Biomedical imaging Ultrasound L1

  1. What is the formula for the speed of a wave c?
    Image Upload 1 where K is bulk modulus of compressibility (N/m2) and rho is density as ever
  2. What is acoustic impedance? What two properties does it link together?
    • An inherent property of a medium
    • Image Upload 2
    • Relates pressure to particle velocity
    • Image Upload 3
  3. What is formula for energy density and what are its units?
    Image Upload 4J/m3
  4. What is formula for ultrasound intensity and what are its units?
    Image Upload 5 watts/m2
  5. Give the reflection formula of a wave at a plane surface between two materials of different impedance values
    Image Upload 6
  6. Give the transmission formula of a wave at a plane surface between two materials of different impedance values
    Image Upload 7
  7. Derive the solutions for reflection at a plane surface
    Image Upload 8
  8. What happens when you get multiple layers of material in the path of an ultrasound wave as shown here?
    Image Upload 9
    You end up with a standing wave
  9. How can you ensure a complete transmission when you have three layers like thisImage Upload 10
    By picking a matching layer of a quarter wavelength
  10. What causes absorption in ultrasound?
    Viscous loss, thermal conduction, structural vibration resonances
  11. What causes attenuation when it comes to ultrasound
    Absorption and scattering
  12. What is the formula for attenuation coefficient in ultrasound?
    • Image Upload 11
    • 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.
  13. 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
  14. How do you determine the thickness of the PZT element
    t = λpzt/2 

    • λpzt = cpzt/f 
    • speed of sound in pzt is (4000m/s)
  15. 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