Principle of the method. The spin echo period with the BE pulse, or the BE-block, is illustrated in Figure . During the BE block under the 1 H-decoupling, the chemical shift for Cα is refocused with the centrally placed BE pulse, while the scalarcouplings to its nearest-neighbor Namide, C' and Cβ spins evolve only when these spins are simultaneously inverted. Thus, after the 1/+2𝐽 $%$& , BE period, the initial Cα ! state remains Cα ! when Cβ spin experiences no inversion, but evolves into the antiphase 2Cα ! Cβ " state when the Cβ spin experiences an inversion (C' is always not inverted). The following z-filter passes the former but not the latter term for subsequent observation, and thus the Cβ inversion is encoded as the Cα signal intensity. For example, if the BE pulse inverts the Cβ " state only within the chemical shifts range of [25, 35] ppm, the Cα signal coupled with Cβ resonating within this particular inversion window vanishes.