Harmonics Flashcards
Harmonics is essentially beam dynamics meaning it is a result of what?
The wave propagating through tissue
As the ultrasound beam propagates, several hormonic frequencies are produces as a result of what?
Wave distortion
The wave distortion is dependent on what?3
- The intensity of the beam
- The distance traveled
- The natured of the tissue
Due to the dependencies, harmonic frequencies are not produced how?
Linearly
Fundamental waves are produced in what type of fashion?
Linear fashion
In terms of harmonics higher pressure means what? 2
- Tissue is compressed
- Higher velocity
In terms of harmonics, Low pressure means what?2
- Tissue expanded
- Lower velocity
What does this image represent?
Harmonics benefit the image in three ways, what are they?
- The harmonic beam is narrower since they are best produced from the most intense part of the beam
- Grating lobes are eliminated as they are too weak to produce harmonics
- Reverberation is greatly reduced or eliminated
Harmonic waves have always been present but we haven’t known what?
How to take advantage of them
Bandpass filtration was developed to do what?
Eliminate the fundamental frequency and allow the harmonic signal to pass through the beam former
Bandpass filtration is similar to what?
Tuning a radio to accept only the frequency that you want to hear
For bandpass filtering to work what needs to be done?
Fundamental (Fo) and second (2Fo) bandwidths must fit within the overall bandwidth without overlapping
Label this picture, what does it represent?
Bandpass filtering
For bandwidths to fit they have to be what?
More narrow
Narrow bandwidth means what? And what does this do?
A longer pulse and this will negatively impact the axial resolution
Pulse inversion is needed for what?
Good axial resolution
Pulse inversion is a technique that can do what? (In terms of harmonics)
Filter out the fundamental and leave only the harmonic signal while maintaining a wide bandwidth
In terms of pulse inversion, a pulse is sent out followed by what?
The inverse of that pulse
When the fundamental echoes return from the first pulse and the inverted pulse, what happens?
They are added together and will cancel each other out. This is not true of a harmonic signal
What are contrast agents?
Liquid suspensions that can be injected into the blood stream to improve the return of echoes for enhanced visualization of blood flow or tissue
Contrast agents must be small enough to do what?
Pass through the capillaries but large enough to give back echoes
Contrast agents must be stable enough to do what?
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 that are contained within a protein, lipid or polymer shell
The gas created by contrast agents creates what?
A large impedance mismatch and the shell keeps the gas from dissolving into the solution (blood)
What can contrast agents do?
Improve lesion detection and characterization and increase doppler signals
When scanning with contrast what is an important consideration?
Output power
At 100% output power what happens to the bubbles and gas?
Bubbles collapse and the gas is dissolved
At 75% power output What happens to the bubbles of contrast?
Bubbles will produce very intense harmonic echoes which increases the contrast between the contrast and tissue
What happens with each bubble, at each bubble?
- Implosion
- Harmonic production
- Resonance
- Static
Label
What is coded excitation?
Newer technology that allows the ability to visualize blood flow in 2D without the need for doppler and the artifacts associated with it
In terms of coded excitation, ultrasound pulses can be digitized to help what?
Reduce noise and improve the overall imaging quality
Label
Blood echoes are very weak and happens as a result of what with conventional scanning?
Blood echoes are weak and are, therefore, rejected with conventional scanning
In terms of coded excitations, the solution is to do what?
Code the pulses so that the real echoes can be differentiated from the noise
In terms of coded excitation, traditional colour doppler is a what kind of image?
A separate image that is transposed onto the 2D image
What does this image represent?
Separate image of colour doppler for coded excitation
Coded excitation gives you simultaneous what?
Tissue and flow without the overlay
What does coded excitation look like?
Intuitive B-Mode like displays with full field of view
In terms of coded excitations, no separate findings for flow means what?
Higher frame rate
The concept of a coded pulses allows for other enhancement as well, what are four?
- Improved sensitivity and supress unwanted signals components
- Improved spatial resolution
- Improved penetration/ contrast
- Technically difficult patients
How does coded excitation improve spatial resolution?
Small lesion identifications
How does coded excitation improves penetration/ contrast?
Subtle contrast differences
How does coded excitation help technically difficult patients? 2
- Improved productivity
- Better IQ and probe versatility
