ultrasound physics

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ultrasound physics
2010-06-09 12:40:49
Final Review

outline to study
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  1. reciprocal
    relationship btwn 2 numbers mutiplies together to equal one
  2. pascal
    unit of measurement for pressure
  3. sound
    is mechanical and longitudinal wave
  4. y- axis
    on a graph the vertical axis
  5. x-axis
    on a graph the horizontal axis
  6. in-phase
    if the rarefactions of 2 waves occur at the same time
  7. destructive interferance
    where the resultant wave is smaller then the one of its components
  8. kg/cm cubed
    proper unit to describe density
  9. waves with different frequencies
    type of wave will exhibit both constuctive and distructive interference
  10. energys
    what wave transfer from one location to another
  11. all types of sound
    mechanical energy transmitted by pressure waves in a medium
  12. vaccum
    sound waves can not travel through
  13. they cause vibrations in the medium
    properties common to all sound sources
  14. medium
    speed of sound depends on
  15. commpressions
    in sound wave, regions where the pressure is higher than normal
  16. longitudinal wave
    thype of sound wave that can propagate through soft tissue ( ultrasound waves)
  17. wavelength
    • dertemined by medium
    • distance a wave travels one period of oscillation of the source
  18. halves
    frequency doubles, wavelength
  19. Snell's Law
    predicts the direction of the transmitted beam
  20. speed of sound in tissue
    • 1540m/s
    • 1.54 mm
  21. period
    • p=1/freq
    • time it takes to complete a single cycle
  22. frequency
    • f= 1/period
    • number of times the wave is repeated per second
    • number of cycles per unit of time
    • determined by source
  23. amplitude
    peak pressure or height of wave
  24. when sound is traveling through same medium if frequency increases
    • wavelength= decreases
    • propagation= stays the same
    • period= decreases
    • amplitude= stays the sam
  25. pulse duration
    • pd=cycle# x period
    • pd=cycle#/freq
    • is the time that the pulse is acually on
  26. duty factor (cycle) for continous wave ultrasound is
  27. spatial pulse length
    space from start of pulse to the end of that pulse
  28. typical freq range in medial ultrasound imaging
    1 to 32 MHz
  29. watts
    unit of power
  30. can sonographer adjust intensity of the US beam?
  31. speed of sound determined by
  32. can pulse duration be changed?
  33. when depth is adjusted, what parametes are affected
    • PRP (
    • PRF (pulse repetition frequency)
    • Duty Factor
  34. if image depth increases
    PRF decreases
  35. PRF unit
  36. aspect of intensity refers to only the transmitted time
  37. sound intensity
    directly proportional to transducer frequency
  38. 7 parameters
    • period
    • frequency
    • amplitude
    • power
    • intensity
    • wavelength
    • speed
  39. acoustic variables
    • pressure (pa)
    • intensity (kg/cm3)
    • distance (unit: cm,ft,mile)
  40. propagation speed
    determined by density and stiffness
  41. if density increases
    speed of sound decreases
  42. intensity doubled
    amplitude quadrupled
  43. power
    • measured in watts
    • rate at which work is done
  44. ultrasound frequency
  45. transducer
    determines the initial amplitude of the sound wave
  46. SPTP
    the highest intensity
  47. attenuation coefficient
    the amount of attenuation per depth traveled
  48. attenuation
    • decreased power, amplitude and intensity
    • determined by path length and freq
    • measured in dB
  49. amplitude and intensity
    are directly related
  50. spatial pulse length
    are denoted by source and medium
  51. can intensity be adjusted by sonographer
  52. rayleigh scatterer
    a red blood cell
  53. acoustic insulator
    thickness is 1/4 wavelength
  54. axial
    • longitudinal
    • range
    • radial
  55. active element
    • PZT
    • .5 or 1/2 wavelength
  56. backing material
    improves resolution by reducing ringing
  57. order of impedance from large to small
    • PZT
    • maching layer
    • skin
  58. low Q factor improved axial resolution and backing material
    imaging transducer
  59. characteristies of increased freq pulse wave transducer
    • thinner PZT crystal
    • faster speed in crystal
  60. focal zone
  61. far zone
  62. transducer diameter affect beam divergance
    after focus, small diameter crystals diverge wider
  63. how does frequency alter beam divergance in far field
    decreased freq diverge more
  64. lateral resolution
    • angular
    • transverse
    • lateral
  65. M-mode
  66. A-mode
  67. B-mode
  68. actual speed in PZT crystal
    influences freq
  69. sonographer can change
    • power
    • density
  70. TGC & over all gain
    brightening screen
  71. ALARA
    as low as reasonably achievable
  72. demodualization
    • use retofication to convert neg voltage to pos voltage
    • uses smoothing to smooth out the bumps
  73. reject
    low level echos don't get into machine
  74. picture element
  75. 28 shades of gray= ? bits
    • 2x2x2x2=16 not enough need 28
    • 2x2x2x2x2=32 enough
    • then we count the 2's
    • so 5 bits
  76. binary numbers
    1's and 0's
  77. types of archieving and storage
    • optical media (lazer, CD)
    • magnetic media (floppy disk)
  78. preprocessing vs postprocessing
    • pre= manipulate TGC, zoom in without loss of resolution
    • post= zoom in but looses detail
  79. how do you find depth
    time- round trip
  80. transducer
    detector of soundwaves by recieving the sound waves from the body
  81. what sound parameter influences axial resolution?
    pulse duration
  82. 2 parameters that influences speed of sound in medium
    stifness and density
  83. how to depolorize a PZT transducer
    • curray point
    • heat up to 365
  84. infrasound
  85. audiable sound
    >20 - 20k
  86. what's focal depth affected by?
    • transducer diameter
    • freq of sound