磁共振定量磁化率图方法和应用研究

The MR quantitative susceptibility mappings (QSM) is an effective and robust way to extract valuable tissue susceptibility information from MRI phase data that has been typically discarded. The QSM would represent an important advancement in MRI technology and have a wide range of applications. In particular, QSM is believed to be a promising technique to identify biomarkers of strong magnetic susceptibility, such as deoxyhemoglobin or iron deposits, as well as to track deposits of iron oxide nanoparticles, to quantify exogenous contrast agents, or to identify calcium deposits.. Currently, there still exist some critical methodological and apppplication issues that need to be addressed. The sequences for QSM require a long echo time in combination with a long scanning time for high resolution and are therefore prone to image artifacts caused by physiological fluctuations, patient motion or system instabilities. QSM reconstruction is numerically complex, including multiple steps, such as phase unwrapping, identification of reliable phase information, background field removal, and application of the inversion. Incorrect phase values due to low signal-to-noise ratios, blood flow, and/or incomplete phase unwrapping produce severe non-local artifacts in susceptibility images. Background field removal may still be problematic near the boundary, as it may be very difficult to differentiate outside from inside sources. For applications, only a limited number of in vivo susceptibility maps have been presented. . In this study, the utility of real-time optical prospective motion correction in combination with naviagtor echo retrospective phase correction will be investigated for quantitative susceptibility mappings in the human brain. We propose to further develop the projection onto dipole field method that was demonstrated to be very promising in our preliminary study. We will also Investigate the values of iron accumulation in the deep gray matter of 240 healthy volunteers of different ages using QSM and establish a baseline of iron deposition from normal volunteers.

磁共振定量磁化率图是近年来磁共振成像技术方面一个新的重要进展，其利用一般成像技术舍弃的相位信息得到局部磁场变化特性，并通过复杂的场到源的反演计算，得到直接并定量的磁化率图。磁共振定量磁化率图得到的磁化率分布与成像参数无关，也不依赖于组织磁化率源与体素间的几何关系，其在科学和临床研究方面具有巨大的应用前景。但是磁共振定量磁化率图重建非常复杂，仍有一些关键的技术问题需要解决，如相位折叠、背景场、运动伪影等，相关应用研究也才刚刚起步。本课题将通过开发整合有有效运动校正功能的磁共振数据采集方法和新的更优重建算法，得到更为可靠、准确的颅脑高分辨定量磁化率分布图。本课题还将利用优化的磁共振定量磁化率图像方法建立正常国人各年龄段脑内定量磁化率的分布，为神经退行性病变等疾病的脑内铁沉积研究提供必要的参考指标。

磁共振定量磁化率图是近年来磁共振成像技术方面一个新的重要进展，其在科学和临床研究方面具有巨大的应用前景，但是仍有一些关键的技术和应用问题尚待解决。 . 本课题主要包括四方面的研究内容：有效减少运动伪影的三维高分辨多回波梯度回波成像方法研究、多回波梯度回波相位可靠性和图像后处理分析方法研究、磁共振定量磁化率技术研究正常国人脑内铁含量、磁共振定量磁化率在神经退行性病变和肝脏铁沉积定量测量等方面的研究等。. 方法学研究的主要结果如下：（1）采用导航回波技术能获取呼吸运动导致的局部磁场波动，因此可用以矫正梯度回波图像回波中随时间变化的相位波动，提高梯度回波成像的图像质量；（2）采用伪随机的方式进行数据采集，结合导航回波技术，并采用压缩感知技术对未受运动影响的数据进行图像重建，可减少运动伪影对图像的干扰；（3）流动补偿序列可以消除血液流动引起的QSM的错误，提高QSM的准确性；（4）采用相位校正的双极读梯度模式得到的主要深部核团的定量磁化率值与单极读梯度模式的结果一致，而双极读梯度模式的定量磁化率图的噪声得到显著下降；（5）同传统的Levenberg-Marquardt计算T2*方法相比，课题组提出的ARLO方法得到的T2*结果与传统的的方法高度一致，但是速度能提高两百倍以上；（6）与传统的加权最小二乘法相比，截断加权最小二乘法可有效提高颅底部位定量磁化率图的图像质量，使其噪声明显下降。. 应用研究的主要结果有：（1）大脑深部核团定量磁化率值与年龄显著相关；（2）帕金森病例组的黑质磁化率值明显高于健康对照组，但R2*值未发现显著差异；因此，QSM能够更加敏感、准确地检测出PD患者黑质的变化，在临床诊断中更具优势。. 本课题通过开发整合有有效运动校正功能的磁共振数据采集方法和新的更优重建算法，得到更为可靠、准确的颅脑高分辨定量磁化率分布图;本课题建立正常国人各年龄段脑内定量磁化率的分布和变化，为神经退行性疾病等病变的脑内铁沉积研究提供必要的参考指标。