principles of MRI test 1

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acmolt
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principles of MRI test 1
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2011-06-09 21:46:05
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principles of mri test 1
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  1. What is the TI time?
    time from 180 degree pulse to 90 degree pulse
  2. What exhibits the longest T1 relaxation time?
    CSF
  3. What controls spatial localization?
    slice select, phase and frequency
  4. T/F: increasing TR increase SNR?
    True
  5. T/F: Increasing slice thickness will increase spatial resolution?
    False: Decreasing slice thickness will increase spatial resolution
  6. What has a long TR and short TE?
    PD weighted images
  7. What has a Short TR and Short TE?
    T1 weighted images
  8. What will be dark in a T1 SE pulse sequence?
    CSF
  9. What will CSF be in a T2 SE pulse sequence?
    Bright White
  10. What are T2* characteristics contributed from?
    magnetic inhomogeneities, varying magnetic susceptibilities, fat and water cycling
  11. What is the benefit of fat saturation?
    is that it nulls fat to better visualize surrounding anatomy
  12. What is Free water protons resonance frequency separation?
    3.5 ppm
  13. What is the pulse sequence know as when refocusing is provided by a 180 degree RF pulse?
    Spin echo pulse sequence
  14. T/F: in proton magnetic resonance spectrum the water shifted down field from TMS is 4.7 ppm?
    true
  15. What sequence is the preparatory pulse a pulse that is applied prior to the gradient echo?
    Turbo
  16. T/F: EPI can be dangerous because of the extremely high magnetic field which can produce
    True
  17. What are the types of GRE image sequence?
    "steady state" and "spoiled"
  18. what and the k-space of the EPI be filled to?
    1 RF pulse
  19. what is a principle hardware characteristic needed in order for EPI to work?
    Shielded gradient
  20. what is the frequency in which images are recorded?
    temporal resolution
  21. what is an array of numbers usually arranged in two dimensions
    matrix
  22. What is the TE in which the operator wishes to weight the image?
    Effective echo time
  23. What is a pulse sequence that closely follows gradient echo imaging. It is acquired when a preparatory pulse is applied followed by several variable flip angles.
    Turbo
  24. What is a hybrid pulse sequence that combines gradient echo and fast spin echo pulse sequences?
    GRASE
  25. What is a pulse sequence that produces a train of gradient echoes by continuously switching the read gradient rapidly inside the envelope of the FID or Spin echo.. it usually fills the k-space with RF pulse.
    Echo Planar
  26. When the _________ gradient is turned off, all of the spins precess with he same frequency but now have different phase.
    phase-encoding
  27. The phase encoding gradient has to be energized for the number of phase encoding steps which is equal to_______.
    Matrix size
  28. _______ is a technique used to alter tissues contrast in MRI.
    Magnetization transfer
  29. What are the 3 principle MRI parameters:
    T1, T2, PD
  30. what uses a large flip angle and has a short TR and short TE?
    T1
  31. what uses a small flip angle has a long TR and short TE?
    PD
  32. what uses a small flip angle and has a long TR with a long TE?
    T2
  33. What makes chemical shift artifact become worse?
    narrow bandwidth and when magnetic field strength increases
  34. What are the parameters of spatial criteria
    size, shape, and position
  35. what is a pulse sequence that starts with a 180 degree RF pulse, followed by another 180 degree RF pulse.
    Inversion recovery
  36. How does IR images produce higher contrast images?
    and the expense of longer imaging times
  37. T/F: during basic SE pulse sequence, the Slice Select gradient (Bss) is always turned on when RFt is turned off?
    false: during basic SE pulse sequence, the Slice Select gradient (Bss) is always turned on when RFt is turned ON
  38. what occurs when there is no transverse magnetization and no signal?
    null point
  39. Fo a t2 weighted pulse sequence the operator should choose a TR of what AND a TE of what?
    TR 500, TE 20
  40. if you increase TR what else will it effect?
    increase SNR
  41. Long TR and Long TE=
    T2 weighted images
  42. What is the most commonly employed MR pulse sequence?
    Spin Echo
  43. In turbo imaging, low spatial frequencies, which contain the patient's course structures, follow a ______ phase-encoding gradient.
    Weak
  44. In turbo imaging, high spatial frequencies which contains patient's fine structures, follow a _______phase-encoding gradient
    Strong
  45. An alpha pulse, represents _________in regards to MRI
    flip angle less than 90 degrees
  46. Faster imaging times will improve ________.
    Temporal resolution
  47. A_______ field is used to rephase spins during GRE imaging.
    Gradient Magnetic
  48. In regards to filling k-space in an EPI sequence, the "blip" is referred to as _______
    Phase Gradient
  49. The fundamental idea of EPI is __________.
    Filling k-space in a single RF pulse
  50. Describe null point in inversion recovery and a pulse sequence we use it in?
    there is a value of T1 where Mz equals zero. Application of a 90 degree RF pulse at this point results in no signal because there is no Z magnetization to rotate onto the XY plane
  51. Describe the appearance of the chemical shift artifact and along which gradient it appears?
    Chemical Shift artifacts are always in the frequency encoding direction and appear as black and bright border
  52. what are 3 ways to optimize MRI images?
  53. List 3 fast acquisition pulse sequences
    Turbo, GRASE, EPI
  54. What is the benefit of MRI gating?
    Gating: a segmentation step that improves turbo imaging. It's purpose is to allow quick images without motion
  55. State the 2 fundamental characteristics in how Gradient Echo differs from spin echo
    In gradient echoes, spins are refoccused with a gradient magnetic field, rather than a 180 degree RF pulse. SE is a long TR, FRE is shorter TR.
  56. Describe effective TE in detail?
    the time interval between the middle of the excitation pulse and the middle of the echo signal that is observed.
  57. Why are STIR and FLAIR pulse sequences used to image musceoskeletal system and central nervous system respectively
    STIR: short time inversion recovery used to image fat. For tissue with a short T1 relaxation time, such as fat, a short T1 allows elimination of the high signal from fat.

    • FLAIR: fluid attenuated inversion recovery; used to image the CNS; fluid has a relatively long T1 and TI's of about 2 sec. are necessary to minimize the signal from fluid
    • structures.
  58. how is k-space filled differently in fast spin echo vs. conventional spin echo and how is the phase gradients involved in both of these processes
    conventional epin-echo: k-space is filled line by line in sequential order from bottom to top. Starts with large, negative phase encoding gradient amplitudes, through the zero phase encoding, then to a large, positive phase encoding amplitude.

    fast spin echo: more than 1 line is filled per TR
  59. describe the difference between steady state and spoiled gradient echo?
    Steady state echo: the condition of constant longitudinal magnetization after repeated alpha pulses

    Spoiled gradient echo: assuming that Mxy is dephased before each alpha pulse

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