磁共振弥散张量成像联合纤维束成像在脑梗死中的应用研究

目的 分析脑梗死患者磁共振弥散张量成像(DTI)和纤维束成像(DTT)的特点,探讨DTI、DTT在对不同时期脑梗死患者诊断的价值。方法分别对58例不同时期脑梗死患者和25名健康志愿者行MRI检查,包括T1WI、T2WI成像、FLAIR及DTI成像,重建部分各向异性(FA)图,对梗死区、健侧相应部位及正常对照组相应部位进...     

应用DTI技术对人脑白质纤维束的初步研究

目的建立扩散张量纤维束成像对人脑白质纤维的显示方法,并应用中国数字化可视人体数据进行对照观察,验证扩散张量成像(DTI)方法的可靠性。方法选择5名健康志愿者进行DTI成像,采用DtiStudio软件进行分析处理,重建出部分各向异性(FA)图、容积比(VR)图、相对各向异性(RA)图、表面扩散系数(ADC)图以及二维彩色张量图。应用中国数字化可视人体数据集断面图像、FA图及彩色FA图进行对照观察,利用fibertracking纤维跟踪软件及3DMRI软件进行三维重建显示脑内主要白质纤维束,辨认脑内白质纤维束的位置、形态。结果应用DTI纤维束成像可以清晰准确地描绘脑白质内主要神经纤维束的解剖图谱,包括联络纤维如弓形纤维、钩束、扣带束、上纵束和下纵束,连合纤维如胼胝体、前连合和穹隆,投射纤维如锥体束、视放射、内侧丘系等。DTI纤维束成像结果与已知解剖知识、中国可视化人体断面图像具有很好的一致性。结论应用DTI纤维束成像可以清晰准确地描绘脑白质内主要神经纤维束的解剖图谱,其结果与中国可视化人体断面图像、已知解剖知识是一致的,应用DTI纤维束成像研究脑内纤维连通性是可靠的。     

磁共振弥散张量成像的脑白质纤维优化重建

磁共振弥散张量成像(DTI)可对大脑白质纤维束的三维几何结构进行无创研究,其主要方法为DTI纤维追踪成像.研究打破现有DTI纤维追踪成像从初始种子区域逐步追踪增长的框架,提出脑白质的纤维优化重建方法,从全局角度描述追踪纤维,通过其对弥散倾向和几何结构的优化估计,重构最优纤维路径.结果表明,该方法可提供连接两个感兴趣区域(ROI)的有效和对称连接,同时通过全局优化手段消除累积噪声及局部随机噪声,提高长距离成像的可靠性;在人工合成数据集和真实人体数据集中均能较好成像,较之现有纤维追踪成像具有更高的可靠性和可重复性.     

MR弥散张量成像在脊柱脊髓疾病诊断中应用的研究进展

目的 探讨MR弥散张量成像(DTI)在脊髓疾病诊断中的应用进展。方法 在PubMed、Springer Link、中国知网数据库中,以“弥散张量成像、脊髓疾病、椎间盘”关键词,查阅2003年1月—2014年12月有关MR-DTI在脊髓疾病应用进展的相关文献,进行分析和总结。结果 MR-DTI体现脊髓病变早期组织空间组成和各组织成分之间水交换功能的改变,并能显示神经纤维束的走行方向,反映脊髓束功能的完整性。MR-DTI已逐渐应用于脊髓型颈椎病的早期诊断、脊髓损伤时期的判断和腰骶椎神经根病变的诊断以及腰椎间盘退变的早期诊断。DTI应用于脊髓疾病的诊断时,由于存在脊髓体积过小、扫描时间过长、运动伪影等不足,阻碍其在脊髓疾病诊断领域的发展。目前,随着并行成像技术、单次激发快速自旋回波序列等新技术的应用,这些问题正在逐步得到解决。结论DTI已在脊柱脊髓领域发挥出常规MR检查不可替代的作用。随着影像学的进步、新技术的应用及经验的丰富,DTI应用存在的阻碍必将得到解决,DTI在脊髓疾病领域的应用具有广阔的前景。     

扩散张量MR成像研究

本文一方面综述了8年来国际上扩散张量磁共振成像(DTI)的研究进展情况。包括总结了到目前为止所使用的4种提高DTI成像精度的方法，并指出精度的提高依赖于成像中脉冲序列的优化、实验方法的完善和后处理算法两个方面。文中比较了目前研究扩散张量的两种基本模型：扩散张量模型和q-空间模型。指出这两种模型侧重应用于不同的场合。前者侧重于研究器官或宏观组织中的扩散，而后者侧重于研究小到细胞尺度(μm量级)的扩散行为。两者在应用研究方面是互补的，所要求的实验条件是有差别的。另一方面结合文献对扩散张量模型的实验条件进行了理论分析。认为b因子取得过高并不合理。并用DTI实验数据和结果进行了初步验证。为了改进扩散张量模型本文探讨了考虑多指数衰减的设想。文中综述了DTI的导出量和一些实验结果，在此基础上分析了设计和优化各向异性指标(DAI)的原则。对于DTI的重要导出结果神经纤维柬成像(fiber tractography)重点分析了造成其成像精度不高的主要因素，指出了改进纤维束传导方向甄选算法和寻求纤维束方向场的几何性质是两种可能的解决办法。     

弥散张量成像对常规性临床应用的初步建立和实现

根据目前国际上被广泛认可的磁共振弥散张量成像(DT-MRI或DTI)处理和表达方法,自行开发出基于PC机的程序(DTI Toolbox based on MATLAB),有效结合第三方软件,为弥散张量成像在常规性临床诊断初步建立有效和完整的测量与分析处理体系,主要包括数据获取、图像预处理、张量可视化、以及脑神经纤维成像。为DTI进入常规性临床应用和检查提供了初步的方案和测量分析体系。     

基于DT-MRI的纤维跟踪及可视化研究

磁共振扩散张量成像(DT-MRI)是一种新的成像技术,比传统的扩散加权成像(DWI)能够更加准确地反映分子扩散的方向.在脑白质这样具有大量纤维束的组织中,水分子的扩散表现出显著的各向异性,从而有可能从张量信息的各向异性入手,跟踪得到白质纤维束的走行方向.本文介绍了DTI的原理、数据采集与处理方法,提出了一种可变步长的纤维跟踪方法,并以VC /ITK/VTK为开发工具实现了DTI分析和纤维跟踪与可视化.     

采用偏微分方程的磁共振弥散张量各向异性扩散滤波去噪

弥散张量磁共振成像(DTI)是无创研究大脑白质结构及其他人体纤维状组织结构的主要工具。由于合成DTI数据的弥散加权成像数据(DWI)易受噪声干扰,需要有效去噪以保证DTI数据精度和后续应用的实现。使用各向异性扩散滤波理论,综合考虑各方向通道DWI数据的几何形态和结构特点,重构其特征向量和特征值,获得统一平滑的结构张量,以期在有效去噪的基础上最大程度地保持DTI数据几何结构和特征。利用所提出方法在合成弥散张量数据上进行仿真,并在真实脑部DTI数据上进行实验。仿真和实验结果表明,该方法能有效减少噪声对DTI数据的影响,较之现有的时频分析去噪方法,可更准确地恢复DTI数据,减少主分量方向的偏差和部分各向异性值的误差。     

一种新的磁共振扩散成像实验参数控制方法

扩散敏感梯度磁度的方向及强度是磁共振扩散成像实验的重要参数，但这二个参数不能由用户通过设备自带的软件设定。本文介绍一种新的方法，通过修改MRI扫描机内部的数据文件，用户可以方便与精确地设定扩散加权成像DWI及扩散张景成像DTI的实验参数，而且可以为MRI扫描机增加新的功能。     

PM滤波方法对提高不同b值弥散张量成像图像质量的应用研究

目的在不同b值条件下,研究PM滤波方法对提高弥散张量成像（DTI）技术图像质量的作用。方法在b值为800～2800s／mm2的条件下分别对模体及志愿者实施DTI．利用改进的PM滤波方法对获得的弥散加权成像（DWI）图像进行处理后求解张量参数．得到反映水分子各向异性扩散程度的FA图。通过比较标准FA图与处理后FA图间的均方根误差（RMSE）．评价PM滤波的效果。结果随着b值的升高,图像信噪比逐渐降低．FA误差逐渐增大。当b值小于2000s／mm2时．经过PM滤波后．可得到RMSE较低的后处理图像。结论b值在1000．2000s／mm2范围内,应用PM滤波方法是提高人脑DTI图像质量的一种有效手段．     

A review of diffusion tensor magnetic resonance imaging computational methods and software tools

In this work we provide an up-to-date short review of computational magnetic resonance imaging (MRI) and software tools that are widely used to process and analyze diffusion-weighted MRI data. A review of different methods used to acquire, model and analyze diffusion-weighted imaging data (DWI) is first provided with focus on diffusion tensor imaging (DTI). The major preprocessing, processing and post-processing procedures applied to DTI data are discussed. A list of freely available software packages to analyze diffusion MRI data is also provided.     

基于扩散张量的脑白质内神经纤维束的可视化技术

介绍了在功能磁共振成像的研究中发展非常快的扩散张量成像技术的基本原理，以及如何利用扩散张量数据来重建脑白质内的神经纤维柬图像。其中主要介绍了白质束成像技术及其优缺点，并且分析了神经纤维束可视化技术的应用前景及其局限性。     

磁共振弥散张量成像几何畸变的三维校准

采用图像非刚体配准的方法校正磁共振弥散张量成像的几何畸变.在3D数据场中,采用仿射变换和B样条的变形配准方法来矫正几何畸变,配准的相似性测度采用互信息为准则.弥散张量成像特定组织间的磁女感性差异引起的几何畸变得到了一定纠正,所采用的方法对畸变有一定的抑制.采用3D配准的方法可以对弥文张量成像的几何畸变进行纠正,明显提高了图像质量.     

Contrast agent-free state-of-the-art magnetic resonance imaging on cerebral small vessel disease – Part 2: Diffusion tensor imaging and functional magnetic resonance imaging

Cerebral small vessel disease (cSVD) has been widely studied using conventional magnetic resonance imaging (MRI) methods, although the association between MRI findings and clinical features of cSVD is not always concordant. We assessed the additional contribution of contrast agent-free, state-of-the-art MRI techniques, particularly diffusion tensor imaging (DTI) and functional magnetic resonance imaging (fMRI), to understand brain damage and structural and functional connectivity impairment related to cSVD. We performed a review following the PICOS worksheet and Search Strategy, including 152 original papers in English, published from 2000 to 2022. For each MRI method, we extracted information about their contributions regarding the origins, pathology, markers, and clinical outcomes in cSVD. In general, DTI studies have shown that changes in mean, radial, and axial diffusivity measures are related to the presence of cSVD. In addition to the classical deficit in executive functions and processing speed, fMRI studies indicate connectivity dysfunctions in other domains, such as sensorimotor, memory, and attention. Neuroimaging metrics have been correlated with the diagnosis, prognosis, and rehabilitation of patients with cSVD. In short, the application of contrast agent-free, state-of-the-art MRI techniques has provided a complete picture of cSVD markers and tools to explore questions that have not yet been clarified about this clinical condition. Longitudinal studies are desirable to look for causal relationships between image biomarkers and clinical outcomes.     

High‐resolution diffusion tensor imaging in cervical spondylotic myelopathy: a preliminary follow‐up study

Diffusion imaging is a promising technique as it can provide microstructural tissue information and thus potentially show viable changes in spinal cord. However, the traditional single‐shot imaging method is limited as a result of various image artifacts. In order to improve measurement accuracy, we used a newly developed, multi‐shot, high‐resolution, diffusion tensor imaging (DTI) method to investigate diffusion metric changes and compare them with T₂‐weighted (T2W) images before and after decompressive surgery for cervical spondylotic myelopathy (CSM). T2W imaging, single‐shot DTI and multi‐shot DTI were employed to scan seven patients with CSM before and 3 months after decompressive surgery. High signal intensities were scored using the T2 W images. DTI metrics, including fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD) and mean diffusivity (MD), were quantified and compared pre‐ and post‐surgery. In addition, the relationship between imaging metrics and neurological assessments was examined. The reproducibility of multi‐shot DTI was also assessed in 10 healthy volunteers. Post‐surgery, the mean grade of cervical canal stenosis was reduced from grade 3 to normal after 3 months. Compared with single‐shot DTI, multi‐shot DTI provided better images with lower artifact levels, especially following surgery, as a result of reduced artifacts from metal implants. The new method also showed acceptable reproducibility. Both FA and RD values from the new acquisition showed significant differences post‐surgery (FA, p = 0.026; RD, p = 0.048). These changes were consistent with neurological assessments. In contrast, T2W images did not show significant changes before and after surgery. Multi‐shot diffusion imaging showed improved image quality over single‐shot DWI, and presented superior performance in diagnosis and recovery monitoring for patients with CSM compared with T2W imaging. DTI metrics can reflect the pathological conditions of spondylotic spinal cord quantitatively and may serve as a sensitive biomarker for potential CSM management.     

Shape-Adaptive DCT for Denoising of 3D Scalar and Tensor Valued Images

During the last ten years or so, diffusion tensor imaging has been used in both research and clinical medical applications. To construct the diffusion tensor images, a large set of direction sensitive magnetic resonance image (MRI) acquisitions are required. These acquisitions in general have a lower signal-to-noise ratio than conventional MRI acquisitions. In this paper, we discuss computationally effective algorithms for noise removal for diffusion tensor magnetic resonance imaging (DTI) using the framework of 3-dimensional shape-adaptive discrete cosine transform. We use local polynomial approximations for the selection of homogeneous regions in the DTI data. These regions are transformed to the frequency domain by a modified discrete cosine transform. In the frequency domain, the noise is removed by thresholding. We perform numerical experiments on 3D synthetical MRI and DTI data and real 3D DTI brain data from a healthy volunteer. The experiments indicate good performance compared to current state-of-the-art methods. The proposed method is well suited for parallelization and could thus dramatically improve the computation speed of denoising schemes for large scale 3D MRI and DTI.     

Correlations between MRS and DTI in cerebral small vessel disease

Cerebral small vessel disease results in lacunar infarcts and cognitive impairment. Diffusion tensor imaging (DTI) demonstrates a reduction in fractional anisotropy and increase in mean diffusivity, which correlates more strongly with cognition than conventional MRI. The underlying pathological basis for these DTI changes is not known. In this study magnetic resonance spectroscopy was used to determine the biochemical basis of these DTI alterations. Twenty-five patients with lacunar stroke and radiological leukoaraiosis were recruited. Chemical shift imaging (CSI) and DTI were performed on a 1.5 T MRI scanner. A region of interest was positioned in the white matter of the centrum semiovale. Multivoxel CSI data were processed and the metabolite ratios estimated. DTI parameters corresponding to the exact region of tissue excited by CSI were obtained. Mean spectroscopy data and DTI values for each subject were correlated. Univariate analysis revealed a positive correlation between N-acetyl aspartate-creatine (NAA/Cr) and fractional anisotropy (r = 0.52, p = 0.008), and a negative correlation with mean diffusivity (r = -0.51, p = 0.009). Results remained little changed after controlling for mean percentage lesion and mean percentage white matter per voxel (with fractional anisotropy r = 0.54, p = 0.008, and with mean diffusivity r = -0.52, p = 0.01). These findings are consistent with axonal loss or dysfunction, or both, accounting for at least part of the DTI abnormalities found in patients with small vessel disease. It provides evidence that DTI identifies axonal disruption in white matter tracts.