Figure 1: Illustration of the IDEAL SPIRAL spectral encoding scheme. It consists of Radiofrequency (RF) pulses applied during an excitation time (t₁), and acquisition with spiral-OUT spatial encoding (t₃-t₂) applied after an echo time (TE=t₂-t₁). Several shots are used to encode the spectral information, which is targeted during the evolution time (TE), while slightly increasing the TE after each shot (TE_m is the echo time of the m^th shot). Three shots are presented, but this pulse sequence is true for m shots.

Figure 2: Illustration of the different cases of the emission/reception frequency switching during the pulse sequence timing, leading to different frequency dependence during the evolution times. Acq-Switch case: f_e-f_r switch before the acquisition at t₂, and the CS behaviour detection is done in reference to f_e. RF-Switch case: f_e-f_r switch before the evolution time at t₁, hence CS behaviour detection done in reference to f_r. Double 0-Switch case: f_e-0 switch for the evolution time at t₁, 0-f_r switch at the end of it at t₂.