Can R₂ ' mapping evaluate hypoxia in renal ischemia reperfusion injury quantitatively? An experimental study

To explore if R₂ ' mapping can assess renal hypoxia in rabbits with ischemia reperfusion injury (IRI).

Forty rabbits were randomly divided into 4 groups according to the clipping time: the sham group and 45 min, 60 min, and 75 min for the mild, moderate, and severe groups (with n = 10 each group), respectively. Intravenous furosemide (FU) was administered 24 h after IRI. All rabbits were performed 5 times (IRI_pre , IRI_24h , FU_5min , FU_12min , and FU_24min ) with a 3.0 Tesla MR. The R₂ ' values and the hypoxic scores were then recorded. The repeated measurement analysis of variance and Spearman correlation analysis was used for statistical analysis.

Compared to the baseline, the medullary R₂ ' values increased significantly 24 h after the IRI (baseline 19.31 ± 1.21 s^-1 , mild group 20.05 ± 1.26 s^-1 , moderate group 25.38 ± 1.38 s^-1 , and severe group 25.79 ± 1.10 s^-1 ; each P < .001). FU led to a significant decrease in the medullary R₂ ' value (sham group 11.17 ± 4.33 s^-1 , mild group 7.80 ± 0.74 s^-1 , moderate group 3.92 ± 0.28 s^-1 , and severe group 3.82 ± 0.23 s^-1 ; each P < .05). Quantitative hypoxic scores revealed significant differences among the 4 groups in the outer medulla (P < .001 each). The medullary R₂ ' differences (before and after intravenous FU) were significantly correlated with the hypoxic scores, respectively (P < .001).

R₂ ' mapping can evaluate the renal hypoxia in the procession of IRI in rabbits and might serve as a quantitative biomarker for IRI.