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Biomedical imaging Ultrasound L1
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What is the formula for the speed of a wave c?
where K is bulk modulus of compressibility (N/m
^{2}
) and rho is density as ever
What is acoustic impedance? What two properties does it link together?
An inherent property of a medium
Relates pressure to particle velocity
What is formula for energy density and what are its
units?
J/m
^{3}
What is formula for ultrasound intensity and what are its
units?
watts/m
^{2}
Give the reflection formula of a wave at a plane surface between two materials of different impedance values
Give the transmission formula of a wave at a plane surface between two materials of different impedance values
Derive the solutions for reflection at a plane surface
What happens when you get multiple layers of material in the path of an ultrasound wave as shown here?
You end up with a standing wave
How can you ensure a complete transmission when you have three layers like this
By picking a matching layer of a quarter wavelength
What causes absorption in ultrasound?
Viscous loss, thermal conduction, structural vibration resonances
What causes attenuation when it comes to ultrasound
Absorption and scattering
What is the formula for attenuation coefficient in ultrasound?
for most tissues, m ~ 1
so most important parameter is '
a'
with units dB/cm/MHz
m=4 for small scatterers and this is rayleigh scattering.
What are the properties of the backing layer and how thick should it be?
Thick
to avoid reflections from back surface
(>5mm)
Lossy
to stop ultrasound reaching back surface
Impedance of backing layer
If too high all backwards sound is coupled into the backing layer (transmission increases)
IN practice make
Z around 5
How do you determine the thickness of the PZT element
t = λ
_{pzt}
/2
λ
_{pzt}
= c
_{pzt}
/f
speed of sound in pzt is (4000m/s)
What is the speed of sound in nylon and pzt?
2500m/s and 4000m/s
Author
keesukim
ID
339564
Card Set
Biomedical imaging Ultrasound L1
Description
ultrasound intro
Updated
2018-05-12T12:08:36Z
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