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Fiber architecture in remodeled myocardium revealed with a quantitative diffusion CMR tractography framework and histological validation

Mekkaoui, Choukri; Huang, Shuning; Chen, Howard H.; Dai, Guangping; Reese, Timothy G.; Kostis, William J.; Thiagalingam, Aravinda; Maurovich-Horvat, Pal; Ruskin, Jeremy N.; Hoffmann, Udo; Jackowski, Marcel Parolin; Sosnovik, David E.
Fonte: BIOMED CENTRAL LTD; LONDON Publicador: BIOMED CENTRAL LTD; LONDON
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
37.21%
Background: The study of myofiber reorganization in the remote zone after myocardial infarction has been performed in 2D. Microstructural reorganization in remodeled hearts, however, can only be fully appreciated by considering myofibers as continuous 3D entities. The aim of this study was therefore to develop a technique for quantitative 3D diffusion CMR tractography of the heart, and to apply this method to quantify fiber architecture in the remote zone of remodeled hearts. Methods: Diffusion Tensor CMR of normal human, sheep, and rat hearts, as well as infarcted sheep hearts was performed ex vivo. Fiber tracts were generated with a fourth-order Runge-Kutta integration technique and classified statistically by the median, mean, maximum, or minimum helix angle (HA) along the tract. An index of tract coherence was derived from the relationship between these HA statistics. Histological validation was performed using phase-contrast microscopy. Results: In normal hearts, the subendocardial and subepicardial myofibers had a positive and negative HA, respectively, forming a symmetric distribution around the midmyocardium. However, in the remote zone of the infarcted hearts, a significant positive shift in HA was observed. The ratio between negative and positive HA variance was reduced from 0.96 +/- 0.16 in normal hearts to 0.22 +/- 0.08 in the remote zone of the remodeled hearts (p<0.05). This was confirmed histologically by the reduction of HA in the subepicardium from -52.03 degrees +/- 2.94 degrees in normal hearts to -37.48 degrees +/- 4.05 degrees in the remote zone of the remodeled hearts (p < 0.05). Conclusions: A significant reorganization of the 3D fiber continuum is observed in the remote zone of remodeled hearts. The positive (rightward) shift in HA in the remote zone is greatest in the subepicardium...

An image-processing toolset for diffusion tensor tractography

Mishra, Arabinda; Lu, Yonggang; Choe, Ann S.; Aldroubi, Akram; Gore, John C.; Anderson, Adam W.; Ding, Zhaohua
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.4%
Diffusion tensor imaging (DTI)-based fiber tractography holds great promise in delineating neuronal fiber tracts and, hence, providing connectivity maps of the neural networks in the human brain. An array of image-processing techniques has to be developed to turn DTI tractography into a practically useful tool. To this end, we have developed a suite of image-processing tools for fiber tractography with improved reliability. This article summarizes the main technical developments we have made to date, which include anisotropic smoothing, anisotropic interpolation, Bayesian fiber tracking and automatic fiber bundling. A primary focus of these techniques is the robustness to noise and partial volume averaging, the two major hurdles to reliable fiber tractography. Performance of these techniques has been comprehensively examined with simulated and in vivo DTI data, demonstrating improvements in the robustness and reliability of DTI tractography.

Resolving crossings in the corticospinal tract by two-tensor streamline tractography: Method and clinical assessment using fMRI

Qazi, Arish A.; Radmanesh, Alireza; O’Donnell, Lauren; Kindlmann, Gordon; Peled, Sharon; Whalen, Stephen; Westin, Carl-Fredrik; Golby, Alexandra J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.46%
An inherent drawback of the traditional diffusion tensor model is its limited ability to provide detailed information about multidirectional fiber architecture within a voxel. This leads to erroneous fiber tractography results in locations where fiber bundles cross each other. This may lead to the inability to visualize clinically important tracts such as the lateral projections of the corticospinal tract. In this report, we present a deterministic two-tensor eXtended Streamline Tractography (XST) technique, which successfully traces through regions of crossing fibers. We evaluated the method on simulated and in vivo human brain data, comparing the results with the traditional single-tensor and with a probabilistic tractography technique. By tracing the corticospinal tract and correlating with fMRI-determined motor cortex in both healthy subjects and patients with brain tumors, we demonstrate that two-tensor deterministic streamline tractography can accurately identify fiber bundles consistent with anatomy and previously not detected by conventional single tensor tractography. When compared to the dense connectivity maps generated by probabilistic tractography, the method is computationally efficient and generates discrete geometric pathways that are simple to visualize and clinically useful. Detection of crossing white matter pathways can improve neurosurgical visualization of functionally relevant white matter areas.

Comparative mouse brain tractography of diffusion magnetic resonance imaging

Moldrich, Randal X.; Pannek, Kerstin; Hoch, Renee; Rubenstein, John L.; Kurniawan, Nyoman D.; Richards, Linda J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.54%
Diffusion magnetic resonance imaging (dMRI) tractography can be employed to simultaneously analyse three-dimensional white matter tracts in the brain. Numerous methods have been proposed to model diffusion-weighted magnetic resonance data for tractography, and we have explored the functionality of some of these for studying white and grey matter pathways in ex vivo mouse brain. Using various deterministic and probabilistic algorithms across a range of regions of interest we found that probabilistic tractography provides a more robust means of visualizing both white and grey matter pathways than deterministic tractography. Importantly, we demonstrate the sensitivity of probabilistic tractography profiles to streamline number, step size, curvature, fiber orientation distribution, and whole-brain versus region of interest seeding. Using anatomically well-defined cortico-thalamic pathways, we show how density maps can permit the topographical assessment of probabilistic tractography. Finally, we show how different tractography approaches can impact on dMRI assessment of tract changes in a mouse deficient for the frontal cortex morphogen, fibroblast growth factor 17. In conclusion, probabilistic tractography can elucidate the phenotypes of mice with neurodegenerative or neurodevelopmental disorders in a quantitative manner.

Quantitative Diffusion Tensor Imaging Tractography Metrics are Associated with Cognitive Performance Among HIV-Infected Patients

Tate, David F.; Conley, Jared; Paul, Robert H.; Coop, Kathryn; Zhang, Song; Zhou, Wenjin; Laidlaw, David H.; Taylor, Lynn E.; Flanigan, Timothy; Navia, Bradford; Cohen, Ronald; Tashima, Karen
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.57%
There have been many studies examining HIV-infection-related alterations of magnetic resonance imaging (MRI) diffusion metrics. However, examining scalar diffusion metrics ignores the orientation aspect of diffusion imaging, which can be captured with tractography. We examined five different tractography metrics obtained from global tractography maps (global tractography FA, average tube length, normalized number of streamtubes, normalized weighted streamtube length, and normalized total number of tubes generated) for differences between HIV positive and negative patients and the association between the metrics and clinical variables of disease severity. We also examined the relationship between these metrics and cognitive performance across a wide range of cognitive domains for the HIV positive and negative patient groups separately. The results demonstrated a significant difference between the groups for global tractography FA (t=2.13, p= 0.04), but not for any of the other tractography metrics examined (p-value range=0.39 to 0.95). There were also several significant associations between the tractography metrics and cognitive performance (i.e., tapping rates, switching 1 and 2, verbal interference, mazes; r≥0.42) for HIV infected patients. In particular...

A Modular Framework for Development and Interlaboratory Sharing and Validation of Diffusion Tensor Tractography Algorithms

Nielsen, Jon F.
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.46%
This Technical Note describes a novel modular framework for development and interlaboratory distribution and validation of 3D tractography algorithms based on in vivo diffusion tensor imaging (DTI) measurements. The proposed framework allows individual MRI research centers to benefit from new tractography algorithms developed at other independent centers by “plugging” new tractography modules directly into their own custom DTI software tools, such as existing graphical user interfaces (GUI) for visualizing brain white matter pathways. The proposed framework is based on the Java 3D programming platform, which provides an object-oriented programming (OOP) model and independence of computer hardware configuration and operating system. To demonstrate the utility of the proposed approach, a complete GUI for interactive DTI tractography was developed, along with two separate and interchangeable modules that implement two different tractography algorithms. Although the application discussed here relates to DTI tractography, the programming concepts presented here should be of interest to anyone who wishes to develop platform-independent GUI applications for interactive 3D visualization.

3D Fiber Tractography with Susceptibility Tensor Imaging

Liu, Chunlei; Li, Wei; Wu, Bing; Jiang, Yi; Johnson, G. Allan
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.4%
Gradient-echo MRI has revealed anisotropic magnetic susceptibility in the brain white matter. This magnetic susceptibility anisotropy can be measured and characterized with susceptibility tensor imaging (STI). In this study, a method of fiber tractography based on STI is proposed and demonstrated in the mouse brain. STI experiments of perfusion-fixed mouse brains were conducted at 7.0 T. The magnetic susceptibility tensor was calculated for each voxel with regularization and decomposed into its eigensystem. The major eigenvector is found to be aligned with the underlying fiber orientation. Following the orientation of the major eigenvector, we are able to map distinctive fiber pathways in 3D. As a comparison, diffusion tensor imaging (DTI) and DTI fiber tractography were also conducted on the same specimens. The relationship between STI and DTI fiber tracts was explored with similarities and differences identified. It is anticipated that the proposed method of STI tractography may provide a new way to study white matter fiber architecture. As STI tractography is based on physical principles that are fundamentally different from DTI, it may also be valuable for the ongoing validation of DTI tractography.

Quantitative Assessment of a Framework for Creating Anatomical Brain Networks via Global Tractography

Li, Longchuan; Rilling, James K.; Preuss, Todd M.; Glasser, Matthew F.; Damen, Frederick W.; Hu, Xiaoping
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.57%
Interregional connections of the brain measured with diffusion tractography can be used to infer valuable information regarding both brain structure and function. However, different tractography algorithms can generate networks that exhibit different characteristics, resulting in poor reproducibility across studies. Therefore, it is important to benchmark different tractography algorithms to quantitatively assess their performance. Here we systematically evaluated a newly introduced tracking algorithm, global tractography, to derive anatomical brain networks in a fiber phantom, 2 post-mortem macaque brains, and 20 living humans, and compared the results with an established local tracking algorithm. Our results demonstrated that global tractography accurately characterized the phantom network in terms of graph-theoretic measures, and significantly outperformed the local tracking approach. Results in brain tissues (post-mortem macaques and in vivo humans), however, showed that although the performance of global tractography demonstrated a trend of improvement, the results were not vastly different than that of local tractography, possibly resulting from the increased fiber complexity of real tissues. When using macaque tracer-derived connections as the ground truth...

A Comprehensive Reliability Assessment of Quantitative Diffusion Tensor Tractography

Wang, Jun Yi; Abdi, Hervé; Bakhadirov, Khamid; Diaz-Arrastia, Ramon; Devous, Michael D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.4%
Diffusion tensor tractography is increasingly used to examine structural connectivity in the brain in various conditions, but its test-retest reliability is understudied. The main purposes of this study were to evaluate 1) the reliability of quantitative measurements of diffusion tensor tractography and 2) the effect on reliability of the number of gradient sampling directions and scan repetition. Images were acquired from ten healthy participants. Ten fiber regions of nine major fiber tracts were reconstructed and quantified using six fiber variables. Intra- and inter-session reliabilities were estimated using intraclass correlation coefficient (ICC) and coefficient of variation (CV), and compared to pinpoint major error sources. Additional pairwise comparisons were made between the reliability of images with 30 directions and NEX 2 (DTI30-2), 30 directions and NEX 1 (DTI30-1), and 15 directions and NEX 2 (DTI15-2) to determine whether increasing gradient directions and scan repetition improved reliability. Of the 60 tractography measurements, 43 showed intersession CV ≤ 10%, ICC ≥ .70, or both for DTI30-2, 40 measurements for DTI30-1, and 37 for DTI15-2. Most of the reliable measurements were associated with the tracts corpus callosum...

Histological Validation of DW-MRI Tractography in Human Postmortem Tissue

Seehaus, Arne K.; Roebroeck, Alard; Chiry, Oriana; Kim, Dae-Shik; Ronen, Itamar; Bratzke, Hansjürgen; Goebel, Rainer; Galuske, Ralf A. W.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.54%
Despite several previous attempts, histological validation of diffusion-weighted magnetic resonance imaging (DW-MRI)-based tractography as true axonal fiber pathways remains difficult. In the present study, we establish a method to compare histological and tractography data precisely enough for statements on the level of single tractography pathways. To this end, we used carbocyanine dyes to trace connections in human postmortem tissue and aligned them to high-resolution DW-MRI of the same tissue processed within the diffusion tensor imaging (DTI) formalism. We provide robust definitions of sensitivity (true positives) and specificity (true negatives) for DTI tractography and characterize tractography paths in terms of receiver operating characteristics. With sensitivity and specificity rates of approximately 80%, we could show a clear correspondence between histological and inferred tracts. Furthermore, we investigated the effect of fractional anisotropy (FA) thresholds for the tractography and identified FA values between 0.02 and 0.08 as optimal in our study. Last, we validated the course of entire tractography curves to move beyond correctness determination based on pairs of single points on a tract. Thus, histological techniques...

Tractography - where do we go from here?

Jbabdi, Saad; Johansen-Berg, Heidi
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.4%
Diffusion tractography offers enormous potential for the study of human brain anatomy. However, as a method to study brain connectivity, tractography suffers from limitations, as it is indirect, inaccurate, and difficult to quantify. Despite these limitations, appropriate use of tractography can be a powerful means to address certain questions. In addition, while some of tractography’s limitations are fundamental, others could be alleviated by methodological and technological advances. This article provides an overview of diffusion MR tractography methods with a focus on how future advances might address challenges in measuring brain connectivity. Parts of this review are somewhat provocative, in the hope that they may trigger discussions possibly lacking in a field where the apparent simplicity of the methods (compared to their FMRI counterparts) can hide some fundamental issues that ultimately hinder the interpretation of findings, and cast doubt as to what tractography can really teach us about human brain anatomy.

Real-time multi-peak tractography for instantaneous connectivity display

Chamberland, Maxime; Whittingstall, Kevin; Fortin, David; Mathieu, David; Descoteaux, Maxime
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 30/05/2014 EN
Relevância na Pesquisa
27.46%
The computerized process of reconstructing white matter tracts from diffusion MRI (dMRI) data is often referred to as tractography. Tractography is nowadays central in structural connectivity since it is the only non-invasive technique to obtain information about brain wiring. Most publicly available tractography techniques and most studies are based on a fixed set of tractography parameters. However, the scale and curvature of fiber bundles can vary from region to region in the brain. Therefore, depending on the area of interest or subject (e.g., healthy control vs. tumor patient), optimal tracking parameters can be dramatically different. As a result, a slight change in tracking parameters may return different connectivity profiles and complicate the interpretation of the results. Having access to tractography parameters can thus be advantageous, as it will help in better isolating those which are sensitive to certain streamline features and potentially converge on optimal settings which are area-specific. In this work, we propose a real-time fiber tracking (RTT) tool which can instantaneously compute and display streamlines. To achieve such real-time performance, we propose a novel evolution equation based on the upsampled principal directions...

Beyond Crossing Fibers: Bootstrap Probabilistic Tractography Using Complex Subvoxel Fiber Geometries

Campbell, Jennifer S. W.; MomayyezSiahkal, Parya; Savadjiev, Peter; Leppert, Ilana R.; Siddiqi, Kaleem; Pike, G. Bruce
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 28/10/2014 EN
Relevância na Pesquisa
27.4%
Diffusion magnetic resonance imaging fiber tractography is a powerful tool for investigating human white matter connectivity in vivo. However, it is prone to false positive and false negative results, making interpretation of the tractography result difficult. Optimal tractography must begin with an accurate description of the subvoxel white matter fiber structure, includes quantification of the uncertainty in the fiber directions obtained, and quantifies the confidence in each reconstructed fiber tract. This paper presents a novel and comprehensive pipeline for fiber tractography that meets the above requirements. The subvoxel fiber geometry is described in detail using a technique that allows not only for straight crossing fibers but for fibers that curve and splay. This technique is repeatedly performed within a residual bootstrap statistical process in order to efficiently quantify the uncertainty in the subvoxel geometries obtained. A robust connectivity index is defined to quantify the confidence in the reconstructed connections. The tractography pipeline is demonstrated in the human brain.

Fiber Architecture in Remodeled Myocardium Revealed with a Quantitative Diffusion CMR Tractography Framework and Histological Validation

Huang, Shuning; Thiagalingam, Aravinda; Jackowski, Marcel P; Mekkaoui, Choukri; Chen, Howard H; Dai, Guangping; Reese, Timothy G.; Kostis, William Jason; Maurovich-Horvat, Pal; Ruskin, Jeremy Neil; Hoffman, Udo; Sosnovik, David E.
Fonte: BioMed Central Publicador: BioMed Central
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
37.21%
Background: The study of myofiber reorganization in the remote zone after myocardial infarction has been performed in 2D. Microstructural reorganization in remodeled hearts, however, can only be fully appreciated by considering myofibers as continuous 3D entities. The aim of this study was therefore to develop a technique for quantitative 3D diffusion CMR tractography of the heart, and to apply this method to quantify fiber architecture in the remote zone of remodeled hearts. Methods: Diffusion Tensor CMR of normal human, sheep, and rat hearts, as well as infarcted sheep hearts was performed ex vivo. Fiber tracts were generated with a fourth-order Runge-Kutta integration technique and classified statistically by the median, mean, maximum, or minimum helix angle (HA) along the tract. An index of tract coherence was derived from the relationship between these HA statistics. Histological validation was performed using phase-contrast microscopy. Results: In normal hearts, the subendocardial and subepicardial myofibers had a positive and negative HA, respectively, forming a symmetric distribution around the midmyocardium. However, in the remote zone of the infarcted hearts, a significant positive shift in HA was observed. The ratio between negative and positive HA variance was reduced from 0.96 ± 0.16 in normal hearts to 0.22 ± 0.08 in the remote zone of the remodeled hearts (p<0.05). This was confirmed histologically by the reduction of HA in the subepicardium from −52.03° ± 2.94° in normal hearts to −37.48° ± 4.05° in the remote zone of the remodeled hearts (p < 0.05). Conclusions: A significant reorganization of the 3D fiber continuum is observed in the remote zone of remodeled hearts. The positive (rightward) shift in HA in the remote zone is greatest in the subepicardium...

The average pathlength map: A diffusion MRI tractography-derived index for studying brain pathology

Pannek, K.; Mathias, J.; Bigler, E.; Brown, G.; Taylor, J.; Rose, S.
Fonte: Academic Press Inc Elsevier Science Publicador: Academic Press Inc Elsevier Science
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
37.4%
Magnetic resonance diffusion tractography provides a powerful tool for the assessment of white matter architecture in vivo. Quantitative tractography metrics, such as streamline length, have successfully been used in the study of brain pathology. To date, these studies have relied on a priori knowledge of which tracts are affected by injury or pathology and manual delineation of regions of interest (ROIs) for use as waypoints in tractography. This limits the analyses to specific tracts under investigation and relies on the accurate and consistent placement of ROIs. We present a fully automated technique for the voxel-wise analysis of streamline length within the entire brain, the Average Pathlength Map (APM). We highlight the precision and reproducibility of voxel-wise average streamline length over time, and assess normal variability of pathlength values in a cohort of 43 healthy participants. Additionally, we demonstrate the utility of this approach by performing voxel-wise comparison between pathlength values obtained from a patient with a severe traumatic brain injury (TBI, Glasgow Coma Scale Score=7) and those from control participants. Our analysis shows that voxel-wise average pathlength values are comparable to fractional anisotropy (FA) in terms of reproducibility and variability. For the TBI patient...

MRI diffusion indices sampled along streamline trajectories: quantitative tractography mapping

Pannek, K.; Mathias, J.; Rose, S.
Fonte: Mary Ann Liebert Publicador: Mary Ann Liebert
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
37.05%
Several useful tractography-derived maps have recently been introduced, such as track density imaging (TDI) and the average pathlength map (APM). Here, an extension to these techniques is introduced by sampling diffusion indices along streamline trajectories (DIST). With this approach, voxels contain summary information of diffusivity measures within streamlines. The diffusion metrics can also be used as weighting factors for streamline number or length, generating DIST-weighted TDI and DIST-weighted APM, respectively. Furthermore, when higher-order models of diffusion are used to estimate the fiber orientation distribution within each voxel, it is possible to obtain directional TDI, APM, DIST, and DIST-weighted TDI and APM. The reproducibility of this approach using two b-values (1000 and 3000 s/mm2) and the effect of pathologic abnormalities are demonstrated.; Kerstin Pannek, Jane L. Mathias, and Stephen E. Rose; This is a copy of an article published in the Brain Connectivity © 2011 Mary Ann Liebert, Inc.; Brain Connectivity is available online at: http://online.liebertpub.com.

TRACTOGRAPHY AND NEURONAVIGATION: A NEW IMPORTANT TOOL FOR OPTIMIZING BRAIN LESION RESECTION?; TRACTOGRAFIA E NEURONAVEGAÇÃO

Coelho, Giselle; Kunzler, Filipe; Lessa, Lucas; Rogério, Ricardo; Epelman, Sidnei; Zanon, Nelci
Fonte: Revista Brasileira de Neurologia e Psiquiatria Publicador: Revista Brasileira de Neurologia e Psiquiatria
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Formato: application/pdf
Publicado em 15/10/2014 POR
Relevância na Pesquisa
37.21%
Diffusion tensor imaging (DTI) is a promising, noninvasive magnetic resonance imaging (MRI) method for studying the anatomical organization of major white matter fiber systems non-invasively. A topic currently is receiving increased attention, is the application of DTI and DTI fiber-tracking in the investigation of patients with intracranial tumors. This has been used in conjunction with neuronavigation systems during surgery, allowing precise tumor identification, and consequently, safe resection. Tractography can be used in combination with neuronavigation for guiding resection of brain lesions. Although this technology, and more specifically pediatric neurosurgery, is still under development, the potential is very promising. More studies will be necessary to establish the correlation of this technology and the supposed lower occurrence of brain shift when compared to conventional neuronavigation. The main goal of this study is to present the author’s experience and to evaluate the possible benefits of neuronavigation associated to tractography, during intracranial surgeries, in children.; Diffusion tensor imaging (DTI)é um método não invasivo promissório de ressonância magnética (RM) para estudo da organização anatômica dos principais tratos de substância branca de forma não invasiva. Um tópico que tem recebido atenção é a aplicação de DTI e tractografia na investigação de pacientes com tumores intracranianos. Isto tem sido utilizado em conjunto com sistemas de neuronavegação durante a cirurgia...

HARDI Methods: tractography reconstructions and automatic parcellation of brain connectivity

Lacerda, Luís Miguel Rosa Sousa Prado de
Fonte: Universidade de Lisboa Publicador: Universidade de Lisboa
Tipo: Dissertação de Mestrado
Publicado em //2012 ENG
Relevância na Pesquisa
37.32%
Tese de mestrado integrado em Engenharia Biomédica e Biofísica (Radiações em Diagnóstico e Terapia), apresentada à Universidade de Lisboa, através da Faculdade de Ciências, 2012; A neuroanatomia humana tem sido objecto de estudo científico desde que surgiu o interesse na organização do corpo humano e nas suas funções, quer como um todo quer através das partes que o constituem. Para atingir este fim, as autópsias foram a primeira forma de revelar algum conhecimento, o qual tem vindo a ser catalogado e sistematizado à medida que a medicina evolui. Passando por novas técnicas de conservação e tratamento de tecido humano, de que são exemplo as dissecções de Klinger, nas quais se fazem secções de material conservado criogenicamente, bem como por estudos histológicos através da utilização de corantes, conseguiu-se uma forma complementar de realizar estes estudos. Permanecia, no entanto, a impossibilidade de analisar in vivo a estrutura e função dos diferentes sistemas que constitutem o Homem. Com o surgimento das técnicas imagiológicas o diagnóstico e monitorização do corpo humano, bem como das patologias a ele associadas, melhoraram consideravelmente. Mais recentemente, com o aparecimento da ressonância magnética (MRI: do Inglês "Magnetic Resonance Imaging")...

Reconstruction of the arcuate fasciculus for surgical planning in the setting of peritumoral edema using two-tensor unscented Kalman filter tractography

Chen, Zhenrui; Tie, Yanmei; Olubiyi, Olutayo; Rigolo, Laura; Mehrtash, Alireza; Norton, Isaiah; Pasternak, Ofer; Rathi, Yogesh; Golby, Alexandra J.; O'Donnell, Lauren J.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
37.62%
Background: Diffusion imaging tractography is increasingly used to trace critical fiber tracts in brain tumor patients to reduce the risk of post-operative neurological deficit. However, the effects of peritumoral edema pose a challenge to conventional tractography using the standard diffusion tensor model. The aim of this study was to present a novel technique using a two-tensor unscented Kalman filter (UKF) algorithm to track the arcuate fasciculus (AF) in brain tumor patients with peritumoral edema. Methods: Ten right-handed patients with left-sided brain tumors in the vicinity of language-related cortex and evidence of significant peritumoral edema were retrospectively selected for the study. All patients underwent 3-Tesla magnetic resonance imaging (MRI) including a diffusion-weighted dataset with 31 directions. Fiber tractography was performed using both single-tensor streamline and two-tensor UKF tractography. A two-regions-of-interest approach was applied to perform the delineation of the AF. Results from the two different tractography algorithms were compared visually and quantitatively. Results: Using single-tensor streamline tractography, the AF appeared disrupted in four patients and contained few fibers in the remaining six patients. Two-tensor UKF tractography delineated an AF that traversed edematous brain areas in all patients. The volume of the AF was significantly larger on two-tensor UKF than on single-tensor streamline tractography (p < 0.01). Conclusions: Two-tensor UKF tractography provides the ability to trace a larger volume AF than single-tensor streamline tractography in the setting of peritumoral edema in brain tumor patients.

A Diffusion MRI Tractography Connectome of the Mouse Brain and Comparison with Neuronal Tracer Data.

Calabrese, E; Badea, A; Cofer, G; Qi, Y; Johnson, GA
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Artigo de Revista Científica Formato: 4628 - 4637
Publicado em /11/2015 ENG
Relevância na Pesquisa
37.46%
Interest in structural brain connectivity has grown with the understanding that abnormal neural connections may play a role in neurologic and psychiatric diseases. Small animal connectivity mapping techniques are particularly important for identifying aberrant connectivity in disease models. Diffusion magnetic resonance imaging tractography can provide nondestructive, 3D, brain-wide connectivity maps, but has historically been limited by low spatial resolution, low signal-to-noise ratio, and the difficulty in estimating multiple fiber orientations within a single image voxel. Small animal diffusion tractography can be substantially improved through the combination of ex vivo MRI with exogenous contrast agents, advanced diffusion acquisition and reconstruction techniques, and probabilistic fiber tracking. Here, we present a comprehensive, probabilistic tractography connectome of the mouse brain at microscopic resolution, and a comparison of these data with a neuronal tracer-based connectivity data from the Allen Brain Atlas. This work serves as a reference database for future tractography studies in the mouse brain, and demonstrates the fundamental differences between tractography and neuronal tracer data.