Dmi 65 MRI Quiz

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Author:
swtjo3joe
ID:
152386
Filename:
Dmi 65 MRI Quiz
Updated:
2012-05-06 20:15:35
Tags:
tesla precession magnetic field larmor equation
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MRI quiz
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  1. what does an electrical current induce?
    magnetic field
  2. why do protons have electric current?
    • because they have a positive charge and spin
    • a moving electric charge = an electrical current
  3. what happens to protons when put into an external magnetic field?
    align themselves in the external magnetic field
  4. how many ways do protons align themselves in an external magnetic field?
    • 2
    • in the direction of the field, parallel to it
    • in the completely opposite direction or anti-parallel
  5. which type of alignment is preferred?
    the one that takes less energy which is parallel to the external magnetic field
  6. what is a precession?
    when objects wobble about an axis
  7. what is precession frequency?
    how many times the protons precess per second
  8. what happens to the precession frequency when the external magnetic field is stronger?
    increases
  9. what is the larmor equation?
    w0 = yB0

    precession frequency (Hz) = gyromagnetic ratio x strength of magnetic field (tesla)
  10. what is an RF pulse?
    radio frequency pulse that is sent to the patient to disturb the protons which are peacefully precessing in alignment with the external magnetic field.
  11. does every RF pulse disturb the alignment of the protons?
    no
  12. how can an RF pulse disturb the peaceful precessing of a proton?
    when the RF is in the same frequency as the proton
  13. what is resonance?
    when the protons pick up somne energy from having the same frequency as the RF pulse that was sent
  14. what kind of magnetization does an RF pulse create?
    transversal magnetization
  15. what two effects are created when an RF pulse that has the same frequency as the precession frequency of the protons are sent?
    • some protons pick up energy and decreases the amount of longtidunal magnetization
    • protons get in synch, start to precess in phase. Their vectors now also add up in a direction transverse to the external magnetic field thus a transversal magnetization is established
  16. what are two the types of MRI antennas used?
    • loop
    • saddle
  17. the magnetic property associated with a spinning proton, neturon, or some nuclei is referred to as a magnetic what?
    moment
  18. what is the symbol for magnetic moment?
    • mew
    • u
  19. when do nuclei possess magnetic properties?
    when they are composed of an odd number of neutrons or protons
  20. which element is the most commonly used or intereacted with in MRI?
    hydrogen
  21. the electromagnetic waves used in MRI are in which portion of the electromagnetic spectrum?
    radio
  22. a radiowave that is transmitted just long enough to flip spinning nuclei away from alignment with the z axis and into precession in the xy plane is called?
    90 degree pulse
  23. a T-1 weighted scan is good for showing what?
    anatomy
  24. a T-2 weighted scan is good for showing what?
    pathology
  25. how does air appear in a t-1 and t-2 scan?
    both dark
  26. how does fluid appear in a t-1 and t-2 scan?
    • t-1 = dark
    • t-2 = bright
  27. how does bone appear in a t-1 and t-2 scan?
    • t-1= bright
    • t-2= dark
  28. how does fat appear in a t-1 and t-2 scan?
    • t-1 = bright
    • t-2 = bright or dark
  29. what is the TR (repitition time) range of a t-1 scan?
    400-750
  30. what is the TE (echo time) range of a t-1 scan?
    5-20
  31. what is the proton density of a t-1 scan?
    1000
  32. what is the TR (repitition time) range of a t-2 scan?
    300-8000
  33. what is the TE (echo time) range of a t-2 scan?
    + or - 100
  34. what is the proton density of a t-2 scan?
    30

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