M2: Bioeffects Flashcards
what is acoustic propagation
the effect of tissue on sound
does diagnostic US use a lower or higher intensity than therapeutic US
lower
3 ways to describe the strength of a wave
amplitude
power
intensity
these can also express the loudness or volume of a sound
formula for intensity
I = P/A or
I is inversely proportional to Amp^2
what happens if you double amplitude
you quadruple intensity
list the acoustic variables
press
density
particle motion
temperature
define amplitude
maximum variation of an acoustic variable…. also the particle displacement, velocity or acoustic pressure of a sound wave
what does amplitude indicate
the strength of the detected echo or the voltage generated in the crystal from a press wave
what determines the initial amplitude of a pulse
power output - determined by the pulser
as a sound wave travels though tissue, what is the reduction in power called
attenuation
5 mechanisms of attenuation
absorption reflection (z values) refraction (diff velocities and non perpendicular insonation) wavefront divergence scatter
does the amplitude of an echo decrease as it returns to the probe
yes
define power
measure of total energy transmitted over the cross sectional area of the beam, per unit time
formula for power
P = I x A
absolute unit of power
watt (joules/s)
relative unit of power
decibel
how many dB is 100% power
0dB
a reduction of 3 dB drops the intensity by how much
1/2 the original intensity
a reduction of 10 dB drops the intensity by how much
0.1 of original intensity
what determines how much power is produced by the transducer
pulser
power output for PW
1140 mW/cm^2
absolute unit of intensity
W/cm^2 or mW/cm^2
relative unit of intensity
decibel
is intensity constant in time or space
no