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The Retinal Vasculature as a Fractal: Methodology, Reliability, and Relationship to Blood Pressure

OPHTHALMOLOGY 2008年第11期115卷 1951-1956页

作者： Liew, Gerald Wang, Jie Jin Cheung, Ning Zhang, Yong Ping Hsu, Wynne Lee, Mong Li Mitchell, Paul Tikellis, Gabriella Taylor, Bronwen Wong, Tien Yin Univ Sydney Ctr Vis Sci Sydney NSW 2006 Australia Univ Melbourne Royal Victorian Eye & Ear Hosp Ctr Eye Res Australia Melbourne Vic Australia Ningbo Univ Technol Sch Elect & Informat Engn Ningbo Peoples R China Natl Univ Singapore Yong Loo Lin Sch Med Singapore Eye Res Inst Singapore 117595 Singapore Natl Univ Singapore Sch Comp Singapore 117548 Singapore

Objective: Fractals represent a type of derived geometric pattern that permits the characterization of the branching pattern of retinal vessels. We examined a new semiautomated method to measure retinal vessel fractals. Design: Methodology study. Participants: Three hundred randomly selected participants from the population-based Blue Mountains Eye Study. methods: We developed a semiautomated computer program to measure the fractal dimension (D-f) of the retinal vessels from digitized images of disk-centered retinal photographs. Two trained graders masked to participant characteristics measured D-f of right eye images of participants. Reliability was determined by repeat grading of the images from 60 participants, and association with systolic and diastolic blood pressure was examined in all 300 participants. Main Outcome Measure: D-f of the retinal vessels. Results: Mean D-f was 1.437 with a standard deviation of 0.025. Intragrader and intergrader reliability estimates were high with intraclass correlation ranging from 0.93 to 0.95. D-f was inversely correlated with age (r = -0.42, P = 0.001) and systolic blood pressure (r = -0.29, P<0.0001). After adjustment for age and sex, mean Df was significantly lower in participants with than without hypertension (D-f difference 0.01, P = 0.02). Conclusions: The D-f of the retinal vessels can be reliably measured from photographs and shows a strong inverse correlation with blood pressure. These data suggest that the D-f may be a measure of early microvascular alterations from elevated blood pressure. Further studies to examine the systemic and ocular correlates of the D-f of the retinal vessels are needed. Financial Disclosure(s). The authors have no proprietary or commercial interest in any materials discussed in this article. Ophthalmology 2008;115:1951-1956 (C) 2008 by the American Academy of Ophthalmology.

关键词： Aged Aged, 80 and over Aging/physiology Blood Pressure/physiology Female Fractals Humans image processing, computer-assisted/methods Male Middle Aged Photography Reproducibility of Results Retinal Vessels/anatomy & histology

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The temporal characteristics of motion processing in hMT/V5+: Combining fMRI and neuronavigated TMS

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NEUROimage 2006年第4期29卷 1326-1335页

作者： Sack, AT Kohler, A Linden, DEJ Goebel, R Muckli, L Maastricht Univ Fac Psychol Dept Neurocognit NL-6200 MD Maastricht Netherlands Max Planck Inst Brain Res Dept Neurophysiol D-60528 Frankfurt Germany Brain Imaging Ctr D-60590 Frankfurt Germany Univ Wales Sch Psychol Bangor Gwynedd Wales Univ Frankfurt Dept Psychiat D-60528 Frankfurt Germany

Functional imaging has demonstrated the specific involvement of the human middle-temporal complex (hMT/V5+) during processing of moving stimuli. Some studies applied transcranial magnetic stimulation (TMS) to investigate the causal relevance of hMT/V5+ for motion perception. Although the studies used similar visual stimuli and TMS parameters, the critical time point of functionally relevant hMT/V5+ activity differed by 100 ms and more. The present study aimed to elucidate further the temporal characteristics of motion processing in hMT/V5+ by investigating all critical time windows currently debated in the literature. In contrast to previous studies, we used TMS neuronavigation based on individual fMRI results of five participants to target hMT/V5+, applying single-pulse TMS at 24 different time windows (-50 till +200 ms relative to stimulus onset). We revealed that TMS significantly impaired motion perception when applied over hMT/V5+ at 40 to 30 ms before as well as 130 to 150 ms after onset of the moving stimuli. While the late effective time window conforms to results from previous experiments, we did not find evidence for an early time window around 0 ms that has been reported in other studies. Our neuronavigation approach enabled us to quantify the inter-individual variance in the exact location of hMT/V5+ and the respective TMS target position on the skull of the participants. Considering that shifting the TMS coil position only by a few millimeters can already lead to a complete loss of TMS effects, our study clearly demonstrates the utility of neuronavigated TMS when investigating specific neuronal effects as in the case of motion processing. (c) 2005 Elsevier Inc. All rights reserved.

关键词： Adult Attention/physiology Brain Mapping/methods Brain Mapping/methods Female Humans image Enhancement/methods image processing, computer-assisted/methods Imaging, Three-Dimensional Magnetic Resonance Imaging/methods Male Motion Perception/physiology Neuronavigation/methods Neurons/physiology Orientation/physiology Pattern Recognition, Visual/physiology Reproducibility of Results Temporal Lobe/physiology Transcranial Magnetic Stimulation Visual Pathways/physiology

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Complementary information from multi-exponential T₂ relaxation and diffusion tensor imaging reveals differences between multiple sclerosis lesions

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NEUROimage 2008年第1期40卷 77-85页

作者： Kolind, Shannon H. Laule, Comelia Vavasour, Irene M. Li, David K. B. Traboulsee, Anthony L. Maedler, Burkhard Moore, G. R. Wayne MacKay, Alex L. Univ British Columbia MRI Res Ctr Vancouver BC V6T 2B5 Canada Univ British Columbia Dept Radiol Vancouver BC V5Z 1M9 Canada Univ British Columbia Dept Med Vancouver BC V5Z 1M9 Canada Univ British Columbia Dept Pathol & Lab Med Vancouver BC V5Z 1M9 Canada

While conventional magnetic resonance imaging (MRI) has long been used to study multiple sclerosis (MS), more sensitive and specific approaches to studying both MS lesions and normal appearing white matter (NAWM) are needed to gain a better understanding of the pathogenesis of the disease. Two MRI techniques thought to offer insight regarding myelin and axonal integrity are T-2 relaxation and diffusion tensor imaging (DTI). In this study, metrics obtained from T-2 relaxation (specifically myclin water content (MWC) and long-T-2 fraction) and DTI experiments (in particular the fractional anisotropy, mean diffusivity < D >, parallel diffusivity lambda(parallel to) and perpendicular diffusivity lambda(perpendicular to)) were compared for 19 MS patients within both lesion and contralateral NAWM with the goal of better understanding how each of the measures are affected by pathology. In particular, it was successfully determined that the detection of a long-T-2 signal within an MS lesion is indicative of a different underlying pathology than is present in lesions without long-T-2 signal. All of the diffusion metrics were significantly different in lesions with a long-T-2 signal than in those without. While no significant correlations were found between MWC and < D >, lambda(parallel to) or lambda(perpendicular to) in NAWM (R-2 = 0.02-0.04, p > 0.07), and only weak correlations were found in lesions without long-T-2 Signal (R-2=0.05-0. 14, p < 0.04), strong correlations were observed in lesions exhibiting long-T-2 signal (R-2 =0.54-0.61, p < 0.0001). (c) 2007 Elsevier Inc. All rights reserved.

关键词： Adult Algorithms Brain/pathology Data Interpretation, Statistical Diffusion Magnetic Resonance Imaging Female Humans image processing, computer-assisted/methods Male Middle Aged Multiple Sclerosis/pathology

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Adaptive smoothing of multi-shell diffusion weighted magnetic resonance data by msPOAS

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NEUROimage 2014年 95卷 90-105页

作者： Becker, S. M. A. Tabelow, K. Mohammadi, S. Weiskopf, N. Polzehl, J. Weierstrass Inst Appl Anal & Stochast Berlin Germany UCL Inst Neurol Wellcome Trust Ctr Neuroimaging London England

We present a novel multi-shell position-orientation adaptive smoothing (msPOAS) method for diffusion weighted magnetic resonance data. Smoothing in voxel and diffusion gradient space is embedded in an iterative adaptive multiscale approach. The adaptive character avoids blurring of the inherent structures and preserves discontinuities. The simultaneous treatment of all q-shells improves the stability compared to single-shell approaches such as the original POAS method. The msPOAS implementation simplifies and speeds up calculations, compared to POAS, facilitating its practical application. Simulations and heuristics support the face validity of the technique and its rigorousness. The characteristics of msPOAS were evaluated on single and multi-shell diffusion data of the human brain. Significant reduction in noise while preserving the fine structure was demonstrated for diffusion weighted images, standard DTI analysis and advanced diffusion models such as NODDI. MsPOAS effectively improves the poor signal-to-noise ratio in highly diffusion weighted multi-shell diffusion data, which is required by recent advanced diffusion micro-structure models. We demonstrate the superiority of the new method compared to other advanced denoising methods. (C) 2014 The Authors. Published by Elsevier Inc.

关键词： Algorithms Artifacts Brain Mapping/methods Brain Mapping/methods Diffusion Magnetic Resonance Imaging/methods Humans image processing, computer-assisted/methods Models, Theoretical

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Machine-learning techniques for building a diagnostic model for very mild dementia

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NEUROimage 2010年第1期52卷 234-244页

作者： Chen, Rong Herskovits, Edward H. Univ Penn Dept Radiol Philadelphia PA 19104 USA

Many researchers have sought to construct diagnostic models to differentiate individuals with very mild dementia (VMD) from healthy elderly people, based on structural magnetic-resonance (MR) images These models have, for the most part, been based on discriminant analysis or logistic regression, with few reports of alternative approaches To determine the relative strengths of different approaches to analyzing structural MR data to distinguish people with VMD from normal elderly control subjects, we evaluated seven different classification approaches, each of which we used to generate a diagnostic model from a training data set acquired from 83 subjects (33 VMD and 50 control) We then evaluated each diagnostic model using an independent data set acquired from 30 subjects (13 VMD and 17 controls) We found that there were significant performance differences across these seven diagnostic models Relative to the diagnostic models generated by discriminant analysis and logistic regression, the diagnostic models generated by other high-performance diagnostic-model generation algorithms manifested increased generalizability when diagnostic models were generated from all atlas structures. (C) 2010 Elsevier Inc. All rights reserved

关键词： Aged Algorithms Artificial Intelligence Atlases as Topic Brain/pathology Databases as Topic Dementia/diagnosis Dementia/pathology Diagnosis, computer-assisted/methods Discriminant Analysis Female Humans image processing, computer-assisted/methods Logistic Models Magnetic Resonance Imaging Male Models, Neurological Sensitivity and Specificity Temporal Lobe/pathology

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The impact of skull-stripping and radio-frequency bins correction on grey-matter segmentation for voxel-based morphometry

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NEUROimage 2008年第4期39卷 1654-1665页

作者： Acosta-Cabronero, Julio Williams, Guy B. Pereira, Joao M. S. Pengas, George Nestor, Peter J. Univ Cambridge Addenbrookes Hosp Sch Clin Med Dept Clin NeurosciWolfson Brain Imaging Ctr Cambridge CB2 0QQ England Univ Cambridge Addenbrookes Hosp Sch Clin Med Dept Clin NeurosciNeurol Unit Cambridge CB2 0QQ England

This study evaluates the application of (i) skull-stripping methods (hybrid watershed algorithm (HWA), brain surface extractor (BSE) and brain-extraction tool (BET2)) and (ii) bias correction algorithms (nonparametric nonuniform intensity normalisation (N3), bias field corrector (BFC) and FMRIB's automated segmentation tool (FAST)) as pre-processing pipelines for the technique of voxel-based morphometry (VBM) using statistical parametric mapping v.5 (SPM5). The pipelines were evaluated using a BrainWeb phantom, and those that performed consistently were further assessed using artificial-lesion masks applied to 10 healthy controls compared to the original unlesioned scans, and finally, 20 Alzheimer's disease (AD) patients versus 23 controls. In each case, pipelines were compared to each other and to those from default SPM5 methodology. The BET2 + N3 pipeline was found to produce the least miswarping to template induced by real abnormalities, and performed consistently better than the other methods for the above experiments. Occasionally, the clusters of significant differences located close to the boundary were dragged out of the glass-brain projections-this could be corrected by adding background noise to low-probability voxels in the grey matter segments. This method was confirmed in a one-dimensional simulation and was preferable to threshold and explicit (simple) masking which excluded true abnormalities. (C) 2007 Elsevier Inc. All rights reserved.

关键词： Adult Aged Algorithms Alzheimer Disease/pathology Brain/anatomy & histology Brain Mapping/methods Brain Mapping/methods Echo-Planar Imaging Female Humans image processing, computer-assisted/methods Male Middle Aged Models, Statistical Skull/anatomy & histology

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An automated strategy for the delineation and parcellation of commissural pathways suitable for clinical populations utilising high angular resolution diffusion imaging tractography

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NEUROimage 2010年第3期50卷 1044-1053页

作者： Pannek, Kerstin Mathias, Jane L. Bigler, Erin D. Brown, Greg Taylor, Jamie D. Rose, Stephen Univ Queensland Clin Res Ctr Brisbane Qld 4029 Australia Univ Queensland Ctr Magnet Resonance Brisbane Qld 4029 Australia Univ Adelaide Sch Psychol Adelaide SA Australia Brigham Young Univ Dept Psychol & Neurosci Provo UT 84602 USA Royal Adelaide Hosp Magnet Resonance Imaging Unit Adelaide SA 5000 Australia Univ Queensland Ctr Med Diagnost Technol Queensland St Lucia Qld Australia

There is a growing interest in understanding;alterations to the interhemispheric transfer of information as a result of brain injury and neurological disease. To facilitate research, we have developed a fully automated method for the accurate extraction of commissural pathways (corpus callosum (CC) and anterior commissure (AC)) and functional parcellation of the CC using a high angular resolution diffusion imaging (HARDI) based probabilistic tractography approach that is applicable to clinical populations. The CC was divided into 33 functional divisions based on its connections to cortical parcellations derived from individual structural images in 8 healthy participants. Probabilistic CC population maps acquired at two different b-values (1000 S mm(-2) and 3000 s mm(-2)) are presented. Topography of the CC was consistent with histology reports. We show that HARD1 data acquired at a higher b-value reveals more callosal-temporal connections than low b-value data. With respect to intra-subject precision, data acquired using a higher b-value show superior reproducibility of the delineated CC area on the midsagittal plane (MSP), as well as the total number of callosal streamlines and the number of clustered callosal streamlines. The AC was delineated in all 8 participants using high b-value HARDI tractography. Cortical projections of the AC were analysed and are in agreement with known anatomy. We conclude that, while data acquired at a lower b-value may be used, this is associated with a loss in quality, both in the delineation of commissural pathways and, potentially, the reproducibility of results over time. (C) 2010 Elsevier Inc. All rights reserved.

关键词： Adolescent Adult Aged Automation Brain/anatomy & histology Diffusion Magnetic Resonance Imaging/methods Female Humans image processing, computer-assisted/methods Male Middle Aged Neural Pathways/anatomy & histology Probability Reproducibility of Results Time Factors

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Variable precision registration via wavelets: Optimal spatial scales for inter-subject registration of functional MRI

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NEUROimage 2006年第1期31卷 197-208页

作者： Suckling, J. Long, C. Triantafyllou, C. Brammer, M. Bullmore, Edward T. Univ Cambridge Addenbrookes Hosp Dept Psychiat Brain Mapping Unit Cambridge CB2 2QQ England HMS MIT MGH Martinos Ctr Biomed Imaging Cambridge MA 02139 USA Kings Coll London Inst Psychiat London WC2R 2LS England

The detection of significantly activated brain regions in multi-subject functional magnetic resonance imaging (fMRI) studies almost invariably entails the coregistration of individual subjects' data in a standard space. Here, we investigate how sensitivity to detect loci of generic activation in such studies may be conditioned by the precision of anatomical registration. We describe a novel algorithm, implemented in the wavelet domain, for inhomogeneous deformation of individual images to match a template. The algorithm matches anatomical features in a coarse-to-fine fashion, first minimising a cost function in terms of relatively coarse spatial features and then proceeding iteratively to match the images in terms of progressively more detailed anatomical features. Applying the method to data acquired from two groups of 12 healthy volunteers (with mean age 27 and 70 years, respectively), during performance of a paired associate learning task, we show that geometrical overlap between template and individual images is monotonically improved, compared to an affine transform, by additional inhomogeneous deformations informed by more detailed features. Likewise, sensitivity to detect activated voxels can be substantially improved, by a factor of 4 or more, if wavelet-mediated deformations informed by medium-sized anatomical features are applied in addition to a preliminary affine transform. However, sensitivity to detect activated voxels was reduced by '' over-registering '' data or matching anatomical features at the finest scales of the wavelet transform. The benefits of variable precision registration are particularly salient for data acquired in older subjects, which showed evidence of greater inter-subject anatomic variability and generally required more extensive local deformation to achieve a satisfactory match to the template image. We conclude that major benefits in sensitivity to detect functional activation in multi-subject fMRI studies can be attained with an

关键词： Adult Age Factors Aged Algorithms Artifacts Brain/anatomy & histology Brain/physiology Brain Mapping Brain Mapping Echo-Planar Imaging/methods Evoked Potentials/physiology Female Humans image Enhancement/methods image processing, computer-assisted/methods Magnetic Resonance Imaging/methods Male Middle Aged Nonlinear Dynamics Oxygen/blood Sensitivity and Specificity Software

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Dissociable controlled retrieval and generalized selection mechanisms in ventrolateral prefrontal cortex

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NEURON 2005年第6期47卷 907-918页

作者： Badre, D Poldrack, RA Paré-Blagoev, EJ Insler, RZ Wagner, AD Stanford Univ Dept Psychol Stanford CA 94305 USA Stanford Univ Neurosci Program Stanford CA 94305 USA MIT Dept Brain & Cognit Sci Cambridge MA 02139 USA Univ Calif Los Angeles Dept Psychol Los Angeles CA 90095 USA Univ Calif Los Angeles Brain Res Inst Los Angeles CA 90095 USA Harvard Univ Grad Sch Educ Cambridge MA 02138 USA Martinos Ctr Biomed Imaging Charlestown MA USA

How does ventrolateral prefrontal cortex (VLPFC) control mnemonic processing? Alternative models propose that VLPFC guides top-down (controlled) retrieval of knowledge from long-term stores or selects goal-relevant products of retrieval from among competitors. A paucity of evidence supports a retrieval/selection distinction, raising the possibility that these models reduce to a common mechanism. Here, four manipulations varied semantic control demands during fMRI: judgment specificity, cue-target-associative strength, competitor dominance, and number of competitors. Factor analysis revealed evidence for a meta-factor that accounted for common behavioral variance across manipulations and for functional variance in left mid-VLPFC. These data support a generalized control process that selects relevant knowledge from among competitors. By contrast, left anterior VLPFC and middle temporal cortex were sensitive to cue-target-associative strength, but not competition, consistent with a control process that retrieves knowledge stored in lateral temporal cortex. Distinct PFC mechanisms mediate top-down retrieval and postretrieval selection.

关键词： Adolescent Adult Brain Mapping Brain Mapping Cues Factor Analysis, Statistical Female Functional Laterality/physiology Generalization (Psychology)/physiology Humans image processing, computer-assisted/methods Judgment/physiology Magnetic Resonance Imaging/methods Male Mental Recall/physiology Oxygen/blood Photic Stimulation/methods Prefrontal Cortex/blood supply Prefrontal Cortex/physiology Reaction Time/physiology Semantics

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Multivariate examination of brain abnormality using both structural and functional MRI

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NEUROimage 2007年第4期36卷 1189-1199页

作者： Fan, Yong Rao, Hengyi Hurt, Hallam Giannetta, Joan Korczykowski, Marc Shera, David Avants, Brian B. Gee, James C. Wang, Jiongjiong Shen, Dinggang Univ Penn Dept Radiol Philadelphia PA 19104 USA Univ Penn Ctr Funct Neuroimaging Dept Neurol Philadelphia PA 19104 USA Childrens Hosp Philadelphia Dept Pediat Div Neonatol Philadelphia PA 19104 USA

A multivariate classification approach has been presented to examine the brain abnormalities, i.e., due to prenatal cocaine exposure, using both structural and functional brain images. First, a regional statistical feature extraction scheme was adopted to capture discriminative features from voxel-wise morphometric and functional representations of brain images, in order to reduce the dimensionality of the features used for classification, as well as to achieve the robustness to registration error and inter-subject variations. Then, this feature extraction method was used in conjunction with a hybrid feature selection method and a nonlinear support vector machine for the classification of brain abnormalities. This brain classification approach has been applied to detecting the brain abnormality associated with prenatal cocaine exposure in adolescents. A promising classification performance was achieved on a data set of 49 subjects (24 normal and 25 prenatally. cocaine-exposed teenagers), with a leave-one-out cross-validation. Experimental results demonstrated the efficacy of our method, as well as the importance of incorporating both structural and functional images for brain classification. Moreover, spatial patterns of group difference derived front the constructed classifier were mostly consistent with the results of the conventional statistical analysis method. Therefore, the proposed approach provided not only a multivariate classification method for detecting brain abnormalities, but also an alternative way for group analysis of multimodality images. (C) 2007 Elsevier Inc. All rights reserved.

关键词： Adolescent Algorithms Artificial Intelligence Brain/drug effects Brain/pathology Brain/physiopathology Cocaine/toxicity Female Humans image Enhancement/methods image processing, computer-assisted/methods Magnetic Resonance Imaging/methods Multivariate Analysis Nonlinear Dynamics Pregnancy Prenatal Exposure Delayed Effects Sensitivity and Specificity Software Street Drugs/toxicity

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