MRI and MRSI: MR images were acquired using an Agilent 4.7T 40 cm horizontal bore MRSpectrometer with a 25 gauss/cm gradient tube interfaced to an Agilent DirectDrive console. Eachanimal was positioned within a Polarean proton-tuned (200.1 MHz) birdcage resonator withquadrature polarization with a Polarean 13Carbon-tuned (50.525 MHz) surface coil positioned overthe right upper quadrant (Polarean: Durham, NC). A detailed description of the parameters used toacquire T2-weighted and contrast-enhanced T1 images is included in the Supplementary Materials &Methods. DNP-13C-MRSI was acquired using a 2D (slab thickness = 10 mm) echoplanarspectroscopic imaging (EPSI) sequence using a spectral bandwidth of 1.1kHz with 128 points,enabling detection of chemical shifts of 22 ppm (37). The FOV was 60 mm x 45 mm with 12 phaseencode steps and 16 frequency encode steps, enabling an in-plane resolution of 3.75 mm x 3.75mm. This sequence required ~2 s to complete and was repeated every ~4 s for a minimum of 10scans per study. Image acquisition was initiated 25 s following the commencement of the injection tomaximize observed lactate. Data were processed and analyzed as described in the SupplementaryMaterials and Methods.