A graphical inversion of the dependence 𝑡 𝑆𝑊 (𝐵 𝑈𝐿𝐹 ) obtained simply by swapping the time and field axes in the graph produces the experimentally optimized shape of the field sweep profile 𝐵 𝑈𝐿𝐹 (𝑡 𝑆𝑊 ) shown in Fig. .c. If needed the total duration of the field sweep can be adjusted by linearly stretching this profile along the time axis. In equation 2 this corresponds to an adjustment of the scaling coefficient 𝐶. Fig. .d demonstrates that a greater transfer efficiency was achieved in the experiment with such an "optimal" profile than with the linear profile. Both a faster buildup at short sweep durations and a greater polarization after long field sweeps are observed. Thus, the experimentally obtained C polarization of 13 C1-allyl pyruvate after a 50 s sweep was increased from P( 13 C) = 6.8 % for the linear profile to P( 13 C) = 8.7 % for the optimal profile. Overall, the optimization of the sweep will be of particular interest in cases where the requirements of constant adiabaticity are difficult to meet. PHIP SAH in allyl pyruvate is a vivid example.