PURPOSE: Ischemic injury in the kidney is a common pathophysiological event associated with both acute kidney injury and chronic kidney disease; however, regional ischemia-reperfusion as seen in thromboembolic renal disease is often undetectable and thus subclinical. Here, we assessed the metabolic alterations following subclinical focal ischemia-reperfusion injury with hyperpolarized [1- 13 C]pyruvate MRI in a porcine model.

METHODS: Five pigs were subjected to 60 min of focal kidney ischemia. After 90 min of reperfusion, a multiparametric proton MRI protocol was performed on a clinical 3T scanner system. Metabolism was evaluated using 13 C MRI following infusion of hyperpolarized [1- 13 C]pyruvate. Ratios of pyruvate to its detectable metabolites (lactate, bicarbonate, and alanine) were used to quantify metabolism.

RESULTS: The focal ischemia-reperfusion injury resulted in injured areas with a mean size of 0.971 cm 3 (±1.019). Compared with the contralateral kidney, the injured areas demonstrated restricted diffusion (1269 ± 83.59 × 10 -6  mm 2 /s vs. 1530 ± 52.73 × 10 -6  mm 2 /s; p = 0.006) and decreased perfusion (158.8 ± 29.4 mL/100 mL/min vs. 274 ± 63.1 mL/100 mL/min; p = 0.014). In the metabolic assessment, the injured areas displayed increased lactate/pyruvate ratios compared with the entire ipsilateral and the contralateral kidney (0.35 ± 0.13 vs. 0.27 ± 0.1 vs. 0.25 ± 0.1; p = 0.0086). Alanine/pyruvate ratio was unaltered, and we were unable to quantify bicarbonate due to low signal.

CONCLUSION: MRI with hyperpolarized [1- 13 C]pyruvate in a clinical setup is capable of detecting the acute, subtle, focal metabolic changes following ischemia. This may prove to be a valuable future addition to the renal MRI suite.