磁共振BOLD和T_(2)-mapping评价盘源性腰痛大鼠椎旁肌功能改变

Evaluation of functional changes of paraspinal muscles in rats with discogenic low back pain using MRBOLD and T_(2)-mapping sequences

目的:探讨磁共振血氧水平依赖(BOLD)和T_(2)-mapping成像技术评价盘源性腰痛大鼠椎旁肌功能改变的潜在价值。方法:在X线透视引导下使用26G针头经左侧后入路穿刺大鼠L_(4-5)和L_(5-6)椎间盘,向髓核内注射PBS溶液2.5μL,构建SD大鼠盘源性腰痛模型(18只);正常对照组大鼠(18只)不做特殊处理。于造模后1天、1周、2周、1个月分别对36只大鼠进行行为学评价,包括步态分析、热板实验、丙酮实验和悬尾实验。造模后1个月对36只大鼠进行3.0T MRI扫描,包括T_(2)-mapping和BOLD序列,测量L_(4-5)和L_(5-6)层面双侧椎旁肌(多裂肌、竖脊肌和腰大肌)的T_(2)和R_(2)^(*)值,取12个ROI的平均值。在造模后1个月的MRI扫描后随机处死腰痛组和正常组各6只大鼠,解剖获取实验鼠L_(4)~L_(6)水平双侧椎旁肌进行免疫荧光染色和Elisa实验,分别评价椎旁肌肌球蛋白重链和TNF-α的表达情况。剩余实验鼠在造模后3个月和6个月分别重复以上实验。结果:行为学评估结果显示,造模后6个月时腰痛组的步态评分高于正常组,且差异具有统计学意义(Z=-2.345,P=0.019);在造模后3和6个月时腰痛组的冷热刺激缩爪时间阈值显著降低、弯腰时间显著增加,与正常组之间的差异均具有统计学意义(P<0.05)。T_(2)-mapping和BOLD成像显示,与正常组相比,腰痛组造模后3和6个月时椎旁肌的T_(2)值显著减小,造模后6个月时R_(2)^(*)值显著增大,且组间差异均具有统计学意义(P<0.05)。免疫荧光染色结果显示,与正常组比较,腰痛组于造模后6个月时椎旁肌肌球重链蛋白1(MYH1)的表达水平增高(Z=-2.882,P=0.004),肌球重链蛋白7(MYH7)的表达水平减低(Z=-2.882,P=0.004)。ELISA实验结果显示,腰痛组椎旁肌的TNF-α表达水平于造模后1个月高于正常组,且差异具有统计学意义(t=-10.279,P<0.001)。结论:BOLD成像及T_(2)-mapping成像技术能够无创性定量评估盘源性腰痛大鼠椎旁肌微结构的变化。

Objective:To explore the potential value of blood oxygen level dependent(BOLD)and T_(2)-mapping magnetic resonance imaging in evaluating the functional changes of paraspinal muscles in rats with discogenic low back pain.Methods:Under the guidance of X-ray fluoroscopy,the discogenic low back pain model of SD rats(18 rats)was established by injecting 2.5μL PBS into the nuc-leus pulposus after puncture of L_(4-5) and L_(5-6) intervertebral discs with 26G needle through lateral posterior approach.18 rats in the normal control(NC)group were normally fed without special treatment.Behavioral evaluation was performed on 36 rats at the 1^(st) day,1 week,2 week,1 month after model establishment respectively,including gait analysis,hot plate test,acetone test and tail suspension test.At the 1 month after model establishment,36 rats were scanned with 3.0T MRI,including T_(2)-mapping and BOLD sequences.T_(2) and R_(2)^(*)values of bilateral paraspinal muscles(multifidus,erector spinae,psoas major muscle)at L_(4-5) and L_(5-6) slices were measured,and the average of 12 ROI was taken.At the 1 month after the model was made,6 rats in the low back pain group and 6 rats in the NC group were randomly euthanized after MRI scanning,and the bilateral paraspinal muscles at L_(4)~L_(6) levels of experimental rats were dissected,and the expression levels of heavy chain protein(MYH)and TNF-αin paraspinal muscles of the low back pain group and the NC group were evaluated by immunofluorescence and Elisa test respectively.The remaining experimental rats repeated the above experiments at 3 months and 6 months after modeling.Results:The behavioral results showed that the gait score in the low back pain group was higher than that in the NC group,at 6 months after modeling,and the diffe-rence was statistically significant(Z=-2.345,P=0.019).The time threshold of paw retraction under hot and cold stimulation decreased significantly from 3 to 6 months after operation(P<0.05),and the bending time was significantly higher than that in the NC group at 3 and 6 months after operation(all P<0.05).The results of T_(2)-mapping and BOLD showed that compared with the NC group,the T_(2) value in the low back pain group was significantly lower in 3 and 6 months after operation,and the R_(2)^(*)value was significantly higher in 6 months after operation(P<0.05).Immunostaining showed that compared with the NC group,the MYH1 expression level of paraspinal muscles increased(Z=-2.882,P=0.004)and the MYH7 expression level decreased in the low back pain group at 6 months after model establishment(Z=-2.882,P=0.004).The results of ELISA showed that the expression level of TNF-αof paraspinal muscles in low back pain group was higher than that of NC group at the one month after modeling,and the difference was statistically significant(t=-10.279,P<0.001).Conclusion:BOLD and T_(2)-mapping imaging can be used to quantitatively evaluate the microstructural changes of paraspinal muscles in rats with discogenic low back pain.