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目的探讨MR血氧水平依赖成像(blood oxygen level-dependent,BOLD)对兔肾缺血再灌注损伤(IRI)的诊断价值。方法健康新西兰大白兔30只,完全随机分成IR 1~3组,建立左肾缺血再灌注模型,3组左肾动脉夹闭时间分别为40、60、80 min,夹闭后松开动脉夹均再灌注48 h。分别于IRI前后行双肾MR冠状位T_2WI及BOLD扫描,检查完成后立即取左肾行病理学检查。分别测量双肾肾皮质(cortex,C)层、外髓(outer medulla,OM)层的R_2~*值,再将左肾与右肾相同区域的R_2~*值做比值(rR_2~*),并计算IRI前后左右肾rR_2~*的差值(△rR_2~*)。IRI前后IR1~3组每组组内兔肾C层和OM层△rR_2~*比较采用配对样本t检验;IR 1~3组C层和OM层△rR_2~*组间两两比较采用LSD检验。结果肾IRI后,IR 1~3组OM层△rR_2~*分别为0.27±0.04、0.47±0.01、0.49±0.01。IR 2、3组OM层△rR_2~*明显高于IR 1组(P<0.01),而IR 2组OM层△rR_2~*与IR 3组差异无统计学意义(P>0.05);IR 1~3组C层△rR_2~*分别为0.12±0.02、0.10±0.02、0.11±0.03,俎间两两比较差异均无统计学意义(P>0.05)。3组OM层△rR_2~*均高于C层(P<0.05)。结论肾脏缺血时间越长再灌注后损伤越重;肾脏缺血时间超过60 min后,肾脏IRI的程度已经达到最大程度。BOLD通过无创地检测肾脏外髓质血氧水平,能间接地反映肾脏IRI随缺血时间变化的趋势特点,有助于肾脏IRI的检出。
Objective To investigate the diagnostic value of MR blood oxygen level-dependent (BOLD) on renal ischemia-reperfusion injury (IRI) in rabbits. Methods Thirty New Zealand white rabbits were randomly divided into IR 1 ~ 3 groups. Left renal ischemia-reperfusion model was established. The left renal artery occlusion time was 40, 60, 80 min in each group, and the artery clamp Reperfusion 48 h. Left and right renal MR angiography T_2WI and BOLD scans were performed before and after IRI respectively. Left renal pathology was performed immediately after the examination. R_2 ~ * values were measured in the layers of cortex, C and outer medulla (OM) of renal cortex and right renal respectively, then the ratio of R_2 ~ * in the same area of left kidney and right kidney was measured. The difference of rR_2 ~ * between before and after IRI (△ rR_2 ~ *) was calculated. The levels of △ rR_2 ~ * in C layer and OM layer in IR1 ~ 3 group before and after IRI were compared by paired t-test; the LSD test was used to compare the △ rR_2 ~ * groups in C layer and OM layer of IR 1 ~ 3 group; . Results After IRI, the △ rR_2 ~ * of OM layer in IR 1 ~ 3 group were 0.27 ± 0.04, 0.47 ± 0.01 and 0.49 ± 0.01, respectively. The △ rR_2 ~ * of OM layer in IR 2,3 group was significantly higher than that in IR 1 group (P <0.01), but there was no significant difference between △ rR_2 ~ * and IR 3 group in OM layer of IR 2 group (P> 0.05) The △ rR_2 ~ * of layer C of ~ 3 groups were 0.12 ± 0.02, 0.10 ± 0.02 and 0.11 ± 0.03, respectively. There was no significant difference between them (P> 0.05). The △ rR_2 ~ * of three OM layers were higher than that of C layer (P <0.05). Conclusion The longer the renal ischemia is, the heavier the injury is after reperfusion. When the renal ischemia time exceeds 60 min, the degree of renal IRI has reached the maximum. BOLD helps to detect renal IRI by non-invasively detecting the renal extra-medullary oxygen level, which can indirectly reflect the trend of renal IRI with ischemic time.