Accuracy in MP2RAGE-based T1-mapping relies on knowledge of the imperfect inversion efficiency (finv) of the inversion pulse. Here we map the inversion efficiency of different adiabatic inversion pulses in human brain at 7T. We identified a mean finv=0.87, which is substantially lower than the finv=0.96 typically assumed in MP2RAGE. We further observed a lower finv in white matter (WM) than in the rest of the cerebrum. Subsequent T1 estimates differed by approximately 80 ms in WM and 200 ms in gray matter (GM) when assuming either finv=0.87 or finv=0.96.