Harmonics & contrast Flashcards
what is harmonics?
the result of a wave propagating through tissue
what is wave distortion dependent on?
- intensity of beam
- distance traveled
- nature of tissue
if you increase frequency what happens to harmonics?
increases
how does harmonics benefit an image?
- beam is narrower because produced from most intense part of beam
- no grading lobes
- reduced reverb
what was developed to eliminate fundamental frequency?
bandpass filtration
- allowed harmonic signal to pass through beam former
what must happen in order for bandpass filtration to work?
fundamental & 2nd harmonic F bandwidths must fit within overall transducer bandwidth
what does a narrow bandwidth mean?
longer pulse
how does a narrow bandwidth affect axial res
longer pulse negatively impacts axial res
what is pulse inversion
- technique that filters out fundamental & leaves harmonic signal while maintaining wide bandwidth
- pulse is sent out followed by the inverse of that pulse
- cancel eachother out
what does it mean when peak rarefractions are close together?
increased frequency
which sound happens in a linear fashion
fundamental
which sound happens in a non linear fashion
harmonics
what are contrast agents/
liquid suspensions that may be injected into blood to improve visualization of blood and tissue
how small are contrast agents?
must be small enough to pass through capillaries but large enough to give back echoes
what percentage of power should you scan at to get intense harmonic echoes when dealing with contrast agents
75% power
