Fig. 1: Diffusion NMR based measurements of molecular exchange.

The pulse sequences for (a) conventional and (b) ultrafast diffusion exchange spectroscopy (DEXSY) measurements. The conventional experiment is repeated multiple times with varying diffusion gradient strength G_D (changed independently for periods D₁ and D₂), while the same data is measured in a single scan by the ultrafast approach. D₁ and D₂ refer to the first and second diffusion encoding periods, τ_M to the mixing time, RF to the radio frequency pulse, G to the gradient pulse, and Δ to the diffusion delay. Subscripts D, C, SD, DD, and RD of G stand for diffusion, crusher, spatial and diffusion encoding, diffusion and dephasing, and read and diffusion, respectively. The arrows overlaying the RF pulses show the direction of frequency sweep. c Illustration of the main difference between the conventional and ultrafast approach. In the conventional experiment, N and M data points, corresponding to the indirect and direct dimension (D₁ and D₂) and characterized by different b values (which are proportional to the gradient strength), are collected in separate experiments, leading to N × M repetitions. In the ultrafast experiment, the same data is spatially encoded into the layers of the sample in a single scan.