[Functional MRI assessment of microstructural and perfusion changes in the kidneys of rats with intrauterine growth restriction]

Abstract

Objectives: To explore the value of functional magnetic resonance imaging (MRI) techniques, including intravoxel incoherent motion (IVIM), T1 mapping, and T2 mapping, in assessing the microstructural and perfusion changes in the kidneys of rats with intrauterine growth restriction (IUGR).

Methods: An IUGR rat model was established through a low-protein diet during pregnancy. Offspring from pregnant rats on a low-protein diet were randomly divided into an IUGR 8-week group and an IUGR 12-week group, while offspring from pregnant rats on a normal diet were divided into a normal 8-week group and a normal 12-week group (n=8 for each group). The apparent diffusion coefficient (ADC), true diffusion coefficient (D_t), pseudo-diffusion coefficient (D^*), perfusion fraction (f), T1 value, and T2 value of the renal cortex and medulla were compared, along with serum creatinine and blood urea nitrogen levels among the groups.

Results: The D_t value in the renal medulla was higher in the IUGR 12-week group than in the IUGR 8-week group, and the D^* value in the renal medulla was lower in the IUGR 12-week group than in both the normal 12-week group and the IUGR 8-week group (P<0.05). The T1 value in the renal medulla was higher than in the cortex in the IUGR 8-week group, and the T1 value in the renal medulla was higher in the IUGR 12-week group than in both the IUGR 8-week group and the normal 12-week group, with the cortical T1 value in the IUGR 12-week group also being higher than that in the normal 12-week group (P<0.05). The T2 values in the renal medulla were higher than those in the cortex across all groups (P<0.05). There were no significant differences in the T2 values of either the cortex or medulla among the groups (P>0.05). There were no significant differences in serum creatinine and blood urea nitrogen levels among the groups (P>0.05). Glomerular hyperplasia and hypertrophy without significant fibrotic changes were observed in the IUGR 8-week group, whereas glomerular atrophy, cystic stenosis, and interstitial inflammatory infiltration and fibrosis were seen in the IUGR 12-week group.

Conclusions: IVIM MRI can be used to assess and dynamically observe the microstructural and perfusion damage in the kidneys of IUGR rats. MRI T1 mapping can be used to evaluate kidney damage in IUGR rats, and the combination of MRI T1 mapping and T2 mapping can further differentiate renal fibrosis in IUGR rats.

Keywords: Functional magnetic resonance imaging; Intrauterine growth restriction; Intravoxel incoherent motion; Kidney; Rat; T1 mapping; T2 mapping.

图1. 实时测量时ROI选区 A：IVIM MRI选区图，可得到真实扩散系数（D_t）、伪扩散系数（D^*）、表观弥散系数（ADC）、灌注分数（f）值；B：T1 mapping MRI选区图，可得到T1值；C：T2 mapping MRI选区图，可得到T2值。

图2. 各组仔鼠肾小球、肾小管HE、Masson染色图（光镜，×400） HE染色结果显示，正常8周组、正常12周组及IUGR 8周组可见肾小球形状完整，肾小囊清晰，IUGR 12周组可见肾小球萎缩，肾小囊消失，箭头指示肾小球结构；正常8周组、正常12周组及IUGR 8周组可见肾小管结构正常，刷状缘清晰，IUGR 12周组可见肾小管结构紊乱，刷状缘脱落，部分可见肾小管上皮细胞脱落，箭头指示肾小管刷状缘。Masson染色结果显示，正常8周组、正常12周组及IUGR 8周组可见肾小球形状完整，肾小囊清晰；IUGR 12周组可见肾小球萎缩，肾小囊消失，蓝染较其余3组明显，提示纤维化改变，箭头指示肾小球结构。正常8周组、正常12周组及IUGR 8周组可见肾小管结构正常，刷状缘清晰，未见显著纤维化改变；IUGR 12周组可见肾小管结构紊乱，刷状缘脱落，部分可见管型，蓝染较其余3组明显，提示纤维化改变，箭头指示肾小管刷状缘。