MR线性扫描扩散加权技术在猪股骨头骨骺缺血模型中的初步应用研究

MR line-scan diffusion imaging in ischemic epiphysis of femoral head： preliminary experimental study in piglets

目的采用MR线性扫描扩散加权成像（LSDWI）技术，观察乳猪股骨头骨骺缺血不同时期的DWI表现特征及变化过程，以期提供骨骺缺血性损害的时间及程度信息。方法25只1周龄大小的乳猪，手术结扎一侧股骨颈处全部供血动脉，引起股骨头骨骺缺血，另一侧作为健康对照侧。分别在术前（25只）及术后3h（25只）、72h（20只）、1周（15只）、3周（10只）、6周（5只）进行LSDWI，计算股骨头骨骺表观扩散系数（ADC）值，采用配对t检验比较缺血侧和对照侧ADC值的差异，观察不同时期ADC值的变化。各时间点LSDWI扫描完成后分别处死5只，行解剖学及组织学研究。结果术后3h，缺血性股骨头的ADC值[（1．22±0．37）×10^-3mm2／s]较正常对照侧[（1．73±0．33）×10^-3mm2／s]显著下降（t=3．914，P〈0．01），术后72hADC值[（2．15±0．32）×10^-3mm2／s]较正常对照侧[（1．70±0．22）×10^-3mm2／s]升高（t=3．348，P〈0．01），其后一直保持上升趋势至术后第6周[缺血侧为（1．61±0．27）×10^-3mm2，对照侧为（1．11±0．45）×10^-3mm2／s]（t=4．136，P〈0．01）。除术后第3周和第6周2个时间点ADC值的变化百分之间差异无统计学意义外（t=2．29，P〉0．05），在整个实验过程中，每2个连续时问点之间ADC值的变化百分差异均有统计学意义（P值均〈0．01）。组织学研究显示，在缺血性股骨头骨骺，首先是软骨细胞和骨细胞死亡，血管塌陷。随时间的变化，出现不同程度的缺血性股骨头骨骺软骨的异常增厚、二次骨化中心内出现软骨岛和局限性的生长板组织结构破坏。结论股骨头骨骺的LSDWI表现特征随缺血时间的延长而变化，通过LSDWI技术能获得股骨头骨骺的ADC值，其作为股骨头缺血和坏死的一个指标，可用于评估缺血性骨骺组织受损时间性信息及程度。

Objective To observe diffusion changes of epiphysis of femoral head with ischemia of difference phases by line-scan diffusion weighted imaging （ LSDWI）, and determine whether LSDWI can provide temporal information and severity about ischemia of epiphysis. Methods Ischemia was surgically induced in one hip of each piglet （ n = 25 ） and the other hip served as a normal control. Piglets were imaged before surgery and at 3 hours, 72 hours and 1, 3 and 6 weeks after surgery by using LSDWI. Apparent diffusion coefficients （ADC） in epiphysis of the femoral heads were calculated. Significant differences in ADC values between ischemia group and control group were found by using paired t-test. After scan at individual time points, 5 piglets were sacrificed for histological study each time. Results The ADC value in the ischemic femoral heads [ （ 1.22 ±0. 37）×10^-3mm2/s] decreased significantly at 3 hours after surgery （t =3.914, P 〈 0. 01 ）, compared to that in control[ （1.73 ± 0. 33 ） ×10^-3mm2/s] , and increased at 72 hours [ （2. 15 ± 0. 32 ） ×10^-3mm2/s versus （1.70± 0. 22） ×10^-3mm2/s ] （t = 3. 348, P 〈 0. 01 ）. Then ADC value kept increasing until 6 weeks after surgery [ （ 1.61 ± 0. 27 ）×10^-3mm2/s in isehemia side vs （ 1.11 ±0. 45） ×10^-3mm2/s/s in the control] （t =4. 136, P 〈0. 01 ）. The percentage change of the ADC value significantly increased at 3 hours,72 hours, 1 and 3 week（s） after the surgery （P 〈0. 01 ） , compared to that at the prior neighboring time point. No significant increase in the percentage change of ADC value was found between the 3rd week and the 6th week after the surgery （ t = 2.29, P 〉 0. 05 ） . Histological examinations revealed abnormal thickening within epiphyseal cartilage, and cartilaginous islands within ossified tissues. Growth disturbance was found in form of focal growth plate disruption. Conclusions Dynamic changes of ADC values were found with the prolonged ischemia of the femoral head by ISDWI. It could serve as a useful marker for evaluating duration and extent of ischemic epiphyseal disruption.