Harmonics & Contrast Flashcards by Brianne Selin

What is harmonics the result of

The wave propagating through tissue

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Harmonics is essentially

Beam dynamics

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As the US beam propagates what happens

Several harmonic frequencies are produced

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Several harmonic frequencies are produced as a result of

Wave distortion

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What is wave distortion dependant on

The intensity of the beam
distance travelled
Nature of the tissue

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Harmonics frequencies are produced in what kind of fashion

Non-linear

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What causes harmonics to be produced non-linearly

Dependencies

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How are fundamental waves produced

In a linear fashion

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High pressure causes what

Tissue is compressed

Higher velocities

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Low pressure cause what

Tissue is expanded

Lower velocities

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What are the three ways that harmonics can benefit the image

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

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What doe you need to create harmonics

Wave distortion

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Why are grating lobes eliminated in the use of harmonics

Too weak to produced harmonics

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Why are harmonic beams narrower

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

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

Mostly main bang, because the fundamental beam causes this

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The bandpass filtration was developed to do what

Eliminate the fundamental frequencies

Allows the harmonic signal to pass through the beam former

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For the bandpass filtering to work what must happen

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

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For the bandwidths to fit that have to be what

More narrow

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What does a narrow bandwidth mean

A longer pulse

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What does a longer pulse do to axial resolution

Negatively impacts it

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Harmonics have a lower what compared to fundamental

Dynamic range

Pulse inversion is

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

How does the pulse inversion work

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

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

They are added together and will cancel each other out

Is pulse inversion a true harmonic signal

What are contrast agents

Liquid suspensions that can be injected into the blood stream

What can contrast agents improve

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

Contrast agents must be

~small enough to pass through the capillaries | ~large enough to give back echoes

What must contrast echoes be stable enough to do

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

The majority of contrast agents are what

Micro bubbles of gas

What are the micro bubbles of gas contained within

A protein Lipid Polymer shell

What does the gas create

A large impedance mismatch

What does the shell do

Keeps the gas from dissolving into the solution (blood)

What can contrast agents do

Improve lesion detection and characterization | Increase doppler signals

When scanning with contrast what is an important consideration

Output power

At 100% power what happens to the bubbles and gas

Bubbles collapse | Gas dissolves

At 75% power what will the bubbles produce

Very intense harmonic echoes

What do the very intense harmonic echoes do

Increase the contrast between the contrast and the tissue

What is coded excitation

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

By eliminating the need for doppler what does it also eliminate

The artifacts associated with doppler

Coded excitation does what to the ultrasound pulse

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

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

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

Detecting what in B-mode is key

Blood reflectors

Blood echoes are what

Very weak and rejected with conventional scanning

What is the solution to detect blood echoes

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

Traditional colour doppler is what in the traditional image

A separate image that is transposed onto the 2D image

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

Coded excitation gives what

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

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

Higher frame rate

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

``` 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 ```