Physics Ch. 17 Flashcards
Creation of an image from sound reflections at twice the frequency of the transmitted sound
harmonic imaging
Sound created by the transducer and transmitted into the body
fundamental frequency
twice the fundamental frequency
harmonic frequency
Harmonic frequency sound waves arise from
non-linear behavior
Harmonic imaging is most useful in __________. Why?
improving poor quality images. Frequency waves undergo less distortion than fundamental waves
What are the two forms of harmonics
tissue, contrast
proportional, symmetrical, even
linear behavior
disproportionate, irregular, uneven
nonlinear behavior
Harmonic frequency sound arises from ______ behavior
nonlinear
As sound waves travel in the body, a minuscule amount of energy is converted from the fundamental frequency to the harmonic frequency
tissue harmonics
Tissue harmonics occur during
transmission
Sound is a
series of compression and rarefactions
Speed travels ____ through compressions and _____ through rarefactions
faster, slower
As sound travels into the tissue, a small amount of energy is transferred from the fundamental frequency to
the harmonic frequency
The strength of the harmonics wave ______ as sound travels in tissue
grows
Significant amount of artifact within the first few centimeters of tissue is due to
- strong beam 2. superficial anatomic layers distort the beam
Tissue harmonic signals _____ exist at extremely ______ depths, the signal does not distort- the develop in deeper tissue
do not, superficial
The use of harmonics ______ the signal-to-noise ratio
increase
Weak sound beams _____ create tissue harmonics. Intermediate sound beams create ______ of tissue harmonics. Strong sound beams create ______ tissue harmonics
do not, tiny amount, significant
Harmonics are produced along the _____ beam
main
Beams that are most likely to create harmonics are least likely to
create artifacts
Tissue harmonics are ____ present as sound leaves the transducer, they are created _____ in the tissues
not, deeper
Tissue harmonics is created during
transmission
Tissue harmonics is _____ in the speed of sound
nonlinear behavior
Imaging technique designed to utilize harmonic reflections, which are distortion free, while eliminating distorted fundamental reflections
pulse inversion harmonics
This technique separates the harmonics from the fundamental frequencies more successfully
pulse inversion harmonics
How does pulse inversion harmonics work
2 pulses are transmitted down each scan line. First pulse is normal, second is inverted. They interfere destructively and cancel each other out and all that is left is harmonic frequency
Pulse inversion harmonics: time frame= / frame rate= / temporal resolution= / spatial resolution=
doubled, halved, reduced, improved
Achieves the same goals as pulse inversion, but uses a different engineering approach
power modulation harmonics
How does power modulation harmonics work
2 pulses are sent down each scan line, second pulse is twice the strength of the first one. first (weaker) does not contain harmonics and the second (stronger) contains harmonics
Power modulation harmonics: frame rate= / temporal resolution=
halved, reduced
microbubbles, gas bubbles encapsulated in a shell
contrast agents
contrast agents/microbubbles are designed to
create strong reflections that light up blood chambers/vessels
What are the two important characteristics of contrast agents
- nature of the outer shell 2. gas that fills the microbubble
An ultrasound pulse interacts with contrast agents, MUCH STRONGER harmonics are generated
contrast harmonics
contrast harmonics are created because the
microbubbles act in a nonlinear manner when struck by sound waves
Contrast harmonics are created during
reflection
What is the nonlinear/uneven behavior in bubble size called
resonance
the microbubble expands during
rarefaction (low pressure)
The amount of contrast harmonics produced may be estimated by the number called the
mechanical index
The MI depends on
the frequency of the transmitted sound and rarefaction pressure of the sound wave
The numerical value of the MI and harmonic production increases with
- lower frequency sound 2. stronger sound waves
Lower MI has
small pressure variation, higher frequency
Higher MI has
large pressure variation, lower frequency
Low MI (less than 0.1) creates linear behavior so
no harmonics
Higher MI (0.1-1.0) creates non linear behavior so
some harmonics
Highest MI (greater than 1.0) creates no linear behavior so
bubble disruption and strongest harmonics
Contrast harmonics created by microbubbles are
much stronger than tissue harmonics
