Formulas
Period is equal to
1 / f
Bandwidth
range of frequencies contained in a pulse
Original frequency is also known as
fundamental frequency
What are the 3 Acoustic variables
Pressure, density, particle vibrations
attenuation is
weakening of sound while it propagates
PRP is equal to
1/PRF
propagation speed is
speed with which a wave moves through a medium
Name of wave with back-and-forth particle motion parallel to direction of wave travel
Longitudinal or mechanical wave
DF percentage for doppler ultrasound
0.5% to 5.0%
Change in direction of sound when it crosses a boundary
refraction
SPL is equal to
(Spatial Pulse Length)
number of cycles in a pulse * wavelength
Time from the beginning of one pulse to the beginning of the next
PRP
regions of low pressure and density
rarefaction
formula for Intensity
P / A
power in a wave divided by the area over which it is distributed
Why is coupling gel necessary for ultrasound?
eliminates thin layer of air that would reflect the sound
wavelength is equal to
c / f
propagation speed / frequency
Duty Factor is
fraction of time that pulsed ultrasound is on
10 DB corresponds to intensity reduction of what percentage
90%
describe 13 us/cm rule
pulse round trip time is 13 us for each cm of distance from source to reflector
average propagation speed in tissue
1.54 mm/us
DF is equal to
PD/PRP
Impendence is
how much of an incident sound wave is reflected back into the first medium
Dominant factor that contributes to absorption of ultrasound in soft tissues
absorption
2 requirements for refraction to occur
oblique incidence
different propagation speed on either side of the boundary
Define Scattering
redirection of sound in many directions by rough surfaces