Is the MRI Signal Highest When Protons Are Coherent or Dephasing?

Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
Sign up Log in
4 replies · 6K views
yephonethaw
Messages
3
Reaction score
0
I would like to ask a question about MRI Spin echo sequence. after first 90 degree RF pulse, the free induction decay occurs. And 180degree refocusing pulse is given again. And echo signal is obtained at TE. My question is that is the the signal highest when the protons are back again in coherence or when they are dephasing again?
 
Physics news on Phys.org
yephonethaw said:
My question is that is the the signal highest when the protons are back again in coherence or when they are dephasing again?
The signal is the highest at TE, which is when they are in coherence.
 
  • Like
Likes   Reactions: yephonethaw
In STIR, 90 degree read out pulse is given at Time to inversion TI( short TI) where the Mz of fat tissue is zero(null point). After giving 90 defree pulse ,Mz is transferred to Mxy plane and since Mz is zero, can Mxy be also zero?

<< Mentor Note -- related question merged into the OP's existing thread >>
 
Last edited by a moderator:
I don't understand the highlighted words and the figure.When 90degree RF pulse is given, is Mz which is zero moved back to -Mz or still staying at transverse magnetization plane?
 

Attachments

  • Screenshot_20181124-090650.png
    Screenshot_20181124-090650.png
    26.6 KB · Views: 405
yephonethaw said:
After giving 90 defree pulse ,Mz is transferred to Mxy plane and since Mz is zero, can Mxy be also zero?
Yes, that is the basis of most magnetization preparation techniques.