Hyperpolarized (13) C,(15) N2 -Urea MRI for assessment of the urea gradient in the porcine kidney.

PURPOSE: A decline in cortico-medullary osmolality gradient of the kidney may serve as an early indicator of pathological disruption of the tubular reabsorption process. The purpose of this study was to investigate the feasibility of hyperpolarized (13) C,(15) N2 -urea MRI as a biomarker of renal function in healthy porcine kidneys resembling the human physiology. METHODS: Five healthy female Danish domestic pigs (weight 30 kg) were scanned at 3 Tesla (T) using a (13) C 3D balanced steady-state MR pulse sequence following injection of hyperpolarized (13) C,(15) N2 -urea via a femoral vein catheter. Images were acquired at different time points after urea injection, and following treatment with furosemide. RESULTS: A gradient in cortico-medullary urea was observed with an intramedullary accumulation 75 s after injection of hyperpolarized (13) C,(15) N2 -urea, whereas images acquired at earlier time points postinjection were dominated by cortical perfusion. Furosemide treatment resulted in an increased urea accumulation in the cortical space, leading to a reduction of the medullary-to-cortical signal ratio of 49%. CONCLUSION: This study demonstrates that hyperpolarized (13) C,(15) N2 -urea MRI is capable of identifying the intrarenal accumulation of urea and can differentiate acute renal functional states in multipapillary kidneys, highlighting the potential for human translation. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.