Objective:To explore the feasibility of chemical exchange saturation transfer (CEST) imaging at 3.0 T MRI in quantifying renal redox metabolism in vitro models and experimental animals.Methods:Redox metabolites in vitro models with physiological concentrations were prepared, including reduced metabolites (glutamate, alanine, glutathione) and oxidized metabolites (2-ketoglutarate, pyruvate, glutathione disulfide, ammonium hydroxide). CEST examinations were performed at 3.0 T MRI. The imaging parameters were as follows: CEST images with different saturation pulse intensity (B 1) (1, 2, 3, 4 μT) and a fixed radio frequency (RF) duration of 2 000 ms; CEST images with different RF durations (1 500 and 2 000 ms) were acquired with a fixed B 1 value of 2 μT to obtain the optimal scanning parameters. CEST examinations with optimized parameters were performed on the left kidneys of seven healthy rabbits, and the differences in magnetic resonance ratio asymmetry (MTR asym) between rabbit renal cortex and outer medulla were measured. A paired t-test was used to compare the differences. Results:The optimal B 1 for CEST examination of redox metabolites was 2 μT, and the optimal RF duration was 2 000 ms. The MTR asym peaks of glutathione disulfide, glutathione, glutamic acid, and alanine were at 3.75, 3.5, 3, and 1.5 ppm, respectively. The MTR asym peaks of pyruvate, 2-ketoglutarate, and ammonium hydroxide were at 1 ppm. The MTR asym peak values of reduced metabolites were higher than those of oxidized metabolites. When the B 1 value was 2 μT and the RF duration was 2 000 ms, the MTR asym signal of the renal cortex was (2.60±1.10) %, (2.86±1.32) %, (3.04±1.06) %, and (2.98±0.91) % at 1, 3, 3.5, and 3.75 ppm, respectively. The MTR asym signal of the outer medulla was (1.00±0.56) %, (2.43±0.94) %, (2.29±0.88) % and (1.98±0.58) %, respectively. The MTR asym signal of the renal cortex was higher than that of the outer medulla, and the differences were statistically significant ( t=3.04, P=0.023; t=2.56, P=0.043; t=3.50, P=0.013; t=3.45, P=0.014). Conclusion:CEST imaging at 3.0 T MRI can be used to quantitatively evaluate redox metabolism of healthy rabbit kidneys in vitro model and normal experimental rabbits.

Objective:To investigate the feasibility of 3.0 T glutamate chemical exchange saturation transfer (GluCEST) imaging in evaluating renal redox metabolism in renal ischemia-reperfusion injury (IRI).Methods:Rabbits in the IRI group ( n=56) underwent surgery by clamping the left renal artery for 45 min and then releasing to establish IRI. Rabbits in the sham group ( n=8) underwent the same operation without clamping the left renal artery. GluCEST MRI was performed before and at 1 h, 12 h, 1 day, 3 days, 7 days, and 14 days after the operations, with eight rabbits in the IRI group sacrificed immediately after each scanning and eight in the sham group sacrificed at 14 days after scanning. The left kidneys were removed for histopathological examination and reactive oxygen species (ROS) fluorescence staining. Differences in the magnetic resonance ratio asymmetry (MTR asym) of the renal cortex and outer medulla among different groups were compared. Correlations between the MTR asym and ROS were analyzed. Results:The MTR asym of the renal cortex in the sham and IRI subgroups were higher than that of the outer medulla ( t=8.16, P<0.001; t=4.78, P=0.002; t=4.94, P=0.002; t=5.76, P=0.001, t=6.68, P<0.001; t=6.40, P<0.001; t=5.16, P=0.001; t=3.30, P=0.013). The MTR asym of the renal cortex and outer medulla in the IRI-1h, IRI-12h, IRI-1d, IRI-3d, IRI-7d, and IRI-14d groups were lower than in the sham and IRI-pre groups (all P<0.05). The MTR asym of the renal cortex and outer medulla in the IRI-1h group were lower than in the IRI-12h, IRI-1d, IRI-3d, IRI-7d, and IRI-14d groups (all P<0.05). The MTR asym of the renal cortex in the IRI-12h group was lower than in the IRI-7d and IRI-14d groups (1.84%±0.09% vs.2.42%±0.19%, 2.41%±0.31%, all P<0.05). The MTR asym of the renal cortex in the IRI-1d group was lower than in the IRI-7d group (1.99%±0.17% vs. 2.42%±0.19%, P=0.008). The MTR asym of the outer medulla in the IRI-12h group was lower than in the IRI-3d, IRI-7d, and IRI-14d groups (1.32%±0.27% vs. 1.79%±0.31%, 1.98%±0.18%, 1.66%±0.40%, respectively, all P<0.05]. The MTR asym of the outer medulla in the IRI-7d group was higher than in the IRI-1d and IRI-14d groups (1.98%±0.18% vs. 1.52%±0.31%, 1.66%±0.40%, all P<0.05). The MTR asym of the renal cortex and outer medulla had a strong negative correlation with the mean fluorescence intensity of ROS ( ρ=-0.889, P<0.001; ρ=-0.784, P<0.001). Conclusion:3.0 T GluCEST imaging can indirectly reflect the changes of renal redox metabolism in renal IRI.