MR横向弛豫时间测定技术对激素诱导兔股骨头缺血坏死模型的定量影像分析

目的 定量研究兔激素性股骨头坏死模型(SANFH)MR横向弛豫时间在造模不同时相的变化规律,探讨所反映的骨髓组分及微结构变化。方法 健康成年纯种新西兰大白兔60只,采用随机区组抽样方法分为空白对照(8只)及造模2、4、6、8周组(各13只)。制作模具小管并行MR T₂ mapping序列MR扫描,评价所得参数即T₂值的稳定性。参照Yamamoto的方法对模型组进行造模处理。造模开始前对空白对照组进行MR扫描,各模型组分别在造模后满2、4、6、8周时行MR扫描,将横向弛豫原始图像数据传至GE AW4.2工作站进行后处理,计算各像素T₂、T₂*值,创建相应参数的彩色编码图,对股骨头区、骺下区及髓腔骺端进行测量域感兴趣区的特征参数值;扫描完成后将实验动物处死,切取股骨头进行组织形态学检查。结果 剔除实验期间死亡动物及无效图像资料,MR检查并获得有效数据的空白对照及造模2、4、6、8周组实际样本量分别为8只(16髋)、10只(20髋)、9只(18髋)、9只(18髋)、10只(20髋)。各模型组及空白对照组T₂值(F=51.601, P＜0.01)、T₂*值(F=36.889, P＜0.01)组间总体差异有统计学意义。造模各组T₂、T₂*值均低于空白对照组,造模早期(2周)出现明显下降,4周降至最低,6、8周出现部分恢复;各解剖区域间T₂(F=86.274, P＜0.01)、T₂*(F=53.172, P＜0.01)值差异有统计学意义;股骨头区T₂、T₂*值高于骺下区及髓腔骺端,骺下区高于髓腔骺端(P值均＜0.05)。组织形态学变化:造模早期表现为骨髓造血细胞减少及脂肪细胞增生,髓内微血管血栓及出血,4周最为显著,之后出现骨组织坏死,骨小梁变细、部分消失,间质反应(充血、水肿、出血)及纤维化。结论 MR横向弛豫时间可敏感地反映SANFH模型骨髓组分及骨小梁微结构特征性改变,为此病早期诊断及病程监控提供了重要的定量影像学方法。

Experimental study on the model of steroid-induced femoral head osteonecrosis by measuring the MR transverse relaxation parameters

Objective To evaluate the marrow composition and microstructurechangesin animal model of steroid-induced avascular osteonecrosis of femoral head(SANFH) by estimating MR transverse relaxation. Methods Sixty pure-bred New Zealand rabbits were divided randomly into 5 groups, including a control group(n=8) and 4(M_2w, M_4w, M_6w, M_8w) experimental groups(n=13×4). Animal model was established according to the Methods mentioned by Yamamoto. At the end of each experiment, MR was performed by GE Signa EXICITE scanner and the original transverse relaxation images were transferred to GE AW4.2 workstations for the further data analysis using functool software. T₂, T₂*values of the region of interest in the femoral head, metaphysis and marrow cavity were calculated, and the color-coded maps were created. Experimental animals were sacrificed and the femoral heads were collected for the followed histomorphological investigation. Results The actual sample size of the control group and the groups of M_2w, M_4w, M_6w, M_8w was 8 (16 hips), 10 (20 hips), 9 (18 hips), 9 (18 hips), 10 (20 hips). Statistical differences in T₂ values(F=51.601, P＜0.01), T₂* values(F=36.889, P＜0.01) were observed between the groups of M_2w, M_4w, M_6w, M_8w and control group in all anatomic femoral regions. The T₂ and T₂* values of the experimental groups were lower than the control group. This decreasing began at the initial stage of the modeling(M_2w), reached the lowest point at M_4w, and then rebounded in group of M_6w and M_8w. The T₂(F=86.274, P＜0.01), T₂*(F=53.172, P＜0.01) values were statistically different between the different anatomical regions. The T₂ and T₂*values of the femoral head area were higher than the metaphyseal and marrow cavity area. It was distinguished that both the amount and the size of fat cells increased in marrow and trabeculae, whereas the hematopoietic tissues decreased. Microthrombi in the arterioles and extravasation of erythrocytes were observed in the femora metaphysic at the earlier stage of the modeling. Such pathologic changes showed particular significance in group M_4w. Then trabecular bone necrosis, inflammatory reaction and fibrosiswereobserved obviously in group of M_6w and M_8w. Conclusions Determination of MR transverse relaxation can sensitively reflect the bone marrow composition and microstructure changes in the SANFH models. This technique may have potential applications in the early diagnosis and monitoring the disease progression of SANFH.