Lifespan Trajectories of White Matter Changes in Rhesus Monkeys
Marek KubickiMadhura BaxiOfer PasternakYingying TangSarina KarmacharyaNatalia ChungaAmanda E. LyallYogesh RathiRyan EckboSylvain BouixFarzad MortazaviGeorge N. PapadimitriouMartha E. ShentonC.-F. WestinRonald KillianyNikos MakrisDouglas L. Rosene
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Abstract:
Progress in neurodevelopmental brain research has been achieved through the use of animal models. Such models not only help understanding biological changes that govern brain development, maturation and aging, but are also essential for identifying possible mechanisms of neurodevelopmental and age-related chronic disorders, and to evaluate possible interventions with potential relevance to human disease. Genetic relationship of rhesus monkeys to humans makes those animals a great candidate for such models. With the typical lifespan of 25 years, they undergo cognitive maturation and aging that is similar to this observed in humans. Quantitative structural neuroimaging has been proposed as one of the candidate in vivo biomarkers for tracking white matter brain maturation and aging. While lifespan trajectories of white matter changes have been mapped in humans, such knowledge is not available for nonhuman primates. Here, we analyze and model lifespan trajectories of white matter microstructure using in vivo diffusion imaging in a sample of 44 rhesus monkeys. We report quantitative parameters (including slopes and peaks) of lifespan trajectories for 8 individual white matter tracts. We show different trajectories for cellular and extracellular microstructural imaging components that are associated with white matter maturation and aging, and discuss similarities and differences between those in humans and rhesus monkeys, the importance of our findings, and future directions for the field. Significance Statement: Quantitative structural neuroimaging has been proposed as one of the candidate in vivo biomarkers for tracking brain maturation and aging. While lifespan trajectories of structural white matter changes have been mapped in humans, such knowledge is not available for rhesus monkeys. We present here results of the analysis and modeling of the lifespan trajectories of white matter microstructure using in vivo diffusion imaging in a sample of 44 rhesus monkeys (age 4–27). We report and anatomically map lifespan changes related to cellular and extracellular microstructural components that are associated with white matter maturation and aging.Keywords:
Imaging genetics
Brain Aging
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 (D̄) and diffusion anisotropy (Aσ) images were computed. D̄ values were measured in ischemic and contralateral gray matter and white matter by using Aσ images to differentiate white matter from gray matter. D̄ images were compared with unidirectional and directionally averaged diffusion-weighted images. RESULTS: In all patients, D̄ images showed two distinct levels of diffusion reduction in the infarct; more severe reduction occurred exclusively in white matter. D̄ values were significantly less in infarcted white matter than in infarcted gray matter, whereas D̄ values in the contralateral white matter and gray matter were not significantly different. Relative to the contralateral side, D̄ 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.
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Diffusion tensor imaging (DTI) has a unique capability to delineate axonal tracts within the white matter, which has not been possible with previous noninvasive imaging techniques. In the past 10 years, we have witnessed a large increase in the use of DTI-based studies and a score of new anatomical knowledge and image analysis tools have been introduced in recent years. This review will provide an overview of the recent advancements in DTI-based studies and new image analysis tools.DTI provided new dimensions for the characterization of white matter anatomy. This characterization of the white matter can be roughly divided into two categories. First, the white matter can be parcellated into constituent white matter tracts, based on pixel-by-pixel orientation and anisotropy information. Second, the DTI information can be extrapolated to obtain three-dimensional connectivity information. Based on these capabilities of DTI, many new image analysis tools are being developed to investigate the status of the white matter.In the past, the white matter has often been treated as one compartment. With DTI and recently developed analysis tools, we can investigate the status of intra-white matter structures and deepen our understanding of white matter structures and their abnormalities under pathological conditions.
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Objective To observe the changes of white matter by using diffusion tensor imaging(DTI) in developmental delay children with normal routine MRI results.Methods Twenty patients(aged 12—36 months) with developmental delay and the twenty cases of monthold matched normal development children were studied by conventional MRI and DTI technology.Fractional anisotropy(FA) and mean diffusivity(MD) values were measured in five regions of deep white matter and four regions of shallow white matter.Comparison were made in FA and MD values of developmental normal and development delay children.Results FA value in shallow white matter of developmental delay children was lower than that of control group(P0.05),MD values in shallow white matter and corpus callosum knee of developmental delay children was higher than that of control group(P0.05).Conclusion DTI may quantify the injuries of white matter microstructure in developmental delay children with normal routine MRI results.
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Diffusion tensor imaging has been increasingly used for studying white matter pathology in rodent models of neurological diseases. Here, applications of diffusion tensor imaging in detecting major and subtle white matter pathology in the mouse CNS are reviewed, followed by several technical details that may be helpful in designing studies that involve diffusion tensor imaging of rodent brain and spinal cord.
Diffusion imaging
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Aims: Diffusion tensor imaging (DTI) allows to study the normal development of white matter tracts. Several studies focused on the supratentorial white matter tracts. Almost no data are available about the temporal changes of DTI scalars for the infratentorial white matter tracts during the progressing myelination. We evaluated the quantitative changes of fractional anisotropy (FA) and mean (MD), axial (AD), and radial (RD) diffusivity within the brainstem and cerebellar white matter tracts from the neonatal period to adolescence.
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Diffusion tensor imaging(DTI) is a novel,sensitive,and quantified technique to detect the diffusion feature of water molecule.In this paper,we reviewed the basic principle and parameters of DTI,the processing methods of DTI data,and the different changes of parameters of DTI with the neonatal brain white matter and gray matter.It showed that parameters of DTI changed regularly with development of premature and neonatal brain white matter,and DTI is helpful to evaluate the development of brain white matter quantitatively.
Brain Development
Diffusion imaging
Gray (unit)
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Diffusion tensor imaging (DTI) could not only reconstruct of the brain white matter neural connectivity,but also show clearly the brain white matter fiber morphology of lesions,either directly or indirectly,which imaged on white matter fiber tracts in the three-dimensional geometric structure by special software for image on the anisotropic thermal motion of water molecules.This paper reviewed the researches on DTI in the assessment of white matter fiber tracts injury and prognosis in patients with stroke.
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Diffusion tensor imaging (DTI) has become a powerful tool for analyzing the structure of white matter. We have proposed a method for detecting nerve fiber bundles in white matter using diffusion tensor images and have applied the method to in vivo brain measurements. Although there are many methods to investigate the connectivity of white matter that are based on principal eigenvector or full tensor propagation. In the proposed method, we use directional diffusion measurements to infer regional white matter connectivity. To assess the connectivity, we compose the map based on the projected tensor distance, then we put a label on the constructed map and segment regionally connected white matter using labels. The purpose of this study is to obtain a quantitative map of white matter connectivity in vivo using diffusion tensor properties.
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Inflammatory fibroid polyps (IFPs) are rare entities. They commonly occur in the stomach, and a fraction of them are present in the small intestines. The exact aetiopathogenesis for IFPs remains unknown. Most small bowel IFPs are asymptomatic and usually go undetected until they produce symptoms. IFPs are responsible for roughly 2% of all small bowel obstructions. They act as a lead point for intussusception, by telescoping into the distal bowel loops. Nearly 85 such cases have been reported in the literature. However, if the IFP is sufficiently large and pedunculated, it could cause mechanical intraluminal obstruction without intussusception. We report one such case in a middle-aged man who had an impending perforation of the terminal ileum caused by an IFP. Resection and anastomosis of the offending segment of the small intestine remains the standard of care. IFPs lack malignant potential and recurrences are rare.
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Abstract Diffusion Tensor Imaging (DTI) is used to characterize the diffusion properties of deviated white matter caused by brain tumors. DTI was recently shown to be very helpful in delineating white matter both within brain lesions and surrounding them. Displacement of white matter fibers may be one of the consequences of tumor growth adjacent to white matter. The combination of white matter mapping with DTI and gray matter mapping using functional MRI, in some cases, facilitated assessment of the relation between the shifted cortical areas and the corresponding white matter tracts. We found that the fractional anisotropy extracted from DTI is increased by 38% in areas of non‐edematous shifted white matter fibers. By contrast, trace apparent diffusion coefficient (ADC) values in those areas were found to be similar to contralateral side and normal control values. Analysis of the three diffusion tensor eigenvalues revealed that the increase in the fractional anisotropy is a result of two processes. The first is the increase in the diffusion parallel to the fibers—λ 1 (by 18%), and the second is the decrease in the diffusion perpendicular to fibers—λ 3 (by 34%) as compared with the contralateral side. These opposing changes cause an increase in the diffusion anisotropy but no change in the trace ADC. It is suggested that the pressure caused by the tumor may lead to an increase in white matter fiber tension, thus causing an increase in λ 1 . On the other hand, the same pressure causes increased fiber density per unit area, leading to a higher degree of restricted diffusion in the extracellular space and, hence, a reduction in λ 3 .
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