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SPI > Harmonics, Contrast Agents, Hemodynamics > Flashcards

Harmonics, Contrast Agents, Hemodynamics Flashcards

1
Q

What is fundamental frequency?

A

Frequency created by the transducer and transmitted into the body

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2
Q

What is harmonic frequency?

A

Twice the fundamental frequency

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3
Q

What is harmonic imaging?

A

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

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4
Q

What kind of behavior do harmonic waves display?

A

Nonlinear behavior

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5
Q

What is a fundamental image?

A

Imaged created by processing reflections that have the same frequency as the transmitted wave

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6
Q

What are the benefits of harmonic imaging?

A
  • Improves poor image quality
  • Waves undergo less distortion
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7
Q

What are the two forms of harmonics?

A

Tissue and contrast

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8
Q

What is linear?

A
  • Proportional or symmetrical
  • Behaves in an even manner
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9
Q

What is nonlinear?

A
  • Irregular or disproportionate
  • Asymmetric
  • Behaves unevenly
  • Harmonics utilize nonlinear behavior
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10
Q

What is tissue harmonics?

A
  • Sound waves travel into the body
  • Small amount of energy converted from fundamental freq to harmonic freq
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11
Q

How is the shape of the sound beam altered?

A

By variations in the speed of sound traveling through tissue

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12
Q

What happens to the harmonic wave strength as sound travels through tissue?

A

Strength grows

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13
Q

Where are the best harmonics produced?

A

Mid field

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14
Q

Where are little harmonic components generated?

A

Near field

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15
Q

Where are harmonics attenuated faster than produced?

A

Far field

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16
Q

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

A

Harmonic frequency waves undergo less distortion than fundamental sound waves

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17
Q

What nonlinear behavior creates tissue harmonics?

A

Sound travels faster through compressions, slower through rarefactions in soft tissue

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18
Q

What occurs in the first few centimeters of tissue during fundamental imaging?

A

Significant amounts of artifact

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19
Q

Why does significant artifact occur in the first few cm of tissue during fundamental imaging?

A
  • Beam is very strong
  • Many different superficial anatomic layers distort the sound beam
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20
Q

Where do tissue harmonics develop? What is the benefit of this?

A
  • Develop deeper in tissues
  • Do not distort
  • “free ride” through superficial tissues & don’t contain noise
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21
Q

How do harmonics affect signal-to-noise ratio?

A

Increase it

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22
Q

Is there another form of nonlinear behavior that further minimizes distortion with tissue harmonics?

A
  • Relationship b/w beam strength & harmonic creation also nonlinear
  • Weak beams do not create harmonics
  • Intermediate strength beams create small amount of harmonics
  • strong beams create significant harmonics
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23
Q

What are contrast agents?

A

Microbubbles, gas bubbles in a shell
IV or swallowed

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24
Q

How do the acoustic properties of contrast agents compare to bio tissues?

A

Contrast agents create strong reflections that light up blood chambers, vessels, etc

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25
Q

What five requirements do contrast agents need to meet?

A
  • safe
  • able to be metabolized
  • long lasting
  • strong reflector
  • small enough to pass through capillaries
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26
Q

How are contrast harmonics created?

A
  • Microbubbles act in a nonlinear manner when struck by sound waves
  • Created during reflection as energy is converted from fundamental to harmonic freq
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27
Q

What nonlinear behavior of a microbubble creates contrast harmonics?

A

Resonance: when a microbubble is within a sound beam, it grows & shrinks in relation to pressure variations

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28
Q

How does the size of a microbubble change based on pressure?

A

Compression: bubble shrinks & pressure inside increases, stabilizes and resists further compression
Rarefaction: bubble expands to a greater extent than it shrinks

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29
Q

What is most important in creating contrast harmonics?

A

Peak rarefaction pressure

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30
Q

What is the mechanical index?

A

Estimates amount of contrast harmonics produced, depends on freq of transmitted sound & rarefaction pressure of sound wave

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31
Q

The mechanical index increases with what?

A

Lower freq sound and stronger sound waves (large pressure variation)

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32
Q

What is the relationship between low MI (<0.1) and harmonics?

A
  • No harmonics
  • Backscatter
  • Linear behavior
  • Higher frequency sound
  • Low beam strength
  • Bubble expands very little
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33
Q

What is the relationship between MI between 0.1-1.0 and harmonics?

A
  • Some harmonics
  • Resonance
  • Nonlinear behavior
  • Lower frequency sound
  • Higher beam strength
  • Bubble expands moderately
34
Q

What is the relationship between MI > 1 and harmonics?

A
  • Strongest harmonics
  • Bubble disruption
  • Extreme nonlinear behavior
  • Lowest frequency sound
  • Highest beam strength
  • Bubble expands greatly
35
Q

What two characteristics of contrasts agents are important when used with harmonic imaging?

A
  • Nature of outer shell
  • Gas that fills microbubble
36
Q

How do the outer shell and the type of gas in the microbubble determine the contrast agents stability?

A
  • Shells trap gas
  • Shells are flexible, rigid shells fracture
  • Larger gas molecules remain trapped, cannot permeate shell as easily
37
Q

How do the strengths of tissue and contrast harmonics compare?

A

Contrast harmonics are much stronger than tissue harmonics

38
Q

Summarize tissue harmonics (4)

A
  • Created during transmission in tissue
  • Occurs as sound propagates in tissue
  • Results from nonlinear behavior of transmitted sound beam
  • Weaker harmonic signal
39
Q

Summarize contrast harmonics (4)

A
  • Created during reflection off of microbubble
  • Occurs only when contrast agents are present & with MIs > 0.1
  • Results from nonlinear behavior of microbubble
  • Stronger harmonic signal
40
Q

What is hemodynamics?

A

Study of blood moving through the circulatory system

41
Q

What is flow?

A

AKA volume flow rate
Indicates volume of blood moving during a particular time
Units/time

42
Q

What is velocity?

A

Speed of fluid moving from one location to another

43
Q

What is pulsatile flow?

A

When blood moves with variable velocity
Blood accelerates & decelerates with cardiac contraction
Arterial

44
Q

What is phasic flow?

A

Blood moves with variable velocity
Blood accelerates & decelerates due to respiration
Venous

45
Q

What is steady flow?

A

Fluid moves as a constant velocity
Venous circulation when breathing is stopped

46
Q

What is laminar flow?

A
  • Normal
  • Flow streamlines are aligned and parallel
  • Layers of blood traveling at individual speeds
47
Q

What is plug flow?

A

All of the layers & blood cells travel at the same velocity

48
Q

What is parabolic flow?

A

Bullet shaped, highest velocity in center of lumen, gradually decreases to its minimum at vessel wall

49
Q

What is the Reynolds number?

A

Predicts whether flow is laminar or turbulent, for laminar flow it is less than 1500

50
Q

What is turbulent flow?

A

Chaotic flow patterns, many directions, many speeds
Small hurricane like patterns
Assoc with CV pathos

51
Q

What sounds are associated with turbulent flow?

A

Murmur or bruit, thrill

52
Q

What is the Reynolds number for turbulent flow?

A

> 2000

53
Q

How does blood flow based on an energy gradient?

A

Moves from a region of high energy to region of low energy

54
Q

When is energy given to blood?

A

During cardiac contraction cycle

55
Q

What are 3 types of energy?

A

Kinetic, pressure, gravitational

56
Q

What is kinetic energy?

A

Associated with moving object
Determined by object’s mass & speed

57
Q

Is the kinetic energy of a ping pong ball or a golf ball greater?

A

Golf ball because of its mass

58
Q

What is pressure energy?

A
  • Stored or potential energy of an object
  • Ability to perform work
59
Q

What is gravitational energy?

A
  • Stored or potential energy of an object
  • Associated with any elevated object
  • Identical objects at the same height have the same gravitational energy
60
Q

What happens to the energy of blood as it travels through the circulatory system?

A

It loses energy

61
Q

What is viscous loss?

A

Thickness of a fluid, the thicker the fluid the more energy is lost

62
Q

What is frictional loss?

A
  • Occurs when flow energy is converted to heat
  • One object rubs against another (RBC-RBC or vessel wall)
63
Q

What is inertial loss?

A
  • Objects in motion stay in motion, objects at rest stay at rest
  • Energy is lost when speed changes (acceleration or deceleration)
64
Q

When does inertial loss occur?

A

During pulsatile flow, phasic flow & in a stenosis

65
Q

What is the effect of stenosis on flow?

A
  • Changes in direction as blood flows in & out of narrow portion of vessel
  • Increased velocity within stenosis
  • Post-stenotic turbulence
  • Pressure gradient: pressure is lower after stenosis than before
  • Conversion of pulsatile to steady flow
66
Q

Where is velocity highest in a vessel with stenosis?

A

Where the vessel is narrowest

67
Q

What is Bernoulli’s Principle?

A
  • Relationship between velocity & pressure in a moving fluid
  • “With steady flow, the sum of all forms of energy is the same everywhere”
  • Sum of kinetic & pressure energy remains constant
68
Q

What factors are important in pressure-flow relationships?

A

Elasticity of vessels, composition of blood & pulsatility of heart contractions

69
Q

How do you calculate pressure gradient?

A

flow x resistance

70
Q

Pressure gradient increases when what increases?

A

flow or resistance

71
Q

Flow increases when what increases OR what decreases?

A

When pressure gradient increases OR resistance decreases

72
Q

What are characteristics of veins?

A
  • Thin walled, easily compressible, easily respond to pressure changes
  • Low pressure, partially blood-filled, partially expanded
  • Low resistance, passive vessels
73
Q

What are the effects of exercise on venous flow?

A
  • Increases venous flow
  • Change from hourglass to oval to round to accomodate volume increase
  • Resistance to flow decreases even more, allows more flow back to heart
  • Once volume passes, vessel collapses
74
Q

Why does breathing affect venous flow?

A
  • Venous system is low pressure
  • Muscles responsible for respiration alter pressures in chest & abdomen
75
Q

Breathing affects which two venous flows?

A
  • Venous flow in legs
  • Venous return to heart which compromises venous flow from the head & arms and flow from IVC to heart
76
Q

What structure has a large role in the effects of breathing on venous flow?

A

Diaphragm

77
Q

How does inspiration impact venous flow?

A
  • Diaphragm moves down & chest expands
  • Decreases pressure in chest, creates suction that increases venous return to heart
  • Venous flow from head, arms, SVC increases
  • Abdomen compresses, increases pressure in abdomen, decreases venous flow from legs
78
Q

How does expiration affect venous flow?

A
  • Diaphragm moves up
  • Chest compresses
  • Increases pressure in chest, reduces venous return to heart from head, arms, SVC
  • Abdomen expands, decreases pressure in abdomen, increases venous flow from legs
79
Q

What is hydrostatic pressure?

A

Pressure related to the weight of blood pressure on a vessel measured at a height above or below the heart

80
Q

Where is hydrostatic pressure optimal?

A

At the level of the heart

81
Q

When supine, how is hydrostatic pressure affected?

A
  • All body parts are at same level as heart
  • Hydrostatic pressure at every level/location is 0
82
Q

How does standing affect hydrostatic pressure?

A
  • At heart level: accurately represents true circulatory pressure
  • Below heart: hydrostatic pressure is positive
  • Above heart: hydrostatic pressure is negative

SPI (9 decks)

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