Foundations Exam 2

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bfreund11
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175367
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Foundations Exam 2
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2012-10-03 20:40:19
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Foundations Exam
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lessons 5-10
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  1. Describe sound energy
    mechanical energy traveling in longitudinal waves
  2. How does sound propagate differently depending on the medium?
    • It travels faster in solid mediums
    • slower in air
  3. Piezoelectric effect
    ultrasound transducers convert ultrasound energy into electrical energy and v.v.
  4. What kind of elements create a piezoelectric effect?
    piezoelectric elements (crystals), the transducer create the US beam and recieve the echos to produce the image
  5. Describe the properties of sound
    • mechanical
    • medium has dramatic effect on waves
    • measured in hertz
    • higher frequency has better resolution and less penetration
  6. what is the range of hZ for US
    • >20,000
    • (higher frequency has better resolution and less penetration)
  7. propagation speed
    • transfer speed of sound through a medium
    • stiffer the medium, higher (faster) propagation speed
  8. propogation speed of common tissues (list from slowest to fastest)
    • air
    • water
    • soft tissue
    • bone
  9. describe pulsed echo technique to include determination of echo depth
    • provides depth information
    • increasing PRF eliminates aliasing
    • CW doesn't ailase but compromise for unknown depth
  10. limitations of pulse repetition frequency (PRF)
    • pulsed doppler may have aliasing (increase PRF to get rid of)
    • CW doesn't ailase but no depth known
  11. Describe beam formation
    • a primary beam will exit transducer
    • beam will be moved thru body to produce image
    • multiple images will produce a real-time exam
  12. What are side lobes?
    US outside the primary beam and may produce  (has to do with beam formation)
  13. How is US reflected?
    • US reflected when there is a change in tissue impedance
    • greater the change=more relfection
  14. impedance
    • term that describes the medium characteristics
    • an acoustic property of a medium that is related to its density and propagation speed
  15. describe how tissue chara. and imaging angles effect the image production
    • Tissue interfaces can be specular or non-specular
    • Specular should be imaged perpendicular (if imaged obliquely artifacts can occur)
    • Non-specular can be imaged an any angle
  16. Specular reflectors
    • create most artifacts
    • image at 90* (allows reflection to return to transducer and produce image)
  17. What is the relationship bewteen frequency, attenuatin, and axial resolution?
    • higher frequencies provide better axial and lateral resolution
    • they attenuate at at higher rate
    • ALWAYS use the highest frequency that provdes adequate penetration
  18. What are the required adjustments to produce an optimum image (dealing w/ freq, attenuation, and res)
    lateral resolution is pimproved in the focal zone and by using multiple/wide focal zones
  19. Describe the relationship b/w focusing, beam width, and lateral resolution
    • where the beam is narrowest (aka focused) = best lateral resolution
    • higher frequencies = narrower beam= better lat resolution
  20. potential bioeffects of Us
    • cavitation
    • thermal effects
    • use lowest power for OB and limit spectral doppler on OB
  21. Attenuation
    • decreases in intensity as sound travels through medium
    • diverges
    • absportion
    • relfections (creates image)
  22. Enhancement related to attenuation
    posterior enhancement due to low attenujation
  23. increased attenuation creates
    shadows (aka bone)
  24. Reverberation
    • attenuation artifacts
    • US beam makes the path more than once
    • extra echoes go into image that don't represent true anatomy
  25. Pulse echo technique represents...
    • info on depth (aka time)
    • horizontal beam location (beam direction)
    • reflector amplitude (brightness) *represents anatomy*
  26. Pulse Repition Frequency (PRF)
    • pulse determines power
    • determined by the "pulser"
    • rate at which sound is pulsed *rythm*
    •  -limited by depth of imaging
  27. DEEP PRF =
    lower PRF "power"
  28. What does the reciever do?
    • processes electrical signals from transducer that represent reflections
    • OPERATOR controls- amplificiation (gain & TCG), dynamic range, and harmonics
  29. TGC (time gain compensation)
    • increases intensity of reflections returning from deeper structures more than superficial structures
    • used to compensate for attenuation
  30. what is TGC depedent on?
    • time it took for relfections to come back
    • controlled according to DEPTH
  31. gain (overall)
    • increases intensity of all reflections on the image
    • does NOT affect penetration
  32. Dynamic Range
    AKA--compression, gray scale range
    • number of grays available for display
    • LARGER the number = more shades of gray = looow contrast
    • PREPROCESSING fucntion
  33. DYNAMIC RANGE
    • preset for exams
    • Vascular- lower DR, black and white
    • Abdomen- medium DR, moderate # of grays
    • Small parts- higher DR, lots of grays
  34. Harmonics
    • new frequency produced from initial sound wave
    • will be a multiple of initial (fundamental) frequency
  35. Harmonics imaging
    • receiving and processing only the harmonic signal
    • reduces artifacts
    • slightly poorer spatial resolution
  36. A mode
    • amplitude mode
    • x & y axis based
    • still used in opthamology
  37. B mode (static)
    • brightness mode
    • reflector brightness representative of reflector intensity
  38. M mode
    • motion mode
    • show motion of structures on single frame
    • AKA fetal hearbeat
    • brightness reflections corresponds with intensity
  39. B scan REAL TIME
    • realtime imaging is created by moving the beam through the patient
    • creates many scan lines per image and many images per second
  40. Scanning formats
    • linear- rectangular FOV (best resolution b/c parallel scan lines)
    • sector- wedge shaped FOV (poorest resolution) aka- pahsed array/ curvilinear transducers)
  41. *KNOBOLOGY*
     Depth
    • deep as needed for area of interest
    • no deeper
  42. *KNOBOLOGY*
     gain
    • start with gain in middle for each exam
    • will not "reset" every exam
    • different numbers on each machine
  43. *KNOBOLOGY*
     TGC
    • makes image uniform
    • vary b/w pts and exams
    • will not "reset"
  44. *KNOBOLOGY*
     Auto-optimize
    • automatic control that adjusts gain
    • can be problematic and jsut needs to be OFF
  45. *KNOBOLOGY*
    frequency/harmonics
    • freq- highest possible that allows for penetration, adjust required for exam
    • harm- help on "technically difficult exams", reduces artifacts
  46. *KNOBOLOGY*
     Focus
    • place at area of interest
    • if entire image important, put it at BOTTOM
    • makes a biiig difference in image quality
    • focal zones will imporve image but decrease frame rate
  47. *KNOBOLOGY*
    Freeze
    • to stop real time image
    • will NOT save at this time
  48. *KNOBOLOGY*
     Store
    • saves current image onto machine hard drive
    • at some point images will go to PACS
  49. ~transducers~
    linear sequenced arrays
    • rectangular
    • groups of crystals
    • parallel scan lines
    • best resolution
    • large footprint
    • "linear"
  50. ~transducers~
     Convex arrays
    • blunted sector
    • groups of crystals
    • scan line seperation-->downfall
    • better than sector
    • large footprint BUT better than linear
    • "Curved"
  51. ~transducers~
    Phased array
    • sector
    • trapezoidal vector
    • Individual crystals
    • scan line seperation -->downfall
    • small foot print
    • "sector"
  52. ~transducers~
    mechanically steered transducers
    • sector or linear (usually sector)
    • poor doppler b/c sloow
  53. Electronic beam focusing
    • time delays
    • operator dependent
  54. imaging frame rate
    • HIGH frame rate = adv. w/ mocing structures = less scan lines= poorer resolution
    • Lower fram rate = adv. w/ non moving structures = more scan lines= better resolution
  55. relationship between PRF, depth, and frame rate
    increased depth= lower PRF = lower frame rate
  56. how can sonographer change the imaging to increase frame rate?
    • narrow FOV with zoom or sector size
    • frame rate control
  57. function of A-D converter
    • controls preprocessing
    • dynamic range control
  58. write- magnification
    • preprocessing
    • improves resolution
    • (use entire matrix less anatomy)
  59. function of digital memory
    • manipulation of image (gray/B-color)
    • cine-loop
    • more bits/pix allows for more shades of gray
  60. read-magnification
    • post processing
    • no improvement to image resolution
    • displays pixels larger
  61. Frame rate
    number of frames per second displayed on the monitor

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