Real-time measurement and correction of both B0 changes and subject motion in diffusion tensor imaging using a double volumetric navigated (DvNav) sequence.
Real-time measurement and correction of both B0 changes and subject motion in diffusion tensor imaging using a double volumetric navigated (DvNav) sequence.
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DOI：
10.1016/j.neuroimage.2015.11.022
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发表时间：
2016-02-01
期刊：
影响因子：
5.7
通讯作者：
Meintjes EM
中科院分区：
文献类型：
--
作者：
Alhamud A;Taylor PA;van der Kouwe AJ;Meintjes EM
扩散张量成像（DTI）需要一组扩散加权测量来获取足够的信息来表征局部结构。MRI扫描仪在DTI扫描开始前通过获取场图自动执行游动过程。由于多种因素（包括铁片线圈加热或主体运动），B0的变化可能在整个DTI采集过程中发生，导致显著的信号失真，导致扩散张量（DT）参数估计扭曲。在这项工作中，我们介绍了一种新的技术，可以同时测量，报告和纠正实时被摄体运动和B0场均匀性的变化，无论是在成像平面内还是通过成像平面。这是通过双体积导航仪（DvNav）实现的，即一对3D EPI采集，与DTI脉冲序列交错。B0场的变化是根据零阶（频率）和一阶（线性梯度）来评估的。DvNav准确估计垫片参数的能力首次在水模体中得到验证。使用标准、运动校正（单导航器，vNav）和DvNav DTI序列对两名健康受试者进行运动和无运动扫描。在一名幻影和两名健康受试者中，还评估了所提出的3D EPI场图与MRI扫描仪的标准3D梯度回波场图之间的性能差异。DvNav序列被证明可以精确测量和纠正手动调整扫描仪中心频率和线性垫片梯度后B0的变化。与其他方法相比，DvNav产生的DTI结果与解剖参考具有更大的空间重叠，特别是在扫描对象运动时。这主要是由于DvNav系统能够纠正每次体积采集之间的垫片变化和主体运动，从而减少剪切变形。
Diffusion tensor imaging (DTI) requires a set of diffusion weighted measurements in order to acquire enough information to characterize local structure. The MRI scanner automatically performs a shimming process by acquiring a field map before the start of a DTI scan. Changes in B0, which can occur throughout the DTI acquisition due to several factors (including heating of the iron shim coils or subject motion), cause significant signal distortions that result in warped diffusion tensor (DT) parameter estimates. In this work we introduce a novel technique to simultaneously measure, report and correct in real time subject motion and changes in B0 field homogeneity, both in and through the imaging plane. This is achieved using double volumetric navigators (DvNav), i.e. a pair of 3D EPI acquisitions, interleaved with the DTI pulse sequence. Changes in the B0 field are evaluated in terms of zero-order (frequency) and first-order (linear gradients) shim. The ability of the DvNav to accurately estimate the shim parameters was first validated in a water phantom. Two healthy subjects were scanned both in the presence and absence of motion using standard, motion corrected (single navigator, vNav), and DvNav DTI sequences. The difference in performance between the proposed 3D EPI field maps and the standard 3D gradient echo field maps of the MRI scanner was also evaluated in a phantom and two healthy subjects. The DvNav sequence was shown to accurately measure and correct changes in B0 following manual adjustments of the scanner’s central frequency and the linear shim gradients. Compared to other methods, the DvNav produced DTI results that showed greater spatial overlap with anatomical references, particularly in scans with subject motion. This is largely due to the ability of the DvNav system to correct shim changes and subject motion between each volume acquisition, thus reducing shear distortion.