ABSTRACT
Objective:To explore the value of susceptibility-weighted imaging (SWI) in quantitative evaluation of iron load in diabetic kidneys.Methods:Thirty two healthy New Zealand white rabbits were randomly divided into diabetic group (DM, n = 20) and control group (NC, n = 12). DM model was established by injecting 5% alloxan solution (100 ml/kg) through ear vein. 12 rats were finally enrolled into the group. NC group was injected with the same dose of normal saline. DM group and NC group were intramuscularly injected with 60 mg/kg iron dextran. The left kidney was scanned by MRI immediately after iron injection (0 weeks) and 12 weeks after feeding. The left kidney was killed after 12 weeks of scanning. The left kidney was examined by Prussian blue staining and atomic absorption spectrophotometer. The value of SWI in quantitative evaluation of renal iron content was evaluated by using the iron content measured by atomic absorption spectrophotometer as the gold standard. On SWI phase diagram, the region of interest (ROI) was manually drawn along the renal cortical vagal area, and the measured phase values were converted into angular radians. Mann Whitney U test was used to compare the blood glucose value and the angle radian value at 0 week and 12 week between the two groups; independent sample t test was used to compare the difference of iron content between the two groups; nonparametric Wilcoxon signed rank test was used to compare the difference of angle radian between DM group and NC group at 0 and 12 weeks; Spearman correlation analysis was used to study the correlation between angle radian value and atomic absorption spectrophotometer results. Results:The blood glucose level in DM group [28.0 (10.6) mmol/L] was significantly higher than that in NC Group [6.5 (1.9) mmol/L], and the difference was statistically significant (U = 0, P<0.001). At week 0, there was no significant difference between DM group [-0.04 (-0.02)] and NC Group [-0.02 (0.06)] in angle radian value (U=105.50, P>0.05); at 12 weeks, the angle radian value of DM group [0.22 (0.17)] was higher than that of NC Group [0.17 (0.05)], the difference was statistically significant (U=35.50, P<0.05). The angle radian of DM group and NC group at 12 weeks were higher than that of 0 weeks, and the differences were statistically significant ( P<0.05). Prussian blue staining showed that iron was mainly deposited in renal cortex, and the blue staining in DM group was more obvious than that in NC group. The signal intensity of renal cortex on SWI images in DM group was significantly lower than that in 0 week group at 12 weeks, and slightly decreased in NC group. The iron content of DM group and NC group were (171.39±20.13) mg/kg and (116.21±28.90) mg/kg, respectively, and the difference was statistically significant ( t=5.428, P<0.001). Spearman correlation analysis showed that the angle radian was positively correlated with iron content ( r=0.67, P<0.001). Conclusions:Diabetic kidneys have more iron deposits than normal kidneys. As a non-invasive, simple and convenient examination technique, SWI has the potential to quantitatively evaluate the iron load of diabetic kidneys.
ABSTRACT
Objective:To explore the value of susceptibility weighted imaging (SWI) in evaluating renal excess iron deposition.Methods:Thirty New Zealand white rabbits were randomly divided into iron group (injected iron dextran) with 15 rabbits and control group with 15 rabbits. All rabbits underwent SWI examination at 0th week before and 8th week after the injection of iron. MRI images of the control and iron group at the 0th and 8th week were analyzed. The phase value of renal cortex was measured on the phase images and the angle radian value was calculated. The distribution of renal iron deposition was observed by Prussian blue stain. The renal iron content was measured by atomic absorption spectrophotometer. The Mann-Whitney U or Wilcoxon test was used to compare the difference in angular radian value between the two groups. The independent sample t test was used to compare the difference in renal iron content between the two groups. Results:Only in iron group at 8th week, the SWI signal intensity of renal cortex was significantly lower than that of medulla. The renal cortical SWI signal intensity of iron group at 8th week was significantly lower than that of iron group at 0th week and control group at 8th week, respectively. The angle radian value of iron group at 8th week [0.202 3(0.161 8, 0.272 5)] was significantly higher than that of iron group at 0th week [-0.045 4 (-0.013 9, 0.008 0)] and control group at 8th week [-0.011 2 (-0.052 9, -0.001 4)], respectively ( Z=-3.408, -4.666, all P<0.05). Only in the iron group at 8th week, the obvious blue iron deposition were observed in renal cortex and few were observed in medulla. The renal iron content [(135.3±14.1) mg/kg] of iron group at 8th week was significantly higher than that [(75.5±9.8) mg/kg] of control group at 8th week ( t=13.938, P<0.001). Conclusions:SWI can evaluate the excess iron deposition in kidney. Excess iron is mainly deposited in the renal cortex and reduces its SWI signal intensity. The angle radian value calculated from the phase value can quantify the iron deposition.