
Non linear
71
Why does low MI sound beams do not create harmonics?
Because the microbubbles expand and contract evenly in a linear fashion
72
When the MI is less than .1 what do the bubbles create?
Backscatter
73
When the MI is intermediate and is between .1-1.0 what is created?
Small amount of harmonics
74
When the MI is high and is greater than 1.0, what is created? What happens to the bubbles?
A substantial amount of harmonic signals. The bubbles may expand and break apart
75
Bubble distribution is an example of what type of behavior?
Non linear
76
Contrast harmonics created by microbubbles are ________ than tissue harmonics.
Stronger
77
Is a small or large gas molecule more likely to leak?
Small

Ultrasound Physics (13 decks)

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