Similarity between structural and proxy estimates of brain connectivity.

Functional magnetic resonance and diffusion weighted imaging have so far made a major contribution to delineation of the brain connectome at the macroscale. While functional connectivity (FC) was shown to be related to structural connectivity (SC) to a certain degree, their spatial overlap is unknown. Even less clear are relations of SC with estimates of connectivity from inter-subject covariance of regional F18-fluorodeoxyglucose uptake (FDGcov) and grey matter volume (GMVcov). Here, we asked to what extent SC underlies three proxy estimates of brain connectivity: FC, FDGcov and GMVcov. Simultaneous PET/MR acquisitions were performed in 56 healthy middle-aged individuals. Similarity between four networks was assessed using Spearman correlation and convergence ratio (CR), a measure of spatial overlap. Spearman correlation coefficient was 0.27 for SC-FC, 0.40 for SC-FDGcov, and 0.15 for SC-GMVcov. Mean CRs were 51% for SC-FC, 48% for SC-FDGcov, and 37% for SC-GMVcov. These results proved to be reproducible and robust against image processing steps. In sum, we found a relevant similarity of SC with FC and FDGcov, while GMVcov consistently showed the weakest similarity. These findings indicate that white matter tracts underlie FDGcov to a similar degree as FC, supporting FDGcov as estimate of functional brain connectivity.

Network structure-function coupling and neurocognition in cerebral small vessel disease.

BACKGROUND: Cerebral small vessel disease is a leading cause of cognitive decline and vascular dementia. Small vessel disease pathology changes structural brain networks, but its impact on functional networks remains poorly understood. Structural and functional networks are closely coupled in healthy individuals, and decoupling is associated with clinical symptoms in other neurological conditions. We tested the hypothesis that structural-functional network coupling is related to neurocognitive outcomes in 262 small vessel disease patients. METHODS: Participants underwent multimodal magnetic resonance imaging and cognitive assessment in 2011 and 2015. Structural connectivity networks were reconstructed using probabilistic diffusion tractography, while functional connectivity networks were estimated from resting-state functional magnetic resonance imaging. Structural and functional networks were then correlated to calculate a measure of structural-functional network coupling for each participant. RESULTS: Lower whole-brain coupling was associated with reduced processing speed and greater apathy both cross-sectionally and longitudinally. In addition, coupling within the cognitive control network was associated with all cognitive outcomes, suggesting that neurocognitive outcomes in small vessel disease may be related to the functioning of this intrinsic connectivity network. CONCLUSIONS: Our work demonstrates the influence of structural-functional connectivity network decoupling in small vessel disease symptomatology. Cognitive control network function may be investigated in future studies.

Cerebral small vessel disease burden and cognitive and functional outcomes after stroke: A multicenter prospective cohort study.

INTRODUCTION: It remains unknown whether the global small vessel disease (SVD) burden predicts post-stroke outcomes. METHODS: In a prospective multicenter study of 666 ischemic and hemorrhagic stroke patients, we quantified magnetic resonance imaging (MRI)-based SVD markers (lacunes, white matter hyperintensities, microbleeds, perivascular spaces) and explored associations with 6- and 12-month cognitive (battery of 15 neuropsychological tests) and functional (modified Rankin scale) outcomes. RESULTS: A global SVD score (range 0-4) was associated with cognitive impairment; worse performance in executive function, attention, language, and visuospatial ability; and worse functional outcome across a 12-month follow-up. Although the global SVD score did not improve prediction, individual SVD markers, assessed across their severity range, improved the calibration, discrimination, and reclassification of predictive models including demographic, clinical, and other imaging factors. DISCUSSION: SVD presence and severity are associated with worse cognitive and functional outcomes 12 months after stroke. Assessing SVD severity may aid prognostication for stroke patients. HIGHLIGHTS: In a multi-center cohort, we explored associations of small vessel disease (SVD) burden with stroke outcomes. SVD burden associates with post-stroke cognitive and functional outcomes. A currently used score of SVD burden does not improve the prediction of poor outcomes. Assessing the severity of SVD lesions adds predictive value beyond known predictors. To add predictive value in assessing SVD in stroke patients, SVD burden scores should integrate lesion severity.

Sex differences of vascular brain lesions in patients with atrial fibrillation.

OBJECTIVE: To examine sex differences in prevalence, volume and distribution of vascular brain lesions on MRI among patients with atrial fibrillation (AF). METHODS: In this cross-sectional analysis, we included 1743 patients with AF (27% women) from the multicentre Swiss Atrial Fibrillation study (SWISS-AF) with available baseline brain MRI. We compared presence and total volume of large non-cortical or cortical infarcts (LNCCIs), small non-cortical infarcts, microbleeds (MB) and white matter hyperintensities (WMH, Fazekas score ≥2 for moderate or severe degree) between men and women with multivariable logistic regression. We generated voxel-based probability maps to assess the anatomical distribution of lesions. RESULTS: We found no strong evidence for an association of female sex with the prevalence of all ischaemic infarcts (LNCCI and SNCI combined; adjusted OR 0.86, 95% CI 0.67 to 1.09, p=0.22), MB (adjusted OR 0.91, 95% CI 0.68 to 1.21, p=0.52) and moderate or severe WMH (adjusted OR 1.15, 95% CI 0.90 to 1.48, p=0.27). However, total WMH volume was 17% larger among women than men (multivariable adjusted multiplicative effect 1.17, 95% CI 1.01 to 1.35; p=0.04). Lesion probability maps showed a right hemispheric preponderance of ischaemic infarcts in both men and women, while WMH were distributed symmetrically. CONCLUSION: Women had higher white matter disease burden than men, while volume and prevalence of other lesions did not differ. Our findings highlight the importance of controlling risk factors for cerebral small vessel disease in patients with AF, especially among women.

Cognitive Improvement After Kidney Transplantation Is Associated With Structural and Functional Changes on MRI.

BACKGROUND: Several studies have reported improved cognitive outcomes after kidney transplantation, but most studies either did not include controls or lacked extensive neuroimaging. In addition, there is uncertainty whether kidney donation is a safe procedure in terms of cognitive outcomes. METHODS: We prospectively studied neurocognitive function in kidney transplant recipients. The primary outcome was change in neurocognitive function after 1 year compared with baseline, which was evaluated using the Amsterdam Neuropsychological Task battery and verbal fluency tests. Secondary outcomes included changes in depression and anxiety (measured by the Hospital Anxiety and Depression scale) and changes in fatigue (measured by the Checklist for Individual Strength). We included kidney donors to control for learning effects, socioeconomic status, and surgery. In addition, kidney transplant recipients were evaluated with MRI scans at baseline and at year 1. The MRI protocol included conventional MRI, automated volumetric measurement, diffusion tensor imaging, magnetic resonance spectroscopy, arterial spin labeling, and a resting state functional MRI. RESULTS: Twenty-seven recipients and 24 donors were included. For both recipients and donors, neuropsychologic testing scores improved 1 year after transplantation (donation). Recipient improvement significantly exceeded donor improvement on tasks measuring attention and working memory. These improvements were associated with increases in white matter volume and N-acetylaspartate/creatine (a marker for neuronal integrity). CONCLUSIONS: Attention and working memory improve significantly 1 year after kidney transplantation. Learning effects do not account for these improvements because recipient improvement in these areas exceeds donor improvement and correlates with an improvement in white matter integrity after transplantation. Kidney donation appears to be a safe procedure in terms of cognitive outcomes.

Machine learning analysis of whole mouse brain vasculature.

Tissue clearing methods enable the imaging of biological specimens without sectioning. However, reliable and scalable analysis of large imaging datasets in three dimensions remains a challenge. Here we developed a deep learning-based framework to quantify and analyze brain vasculature, named Vessel Segmentation & Analysis Pipeline (VesSAP). Our pipeline uses a convolutional neural network (CNN) with a transfer learning approach for segmentation and achieves human-level accuracy. By using VesSAP, we analyzed the vascular features of whole C57BL/6J, CD1 and BALB/c mouse brains at the micrometer scale after registering them to the Allen mouse brain atlas. We report evidence of secondary intracranial collateral vascularization in CD1 mice and find reduced vascularization of the brainstem in comparison to the cerebrum. Thus, VesSAP enables unbiased and scalable quantifications of the angioarchitecture of cleared mouse brains and yields biological insights into the vascular function of the brain.

In vivo widefield calcium imaging of the mouse cortex for analysis of network connectivity in health and brain disease.

The organization of brain areas in functionally connected networks, their dynamic changes, and perturbations in disease states are subject of extensive investigations. Research on functional networks in humans predominantly uses functional magnetic resonance imaging (fMRI). However, adopting fMRI and other functional imaging methods to mice, the most widely used model to study brain physiology and disease, poses major technical challenges and faces important limitations. Hence, there is great demand for alternative imaging modalities for network characterization. Here, we present a refined protocol for in vivo widefield calcium imaging of both cerebral hemispheres in mice expressing a calcium sensor in excitatory neurons. We implemented a stringent protocol for minimizing anesthesia and excluding movement artifacts which both imposed problems in previous approaches. We further adopted a method for unbiased identification of functional cortical areas using independent component analysis (ICA) on resting-state imaging data. Biological relevance of identified components was confirmed using stimulus-dependent cortical activation. To explore this novel approach in a model of focal brain injury, we induced photothrombotic lesions of the motor cortex, determined changes in inter- and intrahemispheric connectivity at multiple time points up to 56 days post-stroke and correlated them with behavioral deficits. We observed a severe loss in interhemispheric connectivity after stroke, which was partially restored in the chronic phase and associated with corresponding behavioral motor deficits. Taken together, we present an improved widefield calcium imaging tool accounting for anesthesia and movement artifacts, adopting an advanced analysis pipeline based on human fMRI algorithms and with superior sensitivity to recovery mechanisms in mouse models compared to behavioral tests. This tool will enable new studies on interhemispheric connectivity in murine models with comparability to human imaging studies for a wide spectrum of neuroscience applications in health and disease.

Decreased CSF Levels of ß-Amyloid in Patients With Cortical Superficial Siderosis.

Background: Cortical superficial siderosis (cSS) represents a key neuroimaging marker of cerebral amyloid angiopathy (CAA) that is associated with intracranial hemorrhages and cognitive impairment. Nevertheless, the association between cSS and core cerebrospinal fluid (CSF) biomarkers for dementia remain unclear. Methods: One hundred and one patients with probable (79%, 80/101) or possible (21%, 21/101) CAA according to the modified Boston criteria and mild cognitive impairment according to Petersen criteria were prospectively included between 2011 and 2016. CSF analyses of ß-amyloid 42, ß-amyloid 40, total tau and phosphorylated tau were performed using sandwich-type enzyme-linked immunosorbent-assay. All patients received MRI and Mini-Mental-State Examination (MMSE). Logistic regression analysis was used to adjust for possible confounders. Results: cSS was present in 61% (62/101). Of those, 53% (33/62) had disseminated cSS and 47% (29/62) focal cSS. ß-amyloid 42 was lower in patients with cSS than in patients without cSS (OR 0.2; 95% CI 0.08-0.6; p = 0.0052) and lower in patients with disseminated cSS than in those with focal cSS (OR 0.02; 95% CI 0.003-0.2; p = 0.00057). Presence of cSS had no association with regard to ß-amyloid 40, total tau and phosphorylated tau. Conclusions: Our results demonstrate that the presence and extent of cSS are associated with reduced CSF ß-amyloid 42 levels. Further studies are needed to investigate the underlying mechanisms of this association.

Harmonizing brain magnetic resonance imaging methods for vascular contributions to neurodegeneration.

INTRODUCTION: Many consequences of cerebrovascular disease are identifiable by magnetic resonance imaging (MRI), but variation in methods limits multicenter studies and pooling of data. The European Union Joint Program on Neurodegenerative Diseases (EU JPND) funded the HARmoNizing Brain Imaging MEthodS for VaScular Contributions to Neurodegeneration (HARNESS) initiative, with a focus on cerebral small vessel disease. METHODS: Surveys, teleconferences, and an in-person workshop were used to identify gaps in knowledge and to develop tools for harmonizing imaging and analysis. RESULTS: A framework for neuroimaging biomarker development was developed based on validating repeatability and reproducibility, biological principles, and feasibility of implementation. The status of current MRI biomarkers was reviewed. A website was created at www.harness-neuroimaging.org with acquisition protocols, a software database, rating scales and case report forms, and a deidentified MRI repository. CONCLUSIONS: The HARNESS initiative provides resources to reduce variability in measurement in MRI studies of cerebral small vessel disease.

Arterial branching and basal ganglia lacunes: A study in pure small vessel disease.

INTRODUCTION: Lacunes are defined morphologically by size and location, but radiological characteristics alone may be unable to distinguish small vessel disease aetiology from alternative mechanisms. We investigated the branching order of arterial vessels associated with basal ganglia lacunes in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), in order to improve the understanding of their pathogenesis in pure cerebral small vessel disease. PATIENTS AND METHODS: Adults with a confirmed diagnosis of CADASIL were included. A pilot study was conducted in a Scottish CADASIL cohort. The Paris-Munich CADASIL cohort was used for independent validation. Lacunes identified on T1-weighted magnetic resonance imaging scans were registered to a standard brain template. A microangiographic template of the basal ganglia vasculature was automatically overlaid onto coronal slices, and raters estimated the vessel branching order related to each lacune. RESULTS: Of 179 lacunes, 150 (84%) were associated with third-order vessels. In 14 incident lacunes, 11 (79%) were associated with third-order vessels. In the pilot study, lacune volume was significantly lower in lacunes associated with third-order vessels (0.04 ml ± 0.04 ml) compared to second-order vessels (0.48 ± 0.16 ml; p < 0.001). DISCUSSION: In this study of CADASIL patients, most lacunes were small and associated with third-order vessel disease. This suggests that these are the vessels primarily affected in cerebral small vessel disease. Microangiographic template techniques could be used to further investigate in a general stroke population whether finding large lacunes originating from higher order vessels indicates an alternative cause of stroke. CONCLUSION: Lacunes in pure small vessel disease are associated with the smallest vessels in the basal ganglia.

Extensive white matter hyperintensities may increase brain volume in cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy.

BACKGROUND AND PURPOSE: The extent of white matter hyperintensities (WMH) is associated with cerebral atrophy in elderly people. WMH is a radiological hallmark of cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), but their relationship with brain volume remains poorly understood. The association between WMH and brain volume was analyzed in a large population of patients with CADASIL. METHODS: Demographic and MRI data of 278 patients recruited from a prospective cohort study were analyzed. Volumes of WMH and lacunar infarcts, number of cerebral microbleeds, and brain parenchymal fraction were measured. Multivariate analysis was used to study the impact of WMH on brain volume at baseline. RESULTS: In univariate analyses, brain parenchymal fraction was negatively associated with age, male sex, and all MRI markers. Multiple regression modeling showed that brain parenchymal fraction was inversely related to age, number of cerebral microbleeds, and normalized volume of lacunar infarcts but positively related to normalized volume of WMH (P<0.001). This positive relationship was independent of the presence/absence of lacunar infarcts or of cerebral microbleeds. Subgroup analysis showed that this association was significant in subjects having normalized volume of WMH ≥6.13 or brain parenchymal fraction ≥86.37% (median values, both P≤0.001). CONCLUSIONS: The results of the present study suggest that extensive WMH may be associated with increase of brain volume in CADASIL. In this disorder, WMH may be related not only to loss of white matter components, but also to a global increase of water content in the cerebral tissue.

White-matter lesions without lacunar infarcts in CADASIL.

To better characterize the clinical spectrum related to white-matter hyperintensities (WMH) in small vessel disease, 66 patients with WMH but without any lacunar infarct were selected out of a cohort of 248 CADASIL individuals. Characteristics of these patients were compared to those of patients with lacunar infarcts. Relationships between the normalized volume of WMH (nWMH), presence of microhemorrhages, brain parenchymal fraction (BPF). and cognitive performances were assessed. The Trail Making Test (TMT) A and B times, Mattis Dementia Rating Scale (MDRS) total score, attention subscore, verbal fluency score and delayed memory recall were significantly correlated with nWMH but not with BPF. Presence of microhemorrhages was associated with worse TMT B time and attention MDRS subscore after adjustment for WMH. All subjects had Mini-Mental Status Examination scores ≥24 and presented with no or only mild disability. These results suggest that CADASIL patients with isolated WMH can present with executive and attention deficit but not with severe disability and that additional lesions are needed to cause significant disability and/or dementia.

Longitudinal changes of cortical morphology in CADASIL.

In CADASIL (Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leucoencephalopathy), a genetic model of subcortical ischemic vascular dementia (SIVD), clinical status was previously found related to cortex morphology. In the present report, alterations of cortex morphology and their links to clinical worsening were investigated in 190 CADASIL patients followed during 24.4 months. Linear models were used to test relationships between: (1) clinical worsening and changes of depth of cortical sulci and of cortical thickness; (2) alterations of cortical morphology and changes of volume of white matter hyperintensities (WMH(v)) and of lacunar lesions (LL(v)). Reduction of sulcal depth was independently associated with increased time to complete trail making test A and B (p < 0.0001 and p = 0.004) and that of cortical thickness to increased disability (modified Rankin's scale, p = 0.008), while brain atrophy was only related to global cognitive worsening (Mattis dementia rating scale, p = 0.002). The impact of volume of lacunar lesions on cortical alterations was larger than that of volume of white matter hyperintensities. Cortical alterations, mainly related to lacunar lesions, evolve parallel to clinical worsening. These results further support the eventual role of cortical alterations in subcortical ischemic vascular dementia.

Effects of gender on the phenotype of CADASIL.

BACKGROUND AND PURPOSE: In the general population, migraine, cerebrovascular diseases, and vascular dementia differ in many aspects between men and women. CADASIL is considered a unique model to investigate migraine with aura, stroke, and dementia related to ischemic small vessel disease. This study aims to evaluate the effect of gender on the main clinical and neuroimaging characteristics of CADASIL. METHODS: Cross-sectional data from 313 CADASIL patients including various clinical and cognitive scores and MRI parameters were compared between men and women, and between those younger and older than the median age of the population corresponding to the usual age of menopause (51 years). RESULTS: At younger than 51 years, migraine with aura was 50% more prevalent in women and stroke was 75% more prevalent in men. After the fifth decade, men had higher National Institutes of Health Stroke Scale and Rankin scores than women and more severe executive dysfunction, although global cognitive scores were similar. Age at first stroke, the number of stroke events, and the prevalence of dementia and psychiatric symptoms did not differ between men and women. Brain volume was lower in men with a trend for a larger volume of lacunar infarcts. CONCLUSIONS: In CADASIL, migraine with aura is more frequent in women and stroke is more frequent in men before the age of menopause. This difference seems to vanish after this age limit but may result in a higher degree of cognitive impairment and cerebral atrophy in men at the late stage of the disease. The presumable role of ovarian hormones in these gender-related differences remains to be explored.

Cortical folding influences migraine aura symptoms in CADASIL.

OBJECTIVE: Migraine with aura is a hallmark of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). In contrast with the majority of CADASIL patients, some affected subjects never experience visual symptoms during their attacks of migraine with aura. The aim of this study was to determine whether specific morphology of the primary visual cortex is associated with the absence of visual symptoms during migraine aura in CADASIL. METHODS: Patients from a large cohort of CADASIL patients, aged <45 years, and with a modified Rankin's scale ≤1 were included in the study. Width and depth of the calcarine sulcus in the primary visual cortex as well as cortical thickness in its neighbourhood were compared between patients with visual and those with non-visual migraine auras. RESULTS: 31 patients had visual symptoms (VA group) while nine reported only non-visual symptoms (NVA group) during their migraine auras. Asymmetry index of the calcarine sulcal depth largely differed between the NVA group and the VA group (0.22±0.1 vs -0.004±0.2; p=1.7×10(-6)). The width of the right calcarine sulcus was significantly lower in the VA group (p=0.04) and cortical thickness was larger in the NVA group (p=0.03). CONCLUSION: The absence of visual symptoms during migraine auras was associated with a profound asymmetry of the primary visual cortex. Aura symptoms seem to be linked to the morphology of the primary visual cortex in CADASIL. This finding potentially reflects more general relationships between spreading depression and cortex morphology in migraine with aura.

Confluent thalamic hyperintensities in CADASIL.

BACKGROUND: CADASIL is responsible for diffuse hyperintensities in the white matter on FLAIR images. These lesions are often associated with focal lesions in the basal ganglia such as lacunar infarctions. The prevalence and significance of diffuse or confluent thalamic hyperintensities (CTH) remain unknown. METHODS: The frequency of hyperintensities on FLAIR images in the thalamus was assessed in 147 CADASIL patients, and signal abnormalities on both FLAIR and T(1)-weighted images were categorized as focal/punctuate or diffuse/confluent by the same reader. The areas of increased diffusion were also analyzed on apparent diffusion coefficient maps. The association of CTH with vascular risk factors, the main clinical manifestations of the disease and MRI markers (brain parenchymal fraction, volume of white matter hyperintensities, volume of lacunar infarcts and number of microbleeds) was analyzed with generalized linear regression models. RESULTS: CTH were detected in 12% of the CADASIL subjects in association with hypointensities on T(1)-weighted images. CTH corresponded to areas of increased diffusion on apparent diffusion coefficient maps. CTH were found significantly associated with age and independently related to the volume of white matter hyperintensities but not to that of lacunar infarctions or to cerebral atrophy after adjustment for age and sex. No significant association was found between CTH and global cognitive performances. CONCLUSION: CTH are observed on FLAIR images in a sizeable proportion of CADASIL patients. They are mainly related to the extent of white matter hyperintensities and do not correlate with cognitive decline. Demyelination and/or loss of glial cells appear to be the most plausible cause of these confluent signal changes in the thalamus.

Ischemic stroke of the cortical "hand knob" area: stroke mechanisms and prognosis.

Cortical ischemic stroke affecting the precentral "hand knob" area is a rare but well known stroke entity. To date, little is known about the underlying stroke mechanisms and the prognosis. Twenty-nine patients admitted to our service between 2003 and 2007 were included in the study on the basis of an acute ischemic infarct of the cortical "hand knob" area confirmed by diffusion-weighted magnetic resonance imaging with contralateral hand paresis. For all patients clinical, epidemiological as well as imaging data at the time point of admission were analysed retrospectively and follow-up data on all patients was obtained. The majority (n = 21/72%) had an isolated infarct of the cortical "hand knob" area. In 23 (79%) patients it was a first ever stroke. Ten patients (34%) had ipsilateral extracranial stenosis of the internal carotid artery (ICA), whereas potential cardiac embolic sources were less frequent (n = 4/14%). No patient exhibited ipsilateral MCA stenosis. All but two patients (93%) had marked atherosclerotic alterations of the ICA. Hypertension was the most prevalent vascular risk factor (n = 23/79%). At follow-up (mean 25.0 months, range 0.4-47.4 months) no patient had died and only one (3%) experienced a recurrent stroke. The majority of patients (79%) reported improvement of hand paresis, 17 (59%) were asymptomatic (modified Rankin score = 0). Only one patient was significantly disabled due to a recurrent stroke. In conclusion, ischemic infarcts affecting the cortical "hand knob" area are frequently associated with atherosclerotic changes of the carotid artery, suggesting an arterio-arterial thrombembolic stroke mechanism. It mostly reflects first ever ischemic stroke, and follow-up data suggest a rather benign course.