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

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SUMMARY

The MRI signal is highest at the echo time (TE) when protons are in coherence, following the application of a 180-degree refocusing pulse after the initial 90-degree RF pulse. During the free induction decay, the signal diminishes as protons begin to dephase. In Short Tau Inversion Recovery (STIR) sequences, the 90-degree readout pulse is applied at the time to inversion (TI), where the longitudinal magnetization (Mz) of fat tissue is at zero. This results in the transfer of Mz to the transverse plane (Mxy), but Mxy cannot also be zero if Mz is zero.

PREREQUISITES
  • Understanding of MRI Spin Echo sequences
  • Knowledge of RF pulse sequences and their effects on proton coherence
  • Familiarity with magnetization preparation techniques
  • Basic principles of free induction decay and echo formation
NEXT STEPS
  • Research the principles of MRI Spin Echo sequences
  • Learn about the effects of RF pulses on proton magnetization
  • Explore Short Tau Inversion Recovery (STIR) techniques in MRI
  • Study the concept of coherence and dephasing in MRI signals
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Radiologists, MRI technicians, and medical physicists interested in optimizing MRI imaging techniques and understanding the dynamics of proton behavior during imaging sequences.

yephonethaw
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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?
 
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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.
 
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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 >>
 
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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?
 

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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.
 

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