High reproducibility of longitudinal relaxation rate (R1) estimation using the variable flip angle approach requires unbiased and precise estimation of the transmit field inhomogeneity. In this context, the Bloch-Siegert (BSS)-based B1+ mapping approaches were evaluated at 3T and 7T and compared to the SE/STE approach. R1 values in grey and white matter were slightly higher with the BSS-based techniques. At 3T, the highest reproducibility was observed with the single-echo BSS approach, using an RF spoiling increment of 90°. At 7T, the reproducibility of the techniques were equivalent in well B0-shimmed regions but diverged in regions of high B0 inhomogenity.