What portion of the ultrasound system (from the flow chart) controls the transducer?
The pulser and the beam former
In a stenosis, where does turbulence occur, in the stenosis, before or after the stensosis?
after the stenosis
Where is your pressure the lowest in a stenosis?
in the stenosis, because this is where the velocities are the highest.
With laminar flow you have concentric rings of flow. Where would the fastest flow be, in the middle or on the edges?
in the middle
What is subdicing?
making the element into smaller pieces. When we make it into smaller pieces, it makes for smaller wavelets that create constructive interference.
What is apodization?
We vary the amount of strength going to the elements where usually the outside elements get weaker signals than the inside, so we don't have all of the extraneous power going to the outside of the beam. Varying the excitation to the inner most crystals, to reduce grating lobes.
What are the tradeoffs of harmonics?
Pulse inversion harmonics reduces frame rate, which causes temporal degradation
What do you do to change your contrast resolution (what would you use), and if you want to change the range of your dynamic signal, what would you use? Both changes use the same change.
compression -- changes both dynamic range and contrast resolution
What's the advantage of PW over CW Doppler?
Range resolution - PW can identify where the return signal is coming from.
How do you get rid of aliasing?
Use a CW probe, change the scale (changing the scale is like changing the PRF), change to a lower frequency transducer, use a shallower imaging depth.
How is a tissue phantom better than the older AIUM phantom?
It can be scanned from multiple plans and can evaluate more of the gray scale.
What kind of calibrations and testing can be done with a tissue phantom?
horizontal calibrations, lateral calibrations, axial resolution, and attenuation.
What cannot be measured with a tissue phantom?
density or power -- it can only image the visual qualities and the accuracy of our measurements.
Name something that can measure the intensity of the sound beam.
Hydraphone or a radiation force balance.
The tissue phantom can measure ______ resolution, _________ resolution, and ________ resolution. It cannot measure _________ resolution.
axial, lateral, contrast
There are no known bioeffects as long as temperatures are kept to less than a _______ change.
2 deg C
With a sound wave, which is more dangerous --focused or unfocused?
unfocused, temperature elevations are more likely to occur.
There are different ways of focusing, what are they?
electronic focusing, internal mechanical focusing, and external mechanical focusing.
Which of the receiver functions can be changed by the sonographer?
amplification, compensation, compression, and rejection
Which of the receiver functions cannot be changed by the sonographer?
demodulation (rectification and smoothing)