We explore the temporal dynamics of tumor and T cell intracellular partial pressure of oxygen (pO2) in a murine flank glioma model receiving chimeric antigen receptor (CAR) T cell therapy. Tumor cells or T cells are intracellularly labeled with perfluorocarbon nanoemulsion prior to injection. 19F MRI relaxation rate measurements are used to elucidate intracellular pO2 in vivo. The tumor pO2 peaks at 3 days post-infusion, commensurate with CAR T cell infiltration and tumor cell killing. Moreover, the absolute 19F signal scales with tumor burden. Overall, 19F pO2 MRI measurements can assay cell-mediated apoptosis and provide insight into effector cell function.