Experiments were carried out on a 3T whole-body scanner (Philips Medical Systems, Best, The Netherlands). A body coil was used for radio-frequency transmission and an 8-channel head coil for reception. Data were acquired according to our published methods28 . PRESS8 and scalar difference editing9 (link) were used for measuring 2HG in brain tumors. For editing, two 20-ms Gaussian 180° pulses, tuned to 1.9 p.p.m., were switched on and off in alternate scans to generate an edited H2 signal at 4.02 p.p.m. in difference spectra. The echo times of PRESS and editing were 97 and 106 ms, respectively. The quantum-mechanical simulations were carried out by means of the product-operator-based transformation matrix algorithm (Supplementary Methods). For in vivo MR scans, following the survey imaging, T2w-FLAIR images were acquired to identify tumor regions. For single-voxel localized data acquisition, a 2×2×2 cm3 voxel was positioned within the tumor mass. PRESS acquisition parameters included sweep width = 2500 Hz, 2048 sampling points, repetition time = 2 s, and 64 averages (scan time 2.1 min). Editing data were acquired with 384 averages (scan time 13 min). An unsuppressed water signal was acquired with echo time = 14 ms and repetition time = 20 s for use as reference in metabolite quantification. Spectroscopic imaging data were acquired, using the optimized PRESS echo time, from a 1.5-cm thick slice with resolution of 1×1 cm2. Undersampling of k-space data by 20% was employed, the scan time being approximately10 min (2 averages; repetition time = 1.3 s). Data were zero filled for the un-acquired k-space points and filtered with a cosine function prior to Fourier transformation.