Chapter 6: interaction of sound and media Flashcards
sound waves weaken or ________________ as they travel in the body.
attenuate
In diagnostic ultrasound, we are often interested in the degree of _________ or the extent of __________.
attenuation; amplification
what is used to quantify the strength of sound beams, electrical signal strength, brightness of images?
Decibel (dB)
decibel notation is ______________ (4)
logarithmic, relative measurement, a comparison, a ratio
decibel notation does not measure absolute numbers, rather _____________ _____________ what does this mean?
relative changes; “doubled or halved”
what do decibels require? what are these? how are they represented?
two intensities; reference (starting level) and actual level; as a ratio (measured divided by starting level)
what do positive decibels report?
signals that are increasing in strength (getting larger)
what do negative decibels describe?
signals that are decreasing
what is the relative change of intensity when reduced to half its original value? When ten times larger?
-3 dB; +10dB
what is attenuation determined by?
path length, frequency of sound
how does distance affect attenuation? what is their relationship?
the farther sound travels, the greater the attenuation and weaker the beam becomes; directly related
how does frequency of sound affect attenuation? what is their relationship?
attenuation is greater in higher frequency sound than in lower frequency sound; directly related
what two factors cause more attenuation?
longer distances; higher frequencies
what two factors cause less attenuation?
shorter distances; lower frequencies
what 3 processes contribute to attenuation?
reflection, scattering, absorption
