DMU physics final

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DMU physics final
2010-09-27 00:43:35

DMU physics
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  1. comet tail
    "reverberation with the spaces squeezed out". appears as solid hyperechoic line directed downward. also called ring down artifact
  2. shadow
    appears as hypoechoic or anechoic region extending downward from very strong attenuating medium. appears when the attenuation is higher in the tissue above the shadow than in surrounding tissue
  3. edge shadow
    appears as hypoechoic region extending along the edge of a curved reflector. also called shadowing by refraction
  4. artifacts
    • reverberations
    • comet tail
    • shadow
    • edge shadow
    • enhancement
    • focal enhancement
    • mirror image
    • speed error
    • lobes
    • refraction
    • lateral resolution
    • axial resolution
    • multi path artifacts
    • curved and oblique reflectors
    • temporal resolution
    • spacial resolution
    • slice thickness
  5. amplitude
    the bigness of the wave. the difference between maximum value and the average or undisturbed value of an acoustic variable
  6. frequency
    the number of particular events that occurs in a specific duration of time
  7. what causes aliasing
    higher frequency transducers. only occur with pulsed doppler. when the doppler sampling rate is too low in comparison to the measured blood velocity
  8. speed of sound in soft tissue
    1540 m/s
  9. speed of sound in lungs
    500 m/s
  10. ways of eliminating aliasing
    • raise the nyquest limit
    • lower frequency transducer
    • new view with shallower sample volume
    • use continuous wave doppler
  11. meaning of different colors in color flow doppler
    • black and white identifies anatomic structures
    • color identifies blood flow velocities and function
  12. when you decrease frequency, you ____ frame rate
  13. eliminating aliasing in pulsed wave doppler
    • lower fequency transducer
    • shallow sample volume
  14. when should you sterilize transducers
    when an instrument penetrates the skin or mucous membrane
  15. mechanical index
    the amount of contrast harmonics produced
  16. pressure sources that contribute to overall intervascular pressure
    • hydrostatic
    • respiration
  17. cavitation
    the interaction of sound waves with microscopic, stabilized gas bubles in tissue
  18. heating
    tissue heating is related to the output characteristics of the transducer and the properties of the tissue
  19. highest temperature which adverse effects have not been demonstrated
    39 deg. C
  20. reverberation
    muliple, equally spaced echoes caused by te bouncing of a sound wave between two strong reflectors positioned parallel to the ultrasound beam
  21. ringdown
    also known as comet tail. appears as solid hyperechoic line directed downward
  22. mirror image
    created when sound reflects off of a strong reflector (mirror), and is redirected toward a second structure causing a replica or second copy to appear deeper
  23. side lobes
    off axis sound beams, created by single element transducer, structures within side lobes can generate reflections and degrade lateral resolution
  24. refraction
    occurs when a sound pulse changes direction during transmission. degrades lateral resolution
  25. sound wave
    • carries energy
    • mechanical wave
    • cannot travel through vacuum
  26. reverberations are produced by?
    the bouncing of the sound wave between two strong reflectors positioned parallel to the ultrasoud beam
  27. absorption
    component of attenuation. occurs when ultrasonic energy is converted into another energy form, such as heat. directly related to frequency
  28. scattering
    the random redirection of sound in many directions. happens when tissue interface is smaller or equal to the wavelength
  29. attenuation
    the decrease in intinsity, power and amplitude as sound travels through a medium
  30. reflection
    portion of the sound beam that is redirected when a beam strikes a boundry

    weakens the portion of the sound wave that continues forward
  31. cause of side lobe artifacts
    when a strong reflector is in the path of the lobe it creates a reflection. the system interprets the reflection as arising from a structure positioned along the beams main axis
  32. cause of grating lobes
    • created by array transducers
    • deminishes lateral resolution
  33. where shadowing artifacts are commonly seen
    beneath the structure, hypoechoic or anechoic
  34. doppler shift
    • directly related to frequency of the transmitted sound.
    • directly related to velocity of blood cells
    • created when transmitted sound waves strike red blood cells
  35. enhancements
    artifact appears as a hyperechoic region beneath tissues with abnormally low attenuation. hyperechoic regions are same color as foreground. opposite of shadowing. helps characterize tissue
  36. when does aliasing occur on doppler
    • with higher frequency transducers
    • deep gate
    • faster blood velocity
  37. quality assurance
    the routing, periodic evaluation of an ultrasound system to guarantee optimal image quality
  38. quality assurance requirements
    assesment of system components, repairs, preventive maintenance, record keeping
  39. tissue equivalent phantom
    ultrasonic features similar to soft tissue, more suitable for modern systems, grayscale, tissue texture, multi-focus and adjustable focus
  40. focusing
    improves lateral resolution by concentrating the sound energy into a narrower beam. external, internal, phased array
  41. what are you changing when you adjust focusing on a scanner
    • beam diameter in near field and focal zone is reduced
    • focal depth is shallower
    • beam diameter in the far zone increases
    • focal zone is smaller
  42. what parameters are not adjustable by operator
    • period
    • frequency
    • wavelength
    • speed
  43. pulse repetition frequency
    the number of pulses that an ultrasound system transmits into the body each second
  44. pulse repetition period
    the time from the start of one pulse to the start of the next pulse
  45. frame rate
    the ability of the system to create numerous frames per second
  46. pulse duration
    the actual time fromthe start of a pulse to the end of that pulse
  47. pulse length
    the distance that a pulse occupies in space from the start oto the end of a pulse
  48. best angle of incidence for grascale
  49. best angle of incidence for doppler
    0 or 180
  50. nyquist limit
    the highest doppler frequency or velocity that can be measured without the appearance of aliasing
  51. 2 types of useful artifacts
    enhancement - helps provide valuable information that helps to characterize tissue

    shadows - valuable diagnostic info that helps characterize tissue
  52. hydrophone
    AKA microprobe. small hypodermic needle with a tiny piece of piezoelectric material attached to its end. measures the characteristics of a sound beam
  53. doppler shift
    AKA doppler frequency - a result of relative motion between the sound source and the receiver. away from transducer is negative
  54. acoustic velocity
    magnitude and direction
  55. advantages of power doppler
    increased sensitivity to low velocity: unaffected by doppler angles (except 90 deg): no aliasing
  56. disadvantages of power dopper
    • no measurement of velocity
    • low frame rates
    • susceptible to motion of transducer
  57. advantages of color doppler
    • mean velocity measurements
    • moderate sensitivity
    • provides two dimensional flow info
  58. disadvantages of color doppler
    • subject to aliasing
    • reduced temporal resolution
  59. A L A R A
    as low as reasonably achievable