Fig. 5.

Gradient recall echo (GRE) image, slice-averaged magnetization maps and radio-frequency (RF) waveforms for four single-spoke excitation strategies: Pseudo birdcage (pBC) mode at short (TE=6 ms) and long TE (TE=30 ms) and 1-spoke with/without optimization of the sub-pulse time shifts (maximum time shift is ±500 us). The target magnetization was MT/M0=0.17 and the slice-thickness was 5 mm. Magnetization maps obtained using the slice-averaged small tip-angle (SA-STA) approximation and using a 3D Bloch simulation (i.e., in-plane and across the slice) show excellent agreement, thus validating Eq. 7 (small differences remain between the Bloch simulation and SA-STA due to the fact that an ideal rectangular slice-profile is assumed in our derivation Eq. 7). GRE images are shown after removal of the receive sensitivity profile and are in very good agreement with magnetization maps in this phantom with little PD/T1/T2 contrast (uniform agar gel). The time-shift optimized 1-spoke strategy was able to recover most of the signal lost in the frontal lobe area due to through-plane dephasing while creating a much more uniform excitation than the birdcage mode. Next to each RF waveform, we show the total pulse energy (integral of the square of the RF pulse) as a fraction of the pBC mode RF pulse’ energy.