Alterations in Multiple Measures of White Matter Integrity in Normal Women at High Risk for Alzheimer\u27s Disease

There is evidence that disruption of white matter (WM) microstructure is an early event in the course of Alzheimer\u27s disease (AD). However, the neurobiological bases of WM microstructural declines in presymptomatic AD are unknown. In the present study we address this issue using a multimodal imaging approach to the study of presymptomatic AD. Participants were 37 high-risk (both family history of dementia and one or more APOE4 alleles) women and 20 low-risk (neither family history nor APOE4) women. Groups were matched for age, education, neuropsychological performance, and vascular factors that could affect white matter. Whole-brain analyses of diffusion tensor imaging data [including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (DA) and radial diffusivity (DR)] and volumetric comparisons of medial temporal lobe (MTL) structures were conducted. Results indicated equivalent entorhinal cortex and hippocampal volumes between risk groups. Nevertheless, the high risk group showed decreased microstructural integrity in WM tracts with direct and secondary connections to the MTL. The predominant alteration in WM integrity in the high AD-risk group was decreased FA not solely driven by either DA or DR changes alone in regions where no MD changes were observed. A second pattern observed in a smaller number of regions involved decreased FA and increased DR. These results suggest that disconnection of MTL-neocortical fiber pathways represents a very early event in the course of AD and suggest that demyelination may represent one contributing mechanism

Diffusion Tensor Imaging Predictors of Episodic Memory Decline in Healthy Elders at Genetic Risk for Alzheimer’s Disease

Objectives: White matter (WM) integrity within the mesial temporal lobe (MTL) is important for episodic memory (EM) functioning. The current study investigated the ability of diffusion tensor imaging (DTI) in MTL WM tracts to predict 3-year changes in EM performance in healthy elders at disproportionately higher genetic risk for Alzheimer’s disease (AD). Methods: Fifty-one cognitively intact elders (52% with family history (FH) of dementia and 33% possessing an Apolipoprotein E ε4 allelle) were administered the Rey Auditory Verbal Learning Test (RAVLT) at study entry and at 3-year follow-up. DTI scanning, conducted at study entry, examined fractional anisotropy and mean, radial and axial diffusion within three MTL WM tracts: uncinate fasciculus (UNC), cingulate-hippocampal (CHG), and fornix-stria terminalis (FxS). Correlations were performed between residualized change scores computed from RAVLT trials 1–5, immediate recall, and delayed recall scores and baseline DTI measures; MTL gray matter (GM) and WM volumes; demographics; and AD genetic and metabolic risk factors. Results: Higher MTL mean and axial diffusivity at baseline significantly predicted 3-year changes in EM, whereas baseline MTL GM and WM volumes, FH, and metabolic risk factors did not. Both ε4 status and DTI correlated with change in immediate recall. Conclusions: Longitudinal EM changes in cognitively intact, healthy elders can be predicted by disruption of the MTL WM microstructure. These results are derived from a sample with a disproportionately higher genetic risk for AD, suggesting that the observed WM disruption in MTL pathways may be related to early neuropathological changes associated with the preclinical stage of AD. (JINS, 2016, 22, 1005–1015

Hippocampal subfields and limbic white matter jointly predict learning rate in older adults

First published online: 04 December 2019Age-related memory impairments have been linked to differences in structural brain parameters, including cerebral white matter (WM) microstructure and hippocampal (HC) volume, but their combined influences are rarely investigated. In a population-based sample of 337 older participants aged 61-82 years (Mage = 69.66, SDage = 3.92 years), we modeled the independent and joint effects of limbic WM microstructure and HC subfield volumes on verbal learning. Participants completed a verbal learning task of recall over five repeated trials and underwent magnetic resonance imaging (MRI), including structural and diffusion scans. We segmented three HC subregions on high-resolution MRI data and sampled mean fractional anisotropy (FA) from bilateral limbic WM tracts identified via deterministic fiber tractography. Using structural equation modeling, we evaluated the associations between learning rate and latent factors representing FA sampled from limbic WM tracts, and HC subfield volumes, and their latent interaction. Results showed limbic WM and the interaction of HC and WM-but not HC volume alone-predicted verbal learning rates. Model decomposition revealed HC volume is only positively associated with learning rate in individuals with higher WM anisotropy. We conclude that the structural characteristics of limbic WM regions and HC volume jointly contribute to verbal learning in older adults

Spinal and encephalic structural damage in spinocerebellar ataxia type 1 : characterization and clinical correlates

Orientador: Marcondes Cavalcante França JuniorTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciências MédicasResumo: A ataxia espinocerebelar do tipo 1 (SCA1) é uma doença neurodegenerativa cuja expressão clínica predominante é a ataxia cerebelar progressiva associada à hiperreflexia profunda e às alterações sacádicas. Causada por expansão instável de uma sequência CAG no gene ATXN1 no cromossomo 6, foi a primeira ataxia espinocerebelar que teve seu substrato genético elucidado. Apesar disso, existem poucos estudos acerca de seus aspectos clínicos e morfológicos, principalmente no que diz respeito às manifestações não motoras e suas correlações estruturais. Desta forma, o objetivo deste trabalho é caracterizar, clínica e morfologicamente, os pacientes com SCA1, utilizando escalas clínicas bem estabelecidas e técnicas multimodais de ressonância magnética. Para tanto, foram recrutados 33 pacientes adultos com teste molecular positivo para SCA1 acompanhados nos serviços de neurologia da UNICAMP e UNIFESP. Os pacientes foram submetidos a exame neurológico pormenorizado, enfatizando aspectos motores e não-motores. Para a graduação da ataxia utilizou-se a Scale for the Assessment and Rating of Ataxia (SARA). Para avaliação de sintomas não-motores utilizou-se a Modified Fatigue Impact Scale (MFIS) para fadiga, Epworth Sleepiness Scale (ESS) para sonolência excessiva diurna, Beck Depression Inventory (BDI) para depressão e Addenbrooke¿s Cognitive Examination ¿ Revised (ACE-R) para cognição. O dano estrutural encefálico e medular foi avaliado por imagens de ressonância magnética ponderadas em T1 e DTI. Para análise, foram utilizadas as ferramentas FreeSurfer, T1 MultiAtlas, DTI MultiAtlas, CERES e SpineSeg. Com o objetivo de avaliar evolutivamente a SCA1, os pacientes foram divididos em três grupos de acordo com o tempo de doença. Variáveis clínicas e imaginológicas foram comparadas nesses grupos a fim de determinar, temporalmente, o padrão evolutivo das alterações no SNC. Os sintomas motores correlacionaram-se diretamente com o dano dos núcleos rubros, medular e cerebelar. Os níveis de fadiga foram significativamente maiores nos pacientes comparado aos controles e apresentaram relação direta com depressão e duração da doença. A depressão foi mais frequente nos pacientes e correlacionou-se com aspectos motores, entretanto, não houve correlação com áreas encefálicas. As alterações cognitivas foram importantes, principalmente nos domínios de memória e fluência, os quais correlacionaram-se diretamente com atrofia na amígdala e lóbulo VIII cerebelar, respectivamente. Evidenciou-se redução da área e aumento da excentricidade significativos na medula cervical dos pacientes quando comparados aos controles. A redução da área medular correlacionou-se diretamente com aspectos motores, apresentando duração e CAGn como possíveis determinantes. Avaliações transversais do encéfalo revelaram danos significativos em áreas primárias e associativas em córtex cerebral, substância cinzenta profunda, córtex cerebelar e subtância branca encefálica, principalmente em regiões infratentoriais. Do ponto de vista evolutivo, verificou-se padrão lesional em sentido caudo-cranial. Por fim, fomos capazes de caracterizar fenoticamente a SCA1 e correlacionar seus aspectos clínicos e estruturaisAbstract: Spinocerebellar ataxia type 1 (SCA1) is a neurodegenerative disease expressed clinically by progressive cerebellar ataxia associated with deep hyperreflexia and saccadic alterations. Caused by unstable expansions of a CAG sequence in the ATXN1 gene on chromosome 6, it was the first spinocerebellar ataxia that had its genetic substrate elucidated. Despite this, there are few studies about its clinical and morphological aspects, mainly regarding non-motor manifestations and their structural correlations. In this way, the objective of this study is to characterize, clinically and morphologically, patients with SCA1, using well-established clinical scales and multimodal magnetic resonance techniques. We have thus evaluated 33 consecutive adult patients regularly followed at UNICAMP and UNIFESP and 33 healthy age-and-sex matched controls. All patients had molecular confirmation of SCA1. The patients underwent detailed neurological examination, emphasizing motor and non-motor aspects. For ataxia quantification, the Scale for the Assessment and Rating of Ataxia (SARA) was used. For the evaluation of non-motor symptoms, we used the Modified Fatigue Impact Scale (MFIS) for fatigue, Epworth Sleepiness Scale (ESS) for excessive daytime sleepiness, Beck Depression Inventory (BDI) for depression and Addenbrooke's Cognitive Examination ¿ Revised (ACE-R) for cognition aspects. The encephalic and spinal structural damage were evaluated by DTI and T1-weighted magnetic resonance imaging. For MRI analyses, the tools FreeSurfer, T1 MultiAtlas, DTI MultiAtlas, CERES and SpineSeg were used. Attempting to analyse the evolution pattern, the patients were divided into three groups according to the disease duration. Clinical and imaging variables were compared in these groups to determine the evolutionary pattern of CNS changes. Motor symptoms correlated to damage of red nuclei, spinal cord and cerebellar cortex. Fatigue levels were significantly higher in patients compared to controls and were directly related to depression and disease duration. Depression was more frequent in patients and correlated to motor aspects, however, there was no association with brain areas. Cognitive alterations were important, especially in memory and fluency domains, which correlated directly to atrophy in the amygdala and cerebellar lobe VIII, respectively. Significant area reduction and eccentricity increase were observed in patients' cervical spinal cord when compared to controls. The reduction of the cord area correlated directly to motor aspects; and duration and CAGn were possible determinants. Cross-sectional brain evaluations revealed significant damage in primary and associative areas in cerebral cortex, deep gray matter, cerebellar cortex and encephalic white matter, especially in infratentorial regions. Analysis of disease course disclosed a caudal-cranial pattern of damage in the CNS. Finally, we were able to phenotypically characterize SCA1 and to correlate its clinical and structural aspectsDoutoradoFisiopatologia MédicaDoutor em Ciência

Delineation of hippocampal subregions using T1-weighted magnetic resonance images at 3 Tesla

Although several novel approaches for hippocampal subregion delineation have been developed, they need to be applied prospectively and may be limited by long scan times, the use of high field (\u3e3T) imaging systems, and limited reliability metrics. Moreover, the majority of MR imaging data collected to date has employed a T1-weighted acquisition, creating a critical need for an approach that provides reliable hippocampal subregion segmentation using such a contrast. We present a highly reliable approach for the identification of six subregions comprising the hippocampal formation from MR images including the subiculum, dentate gyrus/cornu Ammonis 4 (DG/CA4), entorhinal cortex, fimbria, and anterior and posterior segments of cornu Ammonis 1-3 (CA1-3). MR images were obtained in the coronal plane using a standard 3D spoiled gradient sequence acquired on a GE 3T scanner through the whole head in approximately 10 min. The average ICC for inter-rater reliability across right and left volumetric regions-of-interest was 0.85 (range 0.71-0.98, median 0.86) and the average ICC for intra-rater reliability was 0.92 (range 0.66-0.99, median 0.97). The mean Dice index for inter-rater reliability across right and left hemisphere subregions was 0.75 (range 0.70-0.81, median 0.75) and the mean Dice index for intra-rater reliability was 0.85 (range 0.82-0.90, median 0.85). An investigation of hippocampal asymmetry revealed significantly greater right compared to left hemisphere volumes in the anterior segment of CA1-3 and in the subiculum

Cerebral atrophy in mild cognitive impairment and Alzheimer disease: rates and acceleration.

OBJECTIVE: To quantify the regional and global cerebral atrophy rates and assess acceleration rates in healthy controls, subjects with mild cognitive impairment (MCI), and subjects with mild Alzheimer disease (AD). METHODS: Using 0-, 6-, 12-, 18-, 24-, and 36-month MRI scans of controls and subjects with MCI and AD from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database, we calculated volume change of whole brain, hippocampus, and ventricles between all pairs of scans using the boundary shift integral. RESULTS: We found no evidence of acceleration in whole-brain atrophy rates in any group. There was evidence that hippocampal atrophy rates in MCI subjects accelerate by 0.22%/year2 on average (p = 0.037). There was evidence of acceleration in rates of ventricular enlargement in subjects with MCI (p = 0.001) and AD (p < 0.001), with rates estimated to increase by 0.27 mL/year2 (95% confidence interval 0.12, 0.43) and 0.88 mL/year2 (95% confidence interval 0.47, 1.29), respectively. A post hoc analysis suggested that the acceleration of hippocampal loss in MCI subjects was mainly driven by the MCI subjects that were observed to progress to clinical AD within 3 years of baseline, with this group showing hippocampal atrophy rate acceleration of 0.50%/year2 (p = 0.003). CONCLUSIONS: The small acceleration rates suggest a long period of transition to the pathologic losses seen in clinical AD. The acceleration in hippocampal atrophy rates in MCI subjects in the ADNI seems to be driven by those MCI subjects who concurrently progressed to a clinical diagnosis of AD

Multimodal population brain imaging in the UK Biobank prospective epidemiological study

Medical imaging has enormous potential for early disease prediction, but is impeded by the difficulty and expense of acquiring data sets before symptom onset. UK Biobank aims to address this problem directly by acquiring high-quality, consistently acquired imaging data from 100,000 predominantly healthy participants, with health outcomes being tracked over the coming decades. The brain imaging includes structural, diffusion and functional modalities. Along with body and cardiac imaging, genetics, lifestyle measures, biological phenotyping and health records, this imaging is expected to enable discovery of imaging markers of a broad range of diseases at their earliest stages, as well as provide unique insight into disease mechanisms. We describe UK Biobank brain imaging and present results derived from the first 5,000 participants' data release. Although this covers just 5% of the ultimate cohort, it has already yielded a rich range of associations between brain imaging and other measures collected by UK Biobank

Standard‐space atlas of the viscoelastic properties of the human brain

Standard anatomical atlases are common in neuroimaging because they facilitate data analyses and comparisons across subjects and studies. The purpose of this study was to develop a standardized human brain atlas based on the physical mechanical properties (i.e., tissue viscoelasticity) of brain tissue using magnetic resonance elastography (MRE). MRE is a phase contrast-based MRI method that quantifies tissue viscoelasticity noninvasively and in vivo thus providing a macroscopic representation of the microstructural constituents of soft biological tissue. The development of standardized brain MRE atlases are therefore beneficial for comparing neural tissue integrity across populations. Data from a large number of healthy, young adults from multiple studies collected using common MRE acquisition and analysis protocols were assembled (N = 134; 78F/ 56 M; 18–35 years). Nonlinear image registration methods were applied to normalize viscoelastic property maps (shear stiffness, μ, and damping ratio, ξ) to the MNI152 standard structural template within the spatial coordinates of the ICBM-152. We find that average MRE brain templates contain emerging and symmetrized anatomical detail. Leveraging the substantial amount of data assembled, we illustrate that subcortical gray matter structures, white matter tracts, and regions of the cerebral cortex exhibit differing mechanical characteristics. Moreover, we report sex differences in viscoelasticity for specific neuroanatomical structures, which has implications for understanding patterns of individual differences in health and disease. These atlases provide reference values for clinical investigations as well as novel biophysical signatures of neuroanatomy. The templates are made openly available (github.com/mechneurolab/mre134) to foster collaboration across research institutions and to support robust cross-center comparisons

Development and application of a human cortical brain atlas on MRI considering phylogeny = Développement et emploi d’un atlas du cortex cérébral humain réalisé sur IRM et tenant compte de la phylogénie

Le cortex cérébral est une structure en couches complexe qui remplit différents types de fonctions. Au cours de l’histoire des neurosciences, plusieurs atlas corticaux ont été développés pour classifier différentes régions du cortex en tant que zones aux caractéristiques structurelles ou fonctionnelles communes, afin d'étudier et de quantifier les changements aux états sain et pathologique. Cependant, il n'existe pas d'atlas suivant une approche phylogénétique, c'est-à-dire, basée sur les critères d'évolution communs. Ce mémoire présente les étapes de création d'un nouvel atlas dans un modèle d’imagerie par résonance magnétique (IRM) en espace standard (pseudo-Talairach) : le PAN-Atlas, basé sur l'origine phylogénétique commune de chaque zone corticale, et son application sur des scans d’IRM de dix individus pour évaluer sa performance. D’abord, nous avons regroupé les différentes régions corticales en cinq régions d'intérêt (RdI) d'origine phylogénétique connue (archicortex, paléocortex, périarchicortex, proïsocortex, isocortex ou néocortex) sur la base de protocoles de segmentation validés histologiquement par d'autres groupes de chercheurs. Puis, nous avons segmenté ces régions manuellement sur le modèle d’IRM cérébrale moyen MNI-ICBM 2009c, en formant des masques. Par la suite, on a utilisé un pipeline multi-étapes de traitement des images pour réaliser le recalage des masques de notre atlas aux scans pondérés T1 de dix participants sains, en obtenant ainsi des masques automatiques pour chaque RdI. Les masques automatiques ont été évalués après une correction manuelle par le biais de l’indice Dice-kappa, qui quantifie la colocalisation des voxels de chaque masque automatique vs. le masque corrigé manuellement. L’indice a montré une très bonne à excellente performance de notre atlas. Cela a permis l’évaluation et comparaison des volumes corticales de chaque région et la quantification des valeurs de transfert de magnétisation (ITM), qui sont sensibles à la quantité de myéline présente dans le tissu. Ce travail montre que la division régionale du cortex en IRM avec une approche phylogénétique est réalisable à l'aide de notre PAN-Atlas en espace standard et que les masques peuvent être utilisés pour différents types de quantifications, comme les volumes corticaux, ou l’estimation des valeurs de ITM. Notre atlas pourrait éventuellement servir à évaluer les différences entre personnes saines et celles atteintes par des maladies neurodégénératives ou d’autres maladies neurologiques.The cerebral cortex is a complex layered structure that performs different types of functions. Throughout the history of neuroscience, several cortical atlases have been developed to classify/divide different regions of the cortex into areas with common structural or functional characteristics, to then study and quantify changes in healthy and pathological states. However, to date, there is no atlas following a phylogenetic approach, i.e. based on the common evolution criteria. This thesis presents the steps of creation of a new atlas corresponding to a standard MRI template: the PAN-Atlas, based on the common phylogenetic origin of each cortical zone, and its application on MRI scans of ten healthy participants to assess its performance. First, we grouped the different cortical regions into five regions of interest (ROI) of known phylogenetic origin (archicortex, paleocortex, periarchicortex, proisocortex, isocortex or neocortex) based on MRI protocols previously validated through histology by other groups of researchers. Then, we manually segmented these ROIs on the MNI-ICBM 2009c average brain MRI template, creating corresponding masks. We then used a multi-step image processing pipeline to register the atlas’ masks to T1 weighted images of ten healthy participants, generating automatic masks for each scan. The accuracy of these automatic atlas’ masks was assessed after manual correction using Dice-kappa similarity index, to quantify the colocalization of the automatic vs. the manually corrected masks. The Dice-kappa values showed a very good to excellent performance of the automatic atlas’ masks. This allowed the evaluation and comparison of cortical volumes of each ROI, as well as the quantification of magnetization transfer ratio (MTR) values, which are sensitive to myelin content. This work shows that the division of the cortex on MRI following a phylogenetic approach is feasible using our PAN Atlas, and that the masks of the atlas can be used to perform different types of quantifications, such as the ones presented here (cortical volume and MTR per ROI). Our atlas could similarly be used to assess differences between the cortex of healthy individuals and people affected by neurodegenerative diseases and other neurological disorders