扩散张量成像和示踪图评估异体移植肾功能障碍——初步研究

目的评价MR扩散张量成像(DTI)作为无创性的诊断方法,检测急性及慢性移植肾功能障碍和器官微结构改变的能力。方法在1.5TMR设备上对15例异体移植肾功能障碍病人和14名健康志愿者行脂肪抑制平面回波DTI序列(扩散敏感梯度场施加在6个方向上,b值为0、600s/mm2)成     

Diffusion tensor MR imaging and fiber tractography: technical considerations

This second article of the 2-part review builds on the theoretic background provided by the first article to cover the major technical factors that affect image quality in diffusion imaging, including the acquisition sequence, magnet field strength, gradient amplitude, and slew rate as well as multichannel radio-frequency coils and parallel imaging. The sources of many common diffusion image artifacts are also explored in detail. The emphasis is on optimizing these technical factors for state-of-the-art diffusion-weighted imaging and diffusion tensor imaging (DTI) based on the best available evidence in the literature. An overview of current methods for quantitative analysis of DTI data and fiber tractography in clinical research is also provided.     

Diffusion tensor MR imaging and fiber tractography: theoretic underpinnings

In this article, the underlying theory of clinical diffusion MR imaging, including diffusion tensor imaging (DTI) and fiber tractography, is reviewed. First, a brief explanation of the basic physics of diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) mapping is provided. This is followed by an overview of the additional information that can be derived from the diffusion tensor, including diffusion anisotropy, color-encoded fiber orientation maps, and 3D fiber tractography. This article provides the requisite background for the second article in this 2-part review to appear next month, which covers the major technical factors that affect image quality in diffusion MR imaging, including the acquisition sequence, magnet field strength, gradient amplitude and slew rate, and multichannel radio-frequency coils and parallel imaging. The emphasis is on optimizing these factors for state-of-the-art DWI and DTI based on the best available evidence in the literature.     

Diffusion tensor imaging and fiber tractography in Parry-Romberg syndrome

We report a case of Parry-Romberg syndrome in a 32-year-old woman presenting with intermittent headache and mild sensory disturbance. MR imaging revealed minimal asymmetric atrophy of the right hemisphere with a few nonspecific white matter hyperintensities. Diffusion tensor imaging and fiber tractography, however, demonstrated clear fiber derangement, especially in the sensory tract of the right cerebral white matter.     

Diffusion tensor imaging and fiber tractography of C6 rat glioma

PURPOSE: To apply diffusion tensor images using 30 noncollinear directions for diffusion-weighted gradient schemes to characterize diffusion tensor imaging (DTI) features associated with C6 glioma-bearing rat brains, and ideally visualize fiber tractography datasets. MATERIALS AND METHODS: Fiber tractographies of normal male Fischer 344 rat brains were constructed from DTI datasets acquired with a 30 noncollinear diffusion gradient scheme. Cultured C6 cell were intracranially injected into the cortex of male Fischer 344 rats. The time course of the tumor growth was monitored with DTI and fiber tractography using diffusion-weighting gradients in 30 noncollinear directions. RESULTS: Fiber tractographies through the corpus callosum (CC) were easily visualized with the 30-direction gradient scheme, and the fiber trajectories of the motor cortex and striatum were well represented in normal rats. Fiber tractography indicated that the neuronal fibers of the CC were compressed or disappeared by growing C6 glioma, which affected surrounding brain tissue. CONCLUSION: We have demonstrated in this study that fiber tractography with the 30 noncollinear diffusion gradient scheme method can be used to help provide a better understanding regarding the influence of a tumor on the surrounding regions of normal brain tissue in vivo.     

Diffusion tensor tractography of the limbic system

BACKGROUND AND PURPOSE: The limbic system, relevant to memory and emotion, is an interesting subject of study in healthy and diseased individuals. It consists of a network of gray matter structures interconnected by white matter fibers. Although gray matter components of this system have been studied by using MR imaging, the connecting fibers have not been analyzed to the same degree. Cerebrospinal fluid (CSF) signal intensity contamination of the fornix and cingulum, the 2 major white matter tracts of the limbic system, can alter diffusion-tensor imaging (DTI) measurements and affect tractography. We investigated the effect of CSF signal intensity suppression on fiber tracking of the limbic connections and characterized the diffusion properties of these structures in healthy volunteers. METHODS: Nine healthy individuals were scanned with standard and CSF-suppressed DTI. Tractography of the fornix and cingulum was performed for both acquisition methods. We report mean diffusivity and fractional anisotropy measurements of the crus, body, and columns of the fornix, and descending, superior, and anterior portions of the cingulum. RESULTS: Diffusion measurements were improved and tractography was facilitated by using CSF-suppressed DTI. In particular, tract volume increased, whereas decreases of the mean diffusivity and increases of diffusion anisotropy more accurately represented the underlying tissue by minimizing deleterious partial volume averaging from CSF. This was particularly true for the fornix because it is in closest contact to CSF. Diffusion measurements throughout the limbic connections were consistent in healthy volunteers. CONCLUSION: We recommend the use of CSF suppression when performing diffusion-tensor tractography of the limbic system.     

Diffusion tensor imaging and fiber tractography in cervical compressive myelopathy: preliminary results

Objective  

To assess diffusion tensor imaging (DTI) parameters in cervical compressive myelopathy (CCM) patients compared to normal volunteers, to relate them with myelopathy severity, and to relate tractography patterns with postoperative neurologic improvement.     

颞干解剖及白质纤维示踪成像对比研究

目的 应用扩散张量纤维素成像(DTT)技术确定钩状束、前连合、额枕下束和视辐射的三维关系,及其解剖定位标志.方法 研究10个成人尸体头颅标本,观察和测量:岛叶、岛阈、下限沟、Heschl回、颢角和外侧膝状体.并对10名健康志愿者进行脑DTT研究,应用解剖学知识基础上的感兴趣区法进行白质纤维重建.对两者的结果 进行对比.结果 下限沟长(46.3±3.1)mm,从下限沟到颞角上壁的最短距离为(6.5±1.8)mm.岛叶后下点位于Heschi回和下限沟交叉的最前端.在下限沟,此点是视辐射的后界.颞干开始于岛阈,结束于岛叶后下点,长(33.0±2.9)mm.从岛阈到颢角尖端的距离为(10.9±1.7)mm,这正好是颞十长度的1/3.钩状束构成颞干前部的核心,其后为前连合,它们占据颞十前1/3.额枕下束走行于整个颞干.Meyer袢最前界位于颞角前尖端和岛阈之间.视辐射大部存在于颞干中后2/3.结论 在下限沟,岛叶后下点是视辐射后界可靠的标志.岛阈、颢角尖端及岛叶后下点可作为颢干白质纤维束在MRI及术中的解剖标志.     

Diffusion tensor imaging and tractography of the human language pathways: Moving into the clinical realm

The functional correlates of anatomical derangements are of interest to the neurological clinician. Diffusion tensor tractography (DTT) is a relatively new tool in the arsenal of functional neuroimaging, by which to assess white matter tracts in the brain. While much import has been given to tracking corticospinal tracts in neurological disease, studying language pathway interconnections using DTT has largely remained in the research realm. Hardware and software advances have allowed this tool to ease into clinical practice, with several radiologists, neurologists, and neurosurgeons now familiar with its applications. DTT images, although visually appealing, are founded in mathematical equations and assumptions, and require a more than basic understanding of principles and limitations before they can be integrated into routine clinical practice. Cognitive pathways like that of language, that are normally hard to assess and especially more so when pathologically affected, have been at the receiving end of several opposing and often controversial hypotheses, and the past decade has seen the clarification, validation or rejection of several of these by the in vivo charting of functional connectivity using DTT. The focus of this review is to illustrate DTT of the language pathways with emphasis on practical considerations, clinical applications, and limitations. J. Magn. Reson. Imaging 2014;40:1041–1053 . © 2013 Wiley Periodicals, Inc.     

Diffusion tensor imaging and tractography of the median nerve in carpal tunnel syndrome: preliminary results

The purpose was to demonstrate the feasibility of in vivo diffusion tensor imaging (DTI) and tractography of the human median nerve with a 1.5-T MR scanner and to assess potential differences in diffusion between healthy volunteers and patients suffering from carpal tunnel syndrome. The median nerve was examined in 13 patients and 13 healthy volunteers with MR DTI and tractography using a 1.5-T MRI scanner with a dedicated wrist coil. T1-weighted images were performed for anatomical correlation. Mean fractional anisotropy (FA) and mean apparent diffusion coefficient (ADC) values were quantified in the median nerve on tractography images. In all subjects, the nerve orientation and course could be detected with tractography. Mean FA values were significantly lower in patients (p=0.03). However, no statistically significant differences were found for mean ADC values. In vivo assessment of the median nerve in the carpal tunnel using DTI with tractography on a 1.5-T MRI scanner is possible. Microstructural parameters can be easily obtained from tractography images. A significant decrease of mean FA values was found in patients suffering from chronic compression of the median nerve. Further investigations are necessary to determine if mean FA values may be correlated with the severity of nerve entrapment.     

Diffusion tensor tractography of the lower spinal cord

Introduction We employed a diffusion-tensor (DT) imaging technique involving a single-shot echo-planar sequence in combination with parallel imaging for tractography of the lower spinal cord and assessed the feasibility of this technique. Methods Images were obtained at 1.5 T using a five-channel receiver coil. We used a single-shot echo-planar sequence with parallel imaging to acquire diffusion-weighted (DW) images in the axial plane with phase encoding in the right–left direction. A motion-probing gradient was applied in six directions with a b-value of 1,000 s/mm². The scan time was 5 min 15 s. On a reconstructed DW image in the sagittal plane, the spinal cord was included in a single region-of-interest to generate a tractogram of the entire cord in seven volunteers and nine patients with spinal canal stenosis or vertebral metastasis. Results In each subject, although the conus medullaris and cauda equina were continuously visualized, the cord was demonstrated as a bundle of tracts color-coded in the z-axis. Nerve roots were depicted showing color-coding in the x- and y-axes. In the patient group, displacement of the cord was depicted showing changes in the color of the cord. Displacement of the proximal nerve roots was also depicted in the two patients with vertebral metastasis. Conclusion DT imaging using parallel imaging shows potential as a method for routine tractography of the lower spinal cord. This paper was presented at the 91st Scientific Assembly and Annual Meeting of the Radiological Society of North America, November–December, 2005, Chicago, Illinois.     

腕管综合征时正中神经的扩散张量成像和纤维束示踪的初步研究结果

目的是为了显示在1.5TMR设备上进行人活体正中神经扩散张量成像和纤维束示踪的可行性,并评估健康志愿者与腕管综合征病人扩散成像的潜在不同。13例病人     

Diffusion tensor tractography and neuropsychological assessment in patients with vitamin B12 deficiency

Introduction

Structural imaging of the brain does not demonstrate any changes in a vast majority of patients with vitamin B12 deficiency, even in advanced stages. In this study, we aimed to assess and correlate the functional integrity of the brain fiber tracts using diffusion tensor tractography with neuropsychological examination in patients with vitamin B12 deficiency.

Methods

The study was conducted at two tertiary care centers. Thirty-two patients with vitamin B12 deficiency were enrolled and subjected to diffusion tensor tractography, as an extension of diffusion tensor imaging, and neuropsychological assessment. Tests of significance were done to detect changes, pre- and post-vitamin B12 supplementation in the diffusivity parameters (fractional anisotropy and mean diffusivity) and the neuropsychological test scores.

Results

Statistically significant changes were observed in the diffusivity parameters and the neuropsychological test scores between the controls and the patients with vitamin B12deficiency in the pre- and post-treatment phases.

Conclusions

This is the first study to evaluate the diffusion tensor tractography (DTT) parameters in the light of clinical neuropsychological assessment in patients with vitamin B12 deficiency. Utilization of DTT parameters may antedate structural changes and may quantify the neurocognitive deficits.     

Diffusion tensor MR fiber tractography in assessment of inflammatory processes and neoplasms of the cervical cord

Our goal of this research is to assess the value of MR fiber tractography in assessment of inflammatory process and neoplasms of the cervical cord.

Diffusion tensor imaging tractography parameters of limbic system bundles in temporal lobe epilepsy patients

Purpose:

To investigate changes in diffusion tensor imaging (DTI) measures in limbic system white matter of patients with temporal lobe epilepsy (TLE) using diffusion tensor tractography.

Materials and Methods:

DTI metrics including fractional anisotropy (FA), λ1, λ2, λ3, and trace (Tr) coefficients were obtained from tractography for bilateral fornix, superior and inferior cingulum fibers in 18 patients and 10 healthy controls. Hippocampal signal‐to‐noise ratio (SNR) quantitative analysis was performed in order to confirm the magnetic resonance imaging (MRI) hippocampal lesion presence or absence in TLE patients.

Results:

Nine patients presented unilateral hippocampal sclerosis (TLE+HS) and nine patients had no signal abnormalities on conventional MRI (TLE?HS). On the ipsilateral seizure side, all three investigated tracts showed significant DTI indices abnormalities in both patient groups when compared with controls, most marked on the inferior cingulum. Contralateral to the seizure side, the three tracts presented significant DTI parameters in only the TLE+HS group when compared with controls.

Conclusion:

The DTI abnormalities found in the TLE?HS group may suggest that in the inferior cingulum the structural integrity is more affected than in the fornix or superior cingulum white matter bundles. The eigenvalues taken separately add complementary information to the FA and Tr metrics and may be useful indices in better understanding the architectural reorganization of limbic system tracts in TLE patients without HS. J. Magn. Reson. Imaging 2012;36:561–568. © 2012 Wiley Periodicals, Inc.

     

Diffusion tensor tractography of gliomatosis cerebri: fiber tracking through the tumor

In previous reports, tracts obtained by diffusion tensor (DT) fiber tracking were terminated or deviated by the brain tumors or surrounding edema. There has been no report showing diffusion tensor tractography penetrating through the tumor. A case of glioma is reported, whose DT fiber tract passing through the tumor was observed by changing the threshold of fractional anisotropy.     

Diffusion tensor imaging (DTI) and tractography of the brachial plexus: feasibility and initial experience in neoplastic conditions

Introduction  

The objective of this study was to assess the feasibility and potential clinical applications of diffusion tensor imaging (DTI) and tractography in the normal and pathologic brachial plexus prospectively.     

Diffusion tensor MR imaging in chronic spinal cord injury

BACKGROUND AND PURPOSE: Diffusion tensor MR imaging is emerging as an important tool for displaying anatomic changes in the brain after injury or disease but has been less widely applied to disorders of the spinal cord. The aim of this study was to characterize the diffusion properties of the entire human spinal cord in vivo during the chronic stages of spinal cord injury (SCI). These data provide insight into the structural changes that occur as a result of long-term recovery from spinal trauma.MATERIALS AND METHODS: Thirteen neurologically intact subjects and 10 subjects with chronic SCI (>4 years postinjury) were enrolled in this study. A single-shot twice-refocused spin-echo diffusion-weighted echo-planar imaging pulse sequence was used to obtain axial images throughout the entire spinal cord (C1-L1) in <60 minutes.RESULTS: Despite heterogeneity in SCI lesion severity and location, diffusion characteristics of the chronic lesion were significantly elevated compared with those of uninjured controls. Fractional anisotropy was significantly lower at the chronic lesion and appeared dependent on the completeness of the injury. Conversely, mean diffusivity measurements in the upper cervical spinal cord in subjects with SCI were significantly lower than those in controls. These trends suggest that the entire neuraxis may be affected by long-term recovery from spinal trauma.CONCLUSION: These results suggest that diffusion tensor imaging may be useful in the assessment of SCI recovery.

Diffusion tensor imaging (DTI) has been successfully used to characterize structural changes in neural tissue after spinal artery stroke,¹ multiple sclerosis,^2,3 cervical spondylotic myelopathy,⁴ spinal cord compression,⁵ and acute spinal cord injury (SCI)^6,7; however, DTI has not been used to explore the long-term changes in spinal cord structure known to accompany chronic SCI.^8–11 The purpose of this study was to characterize the diffusion values of the entire spinal cord in humans with chronic SCI (>4 years postinjury) by using a clinically available pulse sequence and comparing these data with normative DTI characteristics reported previously.¹² On the basis of previous work,¹³ we hypothesized that diffusion characteristics would be significantly altered throughout the entire length of the spinal cord.DTI research in SCI largely involves the use of experimental animal models to examine changes in diffusivity that accompany the early stages of injury. These studies have suggested overall diffusivity increases and diffusion anisotropy decreases near the injury site^14–18 due to axonal damage and/or vasogenic edema.¹⁵ Although a few studies have been conducted with human spinal cord pathologies,^4–7,19 they have also demonstrated an increase in diffusivity and a decrease in diffusion anisotropy.DTI may be useful for identifying the characteristics of chronic SCI, because structural changes in the spinal cord during the chronic stages may differ from the normal spinal cord and the spinal cord in acute stages of injury. For example, extensive longitudinal spreading of lesions in the late stages of injury creates widespread changes in the spinal cord morphology, including cyst formation and necrosis.²⁰ Changes in diffusivity associated with these structural alterations may make it possible to identify the rostral and caudal extent of a spinal lesion by using DTI. Many therapeutic interventions for rehabilitation after SCI, including functional electric stimulation²¹ and gait training,²² rely on intact spinal motoneurons below the level of the lesion. Incomplete injury in segments below the injury may be particularly difficult to identify by using physical or electrophysiologic measurements because sensory and motor function is often reduced or absent below the level of injury. Thus, DTI provides an opportunity to assess the integrity of the spinal cord.DTI might also be sensitive to changes in the structure of the spinal cord tissue in regions distant from the spinal lesion in chronic injury. Although the chronic stages of SCI are typically considered stable,^23,24 progressive demyelination in chronic SCI has been documented,^8–10 and remyelination, when it occurs, can result in significantly decreased myelin sheath thickness^8,25–27 and preferential loss of large-diameter axons.²⁶ Also, considerable atrophy of the spinal cord occurs in the late stages of SCI, causing the remaining axons to be compressed and tightly packed.¹¹ These changes could increase the attenuation of diffusion barriers, which would be consistent with the decrease in mean diffusivity recently reported in the upper cervical spinal cord rostral to the injury in a small number of subjects with chronic SCI.¹³Thus, the primary aim of this study was to characterize the diffusion properties across the entire spinal cord (C1–L1 vertebral levels) in humans with chronic SCI by using a clinically available DTI pulse sequence. We then compared these data with diffusion characteristics from a previously published young neurologically intact sample.¹²