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Physics 3 > Harmonics & Contrast > Flashcards

Harmonics & Contrast Flashcards

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1
Q

What is harmonics the result of

A

The wave propagating through tissue

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2
Q

Harmonics is essentially

A

Beam dynamics

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3
Q

As the US beam propagates what happens

A

Several harmonic frequencies are produced

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4
Q

Several harmonic frequencies are produced as a result of

A

Wave distortion

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5
Q

What is wave distortion dependant on

A

The intensity of the beam
distance travelled
Nature of the tissue

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6
Q

Harmonics frequencies are produced in what kind of fashion

A

Non-linear

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7
Q

What causes harmonics to be produced non-linearly

A

Dependencies

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8
Q

How are fundamental waves produced

A

In a linear fashion

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9
Q

High pressure causes what

A

Tissue is compressed

Higher velocities

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10
Q

Low pressure cause what

A

Tissue is expanded

Lower velocities

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11
Q

What are the three ways that harmonics can benefit the image

A

Grating lobes are eliminated
Reverberation is greatly reduced or eliminated
Harmonic beam is narrower

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12
Q

What doe you need to create harmonics

A

Wave distortion

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13
Q

Why are grating lobes eliminated in the use of harmonics

A

Too weak to produced harmonics

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14
Q

Why are harmonic beams narrower

A

Because they are produced from the most intense part of the beam

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15
Q

What kind of reverberation is greatly reduced or eliminated with harmonics and why

A

Mostly main bang, because the fundamental beam causes this

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16
Q

The bandpass filtration was developed to do what

A

Eliminate the fundamental frequencies

Allows the harmonic signal to pass through the beam former

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17
Q

For the bandpass filtering to work what must happen

A

The fundamental and second harmonic bandwidths must fit within the overall transducer bandwidth without overlapping

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18
Q

For the bandwidths to fit that have to be what

A

More narrow

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19
Q

What does a narrow bandwidth mean

A

A longer pulse

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20
Q

What does a longer pulse do to axial resolution

A

Negatively impacts it

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21
Q

Harmonics have a lower what compared to fundamental

A

Dynamic range

22
Q

Pulse inversion is

A

A technique that can filter out the fundamental and leave only the harmonic signal while maintaining a wide bandwidth

23
Q

How does the pulse inversion work

A

A pulse is sent out and followed by the inverse of that same pulse

24
Q

When the fundamental echoes return from the first pulse and that inverted pulse what will happen with pulse inversion

A

They are added together and will cancel each other out

25
Q

Is pulse inversion a true harmonic signal

A

No

26
Q

What are contrast agents

A

Liquid suspensions that can be injected into the blood stream

27
Q

What can contrast agents improve

A

The return of echoes for enhanced visualization of blood flow or tissue

28
Q

Contrast agents must be

A

~small enough to pass through the capillaries

~large enough to give back echoes

29
Q

What must contrast echoes be stable enough to do

A

Make it through the heart for several cycles to allow for adequate imaging time

30
Q

The majority of contrast agents are what

A

Micro bubbles of gas

31
Q

What are the micro bubbles of gas contained within

A

A protein
Lipid
Polymer shell

32
Q

What does the gas create

A

A large impedance mismatch

33
Q

What does the shell do

A

Keeps the gas from dissolving into the solution (blood)

34
Q

What can contrast agents do

A

Improve lesion detection and characterization

Increase doppler signals

35
Q

When scanning with contrast what is an important consideration

A

Output power

36
Q

At 100% power what happens to the bubbles and gas

A

Bubbles collapse

Gas dissolves

37
Q

At 75% power what will the bubbles produce

A

Very intense harmonic echoes

38
Q

What do the very intense harmonic echoes do

A

Increase the contrast between the contrast and the tissue

39
Q

What is coded excitation

A

A newer technology that has allowed for the ability to visualize blood flow in 2D without the need for doppler

40
Q

By eliminating the need for doppler what does it also eliminate

A

The artifacts associated with doppler

41
Q

Coded excitation does what to the ultrasound pulse

A

Digitizes the pulse to help reduce noise and improve the overall image quality

42
Q

What are the 3 things doing for each line in the B-flow image

A

~transmit coded sound waves
~decoder enhances flow signal
~flow and tissue displayed as in B-mode

43
Q

Detecting what in B-mode is key

A

Blood reflectors

44
Q

Blood echoes are what

A

Very weak and rejected with conventional scanning

45
Q

What is the solution to detect blood echoes

A

Code the pulses so that real echoes can be differentiated from the noise

46
Q

Traditional colour doppler is what in the traditional image

A

A separate image that is transposed onto the 2D image

47
Q

For colour doppler how many pulses are needed to average the pulse

A

3

48
Q

Coded excitation gives what

A

Simultaneous tissue and flow without the overlay
Intuitive B-mode like display with full field of view
No separate firings for flow

49
Q

What does the no separate firings for flow mean for frame rate

A

Higher frame rate

50
Q

What are the other enhancements that then concept of coded pulses has allowed for

A 
Improved sensitivity 
Suppression of unwanted signal components 
Improved spatial resolution 
       ~small lesion identification 
Improved penetration and contrast 
       ~subtle contrast differences 
Scanning technically difficult patients 
       ~improved productivity

Physics 3 (5 decks)

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