Harmonics, Contrast Agents, Hemodynamics Flashcards
What is fundamental frequency?
Frequency created by the transducer and transmitted into the body
What is harmonic frequency?
Twice the fundamental frequency
What is harmonic imaging?
Creation of an image using sound reflections at twice the frequency of the transmitted sound
What kind of behavior do harmonic waves display?
Nonlinear behavior
What is a fundamental image?
Imaged created by processing reflections that have the same frequency as the transmitted wave
What are the benefits of harmonic imaging?
- Improves poor image quality
- Waves undergo less distortion
What are the two forms of harmonics?
Tissue and contrast
What is linear?
- Proportional or symmetrical
- Behaves in an even manner
What is nonlinear?
- Irregular or disproportionate
- Asymmetric
- Behaves unevenly
- Harmonics utilize nonlinear behavior
What is tissue harmonics?
- Sound waves travel into the body
- Small amount of energy converted from fundamental freq to harmonic freq
How is the shape of the sound beam altered?
By variations in the speed of sound traveling through tissue
What happens to the harmonic wave strength as sound travels through tissue?
Strength grows
Where are the best harmonics produced?
Mid field
Where are little harmonic components generated?
Near field
Where are harmonics attenuated faster than produced?
Far field
Why is harmonic imaging most useful in improving poor image quality?
Harmonic frequency waves undergo less distortion than fundamental sound waves
What nonlinear behavior creates tissue harmonics?
Sound travels faster through compressions, slower through rarefactions in soft tissue
What occurs in the first few centimeters of tissue during fundamental imaging?
Significant amounts of artifact
Why does significant artifact occur in the first few cm of tissue during fundamental imaging?
- Beam is very strong
- Many different superficial anatomic layers distort the sound beam
Where do tissue harmonics develop? What is the benefit of this?
- Develop deeper in tissues
- Do not distort
- “free ride” through superficial tissues & don’t contain noise
How do harmonics affect signal-to-noise ratio?
Increase it
Is there another form of nonlinear behavior that further minimizes distortion with tissue harmonics?
- 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
What are contrast agents?
Microbubbles, gas bubbles in a shell
IV or swallowed
How do the acoustic properties of contrast agents compare to bio tissues?
Contrast agents create strong reflections that light up blood chambers, vessels, etc