Impact of white matter hyperintensities on surrounding white matter tracts

Purpose

It is unclear how white matter hyperintensities disrupt surrounding white matter tracts. The aim of this tractography study was to determine the spatial relationship between diffusion characteristics along white matter tracts and the distance from white matter hyperintensities.

Methods

Diffusion tensor 3-T MRI scans were acquired in 29 participants with white matter hyperintensities. In each subject, tractography by the fiber assignment by continuous tracking method was used to segment corticospinal tracts. Mean diffusivity, radial diffusivity, axial diffusivity, and fractional anisotropy were measured along corticospinal tracts in relation to white matter hyperintensities. Diffusion characteristics along tracts were correlated with distance from white matter hyperintensities and were also compared between tracts traversing and not traversing white matter hyperintensities.

Results

In tracts not traversing through white matter hyperintensities, increasing distance from white matter hyperintensities was associated with decreased mean diffusivity (p?=?0.002) and increased fractional anisotropy (p?=?0.006). In tracts traversing white matter hyperintensities, compared to tracts not traversing white matter hyperintensites, the mean diffusivity was higher at 6–8 voxels, axial diffusivity higher at 4–8 voxels, and radial diffusivity higher at 7 voxels away from white matter hyperintensities (all p?<?0.006).

Conclusion

White matter hyperintensities are associated with two patterns of altered diffusion characteristics in the surrounding white matter tract network. Diffusion characteristics along white matter tracts improve further away from white matter hyperintensities suggestive of a local penumbra pattern. Also, altered diffusion extends further along tracts traversing white matter hyperintensities suggestive of a Wallerian-type degenerative pattern.

     

早期阿尔茨海默病脑白质改变和认知功能损伤的相关性

目的 探讨早期阿尔茨海默病(AD)脑白质变化与认知功能改变的关系.方法 对14例早期AD患者(AD组)和18名健康老年人(ON组)在1.5 T MR扫描仪上进行扩散张量成像(DTI)扫描.在9个感兴趣区测量并比较各向异性分数(FA)和平均扩散系数((-D)).对2组研究对象进行8个标准的神经心理测试,以评价其基本认知能力状态,并对测试结果 进行比较.分析所有研究对象DTI的FA和(-D)测量结果 与神经心理测试评分的相关性.结果 与ON组相比,AD患者在胼胝体压部(分别为0.25±0.03和0.49±0.03)和后顶-颞叶(分别为0.30±0.02和0.28±0.01)FA降低(t值分别为2.481、1.991,P值均＜0.05)、在胼胝体压部D提高(t=1.751,P＜0.05).在8个神经心理行为测试中,AD患者的评分均低于ON组(t值2.803～4.691,P值均＜0.05).相关性研究结果 显示,AD患者胼胝体压部和后顶-颞叶的FA与多个神经心理测试评分呈正相关(r值0.355～0.499,P值均＜0.05),而在较分散的多个部位(-D)与多个神经心理测试评分呈负相关(r值-0.518～-0.350,P值均＜0.05).结论 在AD早期阶段,患者不仅有认知功能的改变,而且还有白质结构的变化,两者存在一定的相关性,表现为脑白质的选择区域性损害,这种损害反映了AD病理机制中皮质间联系的丢失.     

Relationship between white matter hyperintensities volume and the circle of Willis configurations in patients with carotid artery pathology

PurposeWe aimed to assess if there is a difference of distribution and volume of white matter hyperintensities (WMH) in the brain according to the Circle of Willis (CoW) configuration in patients with carotid artery pathology.Material and methodsOne-hundred consecutive patients (79 males, 21 females; mean age 70 years; age range 46–84 years) that underwent brain MRI before carotid endarterectomy (CEA) were included. FLAIR-WMH lesion volume was performed using a semi-automated segmentation technique and the status of the circle of Willis was assessed by two neuroradiologists in consensus.ResultsWe found a prevalence of 55% of variants in the CoW configuration; 22 cases had one variants (40%); 25 cases had two variants (45.45%) and 8 cases showed 3 variants (14.55%). The configuration that was associated with the biggest WMH volume and number of lesions was the A1 + PcoA + PcoA. The PcoA variants were the most prevalent and there was no statistically significant difference in number of lesions and WMH for each vascular territory assessed and the same results were found for AcoA and A1 variants.ConclusionResults of our study suggest that the more common CoW variants are not associated with the presence of an increased WMH or number of lesions whereas uncommon configurations, in particular when 2 or more segment are missing increase the WMH volume and number of lesions. The WHM volume of the MCA territory seems to be more affected by the CoW configuration.     

Volumetric analysis of white matter,gray matter,and CSF using fractional volume analysis

Quantitative cerebral tissue volumes may be useful for an objective assessment of pathological changes in brain. Accurate determination of tissue volumes is complicated, however, by the partial volume averaging (PVA) effect. We have, therefore, developed a new pulse sequence that minimizes the PVA through the use of inversion-recovery (IR) and double inversion-recovery (DIR) techniques. This pulse sequence simultaneously acquires four different sets of images to provide the necessary information for volumetric analysis and reduces potential spatial misregistration of images due to patient motion. The image sets acquired from the proposed pulse sequence are 1) gray matter visible, 2) white matter visible, 3) FLAIR, and 4) fast spin-echo proton-density weighted images. An algorithm has been implemented to correct for differential T₁-weighting and for tissue quantitation.     

Cortical thickness,gray matter volume,and white matter anisotropy and diffusivity in schizophrenia

Introduction  

The study was conducted to evaluate simultaneously gray matter changes and white matter changes in patients with schizophrenia.     

Partial-volume model for determining white matter and gray matter cerebral blood volume for analysis of gliomas

PURPOSE: To model the partial voluming of gray matter (GM) and white matter (WM) in perfusion imaging, and to use this model to estimate the cerebral blood volume (CBV) of pure WM and GM, which could then be used to normalize data across patients in preparation for analyzing tumor perfusion. MATERIALS AND METHODS: Dynamic susceptibility contrast (DSC) perfusion imaging was performed on 20 glioma patients. The perfusion data were registered to the T1 image using rigid-body and non-rigid algorithms. The rCBV for each voxel was computed by gamma-variate fitting and then fit as a linear function of the estimated fractional WM content. The estimated CBV of pure WM was used to normalize across patients, and the resulting tumor CBV values were compared with expectations. RESULTS: Rigid registration improved the correlation between the fractional WM content and CBV for all patients, with non-rigid registration yielding further improvements for all but two patients. The mean GM-to-WM CBV ratio was estimated at 2.15 +/- 0.33 (mean +/- SD). Voxels that exhibited both T1-Gd contrast enhancement and an abnormal proton spectrum were found to have a CBV 2.53 +/- 0.89 times higher than that in the WM. CONCLUSION: A partial-volume model is demonstrated for estimating pure WM and GM CBV. It is also shown that the relationship between the tumor CBV as estimated with this model is generally consistent with expectations based on spectroscopy and imaging.     

飞行员与普通人脑白质高信号检出率及分布比较

目的：比较飞行员和普通人脑白质高信号（white matter hyperintensities,WMHs）的发病情况。方法收集2002年1月—2014年12月来空军总医院健康体检进行头颅MRI检查的现役飞行员290例、普通人910例进行回顾性分析,比较WMHs的发病情况。结果飞行员WMHs者40例,检出率为13.79%;普通人WMHs者83例,检出率为9.12%。飞行员和普通人WMHs年龄差异无统计学意义。本组飞行员和普通人WMHs分布部位类似,差异无统计学意义。本组40例WMHs飞行员蒙特利尔量表评分均≥26分。8例连续执行飞行任务飞行员6个月后WMHs体积增加,差异有统计学意义。结论本组飞行员WMHs的检出率高于普通人。飞行员和普通人WMHs分布部位类似主要位于额叶。飞行员点状WMHs对认知不受影响。飞行员WMHs的体积会随着飞行时间的增加而增加。     

Quantification of white matter and gray matter volumes from three-dimensional magnetic resonance volume studies using fuzzy classifiers

We accurately measured white matter (WM) and gray matter (GM) from three-dimensional (3D) volume studies, using a fuzzy classification technique. The new segmentation method is a modification of a recently published method developed for T1 parametric images. 3D MR images were transformed into pseudo forms of T1 parametric images and segmented into WM and GM voxel fraction images with a set of standardized fuzzy classifiers. This segmentation method was validated with synthesized 3D MR images as phantoms. These phantoms were developed from cryosectioned human brain images located in the superior, middle, and inferior regions of the cerebrum. Phantom volume measurements revealed that, generally, the difference between measured and actual volumes was less than 3% for 1.5-mm simulated brain slices. The average cerebral GM/WM ratio calculated from 3D MR studies in four subjects was 1.77, which compared favorably with the estimate of 1.67 derived from anatomical data. Results indicate that this is an accurate and rapid method for quantifying WM and GM from T1-weighted 3D volume studies.     

MR volume segmentation of gray matter and white matter using manual thresholding: dependence on image brightness.

PURPOSETo describe a quantitative MR imaging segmentation method for determination of the volume of cerebrospinal fluid, gray matter, and white matter in living human brain, and to determine the method''s reliability.METHODSWe developed a computer method that allows rapid, user-friendly determination of cerebrospinal fluid, gray matter, and white matter volumes in a reliable manner, both globally and regionally. This method was applied to a large control population (N = 57).RESULTSInitially, image brightness had a strong correlation with the gray-white ratio (r = .78). Bright images tended to overestimate, dim images to underestimate gray matter volumes. This artifact was corrected for by offsetting each image to an approximately equal brightness. After brightness correction, gray-white ratio was correlated with age (r = -.35). The age-dependent gray-white ratio was similar to that for the same age range in a prior neuropathology report. Interrater reliability was high (.93 intraclass correlation coefficient).CONCLUSIONSThe method described here for gray matter, white matter, and cerebrospinal fluid volume calculation is reliable and valid. A correction method for an artifact related to image brightness was developed.     

Whole-brain T1 mapping in multiple sclerosis: global changes of normal-appearing gray and white matter

PURPOSE: To prospectively investigate whether T1 changes in normal-appearing white matter (WM) and normal-appearing gray matter (GM) in multiple sclerosis (MS) are global or regional and their relationship to disease type. MATERIALS AND METHODS: The institutional ethics review board approved study; written informed consent was obtained. Whole-brain T1 maps were obtained in 67 patients with MS and 24 healthy control subjects with three-dimensional fast low-angle shot flip angle-array method, with correction for B(1) imperfections. Analysis of variance was performed on T1 histogram parameters of global normal-appearing WM and GM. Regional mean T1 values were analyzed with a multilevel approach. Multiple linear regression analysis was performed to investigate associations with clinical disability and overall atrophy. For patients, T2 lesion load was determined. RESULTS: T1 histograms of normal-appearing WM had significantly higher peak positions for patients with MS (792 msec +/- 36 in secondary progressive [SP] MS) than for control subjects (746 msec +/- 23) and were significantly broader and lower (all P < .001). Histograms for cortical normal-appearing GM were significantly shifted (peak positions, 1263 msec +/- 44 in control subjects and 1355 msec +/- 62 in patients with SP MS) (P < .001). Histogram peak positions were significantly higher in SP MS than in relapsing-remitting (RR) and primary progressive MS (P < .05). In SP disease, at least 31% of normal-appearing WM and 20% of cortical normal-appearing GM were affected. In MS, T1 was significantly elevated in all normal-appearing WM and cortical normal-appearing GM regions (all P < .01) but was elevated only in the thalamus in deep GM (P < .05). Cortical T1 histogram peak position was associated with clinical disability; T2 lesion load was not. CONCLUSION: Results suggest that a global disease process affects large parts of both normal-appearing WM and GM in MS and effects are worse for SP MS than for RR MS.     

Automated segmentation and measurement of global white matter lesion volume in patients with multiple sclerosis

A fully automated magnetic resonance (MR) segmentation method for identification and volume measurement of demyelinated white matter has been developed. Spin-echo MR brain scans were performed in 38 patients with multiple sclerosis (MS) and in 46 healthy subjects. Segmentation of normal tissues and white matter lesions (WML) was obtained, based on their relaxation rates and proton density maps. For WML identification, additional criteria included three-dimensional (3D) lesion shape and surrounding tissue composition. Segmented images were generated, and normal brain tissues and WML volumes were obtained. Sensitivity, specificity, and reproducibility of the method were calculated, using the WML identified by two neuroradiologists as the gold standard. The average volume of "abnormal" white matter in normal subjects (false positive) was 0.11 ml (range 0-0.59 ml). In MS patients the average WML volume was 31.0 ml (range 1.1-132.5 ml), with a sensitivity of 87.3%. In the reproducibility study, the mean SD of WML volumes was 2.9 ml. The procedure appears suitable for monitoring disease changes over time. J. Magn. Reson. Imaging 2000;12:799-807.     

The morphologic correlate of incidental punctate white matter hyperintensities on MR images

Postmortem examinations were made of the brains of six patients, 52-63 years old, who exhibited incidental punctate white matter hyperintensities on MR images before death. Our aim was to unravel the morphologic correlate of such lesions. By repeating the MR study after fixation on four specimens, cutting the brain parallel to the MR imaging plane, and examining whole-hemisphere microscopic sections, we optimized lesion identification. The white matter signal abnormalities were better delineated on pre- than postmortem scans, and visual inspection of the brain slices was normal in all but one location. Histologically, we found areas of reduced myelination with atrophy of the neuropil around fibrohyalinotic arteries as well as different stages of perivenous damage. The latter ranged from spongiform transformation of the neuropil and scattered foci of demyelination to large perivenous areas with marked rarefaction of myelinated fibers. Edematous glial swelling in foci of ganglion cell heterotopia caused subcortical white matter hyperintensities in one case. Our results suggest minor perivascular damage but not infarction as the most likely substrate of punctate MR white matter hyperintensities in elderly brains. Histologic correlations with MR images obtained during life or with studies of unfixed material are necessary to analyze such small lesions.     

Reducing the impact of white matter lesions on automated measures of brain gray and white matter volumes

Purpose:

To develop an automated lesion‐filling technique (LEAP; LEsion Automated Preprocessing) that would reduce lesion‐associated brain tissue segmentation bias (which is known to affect automated brain gray [GM] and white matter [WM] tissue segmentations in people who have multiple sclerosis), and a WM lesion simulation tool with which to test it.

Materials and Methods:

Simulated lesions with differing volumes and signal intensities were added to volumetric brain images from three healthy subjects and then automatically filled with values approximating normal WM. We tested the effects of simulated lesions and lesion‐filling correction with LEAP on SPM‐derived tissue volume estimates.

Results:

GM and WM tissue volume estimates were affected by the presence of WM lesions. With simulated lesion volumes of 15 mL at 70% of normal WM intensity, the effect was to increase GM fractional (relative to intracranial) volumes by ≈2.3%, and reduce WM fractions by ≈3.6%. Lesion filling reduced these errors to ≈0.1%.

Conclusion:

The effect of WM lesions on automated GM and WM volume measures may be considerable and thereby obscure real disease‐mediated volume changes. Lesion filling with values approximating normal WM enables more accurate GM and WM volume measures and should be applicable to structural scans independently of the software used for the segmentation. J. Magn. Reson. Imaging 2010. © 2010 Wiley‐Liss, Inc.     

Quantification of gray/white matter in neonates and adults

Quantitation of gray/white matter is important in evaluation of cerebral blood flow, atrophy, and development of the brain. First-order statistical analysis of neonatal computed tomographic (CT) images revealed that there was only a 6 Hounsfield unit (H) difference between gray and white matter compared with the observed 3 H for the standard deviation over the field of a skull water phantom. Scene segmentation methods based on first-order statistics proved unsuccessful in separating gray and white matter. A new regional clustering algorithm based on local textural properties was developed for separation of these structures.     

Carotid artery stenosis and brain connectivity: the role of white matter hyperintensities

Neuroradiology - It is under debate how white matter hyperintensities (WMH) affects the brain connectivity. The objective of this research study is to validate the hypothesis, if and how the WMH...     

Differences between gray matter and white matter water diffusion in stroke: diffusion-tensor MR imaging in 12 patients

PURPOSE: To investigate differences in water diffusion between white matter and gray matter in acute to early subacute stroke with diffusion-tensor magnetic resonance (MR) imaging. MATERIALS AND METHODS: Twelve patients with unilateral middle cerebral arterial infarcts were examined with diffusion tensor-encoded echo-planar MR imaging 17 hours to 5 days after stroke onset. Isotropic diffusion coefficient (D) and diffusion anisotropy (A(sigma)) images were computed. (D) values were measured in ischemic and contralateral gray matter and white matter by using A(sigma) images to differentiate white matter from gray matter. (D) images were compared with unidirectional and directionally averaged diffusion-weighted images. RESULTS: In all patients, (D) images showed two distinct levels of diffusion reduction in the infarct; more severe reduction occurred exclusively in white matter. (D) values were significantly less in infarcted white matter than in infarcted gray matter, whereas (D) values in the contralateral white matter and gray matter were not significantly different. Relative to the contralateral side, (D) values in the infarct were reduced by 46% in white matter and by 31% in gray matter (P <.001). Diffusion-weighted imaging caused underestimation of the magnitude and, in some cases, the spatial extent of the white matter diffusion abnormality. CONCLUSION: Isotropic diffusion is more reduced in white matter than in gray matter in acute to early subacute middle cerebral arterial stroke. Diffusion-tensor imaging may be more sensitive than diffusion-weighted imaging to white matter ischemia.     

Method for combining information from white matter fiber tracking and gray matter parcellation

We introduce a method for combining fiber tracking from diffusion-tensor (DT) imaging with cortical gray matter parcellation from structural high-spatial-resolution 3D spoiled gradient-recalled acquisition in the steady state images. We applied this method to a tumor case to determine the impact of the tumor on white matter architecture. We conclude that this new method for combining structural and DT imaging data is useful for understanding cortical connectivity and the localization of fiber tracts and their relationship with cortical anatomy and brain abnormalities.     

Optimal voxel size for measuring global gray and white matter proton metabolite concentrations using chemical shift imaging.

Quantification of gray and white matter levels of spectroscopically visible metabolites can provide important insights into brain development and pathological conditions. Chemical shift imaging offers a gain in efficiency for estimation of global gray and white matter metabolite concentrations compared to single voxel methods. In the present study, the optimal voxel size is calculated from segmented human brain data and accompanying field maps. The optimal voxel size is found to be approximately 8 cc, but a wide range of values, 4-64 cc, can be chosen with little increase in estimated concentration error (<15%). Magn Reson Med 44:10-18, 2000.