The final step in spatial encoding consists in applying a frequency encoding gradient, when the signal is received, in the last direction (horizontal in our example). This modifies the Larmor frequencies in the horizontal direction throughout the time it is applied. It thus creates proton columns, which all have an identical Larmor frequency.

 

As this gradient is applied simultaneously on receiving the signal, the frequency data is included.

 

Duration of a 2D imaging sequence

 

duree_en

 

With

  • TR = Repetition time
  • NPy = Number of phase encoding steps
  • Nex= Number of excitations