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Physics 2 > Chapter 16 and 17 > Flashcards

Chapter 16 and 17 Flashcards

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1
Q

______ is a method of reporting the extent to which a signal can vary and still be accurately measured “number of available choices “

A

dynamic range

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2
Q

what are the units of dynamic range?

A

decibels

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3
Q

the dynamic range information ______ the more it is processed

A

deceases; components earliest in the imaging has chain process data with the widest dynamic range (transducer), components farther along in the imaging process data with narrower dynamic range (display and storage)

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4
Q

the process of ______ eliminates a problem with components with different dynamic ranges

A

compression (reduces dynamic range) (adjustable)

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5
Q

what are the requirements of compression?

A

the largest signal remains the largest
the smallest signal remains the smallest
the range of signals is reduced

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6
Q

______ dynamic range means fewer gray scale, they are also called high contrast (few choices and black and white)

A

narrow

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7
Q

______ dynamic range means many shades of gray, also called low contrast (many choices and gray scale)

A

wide

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8
Q

The frequency of sound created by the transducer and transmitted into the body is?

A

Fundamental frequency

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9
Q

Twice the fundamental frequency is?

A

Harmonics frequency

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10
Q

Harmonic frequency sound waves arise from ______

A

Nonlinear behavior

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11
Q

The image created by processing reflections that have the same frequency as the transmitted sound

A

Fundamental image

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12
Q

The image created by precessing reflections that are twice the fundamental frequency

A

Harmonic image

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13
Q

Harmonic imaging is most useful in improving poor quality images because harmonic frequency waves undergo less ______ than fundamental sound waves

A

Distortion

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14
Q

What are the two forms of harmonics that is important in US?

A

Tissue harmonics and contrast harmonics

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15
Q

Linear means ______ or symmetrical, linear systems response in an even manner

A

Proportional

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16
Q

Nonlinear means ____ or disproportionate, a system is nonlinear when it behaves unevenly

A

Irregular

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17
Q

Harmonic frequency sound arises from _____ behavior

A

Nonlinear

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18
Q

As a sound wave travels in the body, a minuscule amount of energy is converted from the fundamental frequency to the harmonic frequency- this creates ______ during transmission

A

Tissue harmonics

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19
Q

The ______ variation in speed creates tissue harmonics in the biologic media

A

Nonlinear

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20
Q

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

A

Grows

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21
Q

During fundamental imaging significant amounts of artifact arise within the first few centimeters of tissue, why?

A

The beam is very strong and the many different superficial anatomical layers distort the sound beam

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22
Q

Tissue harmonics develop _____ in tissue

A

Deeper; they do not exist in extremely superficial depths

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23
Q

Harmonics get at ______ through the superficial tissue, remaining distortion free with less noise (but increases signal-to-noise ratio)

A

“Free ride”

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24
Q

______ sound beams create significant tissue harmonic signals (nonlinear)

A

strong

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25
Q

since harmonics arise only in the non-distored main beam, the harmonic image has less distortion, very few harmonics are created in the ______ because they are so weak

A

side lobes; beams that are most likely to create harmonics are least likely to create artifact

26
Q

sound in ______ travels faster than sound in rarefaction

A

compression

27
Q

______ harmonics is an imaging technique specifically designed to utilize harmonic reflections, which are distortion free, while eliminating distorted fundamental reflections

A

pulse inversion

28
Q

______ imaging creates images from the portion of the reflected sound that has the same frequency as the transmitted sound

A

fundamental

29
Q

______ imaging creates images only from harmonic, which is twice the frequency of the transmitted sound

A

harmonic

30
Q

with pulse inversion harmonics, two ______ ultrasound pulses are transmitted down each scan line

A

consecutive

31
Q

the first is a _____ pulse, the second pulse inversion is an _____ copy that is out-of-phase with the first: compression exists in the first pulse, a rarefaction exists in the second

A

typical, inverted

32
Q

the reflections from these pulses are combined in the _____

A

receiver

33
Q

since fundamental portions of the reflections exhibit _____ behavior, the two inverse fundamental signals destructively interfere and completely cancel each other out

A

linear

34
Q

since the harmonic portion of the reflections are in-phased and interfere constructively, they remain while the fundamental portions ______

A

disappear

35
Q

the time required to create a frame is ______ in pulse inversion harmonics, the frame rate is halved and temporal resolution is reduced

A

doubled

36
Q

______ harmonics is another imaging technique specially designed to augment harmonic reflections, which contain less distortion, while eliminating distorted fundamental reflections

A

power modulation; it achieves the same goals as pulse inversion but uses a different engineering approach

37
Q

two constructive US pulses are sent down the same line; the second pulse is ______ the strength of the first one

A

twice; the stronger second reflection contains harmonics

38
Q

in power modulation, during reception the reflection from the first pulses are doubled and then ______ from the second reflection

A

subtracted

39
Q

the fundamental potions cancel each other out in power modulation harmonics, leaving only the harmonic portion of the _____ reflection

A

second

40
Q

contrast agents, also called ______, are gas bubbles encapsulated in a shell; they are injected in the circulation or ingested

A

microbubbles

41
Q

contrast agents have different ______ fingerprint than blood or tissue, they are designed to create strong reflections that accurately “light up” blood chambers, vessels, or other anatomic regions

A

acoustic

42
Q

what are the five requirements for contrast agents?

A

safe, metabolically inert, long lasting, strong reflector of US, and small enough to pass through capillaries

43
Q

as sound pulses interacts with contrast agents, much ______ harmonics are generated, contrast agents are created because microbubbles act in a nonlinear manner when struck by sound waves

A

stronger

44
Q

contrast harmonics are created during ______ as energy is converted from the fundamental frequency to the harmonic frequency

A

reflection

45
Q

when a microbubble is within a sound beam, the bubble grows and shrinks in relation to the ______ variations in sound

A

pressure

46
Q

when exposed to sound beams of adequate strength, contrast harmonics are created because of the nonlinear changes in bubble size, this is called ______

A

resonance

47
Q

during compression the bubbles ______ and the pressure inside the bubble increased, the bubble stabilizes which limits how small the bubble will become

A

shrinks

48
Q

during rarefaction the bubbles ______, a small amount of energy is transferred from the fundamental frequency to the harmonic frequency

A

expands (bubbles expand to a greater extent then they shrink)

49
Q

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

A

mechanical index

50
Q

what does mechanical index depend on?

A

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

51
Q

what is the mechanical index equation?

A

MI= peak rarefaction pressure/ square root of frequency

52
Q

small pressure and higher frequency is?

A

lower mechanical index

53
Q

large pressure variation and lower frequency is?

A

higher mechanical index

54
Q

microbubbles are the size of red blood cells and resonate when exposed to sound in the ______ MHz range, this range is right in the middle of the frequencies used in diagnostic US

A

2 to 4

55
Q

the relationship between the mechanical index and harmonic creation is ______

A

nonlinear

56
Q

______ mechanical sound beams do not create harmonics because the microbubbles expand and contrast evenly in a linear fashion

A

low; when the MI is less than 0.1 bubbles create only backscatter
between 0.1 to 1 create a relatively small amount of harmonics
greater than 1 creates substantial signals

57
Q

with ______ mechanical index sound beams the bubbles may expand and break apart

A

high

58
Q

what are the two important characteristics of contrast agents?

A

the nature of the shell and the gas that fills the microbubble

59
Q

what does the relationship of the shell and the internally trapped gas determine?

A

stability and longevity while circulating in blood
shells trap the gas and increase the effective life of a microbubble
the gas trapped in the interior of the shell also determines the stability of the microbubble
larger gas molecules find the shell less permeable and remain trapped within the bubble

60
Q

contrast harmonics created by microbubbles are much ______ than tissue harmonics

A

stronger

Physics 2 (11 decks)

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