脑铁沉积的MR定量分析方法:定量磁化率成像与横向弛豫率成像比较

摘要

Objective To evaluate the accuracy and sensitivity of quantitative susceptibility mapping (QSM) and transverse relaxation rate (R2*) mapping in the measurement of brain iron deposition. Methods Super paramagnetic iron oxide (SPIO) phantoms and mouse models of Parkinson's disease(PD)related to iron deposition in the substantia nigra(SN)underwent 7.0 T magnetic resonance (MR) scans (Bruker, 70/16) with a multi-echo 3D gradient echo sequence, and the acquired data were processed to obtain QSM and R2*.Linear regression analysis was performed for susceptibility and R2*in the SPIO phantoms containing 5 SPIO concentrations(30,15,7.5,3.75 and 1.875 μg/mL)to evaluate the accuracy of QSM and R2*in quantitative iron analysis.The sensitivities of QSM and R2*mapping in quantitative detection of brain iron deposition were assessed using mouse models of PD induced by 1-methyl-4-phenyl-1,2,3,6-tetrahy-dropyridine(MPTP)in comparison with the control mice. Results In SPIO phantoms,QSM provided a higher accuracy than R2*mapping and their goodness-of-fit coefficients(R2)were 0.98 and 0.89,respectively.In the mouse models of PD and control mice,the susceptibility of the SN was significantly higher in the PD models(5.19 ± 1.58 vs 2.98 ± 0.88,n=5;P<0.05),while the R2*values were similar between the two groups(20.22 ± 0.94 vs 19.74±1.75;P=0.60).Conclusion QSM allows more accurate and sensitive detection of brain iron deposition than R2*,and the susceptibility derived by QSM can be a potentially useful biomarker for studying PD.%目的 比较磁共振铁沉积测量方法——定量磁化率成像(QSM)与横向弛豫率成像(R2*mapping)的准确性与敏感度.方法 5个浓度(30、15、7.5、3.75、1.875 μg/Ml)的超顺磁性氧化铁(SPIO)体模,与铁沉积相关的MPTP(1-methyl-4-phenyl-1,2,3,6-tetrahy-dropyridine)帕金森疾病(PD)小鼠动物模型,均在7.0T布鲁克小动物磁共振下,采用多回波3D梯度回波序列扫描,获得的数据经过后处理得到QSM和R2*.通过SPIO浓度分别与相应浓度下的QSM和R2*均值作线性回归分析,通过拟合优度系数R2值来评估QSM与R2*方法在铁定量分析上的准确性.另外,用QSM与R2*检测MPTP小鼠模型中黑质区域的微量铁沉积变化,通过独立样本t检验比较实验组与对照组的磁化率值、R2*值是否有显著性差异,P<0.05表示差异有统计学意义.结果 SPIO体模实验中,磁化率值与SPIO浓度线性回归的R2约为0.98,而R2*值与SPIO浓度线性回归的R2约为0.89.在检测MPTP小鼠模型黑质区域微量铁沉积变化的实验中,模型组的磁化率为5.19±1.58(均值±标准差,n=5),而对照组为2.98±0.88(n=5),两者存在显著性差异(P=0.026),而测量出来的R2*值分别为20.22±0.94,19.74±1.75,没有显著性差异(P=0.60).结论 体模实验表明了QSM在定量SPIO浓度上比R2*更准确.MPTP小鼠模型的实验表明了QSM比R2*在量化微量铁沉积方面敏感度更高.本文首次提出将QSM技术应用于研究MPTP小鼠模型的脑铁沉积,而实验结果表明QSM定量的磁化率值是有潜力成为研究帕金森病非常有潜力的生物学标记.