Chapter 3: Describing sound waves Flashcards
what do parameters describe?
features of a sound wave
what is the source of a sound wave?
the ultrasound system and transducer
what is another way parameters can be determined?
by the tissue (medium) through which the sound is traveling
what is a period?
the time it takes a wave to vibrate a single cycle, or the time from the start of one cycle to the start of the next cycle
what unit is period reported in? what is period determined by?
time (micro secs, secs, hrs, days); sound source only, not by the medium
what is the typical value of period in diagnostic ultrasound? is period adjustable?
0.06 to 0.5 microseconds; no, not able to change the period
what is frequency? how is the applied in diagnostic ultrasound?
the number of particular events that occur in a specific duration of time; the frequency of a wave is described as the number of cycles that occurs in one second
units of frequency?
units per second; 1/ sec or Hertz ( 1 cycle/ sec = 1 hertz)
what is the typical value of frequency in clinical imaging?
ranges from 2MHz to 15MHz (2 million to 15 million)
what is frequency determined by? is frequency adjustable?
determined by the sound source only, not by the medium; No, cannot change the frequency
what is infrasound?
less than 20 Hz
what is the frequency of audible sound?
bw 20 and 20,000 Hz
what is ultrasound frequncy?
greater than 20,000 Hz
why is frequency important?
affect penetration and image quality
what is the relationship bw period and frequency?
inversely related; reciprocal
what does hertz mean?
events per second
what 3 parameters describe size, magnitude, or strength of a sound wave?
amplitude, power, intensity
what is amplitude? what does this measure?
“bigness” of a wave; diff bw max/min value and the average value of an acoustic variable
what units are used for amplitude?
pressure (Pa), density (g/cm^3), particle motion (distance)
what is the typical values of amplitude?
1-3 million pascalst
what is amplitude determined by?
sound source only
is amplitude adjustable?
yes, can alter initial amplitude of a wave
how is amplitude measured?
from the middle (baseline) to the max or minimum value
how do you measure peak-to-peak amplitude?
diff bw max and min values of an acoustic variable
what is the difference bw amplitude and peak-to-peak amplitude?
peak-to-peak is double
what is power? how does this compare to amplitude?
rate of energy transfer; rate at which work is performed; like amplitude, describes the “bigness” of a wave
what units is power measured in?
watts
what is the typical value of power?
0.004 to 0.090 watts (4 to 90 milliwatts)
what determines power? how does this compare to amplitude?
initial power determined by sound source only, power decreases as sound propagates through the body. Rate at which power decreases as sound propagates depends on charac of the medium and wave; same
is power adjustable?
yes, can alter initial power of a wave
how are power and amplitude related?
power is proportional to the wave’s amplitude squared
what is intensity? how is this calculated?
conc of energy in a sound beam; divide the beam’s power by the beam’s cross-sectional area
how does intensity relate to the other bigness parameters? what does this depend on?
relates how the power in a wave spreads or is distributed in space. Depends on both power in beam and area over which the power is applied.
what units is intensity measured in?
watts/square cm (W/cm^2)
what are the typical values of intensity?
0.01 to 300 W/cm^2
what is intensity determined by? how it this similar to power and amplitude?
initial intensity determined only by sound source; same, intensity changes as sound propagates through body
is intensity adjustable?
yes, can alter initial intensity of a wave
what is the formula for intensity?
intensity (W/cm^2)= Power(w)/area (cm^2)
how are the 3 bigness parameters related?
directly related; when intensity increases, power and amplitude also increase.
what is the relationship bw intensity and power?
intensity is proportional to power
what is the relationship bw intensity and amplitude?
intensity is proportional to the wave’s amplitude squared
what is true about the relationship bw amplitude, power, and intensity?
amplitude is always squared when compared to power or intensity
