股骨头缺血性坏死磁共振成像双线征表现与化学位移伪影的相关性

摘要

Objective To explore the correlation between "double-line sign" and chemical shift artifact in magnetic resonance imaging (MRI) of femoral head avascular necrosis (AVN).Methods Forty patients with unilateral femoral head AVN confirmed by clinical symptoms and imaging examination in Department of Orthopedics of the Central Hospital of Enshi Autonomous Prefecture,Hubei Province from January to December 2015 were enrolled.All patients had 1.5T and 3.0T MRI of hip joint with different frequency encoding directions.The occurrence of chemical shift artifact was observed among different magnetic field intensities and different frequencyencoding directions.The correlation between " double-line sign" and chemical shift artifact was analyzed.Results Detection rates of chemical shift artifact in T1,T2 weighted imaging in 3.0T MRI were significantly higher than those in 1.5T MRI[82.5％ (33/40) vs 62.5％ (25/40),87.5％ (35/40) vs 67.5％ (27/40)] (P ＜ 0.05).The detection rate of chemical shift artifact in different magnetic field intensities decreased after changing frequency-encoding direction;there was no significant difference between 3.0T MRI and 1.5T MRI(P ＞ 0.05).After changing frequency-encoding direction,20 cases(50.0％) of "double-line sign" were detected in fast spin echo T2 weighted imaging.There was still "double-line sign" [85.0％ (34/40)] in short time inversion recovery imaging.Conclusions Chemical shift artifact is significant in high magnetic field intensity.Change of frequencyencoding direction and short time reversal recovery sequence may prevent occurrence of chemical shift artifact.The "double-line sign" in MRI of femoral head AVN is not associated with chemical shift artifact.%目的 探讨股骨头缺血性坏死(AVN)磁共振成像(MRI)“双线征”表现与化学位移伪影的相关性.方法 选取2015年1-12月于湖北省恩施州中心医院骨科关节外科就诊的单侧AVN患者40例,均经临床症状及影像学检查确诊,术前接受1.5T和3.0T MRI不同序列检查,改变相位后再次进行检测.比较不同磁场强度和改变相位前后化学位移伪影出现情况,分析AVN影像学“双线征”表现与化学位移伪影之间的相关性.结果 3.0T MRI的T1加权成像、T2加权成像中化学位移伪影检出率明显高于1.5T MRI[82.5％ (33/40)比62.5％ (25/40)、87.5％ (35/40)比67.5％ (27/40)],差异均有统计学意义(均P＜0.05).改变相位后,不同磁场强度图像中化学位移伪影检出率均下降,且不同磁场强度间差异无统计学意义(P＞0.05).改变相位后,快速自旋回波序列T2加权成像检出“双线征”20例(50.0％).短时间反转恢复序列图像中“双线征”仍然存在,检出率为85.0％ (34/40).结论 磁场强度越高的磁共振仪器产生化学位移伪影越明显,改变相位和短时间反转恢复序列可以抑制化学位移伪影出现,AVN产生的影像学“双线征”表现与化学位移伪影无关.