Tissue hydration in kidneys during preservation: A relaxometric analysis of time-dependent differences between cortex and medulla

Cold preservation of donor organs induces hypothermia-related tissue edema as a result of a reduced activity of the ATP-dependent sodium pump at low temperatures. Hypothermia-induced tissue edema occurs in kidney preservation and is a significant risk factor for delayed graft function (DGF) after transplantation. DGF remains a major problem in kidney transplantation and is significantly associated with preservation injury. The state of hydration of cold-stored organs can be assessed from a biopsy for determination of the wet/dry weight ratio. As a non-invasive method to determine tissue hydration MRI T₁ and T₂ relaxometry can be used. In this study we have compared changes in tissue hydration in UW-preserved porcine kidneys with increasing cold ischemia times (CIT) using wet/dry weight ratio and MR ralaxometry. The results of the two techniques were correlated to evaluate the use of MR relaxometry. Wet/dry weight ratios of the renal cortex decreased with prolonged CIT (P < 0.01) whereas these of the medulla did not change significantly. T₁ values of the cortex decreased with prolonged CIT (P < 0.01). T₂ values of the cortex showed a non-significant decline with increased CIT. No significant changes in T₁ and T₂ were found in the medulla. The correlation between T₁ and the wet/dry weight ratio of the cortex was significant (P = 0.05, linear correlation coefficient 0.8698). We conclude that MR relaxometry can be a valuable non-invasive technique to assess tissue hydration in cadaveric donor kidneys before transplantation.