Fig. 4 Examples of DPFGSE simulations. Examples of DPFGSE simulations. (A) Simulated 1H NMR spectrum of 20 mM GABA (a common metabolite) dissolved in water; water signal dominates the spectrum. (B) The same spectrum simulated in the presence of double pulsed field gradient spin echo (DPFGSE) water suppression. Amplitudes of first and second DPFGSE gradients are 0.1 and 0.15 T/m, respectively; gradient durations are all 1.0 ms; sample size is 15 mm; there are 500 points in the spatial grid; off-resonance selective inversion pulses at the frequency of the water signal are simulated with the Fokker-Planck method (51) and use 10-point Gaussian envelopes. (C) Same as (B), but including spatial diffusion with a diffusion coefficient of 2.6 × 10−9 m2/s. (D) Same as (C), but using DPFGSE signal selection rather than suppression mode. One of the GABA multiplets is selectively excited. (E) Same as (C), but also including spatial flow at 10 mm/s. All simulations run in minutes on a Tesla K40 graphics processing unit (GPU) using Spinach 2.4 and later, and are included in the example set. Ahmed J. Allami et al. Sci Adv 2019;5:eaaw8962 Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution License 4.0 (CC BY).