Fig 1: FEXI, hyperpolarized 13C and diffusion‐weighted images of EL4 lymphoma tumors. Tumors developed and were imaged 6, 7, 8, and 9 days after the subcutaneously injection of EL4 lymphoma tumor cells (ATCC) on the lower back of female mice. a), Representative axial T2‐weighted 1H image (* indicates the gel used to improve B0 shim uniformity and the white arrow points to the tumor). The image orientation is demonstrated on the top right where A: anterior, P: posterior, R: right, L: left. b), AXR, c), ADC) and d), hyperpolarized 13C MFR maps of the solid tumor regions (tumor regions with ADC higher than 12 × 10−4 mm2 s−1 have been excluded) overlaid on a T2‐weighted image. e), Heat map of the percentage of necrotic cells determined from the H&E stained image shown in f). In the left‐most panel of (f), the scale bar = 3 mm. In the other panels of (f), he scale bar = 100 µm (with colored representative regions shown in high magnification). g), AXR, h), ADC and i), MFR scatter plots for the 12 tumor‐bearing animals examined. Each data point represents a tumor voxel value. The horizontal lines correspond to the median values and the whiskers range to the 95% confidence interval for the median values. The voxel values colored in green correspond to an animal that we chose as a reference for low levels of observed necrosis (low AXR and low standard deviation of the AXR in combination with histology, see panel (m). j–l), Correlation plots between the median AXR, MFR and ADC voxel values. m–p), Correlation plots between tumors’ median AXR, MFR voxel values and the mean percentages of necrotic and viable cells. Solid and dotted lines represent the linear regression line and the 95% confidence bands of the best‐fit line, respectively. Each point is labeled with the corresponding animal number (#) and the number of days after tumor cell injection (d.). Correlation coefficients (r) and p‐values were calculated using Spearman correlation; n.s., p > 0.05, * p ≤ 0.05, ** p ≤ 0.01.