Harmonics and Contrast Agents Flashcards
Week 4
What is fundamental frequency?
frequency created by the transducer.
What is harmonic frequency?
2x’s the fundamental frequency.
How does harmonic frequency happen?
during nonlinear behavior
What is fundamental imaging?
created by processing reflections that have the same frequency as transmitted sound.
What are harmonic images?
Images created by processing reflections the are twice the fundamental frequency.
What are 2 forms of harmonics?
- Tissue harmonics
- contrast harmonics
Why is harmonic imaging helpful?
helps improve poor quality images, because harmonic frequency waves undergo less distortion.
What does linear behavior mean?
proportional, linear systems respond in an even manner.
What does nonlinear behavior mean?
Irregular, behaves unevenly.
When are harmonics frequency created?
During transmission
What is tissue harmonics?
The minuscule amount of energy is converted from fundamental frequency to harmonic frequency.
Fundamental imaging will have what?
Lower quality imaging and have more noise.
What is the significance of the gradual development of a harmonic signal?
The minuscule amount of energy that converts from fundamental frequency to harmonic frequency.
Tissue harmonics do not exist where?
Superficial depths.
What are some advantages of tissue harmonics?
- improve signal to noise ratio
Weak beams do not create what?
Tissue harmonics
True of False, Harmonic strength weakens as it propagates deeper in the body?
True
Where is the beam strongest?
At the focus, along the beams main axis.
True or false, Harmonics are present as they leave the transducer?
False
Narrow bandwidth creates degraded what?
Spatial resolution
What is pulse inversion harmonic technique?
2 beams at 180 degrees out of phase completely deconstruct, leaving harmonic signal that the original resonant frequencies create.
What is a disadvantage of pulse inversion harmonics?
frame rate is halved.
What is power modulation?
Where during reception, the reflections from the first pulse is doubled then subtracted from the weaker second wave, completely canceling each other out.
What are some advantages of power modulation?
1.less distortion
2. better spatial resolution
Why is it so significant that only strong sound beams create harmonic signals?
creates less distortion and less noise.
contrast agents are also known as what?
microbubbles
Contrast agents meet what 5 requirements?
- safe
- metabolically inert
- long lasting
- strong reflector of ultrasound
- small enough to pass through capillaries
When is contrast harmonics created?
during reflection
What is resonance?
the contraction and expansion of microbubbles
Saline bubble study is used to evaluate what?
The right side of the heart.
Contrast agents or micro bubbles are used to evaluate what?
the left side of the heart.
What is the goal of using contrast agents?
to create a reflection that helps to delineate the left ventricle wall from blood.
True or false, micro bubbles act in a nonlinear manner when struck by sound?
True
True or false, the impedance of the contrast agent is the same as the impedance of soft tissue?
False, it is different.
What expands the bubble in a contrast agent?
Peak rarefactions expand the bubble.
True or False, grating lobes are capable of producing harmonic signals?
False
The purpose of power modulation harmonic imaging is to…..?
Double and then subtract from the second reflection to remove the fundamental frequency.
Within the first 2cm of tissue harmonics does not exist.
False
What is the name of the image that processes reflections at the same frequency as the transmitted (or resonant) frequency?
Fundamental image
True or False, tissue harmonics are created during harmonics?
True
Agitated saline bubble contrast agents are used for:
Right side evaluation for shunts.
The meaning of resonance with microbubbles contrast agents:
When exposed to beams of adequate strength contrast harmonics are created because of nonlinear changes in bubble size.
The amount of contrast harmonics produced may be estimated by a number called?
Mechanical index
The strength of a tissue harmonic wave grows as the transmitted sound travels deeper into the tissue?
True
