Fig. 1.

¹³C spectra acquired over a period of 1 min after injection of hyperpolarized [1,4-¹³C₂]fumarate into suspensions of intact murine lymphoma cells (≈5 × 10⁷ cells) or lysed cells; these are representative spectra from the data shown in Fig. 2. For clarity, only every third spectrum is shown and each series has been scaled to the maximum fumarate signal. (A) Untreated cells. (B) Cells 16 h after etoposide treatment. (C) Lysed cells. The truncated signal from the hyperpolarized [1,4-¹³C₂]fumarate is at 175.4 ppm, the signal from [1-¹³C]malate at ≈181.8 ppm, and the signal from [4-¹³C]malate at ≈180.6 ppm.