MR pulse sequences

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MR pulse sequences
2015-09-24 09:20:52
pulse sequences
mri pulse sequences
mri pulse sequences
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  1. Why is gradient echo sequence more susceptible to magnetic field inhomogeneities?
    It lacks a 180* refocusing RF pulse
  2. Gradient echo sequences tend to be _____ due to the lack of 180* refocusing pulses, the TR can be _____ and the scan time will be ____
    • fast
    • shorter
    • shorter
  3. In a gradient echo pulse sequences what is used to refocus the protons and create the echo?
    Gradient coils
  4. When does the condition of steady state occur? Result?
    • When the TR in a gradient echo is less than the T2
    • residual transverse magnetization at the time of the next excitation pulse
  5. What are T2* gradient echo?
    sequences requiring high signal from fluid
  6. What are incoherent gradient echo (spoiled gradient echo)?
    Sequences yield T1 contrast due to the removal of residual transverse magnetization before the next excitation
  7. What sequence is particularly useful in evaluation of cranial nerves?
    Balanced steady state sequences
  8. A spoiled gradient echo sequence removes _________
    any residual transverse magnetization prior to the next excitation pulse
  9. Why is "spoiling" used?
    • to reduce steady state (T2*) effect
    • allows for fast scans with T1 contrast
  10. Conventional spin echo sequences begin with ________
    90* RF excitation pulse
  11. In a conventional spin echo what refocuses a decaying spin echo?
    180* RF pulse
  12. How many lines of space are acquired during each TR in a conventional spin echo?
    One line
  13. How many lines of space are acquired per TR in a Fast spin echo sequence?
    multiple (2-50+) lines
  14. In a spin echo sequence, the time between the 90* RF pulse and the 180* RF pulse is ______-
    1/2 TE time (Tau)
  15. In a spin echo pulse sequence, an echo is produced from _________
    a combination of two or more RF pulses
  16. A dual spin echo sequence generates _______for every slice, both with _______ but the same ____
    • two images
    • varying TE's
    • TR
  17. In a dual contrast spin echo, the second echo has ___________than the first echo image
    more T2 contrast but lower SNR