101
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McDonald CR, Leyden KM, Hagler DJ, Kucukboyaci NE, Kemmotsu N, Tecoma ES, Iragui VJ. White matter microstructure complements morphometry for predicting verbal memory in epilepsy. Cortex 2014; 58:139-50. [PMID: 25016097 DOI: 10.1016/j.cortex.2014.05.014] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Revised: 04/02/2014] [Accepted: 05/28/2014] [Indexed: 11/20/2022]
Abstract
Verbal memory is the most commonly impaired cognitive domain in patients with temporal lobe epilepsy (TLE). Although damage to the hippocampus and adjacent temporal lobe structures is known to contribute to memory impairment, little is known of the relative contributions of white versus gray matter structures, or whether microstructural versus morphometric measures of temporal lobe pathology are stronger predictors of impairment. We evaluate whether measures of temporal lobe pathology derived from diffusion tensor imaging (DTI; microstructural) versus structural MRI (sMRI; morphometric) contribute the most to memory performances in TLE, after controlling for hippocampal volume (HCV). DTI and sMRI were performed on 26 patients with TLE and 35 controls. Verbal memory was measured with the Logical Memory (LM) subtest of the Wechsler Memory Scale-III. Hierarchical regression analyses were performed to examine unique contributions of DTI and sMRI measures to verbal memory with HCV entered in block 1. In patients, impaired recall was associated with increased mean diffusivity (MD) of multiple fiber tracts that project through the temporal lobes. In addition, increased MD of the left cortical and bilateral pericortical white matter was associated with impaired recall. After controlling for left HCV, only microstructural measures of white matter pathology contributed to verbal recall. The best predictive model included left HCV and MD of the left inferior longitudinal fasciculus (ILF) and pericortical white matter beneath the left entorhinal cortex. This model explained 60% of the variance in delayed recall and revealed that MD of the left ILF was the strongest predictor. These data reveal that white matter microstructure within the temporal lobe can be used in conjunction with left HCV to enhance the prediction of verbal memory impairment, and speak to the complementary nature of DTI and sMRI for understanding cognitive dysfunction in epilepsy and possibly other memory disorders.
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Affiliation(s)
- Carrie R McDonald
- Department of Psychiatry, University of California, San Diego, CA, USA; Multimodal Imaging Laboratory, University of California, San Diego, CA, USA.
| | - Kelly M Leyden
- Multimodal Imaging Laboratory, University of California, San Diego, CA, USA
| | - Donald J Hagler
- Multimodal Imaging Laboratory, University of California, San Diego, CA, USA; Department of Radiology, University of California, San Diego, CA, USA
| | - Nuri E Kucukboyaci
- Multimodal Imaging Laboratory, University of California, San Diego, CA, USA; San Diego State University/University of California, San Diego Joint Doctoral Program in Clinical Psychology, San Diego, CA, USA
| | - Nobuko Kemmotsu
- Department of Psychiatry, University of California, San Diego, CA, USA; Multimodal Imaging Laboratory, University of California, San Diego, CA, USA
| | - Evelyn S Tecoma
- Department of Neurosciences, University of California, San Diego, CA, USA
| | - Vicente J Iragui
- Department of Neurosciences, University of California, San Diego, CA, USA
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102
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Truong TK, Guidon A, Song AW. Cortical depth dependence of the diffusion anisotropy in the human cortical gray matter in vivo. PLoS One 2014; 9:e91424. [PMID: 24608869 PMCID: PMC3946789 DOI: 10.1371/journal.pone.0091424] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Accepted: 02/11/2014] [Indexed: 11/21/2022] Open
Abstract
Diffusion tensor imaging (DTI) is typically used to study white matter fiber pathways, but may also be valuable to assess the microstructure of cortical gray matter. Although cortical diffusion anisotropy has previously been observed in vivo, its cortical depth dependence has mostly been examined in high-resolution ex vivo studies. This study thus aims to investigate the cortical depth dependence of the diffusion anisotropy in the human cortex in vivo on a clinical 3 T scanner. Specifically, a novel multishot constant-density spiral DTI technique with inherent correction of motion-induced phase errors was used to achieve a high spatial resolution (0.625×0.625×3 mm) and high spatial fidelity with no scan time penalty. The results show: (i) a diffusion anisotropy in the cortical gray matter, with a primarily radial diffusion orientation, as observed in previous ex vivo and in vivo studies, and (ii) a cortical depth dependence of the fractional anisotropy, with consistently higher values in the middle cortical lamina than in the deep and superficial cortical laminae, as observed in previous ex vivo studies. These results, which are consistent across subjects, demonstrate the feasibility of this technique for investigating the cortical depth dependence of the diffusion anisotropy in the human cortex in vivo.
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Affiliation(s)
- Trong-Kha Truong
- Brain Imaging and Analysis Center, Duke University, Durham, North Carolina, United States of America
- * E-mail:
| | - Arnaud Guidon
- Brain Imaging and Analysis Center, Duke University, Durham, North Carolina, United States of America
| | - Allen W. Song
- Brain Imaging and Analysis Center, Duke University, Durham, North Carolina, United States of America
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103
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Wu D, Reisinger D, Xu J, Fatemi SA, van Zijl PCM, Mori S, Zhang J. Localized diffusion magnetic resonance micro-imaging of the live mouse brain. Neuroimage 2014; 91:12-20. [PMID: 24440780 DOI: 10.1016/j.neuroimage.2014.01.014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Revised: 01/06/2014] [Accepted: 01/10/2014] [Indexed: 11/19/2022] Open
Abstract
High-resolution diffusion MRI (dMRI) is useful for resolving complex microstructures in the mouse brain, but technically challenging for in vivo studies due to the long scan time. In this study, selective excitation and a three-dimensional fast imaging sequence were used to achieve in vivo high-resolution dMRI of the mouse brain at 11.7Tesla. By reducing the field of view using spatially selective radio frequency pulses, we were able to focus on targeted brain structures and acquire high angular resolution diffusion imaging (HARDI) data at an isotropic resolution of 0.1mm and 30 diffusion encoding directions in approximately 1h. We investigated the complex tissue microstructures of the mouse hippocampus, cerebellum, and several cortical areas using this localized dMRI approach, and compared the results with histological sections stained with several axonal and dendritic markers. In the mouse visual cortex, the results showed predominately radially arranged structures in an outer layer and tangentially arranged structures in an inner layer, similar to observations from postmortem human brain specimens.
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Affiliation(s)
- Dan Wu
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Dominik Reisinger
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; Division of Neurology and Developmental Medicine, Kennedy Krieger Institute, Baltimore, MD, USA
| | - Jiadi Xu
- F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA
| | - S Ali Fatemi
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; Division of Neurology and Developmental Medicine, Kennedy Krieger Institute, Baltimore, MD, USA
| | - Peter C M van Zijl
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA
| | - Susumu Mori
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA
| | - Jiangyang Zhang
- Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
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104
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Nummenmaa A, McNab JA, Savadjiev P, Okada Y, Hämäläinen MS, Wang R, Wald LL, Pascual-Leone A, Wedeen VJ, Raij T. Targeting of white matter tracts with transcranial magnetic stimulation. Brain Stimul 2013; 7:80-4. [PMID: 24220599 DOI: 10.1016/j.brs.2013.10.001] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Revised: 10/02/2013] [Accepted: 10/09/2013] [Indexed: 10/26/2022] Open
Abstract
BACKGROUND TMS activations of white matter depend not only on the distance from the coil, but also on the orientation of the axons relative to the TMS-induced electric field, and especially on axonal bends that create strong local field gradient maxima. Therefore, tractography contains potentially useful information for TMS targeting. OBJECTIVE/METHODS Here, we utilized 1-mm resolution diffusion and structural T1-weighted MRI to construct large-scale tractography models, and localized TMS white matter activations in motor cortex using electromagnetic forward modeling in a boundary element model (BEM). RESULTS As expected, in sulcal walls, pyramidal cell axonal bends created preferred sites of activation that were not found in gyral crowns. The model agreed with the well-known coil orientation sensitivity of motor cortex, and also suggested unexpected activation distributions emerging from the E-field and tract configurations. We further propose a novel method for computing the optimal coil location and orientation to maximally stimulate a pre-determined axonal bundle. CONCLUSIONS Diffusion MRI tractography with electromagnetic modeling may improve spatial specificity and efficacy of TMS.
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Affiliation(s)
- Aapo Nummenmaa
- MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, MA, USA; Harvard Medical School, MA, USA
| | - Jennifer A McNab
- MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, MA, USA; Harvard Medical School, MA, USA; Department of Radiology, Stanford University, CA, USA
| | - Peter Savadjiev
- Harvard Medical School, MA, USA; Brigham and Women's Hospital, MA, USA
| | - Yoshio Okada
- Harvard Medical School, MA, USA; Department of Neurology, Boston Children's Hospital, MA, USA
| | - Matti S Hämäläinen
- MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, MA, USA; Harvard Medical School, MA, USA; Harvard-MIT Division of Health Sciences and Technology, MA, USA
| | - Ruopeng Wang
- MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, MA, USA; Harvard Medical School, MA, USA
| | - Lawrence L Wald
- MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, MA, USA; Harvard Medical School, MA, USA; Harvard-MIT Division of Health Sciences and Technology, MA, USA
| | - Alvaro Pascual-Leone
- Harvard Medical School, MA, USA; Berenson-Allen Center for Noninvasive Brain Stimulation, Beth Israel Deaconess Medical Center, MA, USA
| | - Van J Wedeen
- MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, MA, USA; Harvard Medical School, MA, USA
| | - Tommi Raij
- MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, MA, USA; Harvard Medical School, MA, USA.
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105
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Sønderby CK, Lundell HM, Søgaard LV, Dyrby TB. Apparent exchange rate imaging in anisotropic systems. Magn Reson Med 2013; 72:756-62. [PMID: 24123426 DOI: 10.1002/mrm.24957] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2013] [Revised: 07/16/2013] [Accepted: 08/26/2013] [Indexed: 11/08/2022]
Abstract
PURPOSE Double-wave diffusion experiments offer the possibility of probing correlation between molecular diffusion at multiple time points. It has recently been shown that this technique is capable of measuring the exchange of water across cellular membranes. The aim of this study was to investigate the effect of macroscopic tissue anisotropy on the measurement of the apparent exchange rate (AXR) in multicompartment systems. METHODS AXR data were collected from yeast and perfusion-fixated brain tissue at high angular resolution on a preclinical imaging system. The AXR was expanded for anisotropic systems by calculating scalar AXR values along the principal directions of the diffusion tensor. RESULTS In yeast, both the AXR and diffusivity were rotational invariant, whereas in fixated brain tissue, the measured AXR was sensitive to the orientation of anisotropic structures. AXR, especially in white matter, was robustly estimated along the first and second principal directions of the diffusion tensor, but increasing noise was seen in the AXR estimates along the third principal direction of the diffusion tensor. CONCLUSION Our results indicate that tissue anisotropy must be considered for AXR estimates in complex biological systems.
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Affiliation(s)
- Casper K Sønderby
- Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Hvidovre, Denmark
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106
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Mangin JF, Fillard P, Cointepas Y, Le Bihan D, Frouin V, Poupon C. Toward global tractography. Neuroimage 2013; 80:290-6. [PMID: 23587688 DOI: 10.1016/j.neuroimage.2013.04.009] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 04/04/2013] [Accepted: 04/07/2013] [Indexed: 01/01/2023] Open
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107
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Abstract
Traumatic coma is associated with disruption of axonal pathways throughout the brain, but the specific pathways involved in humans are incompletely understood. In this study, we used high angular resolution diffusion imaging to map the connectivity of axonal pathways that mediate the 2 critical components of consciousness-arousal and awareness-in the postmortem brain of a 62-year-old woman with acute traumatic coma and in 2 control brains. High angular resolution diffusion imaging tractography guided tissue sampling in the neuropathologic analysis. High angular resolution diffusion imaging tractography demonstrated complete disruption of white matter pathways connecting brainstem arousal nuclei to the basal forebrain and thalamic intralaminar and reticular nuclei. In contrast, hemispheric arousal pathways connecting the thalamus and basal forebrain to the cerebral cortex were only partially disrupted, as were the cortical "awareness pathways." Neuropathologic examination, which used β-amyloid precursor protein and fractin immunomarkers, revealed axonal injury in the white matter of the brainstem and cerebral hemispheres that corresponded to sites of high angular resolution diffusion imaging tract disruption. Axonal injury was also present within the gray matter of the hypothalamus, thalamus, basal forebrain, and cerebral cortex. We propose that traumatic coma may be a subcortical disconnection syndrome related to the disconnection of specific brainstem arousal nuclei from the thalamus and basal forebrain.
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108
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Assaf Y, Alexander DC, Jones DK, Bizzi A, Behrens TEJ, Clark CA, Cohen Y, Dyrby TB, Huppi PS, Knoesche TR, Lebihan D, Parker GJM, Poupon C, Anaby D, Anwander A, Bar L, Barazany D, Blumenfeld-Katzir T, De-Santis S, Duclap D, Figini M, Fischi E, Guevara P, Hubbard P, Hofstetter S, Jbabdi S, Kunz N, Lazeyras F, Lebois A, Liptrot MG, Lundell H, Mangin JF, Dominguez DM, Morozov D, Schreiber J, Seunarine K, Nava S, Poupon C, Riffert T, Sasson E, Schmitt B, Shemesh N, Sotiropoulos SN, Tavor I, Zhang HG, Zhou FL. The CONNECT project: Combining macro- and micro-structure. Neuroimage 2013; 80:273-82. [PMID: 23727318 DOI: 10.1016/j.neuroimage.2013.05.055] [Citation(s) in RCA: 92] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2013] [Revised: 05/06/2013] [Accepted: 05/08/2013] [Indexed: 11/28/2022] Open
Abstract
In recent years, diffusion MRI has become an extremely important tool for studying the morphology of living brain tissue, as it provides unique insights into both its macrostructure and microstructure. Recent applications of diffusion MRI aimed to characterize the structural connectome using tractography to infer connectivity between brain regions. In parallel to the development of tractography, additional diffusion MRI based frameworks (CHARMED, AxCaliber, ActiveAx) were developed enabling the extraction of a multitude of micro-structural parameters (axon diameter distribution, mean axonal diameter and axonal density). This unique insight into both tissue microstructure and connectivity has enormous potential value in understanding the structure and organization of the brain as well as providing unique insights to abnormalities that underpin disease states. The CONNECT (Consortium Of Neuroimagers for the Non-invasive Exploration of brain Connectivity and Tracts) project aimed to combine tractography and micro-structural measures of the living human brain in order to obtain a better estimate of the connectome, while also striving to extend validation of these measurements. This paper summarizes the project and describes the perspective of using micro-structural measures to study the connectome.
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Affiliation(s)
- Yaniv Assaf
- Department of Neurobiology, George S. Wise Faculty of Life Science, Tel Aviv University, Tel Aviv, Israel.
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109
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McNab JA, Edlow BL, Witzel T, Huang SY, Bhat H, Heberlein K, Feiweier T, Liu K, Keil B, Cohen-Adad J, Tisdall MD, Folkerth RD, Kinney HC, Wald LL. The Human Connectome Project and beyond: initial applications of 300 mT/m gradients. Neuroimage 2013; 80:234-45. [PMID: 23711537 DOI: 10.1016/j.neuroimage.2013.05.074] [Citation(s) in RCA: 248] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2013] [Revised: 05/07/2013] [Accepted: 05/13/2013] [Indexed: 01/01/2023] Open
Abstract
The engineering of a 3 T human MRI scanner equipped with 300 mT/m gradients - the strongest gradients ever built for an in vivo human MRI scanner - was a major component of the NIH Blueprint Human Connectome Project (HCP). This effort was motivated by the HCP's goal of mapping, as completely as possible, the macroscopic structural connections of the in vivo healthy, adult human brain using diffusion tractography. Yet, the 300 mT/m gradient system is well suited to many additional types of diffusion measurements. Here, we present three initial applications of the 300 mT/m gradients that fall outside the immediate scope of the HCP. These include: 1) diffusion tractography to study the anatomy of consciousness and the mechanisms of brain recovery following traumatic coma; 2) q-space measurements of axon diameter distributions in the in vivo human brain and 3) postmortem diffusion tractography as an adjunct to standard histopathological analysis. We show that the improved sensitivity and diffusion-resolution provided by the gradients are rapidly enabling human applications of techniques that were previously possible only for in vitro and animal models on small-bore scanners, thereby creating novel opportunities to map the microstructure of the human brain in health and disease.
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Affiliation(s)
- Jennifer A McNab
- Department of Radiology, Stanford University, RM Lucas Center for Imaging, Stanford, CA, USA.
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110
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Using high angular resolution diffusion imaging data to discriminate cortical regions. PLoS One 2013; 8:e63842. [PMID: 23691102 PMCID: PMC3656939 DOI: 10.1371/journal.pone.0063842] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2012] [Accepted: 04/08/2013] [Indexed: 11/19/2022] Open
Abstract
Brodmann’s 100–year–old summary map has been widely used for cortical localization in neuroscience. There is a pressing need to update this map using non–invasive, high–resolution and reproducible data, in a way that captures individual variability. We demonstrate here that standard HARDI data has sufficiently diverse directional variation among grey matter regions to inform parcellation into distinct functional regions, and that this variation is reproducible across scans. This characterization of the signal variation as non–random and reproducible is the critical condition for successful cortical parcellation using HARDI data. This paper is a first step towards an individual cortex–wide map of grey matter microstructure, The gray/white matter and pial boundaries were identified on the high–resolution structural MRI images. Two HARDI data sets were collected from each individual and aligned with the corresponding structural image. At each vertex point on the surface tessellation, the diffusion–weighted signal was extracted from each image in the HARDI data set at a point, half way between gray/white matter and pial boundaries. We then derived several features of the HARDI profile with respect to the local cortical normal direction, as well as several fully orientationally invariant features. These features were taken as a fingerprint of the underlying grey matter tissue, and used to distinguish separate cortical areas. A support–vector machine classifier, trained on three distinct areas in repeat 1 achieved 80–82% correct classification of the same three areas in the unseen data from repeat 2 in three volunteers. Though gray matter anisotropy has been mostly overlooked hitherto, this approach may eventually form the foundation of a new cortical parcellation method in living humans. Our approach allows for further studies on the consistency of HARDI based parcellation across subjects and comparison with independent microstructural measures such as ex–vivo histology.
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111
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Hansen MB, Jespersen SN, Leigland LA, Kroenke CD. Using diffusion anisotropy to characterize neuronal morphology in gray matter: the orientation distribution of axons and dendrites in the NeuroMorpho.org database. Front Integr Neurosci 2013; 7:31. [PMID: 23675327 PMCID: PMC3653140 DOI: 10.3389/fnint.2013.00031] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2012] [Accepted: 04/16/2013] [Indexed: 01/07/2023] Open
Abstract
Accurate mathematical modeling is integral to the ability to interpret diffusion magnetic resonance (MR) imaging data in terms of cellular structure in brain gray matter (GM). In previous work, we derived expressions to facilitate the determination of the orientation distribution of axonal and dendritic processes from diffusion MR data. Here we utilize neuron reconstructions available in the NeuroMorpho database (www.neuromorpho.org) to assess the validity of the model we proposed by comparing morphological properties of the neurons to predictions based on diffusion MR simulations using the reconstructed neuron models. Initially, the method for directly determining neurite orientation distributions is shown to not depend on the line length used to quantify cylindrical elements. Further variability in neuron morphology is characterized relative to neuron type, species, and laboratory of origin. Subsequently, diffusion MR signals are simulated based on human neocortical neuron reconstructions. This reveals a bias in which diffusion MR data predict neuron orientation distributions to have artificially low anisotropy. This bias is shown to arise from shortcomings (already at relatively low diffusion weighting) in the Gaussian approximation of diffusion, in the presence of restrictive barriers, and data analysis methods involving higher moments of the cumulant expansion are shown to be capable of reducing the magnitude of the observed bias.
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Affiliation(s)
- Mikkel B Hansen
- Center for Functionally Integrative Neuroscience and MINDLab, NeuroCampus Aarhus, Aarhus University Aarhus, Denmark
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112
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McNab JA, Polimeni JR, Wang R, Augustinack JC, Fujimoto K, Stevens A, Triantafyllou C, Janssens T, Farivar R, Folkerth RD, Vanduffel W, Wald LL. Surface based analysis of diffusion orientation for identifying architectonic domains in the in vivo human cortex. Neuroimage 2013; 69:87-100. [PMID: 23247190 PMCID: PMC3557597 DOI: 10.1016/j.neuroimage.2012.11.065] [Citation(s) in RCA: 113] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2012] [Revised: 11/27/2012] [Accepted: 11/30/2012] [Indexed: 11/15/2022] Open
Abstract
Diffusion tensor MRI is sensitive to the coherent structure of brain tissue and is commonly used to study large-scale white matter structure. Diffusion in gray matter is more isotropic, however, several groups have observed coherent patterns of diffusion anisotropy within the cerebral cortical gray matter. We extend the study of cortical diffusion anisotropy by relating it to the local coordinate system of the folded cerebral cortex. We use 1mm and sub-millimeter isotropic resolution diffusion imaging to perform a laminar analysis of the principal diffusion orientation, fractional anisotropy, mean diffusivity and partial volume effects. Data from 6 in vivo human subjects, a fixed human brain specimen and an anesthetized macaque were examined. Large regions of cortex show a radial diffusion orientation. In vivo human and macaque data displayed a sharp transition from radial to tangential diffusion orientation at the border between primary motor and somatosensory cortex, and some evidence of tangential diffusion in secondary somatosensory cortex and primary auditory cortex. Ex vivo diffusion imaging in a human tissue sample showed some tangential diffusion orientation in S1 but mostly radial diffusion orientations in both M1 and S1.
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Affiliation(s)
- Jennifer A McNab
- R.M. Lucas Center for Imaging, Radiology, Stanford University, Stanford, CA 94305, USA.
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113
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Budde MD, Annese J. Quantification of anisotropy and fiber orientation in human brain histological sections. Front Integr Neurosci 2013; 7:3. [PMID: 23378830 PMCID: PMC3561729 DOI: 10.3389/fnint.2013.00003] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Accepted: 01/11/2013] [Indexed: 11/16/2022] Open
Abstract
Diffusion weighted imaging (DWI) has provided unparalleled insight into the microscopic structure and organization of the central nervous system. Diffusion tensor imaging (DTI) and other models of the diffusion MRI signal extract microstructural properties of tissues with relevance to the normal and injured brain. Despite the prevalence of such techniques and applications, accurate and large-scale validation has proven difficult, particularly in the human brain. In this report, human brain sections obtained from a digital public brain bank were employed to quantify anisotropy and fiber orientation using structure tensor analysis. The derived maps depict the intricate complexity of white matter fibers at a resolution not attainable with current DWI experiments. Moreover, the effects of multiple fiber bundles (i.e., crossing fibers) and intravoxel fiber dispersion were demonstrated. Examination of the cortex and hippocampal regions validated-specific features of previous in vivo and ex vivo DTI studies of the human brain. Despite the limitation to two dimensions, the resulting images provide a unique depiction of white matter organization at resolutions currently unattainable with DWI. The method of analysis may be used to validate tissue properties derived from DTI and alternative models of the diffusion signal.
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Affiliation(s)
- Matthew D Budde
- Department of Neurosurgery, Medical College of Wisconsin Milwaukee, WI, USA
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114
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Kleinnijenhuis M, Zerbi V, Küsters B, Slump CH, Barth M, van Cappellen van Walsum AM. Layer-specific diffusion weighted imaging in human primary visual cortex in vitro. Cortex 2012; 49:2569-82. [PMID: 23347559 DOI: 10.1016/j.cortex.2012.11.015] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2012] [Revised: 10/16/2012] [Accepted: 11/24/2012] [Indexed: 12/14/2022]
Abstract
One of the most prominent characteristics of the human neocortex is its laminated structure. The first person to observe this was Francesco Gennari in the second half the 18th century: in the middle of the depth of primary visual cortex, myelinated fibres are so abundant that he could observe them with bare eyes as a white line. Because of its saliency, the stria of Gennari has a rich history in cyto- and myeloarchitectural research as well as in magnetic resonance (MR) microscopy. In the present paper we show for the first time the layered structure of the human neocortex with ex vivo diffusion weighted imaging (DWI). To achieve the necessary spatial and angular resolution, primary visual cortex samples were scanned on an 11.7 T small-animal MR system to characterize the diffusion properties of the cortical laminae and the stria of Gennari in particular. The results demonstrated that fractional anisotropy varied over cortical depth, showing reduced anisotropy in the stria of Gennari, the inner band of Baillarger and the deepest layer of the cortex. Orientation density functions showed multiple components in the stria of Gennari and deeper layers of the cortex. Potential applications of layer-specific diffusion imaging include characterization of clinical abnormalities, cortical mapping and (intra)cortical tractography. We conclude that future high-resolution in vivo cortical DWI investigations should take into account the layer-specificity of the diffusion properties.
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Affiliation(s)
- Michiel Kleinnijenhuis
- Department of Anatomy, Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands; Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, Netherlands
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