EPSI data were available from a database of patients with glioblastoma previously enrolled in a phase II clinical trial (23 (link)) who received post-surgical scans. All scans were conducted in a 3T MRI scanner with a 32-channel head coil (Siemens Medical) and were obtained following surgical resection but prior to the start of radiation therapy and chemotherapy. Anatomic volumes obtained used a T1-weighted (T1w) magnetization-prepared rapid gradient echo pulse sequence (TR = 1900 ms, TE = 3.52 ms, 256 × 256 matrix, flip angle (FA) = 9°). A whole-brain 3D EPSI sequence (TR = 1551 ms, TE = 17.6 ms, FA = 71°, final matrix size of 64 × 64 × 32) was obtained during the same scanning session, as previously reported (3 (link)). Both sequences were obtained at a +15 degree tilt in the sagittal plane from the anterior commissure-posterior commissure line in order to capture the entire cerebrum while minimizing acquisition in the clivus, sinuses, and retro-orbital fat. An oblique saturation band was placed in the sagittal plane from the optic chiasm to the cerebellum to suppress signal from those regions. Image reconstruction and formation of metabolite images were carried out using the Metabolite Imaging and Data Analysis System (MIDAS) package (5 (link),6 (link)). Briefly, this processing includes spatial reconstruction, frequency alignment, B0 field correction, co-registration of the T1w and EPSI volumes, registration of the T1w volume to an anatomic atlas, lipid suppression, spectral fitting, and normalization with internal water signal to produce relative concentrations of metabolites. Additionally, pre-filtering of data using algorithms built into MIDAS was applied to all data to replicate the workflow currently used in clinical studies. First, a mask based on an anatomic atlas was applied to exclude voxels outside of the brain, which drastically reduces the number of voxels to be analyzed. Voxels with a water linewidth > 18 Hz, as calculated from T2 decay, were removed prior to spectral fitting to save computation time. After fitting, voxels with a metabolite linewidth > 18 Hz were also removed; this step served as an initial filter to remove spectra known to be of poor quality prior to visual review. A representative volume contained 10,298 voxels after filtering, however, since the data is also interpolated and smoothed in each dimension during reconstruction it is estimated that approximately 1,280 independent spectra remain within the brain volume. Spectra were then randomly sampled from a grid with a skip factor of 2, including both regions of tumor and healthy tissue, and exported for analysis. A total of 8,894 spectra collected from 9 patients with glioblastoma were collected.