Performing Real-Time Interactive Fiber Tracking

Fiber tracking is a technique that, based on a diffusion tensor magnetic resonance imaging dataset, locates the fiber bundles in the human brain. Because it is a computationally expensive process, the interactivity of current fiber tracking tools is limited. We propose a new approach, which we termed real-time interactive fiber tracking, which aims at providing a rich and intuitive environment for the neuroradiologist. In this approach, fiber tracking is executed automatically every time the user acts upon the application. Particularly, when the volume of interest from which fiber trajectories are calculated is moved on the screen, fiber tracking is executed, even while it is being moved. We present our fiber tracking tool, which implements the real-time fiber tracking concept by using the video card’s graphics processing units to execute the fiber tracking algorithm. Results show that real-time interactive fiber tracking is feasible on computers equipped with common, low-cost video cards.     

三维脑白质纤维束示踪成像

目的使用磁共振弥散张量成像数据三维示踪大脑白质纤维束。方法对18名健康自愿者使用弥散加权-回波平面成像(DW-EPI)序列进行头部DTI检查。输出DICOM格式的DTI图像数据并根据已知的脑白质纤维束的解剖学知识,选取起始区、目标区、回避区,使用Diffusion Tensor VisualizerⅡ软件进行脑白质纤维束示踪三维重建。结果大脑的连合系、联络系和投射系的各种脑白质纤维束的结构和其在三维空间的走行可在每例实验对象的三维示踪结果显示,与解剖学所描述相对比基本一致。结论使用三维脑白质纤维束示踪成像可以在活体立体直观地显示大脑的各种脑白质纤维束。不仅可以用于解剖学教学,还对临床神经系统疾病的辅助诊断和科学研究有潜在的应用价值。     

A multiple streamline approach to high angular resolution diffusion tractography

Diffusion-weighted magnetic resonance imaging has the ability to map neuronal architecture by estimating the 3D diffusion displacement within fibrous brain structures. This approach has non-invasively been demonstrated in the human brain with diffusion tensor tractography. Despite its valuable application in neuroscience and clinical studies however, it faces an inherent limit in mapping fiber tracts through areas with intervoxel incoherence. Recent advances in high angular resolution diffusion imaging have surpassed this limit and have the ability to resolve the complex fiber intercrossing within each MR voxel. To connect the fiber tracts from a multi-fiber system, this study proposed a modified fiber assignment using the continuous tracking (MFACT) algorithm and a tracking browser to propagate tracts along complex diffusion profiles. The Q-ball imaging method was adopted to acquire the diffusion displacements. Human motor pathways with seed points from the internal capsule, motor cortex, and pons were studied respectively. The results were consistent with known anatomy and demonstrated the promising potential of the MFACT method in mapping the complex neuronal architecture in the human brain.     

Fast low‐angle shot diffusion tensor imaging with stimulated echo encoding in the muscle of rabbit shank

In the past, spin‐echo (SE) echo planar imaging(EPI)‐based diffusion tensor imaging (DTI) has been widely used to study the fiber structure of skeletal muscles in vivo. However, this sequence has several shortcomings when measuring restricted diffusion in small animals, such as its sensitivity to susceptibility‐related distortions and a relatively short applicable diffusion time. To address these limitations, in the current work, a stimulated echo acquisition mode (STEAM) MRI technique, in combination with fast low‐angle shot (FLASH) readout (turbo‐STEAM MRI), was implemented and adjusted for DTI in skeletal muscles. Signal preparation using stimulated echoes enables longer effective diffusion times, and thus the detection of restricted diffusion within muscular tissue with intracellular distances up to 100 µm. Furthermore, it has a reduced penalty for fast T₂ muscle signal decay, but at the expense of 50% signal loss compared with a SE preparation. Turbo‐STEAM MRI facilitates high‐resolution DTI of skeletal muscle without introducing susceptibility‐related distortions. To demonstrate its applicability, we carried out rabbit in vivo measurements on a human whole‐body 3 T scanner. DTI parameters of the shank muscles were extracted, including the apparent diffusion coefficient, fractional anisotropy, eigenvalues and eigenvectors. Eigenvectors were used to calculate maps of structural parameters, such as the planar index and the polar coordinates θ and ? of the largest eigenvector. These parameters were compared between three muscles. θ and ? showed clear differences between the three muscles, reflecting different pennation angles of the underlying fiber structures. Fiber tractography was performed to visualize and analyze the architecture of skeletal pennate muscles. Optimization of tracking parameters and utilization of T₂‐weighted images for improved muscle boundary detection enabled the determination of additional parameters, such as the mean fiber length. The presented results support the applicability of turbo‐STEAM MRI as a promising method for quantitative DTI analysis and fiber tractography in skeletal muscles. Copyright © 2013 John Wiley & Sons, Ltd.     

We Built This House; It’s Time to Move in: Leveraging Existing DICOM Structure to More Completely Utilize Readily Available Detailed Contrast Administration Information

The Digital Imaging and Communications in Medicine (DICOM) standard is the universal format for interoperability in medical imaging. In addition to imaging data, DICOM has evolved to support a wide range of imaging metadata including contrast administration data that is readily available from many modern contrast injectors. Contrast agent, route of administration, start and stop time, volume, flow rate, and duration can be recorded using DICOM attributes [1]. While this information is sparsely and inconsistently recorded in routine clinical practice, it could potentially be of significant diagnostic value. This work will describe parameters recorded by automatic contrast injectors, summarize the DICOM mechanisms available for tracking contrast injection data, and discuss the role of such data in clinical radiology.     

Repeatability of DTI‐based skeletal muscle fiber tracking

Diffusion tensor imaging (DTI)‐based muscle fiber tracking enables the measurement of muscle architectural parameters, such as pennation angle (θ) and fiber tract length (L_ft), throughout the entire muscle. Little is known, however, about the repeatability of either the muscle architectural measures or the underlying diffusion measures. Therefore, the goal of this study was to investigate the repeatability of DTI fiber tracking‐based measurements and θ and L_ft. Four DTI acquisitions were performed on two days that allowed for between acquisition, within day, and between day analyses. The eigenvalues and fractional anisotropy were calculated at the maximum cross‐sectional area of, and fiber tracking was performed in, the tibialis anterior muscle of nine healthy subjects. The between acquisitions condition had the highest repeatability for the DTI indices and the architectural parameters. The overall inter class correlation coefficients (ICC's) were greater than 0.6 for both θ and L_ft and the repeatability coefficients were θ < 10.2° and L_ft < 50 mm. In conclusion, under the experimental and data analysis conditions used, the repeatability of the diffusion measures is very good and repeatability of the architectural measurements is acceptable. Therefore, this study demonstrates the feasibility for longitudinal studies of alterations in muscle architecture using DTI‐based fiber tracking, under similar noise conditions and with similar diffusion characteristics. Copyright © 2010 John Wiley & Sons, Ltd.     

Estimation of white matter connectivity based on a three-dimensional directional diffusion function in diffusion tensor MRI

Diffusion tensor (DT) magnetic resonance imaging (MRI) provides the directional information of local neuronal fibers, and has been used to estimate the neuroanatomical connectivity in the cerebral white matter. Several methods for white matter tractography have been developed based on DT-MRI. However, it has been difficult to estimate the white matter tract pathways in the fiber crossing and branching region because of the ambiguity of the principal eigenvector and/or low anisotropy due to the partial volume effect. In this paper, we proposed a new method for white matter tractography, which permits fiber tract branching and passing through crossing regions. Our tractography method is based on a three-dimensional (3D) directional diffusion function (DDF), which was given by a 3D anisotropic Gaussian function defined by normalized three eigenvalues and their corresponding eigenvectors of DT. The DDF was used for generation of a 3D directional diffusion field and for determination of the connectivity between the voxels in fiber tracking. To extract the white matter tract region, DDF-based tractography (DDFT) method used the directional diffusion field instead of a threshold fractional anisotropy map, which has been used in the conventional methods, so that low anisotropy voxels in the branching and crossing regions may be included. We applied the DDFT method and two conventional tractography methods (a streamline technique and a tensorline algorithm) to DT-MRI data of five normal subjects for visualizing the pyramidal tract. Our method visualized the pathways connected to a large portion of the primary motor cortex, including foot, hand and face motor areas, passing through the crossing regions with other white matter tracts in all subjects, whereas the conventional methods showed only a small portion of the pyramidal tract. The pyramidal tract pathways estimated by our method were consistent with the neuroanatomical knowledge. In conclusion, the DDFT method may be useful in assisting neuroradiologists in estimating the white matter tracts.     

Quantitative fiber tracking of lateral and interhemispheric white matter systems in normal aging: relations to timed performance

The integrity of white matter, as measured in vivo with diffusion tensor imaging (DTI), is disrupted in normal aging. A current consensus is that in adults advancing age affects anterior brain regions disproportionately more than posterior regions; however, the mainstay of studies supporting this anterior-posterior gradient is based primarily on measures of the corpus callosum. Using our quantitative fiber tracking approach, we assessed fiber tract integrity of samples of major white matter cortical, subcortical, interhemispheric, and cerebellar systems (11 bilateral and 2 callosal) on DTI data collected at 1.5T magnet strength. Participants were 55 men (age 20-78 years) and 65 women (age 28-81 years), deemed healthy and cognitively intact following interview and behavioral testing. Fiber integrity was measured as orientational diffusion coherence (fractional anisotropy, FA) and magnitude of diffusion, which was quantified separately for longitudinal diffusivity (lambdaL), an index of axonal length or number, and transverse diffusivity (lambdaT), an index of myelin integrity. Aging effects were more evident in diffusivity than FA measures. Men and women, examined separately, showed similar age-related increases in longitudinal and transverse diffusivity in fibers of the internal and external capsules bilaterally and the fornix. FA was lower and diffusivity higher in anterior than posterior fibers of regional paired comparisons (genu versus splenium and frontal versus occipital forceps). Diffusivity with older age was generally greater or FA lower in the superior than inferior fiber systems (longitudinal fasciculi, cingulate bundles), with little to no evidence for age-related degradation in pontine or cerebellar systems. The most striking sex difference emerged for the corpus callosum, for which men showed significant decline in FA and increase in longitudinal and transverse diffusivity in the genu but not splenium. By contrast, in women the age effect was present in both callosal regions, albeit modestly more so in the genu than splenium. Functional meaningfulness of these age-related differences was supported by significant correlations between DTI signs of white matter degradation and poorer performance on cognitive or motor tests. This survey of multiple fiber systems throughout the brain revealed a differential pattern of age's effect on regional FA and diffusivity and suggests mechanisms of functional degradation, attributed at least in part to compromised fiber microstructure affecting myelin and axonal morphology.     

DICOM介质存储的实现技术

实用利用可移动的存储介质进行DICOM医学图像的数据存储与交换。方法提出DICOM介质存储的三层模型,基于五种基本操作和根据实际临床需要设计的两种操作,将介质存储方案分为两个模块即数据导入和数据导出。结果根据本文实现的应用软件可以实现符合DICOM标准的介质存储,并适当扩充了功能,较好地满足了医疗图像的数据存储与交换的要求。结论在实现标准的过程中,可以找到一种不同的方式,使得软件更适合临床环境,可以根据实际需要在符合标准的基础上进行功能扩充。     

医学图像DICOM格式转换软件的设计与实现

PACS（图像存档与通讯系统）应遵循DICOM（医学数字图像通讯）标准。目前国内存在大量不符合DICOM标准的影像设备,为了使这些设备也应用于PACS,我们使用面向对象方法设计和实现了一个具有良好扩充性的格式转换工具包,可进行DICOM格式与各种通用图像格式之间的转换,并具有视频输入与格式转换工具包,可进行DICOM格式与各种通用图像格式之间的转换,并具有视频输入与扫描仪输入的接口。该工具包提供一组DICOM API,可供Windows平台的各种编程环境使用。     

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。     

In vivo visualization of the levator ani muscle subdivisions using MR fiber tractography with diffusion tensor imaging

Understanding the levator ani complex architecture is of major clinical relevance. The aim of this study was to determine the feasibility of magnetic resonance (MR) fiber tractography with diffusion tensor imaging (DTI) as a tool for the three-dimensional (3D) representation of normal subdivisions of the levator ani. Ten young nulliparous female volunteers underwent DTI at 1.5 T MR imaging. Diffusion-weighted axial sequence of the pelvic floor was performed with additional T2-weighted multiplanar sequences for anatomical reference. Fiber tractography for visualization of each Terminologia Anatomica-listed major levator ani subdivision was performed. Numeric muscular fibers extracted after tractography were judged as accurate when localized within the boundaries of the muscle, and inaccurate when projecting out of the boundaries of the muscle. From the fiber tracking of each subdivision the number of numeric fibers (inaccurate and accurate) and a score (from 3 to 0) of the adequacy of the 3D representation were calculated. All but two volunteers completed the protocol. The mean number of accurate fibers was 17 ± 2 for the pubovisceralis, 14 ± 6 for the puborectalis and 1 ± 1 for the iliococcygeus. The quality of the 3D representation was judged as good (score = 2) for the pubovisceralis and puborectalis, and inaccurate (score = 0) for the iliococcygeus. Our study is the first step to a 3D visualization of the three major levator ani subdivisions, which could help to better understand their in vivo functional anatomy.     

基于扩散形状的DTI纤维跟踪算法研究

到目前为止，研究者们已经提出了许多种神经纤维束的三维可视化技术，其中，基于扩散跟踪的白质束成像技术在白质纤维束的可视化和分析中使用得最多。本文针对现有纤维跟踪算法存在的问题，提出了基于扩散形状的纤维跟踪算法，该算法结合了流线跟踪（streamline tracking，STT）法与张量弯曲（tensor deflection，TEND）法的优点，对不同的扩散形状采用不同的跟踪方向，尤其在平面扩散的情况提出了更接近纤维走行的跟踪方法，减少了跟踪方向与实际纤维走行的误差，能更完整、更准确地显示大脑白质的纤维走行。     

融合白质fMRI的dMRI纤维追踪重建研究

基于弥散磁共振成像(dMRI)的纤维束重建,是分析大脑白质结构的主要工具。现有的纤维追踪成像算法受dMRI分辨率及成像机理约束,在构建大脑白质灰质边界区域的纤维时成像性能和准确性大大下降。为克服该缺陷,提出一种结合功能磁共振成像(fMRI)的新型dMRI纤维追踪成像算法。该算法引入表征白质中fMRI信号各向异性的空间相关张量间接描述纤维束的几何结构信息,结合粒子滤波理论估算追踪下一体素的方向概率分布,重建可靠连接白质灰质边界区域的三维结构。将所提出算法在8位成年人视觉刺激的功能图像上进行追踪成像实验,每例重建800根纤维,重建纤维的平均长度可达(18.47±1.82)mm,沿白质灰质界面流线端点的覆盖率为25.15%±1.86%。通过在视放射区域与DWI重建结果对比可看出,所提出的方法可有效重建大脑白质纤维路径,特别对由于部分容积效应导致对灰白质交界面纤维束重建存在较大误差的区域,较现有方法可获得更准确效果。     

Diffusion MRI fiber tractography of the brain

The ability of fiber tractography to delineate non‐invasively the white matter fiber pathways of the brain raises possibilities for clinical applications and offers enormous potential for neuroscience. In the last decade, fiber tracking has become the method of choice to investigate quantitative MRI parameters in specific bundles of white matter. For neurosurgeons, it is quickly becoming an invaluable tool for the planning of surgery, allowing for visualization and localization of important white matter pathways before and even during surgery. Fiber tracking has also claimed a central role in the field of “connectomics,” a technique that builds and studies comprehensive maps of the complex network of connections within the brain, and to which significant resources have been allocated worldwide. Despite its unique abilities and exciting applications, fiber tracking is not without controversy, in particular when it comes to its interpretation. As neuroscientists are eager to study the brain's connectivity, the quantification of tractography‐derived “connection strengths” between distant brain regions is becoming increasingly popular. However, this practice is often frowned upon by fiber‐tracking experts. In light of this controversy, this paper provides an overview of the key concepts of tractography, the technical considerations at play, and the different types of tractography algorithm, as well as the common misconceptions and mistakes that surround them. We also highlight the ongoing challenges related to fiber tracking. While recent methodological developments have vastly increased the biological accuracy of fiber tractograms, one should be aware that, even with state‐of‐the‐art techniques, many issues that severely bias the resulting structural “connectomes” remain unresolved.     

大脑锥体束华勒氏变性影像学研究进展

原发性脑损伤可导致病灶远端的锥体束发生华勒氏病变,基于磁共振技术(magnetic resonance imaging,MRI)的弥散加权成像(diffusion weighted imaging,DWI)、弥散张量成像(diffusion tensor imaging,DTI)等成像技术对于华勒氏变性的检测有不同的特点和优势,本文针对华勒氏变性各个阶段不同的影像学表现进行了综述,并对临床检测早期华勒氏变性做出了指导。     

磁共振弥散张量成像的质量控制

磁共振弥散张量成像（DTI）是诊断和分析神经系统疾病的重要方法,但其目前发展受空间分辨率、信噪比及图像质量等限制。本文对近年来MRI系统基础质量保证方法、DTI参数定性测量方法、用于扩散成像的软件方法以及不同纤维跟踪方法等进行综述。     

Development of FRP composite structural biomaterials: ultimate strength of the fiber/matrix interfacial bond in in vivo simulated environments.

Fiber reinforced polymer (FRP) composites are being developed as alternatives to metals for structural orthopedic implant applications. FRP composite fracture behavior and environmental interactions are distinctly different from those which occur in metals. These differences must be accounted for in the design and evaluation of implant performance. Fiber/matrix interfacial bond strength in a FRP composite is known to strongly influence fracture behavior. The interfacial bond strength of four candidate fiber/matrix combinations (carbon fiber/polycarbonate, carbon fiber/polysulfone, polyaramid fiber/polycarbonate, polyaramid fiber/polysulfone) were investigated at 37 degrees C in dry and in vivo simulated (saline, exudate) environments. Ultimate bond strength was measured by a single fiber-microdroplet pull-out test. Dry bond strengths were significantly decreased following exposure to either saline or exudate with bond strength loss being approximately equal in both the saline and exudate. Bond strength loss is attributed to the diffusion of water and/or salt ions into the sample and their interaction with interfacial bonding. Because bond degradation is dependent upon diffusion, diffusional equilibrium must be obtained in composite test samples before the full effect of the test environment upon composite mechanical behavior can be determined.     

An efficient architecture to support digital pathology in standard medical imaging repositories

In the past decade, digital pathology and whole-slide imaging (WSI) have been gaining momentum with the proliferation of digital scanners from different manufacturers. The literature reports significant advantages associated with the adoption of digital images in pathology, namely, improvements in diagnostic accuracy and better support for telepathology. Moreover, it also offers new clinical and research applications. However, numerous barriers have been slowing the adoption of WSI, among which the most important are performance issues associated with storage and distribution of huge volumes of data, and lack of interoperability with other hospital information systems, most notably Picture Archive and Communications Systems (PACS) based on the DICOM standard.This article proposes an architecture of a Web Pathology PACS fully compliant with DICOM standard communications and data formats. The solution includes a PACS Archive responsible for storing whole-slide imaging data in DICOM WSI format and offers a communication interface based on the most recent DICOM Web services. The second component is a zero-footprint viewer that runs in any web-browser. It consumes data using the PACS archive standard web services. Moreover, it features a tiling engine especially suited to deal with the WSI image pyramids. These components were designed with special focus on efficiency and usability. The performance of our system was assessed through a comparative analysis of the state-of-the-art solutions. The results demonstrate that it is possible to have a very competitive solution based on standard workflows.