Hyperpolarized 13 C, 15 N 2 -urea T 2 relaxation changes in acute kidney injury.

PURPOSE: To investigate the correlation between renal ischemia and 13 C-urea T2 relaxation rate in an acute kidney injury (AKI) rat model.

METHODS: Six rats subjected to unilateral renal ischemia were investigated. Creatinine clearance, urine output, plasma creatinine as well as blood-urea nitrogen (BUN) values were acquired before and after the procedure. 1 H T2* mapping was acquired using blood oxygenation level dependent (BOLD) MRI and hyperpolarized 13 C-urea T2 mapping was acquired using a 2D golden-angle radial approach. Kidney perfusion was estimated using noncontrast flow alternating inversion recovery arterial spin labeling.

RESULTS: All rats showed clinical signs of AKI with increased plasma creatinine and increased BUN. Whole kidney 13 C-urea T2 significantly decreased 26% (P = 0.001) 24 h after reperfusion. A significantly different (3.7 times steeper; P = 0.008) osmolality gradient was observed in the contralateral kidney (P = 0.008; R2  = 0.86) compared with the postischemic kidney (P = 0.0004, R2 =0.97). Whole kidney T2* signal (P = 0.14) and T2* gradient (P = 0.26) was similar between the two kidneys. Oxygen availability dependency on 13 C-urea T2 was investigated by means of the correlation between the BOLD and T2 signals; a statistically significant difference (P = 0.03) was found in the contralateral kidney (P = 0.0001; R2  = 0.95), but not in the postischemic kidney (P = 0.31; R2  = 0.25).

CONCLUSION: We demonstrate that hyperpolarized [13 C,15 N2 ]urea T2 relaxation correlates with renal oxygen tension ( T2*) in the healthy contralateral kidney, but not in the postischemic kidney. The whole kidney T2 relaxation difference between the postischemic and contralateral kidney may originate from altered blood volume in the postischemic kidney. Magn Reson Med 80:696-702, 2018. © 2017 International Society for Magnetic Resonance in Medicine.