Ultrasound Terms & Concepts

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Author:
bjlewis44
ID:
192477
Filename:
Ultrasound Terms & Concepts
Updated:
2013-01-15 00:44:57
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ultrasound echo
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US terms
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  1. Ultrasound
    High frequency "sounds" inaudible to the human hear. >20kHz
  2. Sound
    • traveling variation of acoustic variables
    • ; audible 20Hz - 20kHz
  3. Frequency
    number of cycles in a wave that occur in one second.
  4. Acoustic variables
    • Pressure
    • Density
    • Particle Motion
  5. Wave
    traveling variation of some quantity or quantities
  6. Hertz
    one cycles per second (Hz)
  7. Kilohertz
    • 1000 cycles per second
    • kHz
  8. Megahertz
    • in million cycles per second
    • MHz
  9. Infra
    "below" audible sounds and is a frequency too low for human hearing
  10. ultrasound
    "above" a frequency too high for human hearing.
  11. Period
    time it takes for one cycle
  12. Frequency and period relationship?
    • Inverse.
    • As frequency increases period decreases.
  13. Wavelength
    the length of a cycles in space
  14. Propagation Speed
    speed at which a wave moves through a medium
  15. Frequency and Wavelength relationship?
    • inversely
    • as frequency increases, wavelength decreases
  16. Propagation speeds in solids and gases
    • highest in solids
    • lower in gases
  17. Propagation speed in tissue
    1.54 mm/microsec.
  18. Harmonics
    even and odd multiples of fundamental frequency
  19. What is PRF?
    • Pulsed Repetition Frequency
    • # of pules per second
  20. What is PRP
    time from beginning of one pulse to the next
  21. PRF and PRP relationship?
    inversely

    • PRF increases
    • PRP decreases
  22. Pulse duration
    TIME for a pulse to occur
  23. Duty Factor
    fraction of TIME that pulsed ultrasound is on
  24. PRP increases, PRP decreases and Duty Factor...
    increases
  25. Spatial Pulse Length
    DISTANCE in space that a pulse takes up
  26. # of Cycles in a pulse increases, SPL increaces. If frequency increases, wavelength and SPL....
    decrease
  27. What do shorter pulses do to image resolution
    improves resolution
  28. Bandwidth
    range of frequencies contained in a pulse
  29. Intensity (I)
    rate at which energy passes through a unit area
  30. How is Intesity related to power?
    • proportional
    • Intensity = power (mW)/area (cm^2)
  31. If beam power increases, intensity increases. If beam area ____, intensity _____.
    • decreases
    • increases
  32. If frequency increases penetration ______
    decreases
  33. Attenuation
    weakening of sound as it propagates
  34. If the attenuation coefficient ______, attenuation ______
    • increases
    • increases
  35. If path length _____ attenuation ______
    • increases
    • increases
  36. As frequency ______ increases, attenuation ______.
    • increases
    • increases
  37. Perpendicular Incidence
    denotes a directoin of travelĀ  of US wave perpendicular to the boundary between two media.
  38. Impedance
    determines how much of an incident sound wave is reflected back into the first medium and how much is transmitted into the second medium.
  39. If density _____, impedance ______.
    If propogation speed _______, impedance _____.
    • increases
    • increases
    • increases
    • increases
  40. Oblique incidence
    denotes a direction of travel of the incident US that is NOT perpendicular to the boundary between two medium.
  41. Refraction
    "turn aside" - change of direction of sound when it crosses a boundary
  42. Scattering
    redirection of sound in many directions by rough surfaces, like tissue and blood.
  43. Backscatter
    sound scattered in the direction from which it came.
  44. Speckle
    grainy dots or "noise" in the display representing interference between constructive and destructive.

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