扩散加权成像单指数和双指数模型评估单侧输尿管梗阻大鼠肾脏扩散及微灌注变化

Diffusion and Microperfusion Changes in Rats with Unilateral Ureteral Obstruction Using Mono-and Bi-exponential Model Diffusion Weighted Imaging

目的探讨扩散加权成像(DWI)单指数和双指数模型评估大鼠单侧输尿管梗阻(UUO)后肾脏扩散改变及微灌注改变的能力,为早期诊断及治疗梗阻性肾病提供依据。材料与方法 21只大鼠按照随机数字表法平均分为7组,除对照组外,其余6组大鼠结扎左侧输尿管建立UUO模型。对照组与UUO大鼠分别于术前及UUO后6 h、12 h、1 d、2 d、3 d、7 d行双肾多b值DWI检查获得ADC图,b值取0、20、40、60、80、100、140、180、240、300、500、1000、1500 s/mm2,并利用双指数模型计算灌注分数f图及纯扩散系数D图,分析UUO后不同时间点患肾、健肾及对照组间肾皮、髓质ADC值、f值和D值的变化。结果 UUO后各时间点患肾皮、髓质ADC值均显著低于健肾(t=-9.809^-3.666、-8.703^-5.843,P<0.01),UUO后3 d患肾皮质ADC值低于对照组(t=2.236,P<0.05);UUO后6 h、12 h、1 d、3d健肾皮、髓质ADC值均高于对照组(t=-10.030^-2.724,P<0.05)。患肾皮质f值均低于对照组及健肾(t=2.553~7.984、-6.418^-2.519,P<0.05);患肾髓质f值均低于健肾(t=-6.245^-3.408,P<0.01),但患肾髓质f值仅UUO后12 h和7 d低于对照组(t=2.264、2.453,P<0.05)。UUO后6 h、12 h、1 d、2 d、7 d患肾皮质D值均高于对照组(t=-7.638^-3.007,P<0.05),髓质D值UUO后2 d开始持续高于对照组及健肾(t=-4.069^-3.040、2.799~3.079,P<0.05),但健肾髓质D值与对照组无显著差异,健肾皮质D值仅UUO后1 d、3 d、7 d高于对照组(t=-2.898、-2.462、-2.628,P<0.05)。结论双指数模型较单指数模型更好地评估梗阻性肾病肾实质扩散的改变,并可以反映肾皮质的微灌注变化。

Purpose To investigate the potential of mono- and bi-exponential model diffusion weighted imaging （DWI） in evaluating kidney changes in diffusion and microperfusion in rats with unilateral ureteral obstruction （UUO）. Materials and Methods Twenty-one rats were divided into seven groups using random number table. There were one normal control group and six groups with UUO. UUO groups underwent DWI using multiple b-values （b=0, 20, 40, 60, 80, 100, 140, 180, 240, 300, 500, 1000 and 1500 s/mm^2） presurgery and at 6 hours, 12 hours, l day, 2 days, 3 days and 7 days after surgically created UUO to obtain the ADC maps. Perfusion fraction f map and pure diffusion coefficient D map were calculated using bi- exponential model. ADC, f and D values in the cortical and medullary regions were compared between diseased and contralateral kidneys at different time points. Results Cortical and medullary ADCs in UUO kidneys were significantly lower than those of contralateral kidneys （t= -9.809- -3.666 and - 8.703- -5.843, P〈0.01）. At 3 days after surgery, conical ADCs of UUO kidneys were lower than those of normal controls （t=2.236, P〈0.05）. Cortical and medullary ADCs of contralateral kidneys were higher than those of normal controls at 6 hours, 12 hours, 1 day and 3 days after operation （t=- - 10.030- -2.724, P〈0.05）. Compared with both normal controls and contralateral kidneys, there was significant decrease in cortical f values of UUO kidneys （t=2.553-7.984 and -6.418- -2.519, P〈0.05）. The medullary f values of UUO kidneys were lower than those of contralateral kidneys （t= --6.245- -3.408, P〈0.01）. This was lower than that of normal controls only at 12 hours and 7 days after surgery （t=-2.264 and 2.453, P〈0.05）. Conical D values of UUO kidneys were higber than that of normal controls at 6 hours, 12 hours, l day, 2 days and 7 days after surgery （t= - 7.638- - 3.007, P〈0.05）. The medullary D values of UUO kidneys were higher than those of contralateral kidneys and normal controls beginning at 2 days after surgery （t=- -4.069- -3.040 and 2.799-3.079, P〈0.05）. There was no significant difference in medullary D values between contralateral kidneys and normal controls. The conical D values of contralateral kidneys were higher than those of normal controls at l day, 3 days and 7 days after surgery （t= -2.898, -2.462 and - 2.628, P〈0.05）. Conclusion Biexponential model is superior to monoexponential model in evaluating changes in parenchymal diffusion and microperfusinn in obstructive nephropathy.