| Purpose:To investigate the value of monoexponential,biexponential and kurtosis models based on multi-b-value MR diffusion imaging for evaluating the change of unilateral renal microstructure of the cold ischemia-reperfusion injury(CIRI)model in rats,combined with its physiological changes.Then to evaluate the changes of renal function and microstructure for cold ischemia time(CIT)1h and 2h of CIRI model,using the whole renal volume histogram based on diffusion kurtosis imaging(DKI).Methods:In part 1,40 male SD rats were randomly divided into experimental group and sham operation group,20 rats in each group.In the experimental group,the blood vessels of the left renal pedicle were clipped.The left kidney was injected with perfusion fluid until it was pale,and then ice chips were placed around the kidney for 1 hour.And then the right kidney was cut after the clipping was removed.In the sham operation group,only the right kidney was removed.5 rats at 1h,1d,2 and 5 days after operation were randomly selected for multi-b-value diffusion weighted imaging(DWI)and conventional MRI for each group.Then the blood of abdominal aorta was taken for laboratory testing.The left kidney was taken for Morphological score of pathological examination after death.At the same time,the normal group(without any treatment)was added to 5 as the control group.MRI images were processed to generate monoexponential(apparent diffusion coefficient ADC),biexponential(real diffusion coefficient D,false diffusion coefficient DP value and perfusion fraction f)and kurtosis model(mean diffusion coefficient MK,mean peak MD)parameter maps.The renal cortex and medulla of all rats were measured.In part 2,20 SD rats were added to the experimental group for 2 hours of cold ischemia time,and 5 rats were randomly selected for DKI and conventional MRI at 1h,1,2 and 5 days after operation,followed by laboratory examination and pathological score.All rats in the experimental group(CIT 1h and CIT 2h group)and normal group were analyzed with MD and MK histograms.The difference of MRI parameters between the renal cortex and medulla of all rats was analyzed by paired samplet test.One way analysis of variance(ANOVA)was used to compare the differences of MRI parameters,laboratory indexes and pathomorphological scores of kidney cortex and medulla at different time points and in groups.To analyze the correlation between the parameters of renal cortex and medulla MRI in each group and the laboratory indexes and pathomorphology scores.Results:(1)There was damage and repair at different time points after operation in Ciri model of rat kidney:the diffusion of water molecules in cortex and medulla was significantly limited at 1 h after operation,which was related to the decrease of microcirculation perfusion;at 1 day,the damage of renal tubular epithelium began to repair,and the MD of cortex and medulla was significantly increased at 2 days after operation,which indicated that the diffusion of water molecules was quickly recovered,especially the cortex,but the recovery of microcirculation perfusion was slow;at 5 days,the MK of cortex and medulla was restored;the water heterogeneity was significantly improved.(2)Compared with the normal group,the MD and f value of cortex in the experimental group(CIT 1h group)and the sham operation group were significantly lower than those in the normal and sham operation groups at 1 h postoperatively;the MK and f value of cortex were significantly low at 1d;the MD value of cortex was significantly high at 2d.At 1h after operation,MD,D,ADC and f of medulla were significantly lowerp.At 1d after operation,MD and MK of medulla were significantly lower than those of normal and sham operation groups.(3)Histogram analysis showed that the histogram distribution of MD and MK in the normal group was similar to the normal distribution,while that in the experimental group was non normal distribution at 1 h and 1 d after operation,and the peak value of MD was shifted to the left,especially in the CIT 2h group.At 1 h and 1 d after operation,the peak value of MK first shifted to the right,then to the left,and gradually tended to the normal distribution at 2 d and 5 d after operation.(4)In the CIT 2 h group,the diffusion of water molecules was significantly limited compared with that in the 1 h group,and the heterogeneity of the diffusion of water molecules was large.On the 1d after operation,the diffusion of water molecules was improved,which was still obvious compared with that in the 1 h group,and the recovery was slow.On the 5d after operation,although the diffusion of water molecules was not different from that in the normal group and the 1 h group,the heterogeneity in the tissue was obvious,suggesting the complexity of prolonging the ischemic time.(5)There were significant differences in the mean,5%,25%,50%,75%and 95%of renal MD at different time points after CIT 1 and 2 hours(P<0.05),and in the mean,75%and 95%of MK at different time points(P<0.05).(6)The MD value of cortex and MK value of medulla in the experimental group(CIT 1h group)were positively correlated with the brush border injury of renal tubules.There was a moderate positive correlation between cortical f and tubulodilation score.In the experimental group and the sham operation group,the DP value of cortex was positively correlated with BUN,and the MK value of medulla was moderately correlated with SOD.In CIT 2 h group,the mean and percentiles of MD in whole kidney were negatively correlated with pathological score.Conclusions:The biexponential and kurtosis models based on multi-b-value MR diffusion imaging are better than that of monoexponential model.It can be used to evaluate the diffusion of water molecules,microcirculation perfusion and microstructure changes of renal tissue,quantitatively and noninvasively.Cortical perfusion decreased in the early stage after CIRI,and the diffusion of water molecules recoverd faster than that of microcirculation perfusion.The whole kidney volume histogram analysis based on DKI image can provided more quantitative information for the comparison of renal structure differences in different CIT groups of CIRI rat model. |
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