| Part 1 2D Susceptibility Weighted Imaging in normal rabbit kidneyObjective: To evaluate the feasibility of Susceptibility Weighted Imaging(SWI) in kidney, and to observe the characteristics of parameters and images of SWI in normal rabbit kidneys.Materials and methods: The T2 WI and SWI images of normal kidneys of 40 healthy New Zealand white rabbits were obtained with 3.0T MRI scanner. The mean signal intensities within OM and Cx of left kidney on T2 WI and SWI were measured and compared. Meanwhile, CNRs of OM were calculated. The differences signal intensities of OM and Cx in renal T2 WI and SWI images were compared with Mann-Whitney U test. Independent sample t-test was used to compare the differences of CNR of OM between T2 WI and SWI images. P <0.05 was considered statistically significant.Results: In T2 WI, the signal characteristics of normal kidneys from inside to outside were sequentially displayed "white- black- white- black" signal band. Among them,the inner medulla had a significant high signal. The outer medulla can be divided into two layers, the inner layer was showed a low signal arc, while outer layer was showed a cambered high signal band. And the signal of cortex was slightly lower. In SWI, the signal characteristics of normal kidneys from inside to outside were showed "white-black- white" signal band. The inner medulla had a significant high signal.The outer medulla was showed significantly lower signal band, and cortex had slightly higher signal which had a clear boundary with outer medulla. In T2 WI, the signal intensities of renal OM and Cx had no significant difference(P >0.05), while in SWI, the signal intensities of OM ??were significantly smaller than Cx(P<0.01). The CNR of OM was significantly higher on SWI than on T2WI(P <0.05). SD values of OM on T2 WI and SWI were 3.5±0.6 and 4.4±0.7, respectively. CNR of OM in T2WI(18.6 ± 4.2) was significantly lower than that in SWI(27.1 ± 3.6)(P <0.05).Conclusion: This study showed the feasibility of renal 2D-SWI that can obtain images with good tissue contrast of renal cortex and medullary, and CNR of OM in SWI was higher than it in T2 WI. In addition, SWI was also an effective method to reflect physiological characteristics of both the cortex and the medulla.Part 2 Semi-quantitative analysis of renal ischemia reperfusion injury in rabbit with Susceptibility Weighted ImagingObjective: To assess the feasibility of 2D-SWI as a tool to evaluate the changes of kidney in IRI model of rabbits, by means of comparing the characteristics of OM between the control group and experimental group, and evaluate the diagnostic value of the 2D-SWI of renal IRI.Materials and methods : 40 healthy New Zealand white rabbits were used in this experiment, which were divided randomly into two groups: control group(n=8) and IRI group(n=32).According to the time of reperfusion, the IRI group were divided into four subgroups : IRI 1h(n = 8), IRI 12h(n = 8), IRI 24h(n = 8), IRI 48h(n = 8). All the rabbits of IRI group were subjected to the following operation. After deep anesthesia,the artery and vein of left renal were clamped and maintained for 60 minutes. Then reperfusion was performed by releasing the clamp. The rabbits in IRI group underwent2D-SWI examinations respectively at the time of 1h, 12 h, 24 h and 48 h after reperfusion.The rabbits of Co group didn’t take the IRI operation while underwent MRI examination directly. The transversal scanning sequence included T2 WI and 2D-SWI.All the rabbits were killed after the MRI examination, and nephrectomy was performed immediately to remove the left kidneys for histopathologic analysis. The OM of healthy kidneys was a continuous and intact hypointense band. A 6-point confidence level scale was used to obtain a semi-quantitative assessment of the integrity of OM on SWI(0, no hypointense band; 1, 0 <residual hypointense band ≤25%; 2, 25% <residual hypointense band ≤50%; 3, 50% <residual hypointense band ≤75%; 4, 75% <residual hypointense band <100%; 5, a continuous and intact hypointense band). Kruskal-Wallis test was used to compare the differences of the integrity of OM in each subgroup and Co group.P <0.05 was considered statistically significant.Results: The median of the integrity of OM in control group and four sungroups were5.00,1.00,2.00,4.50,5.00,respectively. Mean scores of IRI 1h group and 12 h group on SWI were both significantly lower than those on control group(P<0.05). Mean scores of IRI 24 h group and IRI 48 h group on SWI were both significantly higher than IRI 1h group(P<0.05), and mean score of IRI 48 h group was significantly higher than that of IRI 12 h group(P<0.05).Histological changes of renal OM of IRI 1h group were distinctive, with obvious sign of edema and ballooning degeneration of renal tubular epithelial cells. A majority of the capillaries and vasa recta surrounding the tubules were compressed by the swelling tubular epithelial cells, and the vascular area decreased obviously. Of IRI 12 h group, edema and vascular compression was also remarkable, with a small part of the tubular lumens showing dilatation and protein casts. Of IRI 24 h and 48 h group, necrosis in tubular epithelial cells and intratubular casts were more than the above three groups,but edema was lighter, resulting in part of peritubular blood vessels were filled, and the vascular area increased.Conclusion: The integrity of OM in 2D-SWI images was changed with the time after IRI. The semi-quantitative analysis of 2D-SWI can be used to assess the changes of OM in IRI kidneys. |
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