Microvasculature of the human cerebral white matter: arteries of the deep white matter

The relationship of white matter tract orientation to vascular geometry in the human brain

The white matter of the human brain exhibits highly ordered anisotropic structures of both axonal nerve fibers and cerebral vasculature. Separately, the anisotropic nature of white matter axons and white matter vasculature have been shown to cause an orientation dependence on various MRI contrasts used to study the structure and function of the brain; however, little is known of the relationship between axonal and vascular orientations. Thus, the aim of this study is to compare the orientation between nerve fibers and vasculature within the white matter. To do this, we use diffusion MRI and susceptibility weighted imaging acquired in the same healthy young adult volunteers and analyze the alignment between white matter fibers and blood vessels in different brain regions, and along different pathways, to determine the degree of alignment between these structures. We first describe vascular orientation throughout the brain and note several regions with consistent orientations across individuals. Next, we find that vasculature does not necessarily align with the dominant direction of white matter in many regions, but, due to the presence of crossing fiber populations, does align with at least some white matter within each MRI voxel. Even though the spatial patterns of blood vessels run in parallel to several white matter tracts, they do not do so along the entire pathway, nor for all pathways, suggesting that vasculature does not supply/drain blood in a tract-specific manner. Overall, these findings suggest that the vascular architecture within the white matter is closely related to, but not the same as, the organization of neural pathways. This study contributes to a better understanding of the microstructural arrangement of the brain and may have implications for interpreting neuroimaging data in health and disease.

Volume and Permeability of White Matter Hyperintensity on Cognition: A DCE Imaging Study of an Older Cohort With and Without Cognitive Impairment

BACKGROUND

The impact of blood-brain barrier (BBB) leakage on white matter hyperintensity (WMH) subtypes (location) and its association with clinical factors and cognition remains unclear.

PURPOSE

To investigate the relationship between WMH volume, permeability, clinical factors, and cognition in older individuals across the cognitive spectrum.

STUDY TYPE

Prospective, cross-sectional.

SUBJECTS

A total of 193 older adults with/without cognitive impairment; 128 females; mean age 70.1 years (standard deviation 6.8).

FIELD STRENGTH/SEQUENCE

3 T, GE Dynamic contrast-enhanced, three-dimensional (3D) Magnetization-prepared rapid gradient-echo (MPRAGE T1WI), 3D fluid-attenuated inversion recovery (FLAIR).

ASSESSMENT

Periventricular WMH (PWMH), deep WMH (DWMH), and normal-appearing white matter (NAWM) were segmented using FMRIB automatic segmentation tool algorithms on 3D FLAIR. Hippocampal volume and cortex volume were segmented on 3D T1WI. BBB permeability (Ktrans) and blood plasma volume (Vp) were determined using the Patlak model. Vascular risk factors and cognition were assessed.

STATISTICAL TESTS

Univariate and multivariate analyses were performed to identify factors associated with WMH permeability. Logistic regression analysis assessed the association between WMH imaging features and cognition, adjusting for age, sex, apolipoprotein E4 status, education, and brain volumes. A P-value <0.05 was considered significant.

RESULTS

PWMH exhibited higher Ktrans (0.598 ± 0.509 × 10-3 minute-1) compared to DWMH (0.496 ± 0.478 × 10-3 minute-1) and NAWM (0.476 ± 0.398 × 10-3 minute-1). Smaller PWMH volume and cardiovascular disease (CVD) history were significantly associated with higher Ktrans in PWMH. In DWMH, higher Ktrans were associated with CVD history and cortical volume. In NAWM, it was linked to CVD history and dyslipidemia. Larger PWMH volume (odds ratio [OR] 1.106, confidence interval [CI]: 1.021-1.197) and smaller hippocampal volume (OR 0.069; CI: 0.019-0.253) were independently linked to worse global cognition after covariate adjustment.

DATA CONCLUSION

Elevated BBB leakage in PWMH was associated with lower PWMH volume and prior CVD history. Notably, PWMH volume, rather than permeability, was correlated with cognitive decline, suggesting that BBB leakage in WMH may be a consequence of CVD rather than indicate disease progression.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 3.

The relationship of white matter tract orientation to vascular geometry in the human brain

The white matter of the human brain exhibits highly ordered anisotropic structures of both axonal nerve fibers and cerebral vasculature. Separately, the anisotropic nature of white matter axons and white matter vasculature have been shown to cause an orientation dependence on various MRI contrasts used to study the structure and function of the brain; however, little is known of the relationship between axonal and vascular orientations. Thus, the aim of this study is to compare the orientation between nerve fibers and vasculature within the white matter. To do this, we use diffusion MRI and susceptibility weighted imaging acquired in the same healthy young adult volunteers and analyze the alignment between white matter fibers and blood vessels in different brain regions, and along different pathways, to determine the degree of alignment between these structures. We first describe vascular orientation throughout the brain and note several regions with consistent orientations across individuals. Next, we find that vasculature does not necessarily align with the dominant direction of white matter in many regions, but, due to the presence of crossing fiber populations, does align with at least some white matter within each MRI voxel. Even though the spatial patterns of blood vessels run in parallel to several white matter tracts, they do not do so along the entire pathway, nor for all pathways, suggesting that vasculature does not supply/drain blood in a tract-specific manner. Overall, these findings suggest that the vascular architecture within the white matter is closely related to, but not the same as, the organization of neural pathways. This study contributes to a better understanding of the microstructural arrangement of the brain and may have implications for interpreting neuroimaging data in health and disease.

All Three Supersystems-Nervous, Vascular, and Immune-Contribute to the Cortical Infarcts After Subarachnoid Hemorrhage

The recently published DISCHARGE-1 trial supports the observations of earlier autopsy and neuroimaging studies that almost 70% of all focal brain damage after aneurysmal subarachnoid hemorrhage are anemic infarcts of the cortex, often also affecting the white matter immediately below. The infarcts are not limited by the usual vascular territories. About two-fifths of the ischemic damage occurs within ~ 48 h; the remaining three-fifths are delayed (within ~ 3 weeks). Using neuromonitoring technology in combination with longitudinal neuroimaging, the entire sequence of both early and delayed cortical infarct development after subarachnoid hemorrhage has recently been recorded in patients. Characteristically, cortical infarcts are caused by acute severe vasospastic events, so-called spreading ischemia, triggered by spontaneously occurring spreading depolarization. In locations where a spreading depolarization passes through, cerebral blood flow can drastically drop within a few seconds and remain suppressed for minutes or even hours, often followed by high-amplitude, sustained hyperemia. In spreading depolarization, neurons lead the event, and the other cells of the neurovascular unit (endothelium, vascular smooth muscle, pericytes, astrocytes, microglia, oligodendrocytes) follow. However, dysregulation in cells of all three supersystems-nervous, vascular, and immune-is very likely involved in the dysfunction of the neurovascular unit underlying spreading ischemia. It is assumed that subarachnoid blood, which lies directly on the cortex and enters the parenchyma via glymphatic channels, triggers these dysregulations. This review discusses the neuroglial, neurovascular, and neuroimmunological dysregulations in the context of spreading depolarization and spreading ischemia as critical elements in the pathogenesis of cortical infarcts after subarachnoid hemorrhage.

Mapping Activity and Functional Organisation of the Motor and Visual Pathways Using ADC-fMRI in the Human Brain

In contrast to blood-oxygenation level-dependent (BOLD) functional MRI (fMRI), which relies on changes in blood flow and oxygenation levels to infer brain activity, diffusion fMRI (DfMRI) investigates brain dynamics by monitoring alterations in the apparent diffusion coefficient (ADC) of water. These ADC changes may arise from fluctuations in neuronal morphology, providing a distinctive perspective on neural activity. The potential of ADC as an fMRI contrast (ADC-fMRI) lies in its capacity to reveal neural activity independently of neurovascular coupling, thus yielding complementary insights into brain function. To demonstrate the specificity and value of ADC-fMRI, both ADC- and BOLD-fMRI data were collected at 3 T in human subjects during visual stimulation and motor tasks. The first aim of this study was to identify an acquisition design for ADC that minimises BOLD contributions. By examining the timings in responses, we report that ADC 0/1 timeseries (acquired with b values of 0 and 1 ms/μm 2 $$ {\upmu \mathrm{m}}^2 $$ ) exhibit residual vascular contamination, while ADC 0.2/1 timeseries (with b values of 0.2 and 1 ms/μm 2 $$ {\upmu \mathrm{m}}^2 $$ ) show minimal BOLD influence and higher sensitivity to neuromorphological coupling. Second, a general linear model was employed to identify activation clusters for ADC 0.2/1 and BOLD, from which the average ADC and BOLD responses were calculated. The negative ADC response exhibited a significantly reduced delay relative to the task onset and offset as compared to BOLD. This early onset further supports the notion that ADC is sensitive to neuromorphological rather than neurovascular coupling. Remarkably, in the group-level analysis, positive BOLD activation clusters were detected in the visual and motor cortices, while the negative ADC clusters mainly highlighted pathways in white matter connected to the motor cortex. In the averaged individual level analysis, negative ADC activation clusters were also present in the visual cortex. This finding confirmed the reliability of negative ADC as an indicator of brain function, even in regions with lower vascularisation such as white matter. Finally, we established that ADC-fMRI time courses yield the expected functional organisation of the visual system, including both grey and white matter regions of interest. Functional connectivity matrices were used to perform hierarchical clustering of brain regions, where ADC-fMRI successfully reproduced the expected structure of the dorsal and ventral visual pathways. This organisation was not replicated with the b = 0.2 ms/μm 2 $$ {\upmu \mathrm{m}}^2 $$ diffusion-weighted time courses, which can be seen as a proxy for BOLD (via T2-weighting). These findings underscore the robustness of ADC time courses in functional MRI studies, offering complementary insights into BOLD-fMRI regarding brain function and connectivity patterns.

White matter aging and its impact on brain function

Aging has a detrimental impact on white matter, resulting in reduced volume, compromised structural integrity of myelinated axons, and an increase in white matter hyperintensities. These changes are closely linked to cognitive decline and neurological disabilities. The deterioration of myelin and its diminished ability to regenerate as we age further contribute to the progression of neurodegenerative disorders. Understanding these changes is crucial for devising effective disease prevention strategies. Here, we will discuss the structural alterations in white matter that occur with aging and examine the cellular and molecular mechanisms driving these aging-related transformations. We highlight how the progressive disruption of white matter may initiate a self-perpetuating cycle of inflammation and neural damage.

Dynamic fluctuations in brain iron content during migraine attacks: insights from relaxometry and diffusion tensor imaging

Background

There is evidence that iron metabolism may play a role in the underlying pathophysiological mechanism of migraine. Studies using R 2 ∗ (=1/ T 2 ∗ ) relaxometry, a common MRI-based iron mapping technique, have reported increased R 2 ∗ values in various brain structures of migraineurs, indicating iron accumulation compared to healthy controls.

Purpose

To investigate whether there are short-term changes in R 2 ∗ during a migraine attack.

Population

26-year-old male patient diagnosed with episodic migraine with aura according to ICHD-3 criteria.

Sequence

3 T, 64-channel head coil, for quantification of R 2 ∗ relaxation a multi-echo gradient echo (GRE) sequence with TE = 4.92, 9.84, 14.7, 19.6, 24.6 and 29.51 ms, TR = 35 ms, flip angle = 15°, and 0.9 × 0.9 × 0.9 mm3 isotropic resolution was used.

Assessment

Quantitative MRI, including R 2 ∗ relaxometry and diffusion tensor imaging (DTI), was acquired from a migraine patient on 21 consecutive days, including migraine-free days and days with a migraine attack.

Statistical test

Statistical analysis was performed using R, the Shapiro-Wilk test, the t-test and Mann Whitney U test, analysis of variance (ANOVA) or Kruskal-Wallis test, depending on the distribution of the data. p-value <0.05 was considered significant.

Results

Significant difference in R 2 ∗ was found between the left and right hemispheres during a migraine attack. An increase in R 2 ∗ was observed in the left hemisphere, whereas in the right hemisphere R 2 ∗ was found to decrease. In the left cerebral white matter, R 2 ∗ increased by 1.8% (p = 0.021), in the right cerebral white matter, R 2 ∗ anisotropy decreased by 17% (p = 0.011) during a migraine attack.

Data conclusion

Our study showed a decrease and increase in iron content during the migraine cycle. Furthermore, during a migraine attack, white matter iron content increased, accompanied by a decrease in anisotropic tissue components, suggesting additional changes in vascular components.

Hemodynamic Insights Into the Asymmetrical Medullary Vein Sign on T2* Imaging in Hyperacute M1 Occlusion

Background In treating acute ischemic stroke (AIS), asymmetrical vein signs (AVS) on blood-oxygen-level-dependent imaging reflect increased deoxyhemoglobin levels due to increased oxygen extraction fraction. Meanwhile, although veins connecting pial and deep venous systems, such as transcerebral veins, are well studied, dynamic observation of these veins remains challenging. This study aimed to elucidate the venous flow of the deep white matter (DWM), focusing on medullary AVS in patients with hyperacute cardioembolic M1 occlusion. Methods This retrospective cross-sectional study involved 50 patients with AIS caused by M1 occlusion who received mechanical thrombectomy at Kameda Medical Center from July 2018 to December 2021. The study investigated medullary AVS and their association with angiographic collateral flow grades and occlusion locations. Welch's t-test was used for continuous variables, while Fisher's exact test was employed for categorical variables. Results A total of 41 patients were eligible for analysis. No significant association was found between medullary AVS and angiographic collateral flow grade (p=1.000); however, a significant association was observed between proximal M1 occlusion and medullary AVS (p=0.006), supporting the hypothesis that medullary AVS is significantly influenced by ischemic conditions in the territory of lenticulostriate arteries. Conclusion Three possible mechanisms for medullary AVS were considered: local ischemia in the DWM, ventriculopetal ischemic venous flow from the pial veins, and ventriculofugal ischemic venous flow from the basal ganglia. The results of the present study and the fact that the DWM is exclusively perfused by the cortical arteries favor the ventriculofugal flow hypothesis as the mechanism of medullary AVS. Although direct observation of the veins in the DWM by cerebral angiography is challenging, it can be deduced indirectly.

The Hemorrhagic Side of Primary Angiitis of the Central Nervous System (PACNS)

Primary Angiitis of the Central Nervous System (PACNS) is a rare cerebrovascular disease involving the arteries of the leptomeninges, brain and spinal cord. Its diagnosis can be challenging, and the current diagnostic criteria show several limitations. Among the clinical and neuroimaging manifestations of PACNS, intracranial bleeding, particularly intracerebral hemorrhage (ICH), is poorly described in the available literature, and it is considered infrequent. This review aims to summarize the available data addressing this issue with a dedicated focus on the clinical, neuroradiological and neuropathological perspectives. Moreover, the limitations of the actual data and the unanswered questions about hemorrhagic PACNS are addressed from a double point of view (PACNS subtyping and ICH etiology). Fewer than 20% of patients diagnosed as PACNS had an ICH during the course of the disease, and in cases where ICH was reported, it usually did not occur at presentation. As trigger factors, both sympathomimetic drugs and illicit drugs have been proposed, under the hypothesis of an inflammatory response due to vasoconstriction in the distal cerebral arteries. Most neuroradiological descriptions documented a lobar location, and both the large-vessel PACNS (LV-PACNS) and small-vessel PACNS (SV-PACNS) subtypes might be the underlying associated phenotypes. Surprisingly, amyloid beta deposition was not associated with ICH when histopathology was available. Moreover, PACNS is not explicitly included in the etiological classification of spontaneous ICH. This issue has received little attention in the past, and it could be addressed in future prospective studies.

Anatomical landmarks during high-magnification microsurgery for a safe and effective resection of high-grade gliomas: how I do it

BACKGROUND

Gross total resection, when possible, is the first crucial treatment for high-grade gliomas, as it has been demonstrated to be associated with longer survival. Different intraoperative tools, such as neuronavigation, fluorescent agents, and intra-operative ultrasound, have been developed to help neurosurgeons to extend the resection.

METHODS

We describe the high-magnification microsurgery technique used during the first surgical removal for high-grade gliomas. We illustrate the key anatomical "markers" of normal brain parenchyma, which guide the surgery.

CONCLUSION

High-magnification microsurgery is an anatomically based approach that allows the identification of key anatomical "markers" of normal brain parenchyma in order to resect high-grade gliomas safely and effectively.

Characteristics and Clinical Implication of White Matter Lesions in Patients With Adult Moyamoya Disease

BACKGROUND AND OBJECTIVES

White matter hyperintensities (WMHs) are reportedly increased in moyamoya disease (MMD); however, their clinical importance is not well-established owing to their pathophysiologic heterogeneity by distribution. This study aimed to evaluate the burden and pattern of WMHs and its clinical implications in the MMD trajectory.

METHODS

Adult patients with MMD without significant structural lesions were 1:1 propensity score-matched with healthy controls for sex and vascular risk factors. The total, periventricular, and subcortical WMH volumes were segmented and quantified fully automatically. WMH volumes were detrended by age and compared between the 2 groups. MMD severity based on Suzuki stage and future ischemic events were assessed for their association with WMH volumes.

RESULTS

A total of 161 pairs of patients with MMD and controls were analyzed. MMD significantly correlated with increased total WMH volume (B [standard error], 0.126 [0.030]; p < 0.001), periventricular WMH volume (0.114 [0.027]; p < 0.001), and periventricular-to-subcortical ratio (0.090 [0.034]; p = 0.009). In the MMD subgroup (n = 187), advanced MMD had an independent association with the total WMH volume (0.120 [0.035]; p < 0.001), periventricular WMH volume (0.110 [0.031]; p < 0.001), and periventricular-to-subcortical ratio (0.139 [0.038]; p < 0.001). Periventricular WMH volume (adjusted hazard ratio [95% confidence interval], 5.12 [1.26-20.79]) and periventricular-to-subcortical ratio (3.80 [1.51-9.56]) were associated with future ischemic events in patients with medically followed up MMD. However, no demonstrable association was found between subcortical WMH volume and MMD, MMD severity, or future ischemic events.

DISCUSSION

Periventricular WMHs, but not subcortical WMHs, may represent the main pathophysiology of MMD. Periventricular WMHs may be used as a marker for ischemic vulnerability in patients with MMD.

Microvascular Environment Influences Brain Microvascular Heterogeneity: Relative Roles of Astrocytes and Oligodendrocytes for the EPCR Expression in the Brain Endothelium

Postmortem neuropathology shows clear regional differences in many brain diseases. For example, brains from cerebral malaria (CM) patients show more hemorrhagic punctae in the brain's white matter (WM) than grey matter (GM). The underlying reason for these differential pathologies is unknown. Here, we assessed the effect of the vascular microenvironment on brain endothelial phenotype, focusing endothelial protein C receptor (EPCR). We demonstrate that the basal level of EPCR expression in cerebral microvessels is heterogeneous in the WM compared to the GM. We used in vitro brain endothelial cell cultures and showed that the upregulation of EPCR expression was associated with exposure to oligodendrocyte conditioned media (OCM) compared to astrocyte conditioned media (ACM). Our findings shed light on the origin of the heterogeneity of molecular phenotypes at the microvascular level and might help better understand the variation in pathology seen in CM and other neuropathologies associated with vasculature in various brain regions.

White matter BOLD signals at 7 Tesla reveal visual field maps in optic radiation and vertical occipital fasciculus

There is growing evidence that blood-oxygen-level-dependent (BOLD) activity in the white matter (WM) can be detected by functional magnetic resonance imaging (fMRI). However, the functional relevance and significance of WM BOLD signals remain controversial. Here we investigated whether 7T BOLD fMRI can reveal fine-scale functional organizations of a WM bundle. Population receptive field (pRF) analyses of the 7T retinotopy dataset from the Human Connectome Project revealed clear contralateral retinotopic organizations of two visual WM bundles: the optic radiation (OR) and the vertical occipital fasciculus (VOF). The retinotopic maps of OR are highly consistent with post-mortem dissections and diffusion tractographies, while the VOF maps are compatible with the dorsal and ventral visual areas connected by the WM. Similar to the grey matter (GM) visual areas, both WM bundles show over-representations of the central visual field and increasing pRF size with eccentricity. Hemodynamic response functions of visual WM were slower and wider compared with those of GM areas. These findings clearly demonstrate that WM BOLD at 7 Tesla is closely coupled with neural activity related to axons, encoding highly specific information that can be used to characterize fine-scale functional organizations of a WM bundle.

Development of cortical microvascularization in Moyamoya disease using the maximum intensity projection method from three-dimensional rotational angiography

BACKGROUND

Neurosurgeons often experience increased cortical microvascularization in Moyamoya disease (MMD). However, there are no previous reports that radiologically evaluated preoperative cortical microvascularization. We investigated the development of cortical microvascularization and clinical characteristics of MMD using the maximum intensity projection (MIP) method.

METHODS

We enrolled 64 patients at our institution, including patients with MMD (n = 26), intracranial atherosclerotic disease (ICAD; n = 18), and unruptured cerebral aneurysms (n = 20) as the control group. All patients underwent three-dimensional rotational angiography (3D-RA). The 3D-RA images were reconstructed using partial MIP images. Cortical microvascularization was defined as the vessels that branched off from the cerebral arteries and were classified as grade 0-2 depending on their development.

RESULTS

Cortical microvascularization observed in patients with MMD was classified into grade 0 (n = 4, 8.9%), grade 1 (n = 17, 37.8%), and grade 2 (n = 24, 53.3%). The development of cortical microvascularization was more common in the MMD group than in the other groups. The inter-rater reliability measured using weighted kappa was 0.68 (95% confidence interval = 0.56-0.80). There were no significant differences in cortical microvascularization according to the onset type and hemispheres. Cortical microvascularization correlated with periventricular anastomosis. Most patients with Suzuki classifications 2-5 developed cortical microvascularization.

CONCLUSION

Cortical microvascularization was characteristic of patients with MMD. These findings developed in the early stages of MMD and may act as a bridge to the development of periventricular anastomosis.

Classification of white matter lesions and characteristics of small vessel disease markers

OBJECTIVES

Radiological markers for cerebral small vessel disease (SVD) may have different biological underpinnings in their development. We attempted to categorize SVD burden by integrating white matter signal abnormalities (WMSA) features and secondary presence of lacunes, microbleeds, and enlarged perivascular spaces.

METHODS

Data were acquired from 610 older adults (aged > 40 years) who underwent brain magnetic resonance imaging exam as part of a health checkup. The WMSA were classified individually by the number and size of non-contiguous lesions, distribution, and contrast. Age-detrended lacunes, microbleeds, and enlarged perivascular space were quantified to further categorize individuals. Clinical and laboratory values were compared across the individual classes.

RESULTS

Class I was characterized by multiple, small, deep WMSA but a low burden of lacunes and microbleeds; class II had large periventricular WMSA and a high burden of lacunes and microbleeds; and class III had limited juxtaventricular WMSA and lacked lacunes and microbleeds. Class II was associated with older age, diabetes, and a relatively higher neutrophil-to-lymphocyte ratio. Smoking and higher uric acid levels were associated with an increased risk of class I.

CONCLUSION

The heterogeneity of SVD was categorized into three classes with distinct clinical correlates. This categorization will improve our understanding of SVD pathophysiology, risk stratification, and outcome prediction.

KEY POINTS

• Classification of white matter signal abnormality (WMSA) features was associated with different characteristic of lacunes, microbleeds, and enlarged perivascular space and clinical variability. • Class I was characterized by multiple, small, deep WMSA but a low burden of lacunes and microbleeds. Class II had large periventricular WMSA and a high burden of lacunes and microbleeds. Class III had limited juxtaventricular WMSA and lacked lacunes and microbleeds. • Class II was associated with older age, diabetes, and higher neutrophil-to-lymphocyte ratio. Smoking and higher uric acid levels were associated with an increased risk of class I.

Using ex vivo arterial injection and dissection to assess white matter vascularization

Advances in the techniques for assessing human cerebral white matter have recently contributed to greater attention to structural connectivity. Yet, little is known about the vascularization of most white matter fasciculi and the fascicular composition of the vascular territories. This paper presents an original method to label the arterial supply of macroscopic white matter fasciculi based on a standardized protocol for post-mortem injection of colored material into main cerebral arteries combined with a novel fiber dissection technique. Twelve whole human cerebral hemispheres obtained post-mortem were included. A detailed description of every step, from obtaining the specimen to image acquisition of its dissection, is provided. Injection and dissection were reproducible and manageable without any sophisticated equipment. They successfully showed the arterial supply of the dissected fasciculi. In addition, we discuss the challenges we faced and overcame during the development of the presented method, highlight its originality. Henceforth, this innovative method serves as a tool to provide a precise anatomical description of the vascularization of the main white matter tracts.

Potentially toxic elements in the brains of people with multiple sclerosis

Potentially toxic elements such as lead and aluminium have been proposed to play a role in the pathogenesis of multiple sclerosis (MS), since their neurotoxic mechanisms mimic many of the pathogenetic processes in MS. We therefore examined the distribution of several potentially toxic elements in the autopsied brains of people with and without MS, using two methods of elemental bio-imaging. Toxicants detected in the locus ceruleus were used as indicators of past exposures. Autometallography of paraffin sections from multiple brain regions of 21 MS patients and 109 controls detected inorganic mercury, silver, or bismuth in many locus ceruleus neurons of both groups, and in widespread blood vessels, oligodendrocytes, astrocytes, and neurons of four MS patients and one control. Laser ablation-inductively coupled plasma-mass spectrometry imaging of pons paraffin sections from all MS patients and 12 controls showed that combinations of iron, silver, lead, aluminium, mercury, nickel, and bismuth were present more often in the locus ceruleus of MS patients and were located predominantly in white matter tracts. Based on these results, we propose that metal toxicants in locus ceruleus neurons weaken the blood-brain barrier, enabling multiple interacting toxicants to pass through blood vessels and enter astrocytes and oligodendroglia, leading to demyelination.

Magnetic resonance imaging reveals microemboli-mediated pathological changes in brain microstructure in diabetic rats: relevance to vascular cognitive impairment/dementia

Diabetes doubles the risk of vascular cognitive impairment, but the underlying reasons remain unclear. In the present study, we determined the temporal and spatial changes in the brain structure after microemboli (ME) injection using diffusion MRI (dMRI). Control and diabetic rats received cholesterol crystal ME (40-70 µm) injections. Cognitive tests were followed up to 16 weeks, while dMRI scans were performed at baseline and 12 weeks post-ME. The novel object recognition test had a lower d2 recognition index along with a decrease in spontaneous alternations in the Y maze test in diabetic rats with ME. dMRI showed that ME injection caused infarction in two diabetic animals (n=5) but none in controls (n=6). In diabetes, radial diffusivity (DR) was increased while fractional anisotropy (FA) was decreased in the cortex, indicating loss of tissue integrity and edema. In the dorsal hippocampus, mean diffusivity (MD), axial diffusivity (DA), and DR were significantly increased, indicating loss of axons and myelin damage. Histological analyses confirmed more tissue damage and microglial activation in diabetic rats with ME. These results suggest that ME injury and associated cerebrovascular dysfunction are greater in diabetes, which may cause cognitive deficits. Strategies to improve vascular function can be a preventive and therapeutic approach for vascular cognitive impairment.

Aging astrocytes metabolically support aging axon function by proficiently regulating astrocyte-neuron lactate shuttle

The astrocyte-neuron lactate shuttle (ANLS) is an essential metabolic support system that uptakes glucose, stores it as glycogen in astrocytes, and provides glycogen-derived lactate for axonal function. Aging intrinsically increases the vulnerability of white matter (WM) to injury. Therefore, we investigated the regulation of this shuttle to understand vascular-glial metabolic coupling to support axonal function during aging in two different WM tracts. Aging astrocytes displayed larger cell bodies and thicker horizontal processes in contrast to thinner vertically oriented processes of young astrocytes. Aging axons recovered less following aglycemia in mouse optic nerves (MONs) compared to young axons, although providing lactate during aglycemia equally supported young and aging axonal function. Incubating MONs in high glucose to upregulate glycogen stores in astrocytes delayed loss of function during aglycemia and improved recovery in both young and aging axons. Providing lactate during recovery from aglycemia unmasked a metabolic switch from glucose to lactate in aging axons. Young and aging corpus callosum consisting of a mixture of myelinated and unmyelinated axons sustained their function fully when lactate was available during aglycemia and surprisingly showed a greater resilience to aglycemia compared to fully myelinated axons of optic nerve. We conclude that lactate is a universal substrate for axons independent of their myelination content and age.

Static and dynamic BOLD fMRI components along white matter fibre tracts and their dependence on the orientation of the local diffusion tensor axis relative to the B0-field

Recent studies have reported functional MRI (fMRI) activation within cerebral white matter (WM) using blood-oxygenation-level-dependent (BOLD) contrast. Many blood vessels in WM run parallel to the fibre bundles, and other studies observed dependence of susceptibility contrast-based measures of blood volume on the local orientation of the fibre bundles relative to the magnetic field or B₀ axis. Motivated by this, we characterized the dependence of gradient-echo BOLD fMRI on fibre orientation (estimated by the local diffusion tensor) relative to the B₀ axis to test whether the alignment between bundles and vessels imparts an orientation dependence on resting-state BOLD fluctuations in the WM. We found that the baseline signal level of the T₂*-weighted data is 11% higher in voxels containing fibres parallel to B₀ than those containing perpendicular fibres, consistent with a static influence of either fibre or vessel orientation on local T₂* values. We also found that BOLD fluctuations in most bundles exhibit orientation effects expected from oxygenation changes, with larger amplitudes from voxels containing perpendicular fibres. Different magnitudes of this orientation effect were observed across the major WM bundles, with inferior fasciculus, corpus callosum and optic radiation exhibiting 14-19% higher fluctuations in voxels containing perpendicular compared to parallel fibres.

Combined functional and structural imaging of brain white matter reveals stage-dependent impairment in multiple system atrophy of cerebellar type

Advances in fMRI of brain white matter (WM) have established the feasibility of understanding how functional signals of WM evolve with brain diseases. By combining functional signals with structural features of WM, the current study characterizes functional and structural impairments of WM in cerebelar type multiple system atrophy, with the goal to derive new mechanistic insights into the pathological progression of this disease. Our analysis of 30 well-diagnosed patients revealed pronounced decreases in functional connectivity in WM bundles of the cerebellum and brainstem, and concomitant local structural alterations that depended on the disease stage. The novel findings implicate a critical time point in the pathological evolution of the disease, which could guide optimal therapeutic interventions. Furthermore, fMRI signals of impaired WM bundles exhibited superior sensitivity in differentiating initial disease development, which demonstrates great potential of using these signals to inform disease management.

Latency structure of BOLD signals within white matter in resting-state fMRI

PURPOSE

Previous studies have demonstrated that BOLD signals in gray matter in resting-state functional MRI (RSfMRI) have variable time lags, representing apparent propagations of fMRI BOLD signals in gray matter. We complemented existing findings and explored the corresponding variations of signal latencies in white matter.

METHODS

We used data from the Brain Genomics Superstruct Project, consisting of 1412 subjects (both sexes included) and divided the dataset into ten equal groups to study both the patterns and reproducibility of latency estimates within white matter. We constructed latency matrices by computing cross-covariances between voxel pairs. We also applied a clustering analysis to identify functional networks within white matter, based on which latency analysis was also performed to investigate lead/lag relationship at network level. A dataset consisting of various sensory states (eyes closed, eyes open and eyes open with fixation) was also included to examine the relationship between latency structure and different states.

RESULTS

Projections of voxel latencies from the latency matrices were highly correlated (average Pearson correlation coefficient = 0.89) across the subgroups, confirming the reproducibility and structure of signal lags in white matter. Analysis of latencies within and between networks revealed a similar pattern of inter- and intra-network communication to that reported for gray matter. Moreover, a dominant direction, from inferior to superior regions, of BOLD signal propagation was revealed by higher resolution clustering. The variations of lag structure within white matter are associated with different sensory states.

CONCLUSIONS

These findings provide additional insight into the character and roles of white matter BOLD signals in brain functions.

Magnetic susceptibility anisotropy in normal appearing white matter in multiple sclerosis from single-orientation acquisition

Quantitative susceptibility mapping (QSM) has been successfully applied to study changes in deep grey matter nuclei as well as in lesional tissue, but its application to white matter has been complicated by the observed orientation dependence of gradient echo signal. The anisotropic susceptibility tensor is thought to be at the origin of this orientation dependence, and magnetic susceptibility anisotropy (MSA) derived from this tensor has been proposed as a marker of the state and integrity of the myelin sheath and may therefore be of particular interest for the study of demyelinating pathologies such as multiple sclerosis (MS). Reconstruction of the susceptibility tensor, however, requires repeated measurements with multiple head orientations, rendering the approach impractical for clinical applications. In this study, we combined single-orientation QSM with fibre orientation information to assess apparent MSA in three white matter tracts, i.e., optic radiation (OR), splenium of the corpus callosum (SCC), and superior longitudinal fascicle (SLF), in two cohorts of 64 healthy controls and 89 MS patients. The apparent MSA showed a significant decrease in optic radiation in the MS cohort compared with healthy controls. It decreased in the MS cohort with increasing lesion load in OR and with disease duration in the splenium. All of this suggests demyelination in normal appearing white matter. However, the apparent MSA observed in the SLF pointed to potential systematic issues that require further exploration to realize the full potential of the presented approach. Despite the limitations of such single-orientation ROI-specific estimation, we believe that our clinically feasible approach to study degenerative changes in WM is worthy of further investigation.

Current understanding and future potential applications of cerebral microvascular imaging in infants

Microvascular imaging is an advanced Doppler ultrasound technique that detects slow flow in microvessels by suppressing clutter signal and motion-related artifacts. The technique has been applied in several conditions to assess organ perfusion and lesion characteristics. In this pictorial review, we aim to describe current knowledge of the technique, particularly its diagnostic utility in the infant brain, and expand on the unexplored but promising clinical applications of microvascular imaging in the brain with case illustrations.

Imaging of the pial arterial vasculature of the human brain in vivo using high-resolution 7T time-of-flight angiography

The pial arterial vasculature of the human brain is the only blood supply to the neocortex, but quantitative data on the morphology and topology of these mesoscopic arteries (diameter 50–300 µm) remains scarce. Because it is commonly assumed that blood flow velocities in these vessels are prohibitively slow, non-invasive time-of-flight magnetic resonance angiography (TOF-MRA)—which is well suited to high 3D imaging resolutions—has not been applied to imaging the pial arteries. Here, we provide a theoretical framework that outlines how TOF-MRA can visualize small pial arteries in vivo, by employing extremely small voxels at the size of individual vessels. We then provide evidence for this theory by imaging the pial arteries at 140 µm isotropic resolution using a 7 Tesla (T) magnetic resonance imaging (MRI) scanner and prospective motion correction, and show that pial arteries one voxel width in diameter can be detected. We conclude that imaging pial arteries is not limited by slow blood flow, but instead by achievable image resolution. This study represents the first targeted, comprehensive account of imaging pial arteries in vivo in the human brain. This ultra-high-resolution angiography will enable the characterization of pial vascular anatomy across the brain to investigate patterns of blood supply and relationships between vascular and functional architecture.

Presenting Step-Ladder Expansive Cranioplasty as the Next Step After Decompressive Hemicraniectomy: It Is Different!

Context: Decompressive hemicraniectomy (DC) is the final surgical remedy for refractory raised intracranial pressure (ICP). Even with years of experience and profound refination of technique, the procedure has less rewarding results in traumatic brain injury (TBI). Besides, arrangements for bone flap preservation and the necessity of follow-up surgery in the form of cranioplasty bring in unavoidable monetary and logistic burdens to the patients. Step-ladder expansive cranioplasty was conceptualized as an alternative to achieve adequate intracranial volume expansion to help normalize ICP, with immediate reinstitution of the Monro-Kellie doctrine. It is also expected to prevent cerebral cortical pressure injury to the cortex underlying the craniectomy defect. The evolution of this concept, as worked out on different models, the surgical technique, and our experience with this technique are discussed in this article. Evidence Acquisition: Multiple research projects undertaken by our team to build up the concept and acquire data necessary to plan the surgical procedure have been published over last eight years. This review article attempts to evaluate the existing knowledge and our clinical experience so far. Results: Step-ladder expansive cranioplasty allows an assured centrifugal displacement of the inner table and underlying dural bag at craniotomy site by at least 9 mm, thereby achieving a minimum volume expansion of 120 cc. Both of these parameters can be increased as desired, if considered necessary by the surgeon. Conclusions: Step-ladder expansive cranioplasty offers an alternative that takes the centripetal pressure exerted by the combination of the tensile strength of the scalp and atmospheric pressure off the brain surface while achieving an assured augmentation of intracranial volume that can be optimized on a case-to-case basis, based on our future understanding of the subject. While it can be a single-stage surgery for those satisfied with the cosmesis, a revision cranioplasty (if required) will be easier, cheaper, and cosmetically superior to achieving cover over a craniotomy defect routinely done after DC.

Cellular distribution of C-C motif chemokine ligand 2 like immunoreactivities in frontal cortex and corpus callosum of normal and lipopolysaccharide treated animal

BACKGROUND

C-C motif chemokine ligand 2 (CCL2) is reported to be involved in the pathogenesis of various neurological and/or psychiatric diseases. Tissue or cellular expression of CCL2, in normal or pathological condition, may play an essential role in recruiting monocytes or macrophages into targeted organs, and be involved in a certain pathogenic mechanism. However, few studies focused on tissue and cellular distribution of the CCL2 peptide in brain grey and white matters (GM, WM), and the changes of the GM and WM cellular CCL2 level in septic or endotoxic encephalopathy was not explored. Hence, the CCL2 cellular distribution in the front brain cortex and the corpus callosum (CC) was investigated in the present work by using immunofluorescent staining.

RESULTS

(1) CCL2 like immunoreactivity (CCL2-ir) in the CC is evidently higher than the cortex. When the measurement includes ependymal layer attached to the CC, CCL2-ir intensity is significantly higher than cortex. (2) Structures in perivascular areas, most of them are GFAP positive, contribute major CCL2-ir positive profiles in both GM and WM, but apparently more in the CC, where they are bilaterally distributed in the lateral CC between the cingulate cortex and ventricles. (3) The neuron-like CCL2-ir positive cells in cortex are significantly more than in the CC, and that number is significantly increased in the cortex following systemic lipopolysaccharide (LPS), but not in the CC. (4) In addition to CCL2-ir positive perivascular rings, more CCL2-ir filled cashew shape elements are observed, probably inside of microvasculature, especially in the CC following systemic LPS. (5) Few macrophage/microglia marker-Iba-1 and CCL2-ir co-labeled structures especially the soma is found in normal cortex and CC; the co-localizations are significantly augmented following systemic LPS, and co-labeled amoeba like somata are presented. (6) CCL2-ir and astrocyte marker GFAP or Iba-1 double labeled structures are also observed within the ependymal layer. No accumulation of neutrophils was detected.

CONCLUSION

There exist differences in the cellular distribution of the CCL2 peptide in frontal cortex GM and subcortical WM-CC, in both the physiological condition and experimental endotoxemia. Which might cause different pathological change in the GM and WM.

Pathogeneses and Imaging Features of Cerebral White Matter Lesions of Vascular Origins

White matter lesion (WML), also known as white matter hyperintensities or leukoaraiosis, was first termed in 1986 to describe the hyperintense signals on T2-weighted imaging (T2WI) and fluid-attenuated inversion recovery (FLAIR) maps. Over the past decades, a growing body of pathophysiological findings regarding WMLs have been discovered and discussed. Currently, the generally accepted WML pathogeneses mainly include hypoxia-ischemia, endothelial dysfunction, blood-brain barrier disruption, and infiltration of inflammatory mediators or cytokines. However, none of them can explain the whole dynamics of WML formation. Herein, we primarily focus on the pathogeneses and neuroimaging features of vascular WMLs. To achieve this goal, we searched papers with any type published in PubMed from 1950 to 2020 and cross-referenced the keywords including "leukoencephalopathy", "leukoaraiosis", "white matter hyperintensity", "white matter lesion", "pathogenesis", "pathology", "pathophysiology", and "neuroimaging". Moreover, references of the selected articles were browsed and searched for additional pertinent articles. We believe this work will supply the robust references for clinicians to further understand the different WML patterns of varying vascular etiologies and thus make customized treatment.

Cerebral white matter vasculature: still uncharted?

White matter vasculature plays a major role in the pathophysiology of permanent neurological deficits following a stroke or progressive cognitive alteration related to small vessel disease. Thus, knowledge of the complex vascularization and functional aspects of the deep white matter territories is paramount to comprehend clinical manifestations of brain ischemia. This review provides a structured presentation of the existing knowledge of the vascularization of the human cerebral white matter from seminal historical studies to the current literature. First, we revisit the highlights of prenatal development of the endoparenchymal telencephalic vascular system that are crucial for the understanding of vessel organization in the adult. Second, we reveal the tangled history of debates on the existence, clinical significance, and physiological role of leptomeningeal anastomoses. Then, we present how conceptions on white matter vascularization transitioned from the mixed ventriculopetal/ventriculofugal theory, in which a low-flow area was interposed in between concurrent arterial flows, to the purely ventriculopetal theory. The latter model explains variable white matter sensitivity to ischemia by various organizations of ventriculopetal vessel terminals having different origin/length properties and interconnection patterns. Next, arteries supplying primarily the white matter are described according to their length and overall structure. Furthermore, the known distribution territories, to date, are studied in relation to primary anatomical structures of the human cerebral white matter, emphasizing the sparsity of the "ground-truth" data available in the literature. Finally, the implications for both large vessel occlusion and chronic small vessel disease are discussed, as well as the insights from neuroimaging. All things considered, we identify the need for further research on deep white matter vascularization, especially regarding the arterial supply of white matter fiber tracts.

Selective extension of cerebral vascular calcification in an autopsy case of Fahr's syndrome associated with asymptomatic hypoparathyroidism

We report an autopsy case of Fahr's syndrome in an 85-year-old woman associated with asymptomatic hypoparathyroidism. The patient was diagnosed as having brain calcification at 65 years of age. She developed mild dementia at 75, parkinsonism at 76, and severe dementia at 82. Computed tomography revealed extensive, symmetric intracranial calcification, involving both sides of the basal ganglia and cerebellar dentate nuclei, and severe cerebral atrophy that developed afterwards. A neuropathological examination revealed intracranial calcification, particularly in the wall of the arterioles and capillaries having numerous calcium deposits. Severe vascular calcification and severe neuronal loss without α-synuclein accumulation were found in the substantia nigra. There were high-level neuropathological changes indicative of Alzheimer's disease. Although the colocalization of calcium and amyloid-β deposits in the same arterial wall was rare, both of them were located in a similar layer of the arterial wall. The vascular calcification in the basal ganglia spread continuously through the corona radiata into the selective cerebral areas along the medullary arteries, but did not involve the corpus callosum or insular region. Stone formation was observed at the corona radiata adjacent to the superolateral angles of the lateral ventricles. We hypothesized that there would be a stereotypical extension pattern of vascular calcification related to the arrangement of penetrating arteries in Fahr's syndrome.

A Comparison of CVR Magnitude and Delay Assessed at 1.5 and 3T in Patients With Cerebral Small Vessel Disease

BACKGROUND

Cerebrovascular reactivity (CVR) measures blood flow change in response to a vasoactive stimulus. Impairment is associated with several neurological conditions and can be measured using blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI). Field strength affects the BOLD signal, but the effect on CVR is unquantified in patient populations.

METHODS

We recruited patients with minor ischemic stroke and assessed CVR magnitude and delay time at 3 and 1.5 Tesla using BOLD MRI during a hypercapnic challenge. We assessed subcortical gray (GM) and white matter (WM) differences using Wilcoxon signed rank tests and scatterplots. Additionally, we explored associations with demographic factors, WM hyperintensity burden, and small vessel disease score.

RESULTS

Eighteen of twenty patients provided usable data. At 3T vs. 1.5T: mean CVR magnitude showed less variance (WM 3T: 0.062 ± 0.018%/mmHg, range 0.035, 0.093; 1.5T: 0.057 ± 0.024%/mmHg, range 0.016, 0.094) but was not systematically higher (Wilcoxon signal rank tests, WM: r = -0.33, confidence interval (CI): -0.013, 0.003, p = 0.167); delay showed similar variance (WM 3T: 40 ± 12 s, range: 12, 56; 1.5T: 31 ± 13 s, range 6, 50) and was shorter in GM (r = 0.33, CI: -2, 9, p = 0.164) and longer in WM (r = -0.59, CI: -16, -2, p = 0.010). Patients with higher disease severity tended to have lower CVR at 1.5 and 3T.

CONCLUSION

Mean CVR magnitude at 3T was similar to 1.5T but showed less variance. GM/WM delay differences may be affected by low signal-to-noise ratio among other factors. Although 3T may reduce variance in CVR magnitude, CVR is readily assessable at 1.5T and reveals comparable associations and trends with disease severity.

An Overview of Venous Abnormalities Related to the Development of Lesions in Multiple Sclerosis

The etiology of multiple sclerosis (MS) is currently understood to be autoimmune. However, there is a long history and growing evidence for disrupted vasculature and flow within the disease pathology. A broad review of the literature related to vascular effects in MS revealed a suggestive role for abnormal flow in the medullary vein system. Evidence for venous involvement in multiple sclerosis dates back to the early pathological work by Charcot and Bourneville, in the mid-nineteenth century. Pioneering work by Adams in the 1980s demonstrated vasculitis within the walls of veins and venules proximal to active MS lesions. And more recently, magnetic resonance imaging (MRI) has been used to show manifestations of the central vein as a precursor to the development of new MS lesions, and high-resolution MRI using Ferumoxytol has been used to reveal the microvasculature that has previously only been demonstrated in cadaver brains. Both approaches may shed new light into the structural changes occurring in MS lesions. The material covered in this review shows that multiple pathophysiological events may occur sequentially, in parallel, or in a vicious circle which include: endothelial damage, venous collagenosis and fibrin deposition, loss of vessel compliance, venous hypertension, perfusion reduction followed by ischemia, medullary vein dilation and local vascular remodeling. We come to the conclusion that a potential source of MS lesions is due to locally disrupted flow which in turn leads to remodeling of the medullary veins followed by endothelial damage with the subsequent escape of glial cells, cytokines, etc. These ultimately lead to the cascade of inflammatory and demyelinating events which ensue in the course of the disease.

Brain microvasculature has a common topology with local differences in geometry that match metabolic load

The microvasculature underlies the supply networks that support neuronal activity within heterogeneous brain regions. What are common versus heterogeneous aspects of the connectivity, density, and orientation of capillary networks? To address this, we imaged, reconstructed, and analyzed the microvasculature connectome in whole adult mice brains with sub-micrometer resolution. Graph analysis revealed common network topology across the brain that leads to a shared structural robustness against the rarefaction of vessels. Geometrical analysis, based on anatomically accurate reconstructions, uncovered a scaling law that links length density, i.e., the length of vessel per volume, with tissue-to-vessel distances. We then derive a formula that connects regional differences in metabolism to differences in length density and, further, predicts a common value of maximum tissue oxygen tension across the brain. Last, the orientation of capillaries is weakly anisotropic with the exception of a few strongly anisotropic regions; this variation can impact the interpretation of fMRI data.

Hemodynamic impairments within individual watershed areas in asymptomatic carotid artery stenosis by multimodal MRI

Improved understanding of complex hemodynamic impairments in asymptomatic internal carotid artery stenosis (ICAS) is crucial to better assess stroke risks. Multimodal MRI is ideal for measuring brain hemodynamics and has the potential to improve diagnostics and treatment selections. We applied MRI-based perfusion and oxygenation-sensitive imaging in ICAS with the hypothesis that the sensitivity to hemodynamic impairments will improve within individual watershed areas (iWSA). We studied cerebral blood flow (CBF), cerebrovascular reactivity (CVR), relative cerebral blood volume (rCBV), relative oxygen extraction fraction (rOEF), oxygen extraction capacity (OEC) and capillary transit-time heterogeneity (CTH) in 29 patients with asymptomatic, unilateral ICAS (age 70.3 ± 7.0 y) and 30 age-matched healthy controls. In ICAS, we found significant impairments of CBF, CVR, rCBV, OEC, and CTH (strongest lateralization ΔCVR = -24%), but not of rOEF. Although the spatial overlap of compromised hemodynamic parameters within each patient varied in a complex manner, most pronounced changes of CBF, CVR and rCBV were detected within iWSAs (strongest effect ΔCVR = +117%). At the same time, CTH impairments were iWSA independent, indicating widespread dysfunction of capillary-level oxygen diffusivity. In summary, complementary MRI-based perfusion and oxygenation parameters offer deeper perspectives on complex microvascular impairments in individual patients. Furthermore, knowledge about iWSAs improves the sensitivity to hemodynamic impairments.

Heterogeneity of Cerebral White Matter Lesions and Clinical Correlates in Older Adults

BACKGROUND AND PURPOSE

Cerebral white matter signal abnormalities (WMSAs) are a significant radiological marker associated with brain and vascular aging. However, understanding their clinical impact is limited because of their pathobiological heterogeneity. We determined whether use of robust reliable automated procedures can distinguish WMSA classes with different clinical consequences.

METHODS

Data from generally healthy participants aged >50 years with moderate or greater WMSA were selected from the Human Connectome Project-Aging (n=130). WMSAs were segmented on T1 imaging. Features extracted from WMSA included total and regional volume, number of discontinuous clusters, size of noncontiguous lesion, contrast of lesion intensity relative to surrounding normal appearing tissue using a fully automated procedure. Hierarchical clustering was used to classify individuals into distinct classes of WMSA. Radiological and clinical variability was evaluated across the individual WMSA classes.

RESULTS

Class I was characterized by multiple, small, lower-contrast lesions predominantly in the deep WM; class II by large, confluent lesions in the periventricular WM; and class III by higher-contrast lesions restricted to the juxtaventricular WM. Class II was associated with lower myelin content than the other 2 classes. Class II was more prevalent in older subjects and was associated with a higher prevalence of hypertension and lower physical activity levels. Poor sleep quality was associated with a greater risk of class I.

CONCLUSIONS

We classified heterogeneous subsets of cerebral white matter lesions into distinct classes that have different clinical risk factors. This new method for identifying classes of WMSA will be important in understanding the underlying pathophysiology and in determining the impact on clinical outcomes.

The Cerebro-Renal System- Anatomical and Physiological Considerations

The brain and kidney both uniquely are highly susceptible to vascular injury from shared vascular risk factors. However these are not sufficient to explain the complete extent of cerebrovascular disease especially small vessel disease in its myriad presentations that patients with chronic kidney disease manifest. They both require a large amount of blood supply to function optimally. Shared anatomical and physiological factors such as the presence of strain vessels, the local vascular autoregulation that control blood supply possible, results in the vulnerability of these organs to the vascular risk factors. Because it is a bidirectional system where each affects the other, it is best considered as a cerebro-renal unit.

Revealing vascular abnormalities and measuring small vessel density in multiple sclerosis lesions using USPIO

BACKGROUND AND PURPOSE

Multiple Sclerosis (MS) is a progressive, inflammatory, neuro-degenerative disease of the central nervous system (CNS) characterized by a wide range of histopathological features including vascular abnormalities. In this study, an ultra-small superparamagnetic iron oxide (USPIO) contrast agent, Ferumoxytol, was administered to induce an increase in susceptibility for both arteries and veins to help better reveal the cerebral microvasculature. The purpose of this work was to examine the presence of vascular abnormalities and vascular density in MS lesions using high-resolution susceptibility weighted imaging (SWI).

METHODS

Six subjects with relapsing remitting MS (RRMS, age = 47.3 ± 11.8 years with 3 females and 3 males) and fourteen age-matched healthy controls were scanned at 3 T with SWI acquired before and after the infusion of Ferumoxytol. Composite data was generated by registering the FLAIR data to the high resolution SWI data in order to highlight the vascular information in MS lesions. Both the central vein sign (CVS) and, a new measure, the multiple vessel sign (MVS) were identified, along with any vascular abnormalities, in the lesions on pre- and post-contrast SWI-FLAIR fusion data. The small vessel density within the periventricular normal-appearing white matter (NAWM) and the periventricular lesions were compared for all subjects.

RESULTS

Averaged across two independent raters, a total of 530 lesions were identified across all patients. The total number of lesions with vascularity on pre- and post-contrast data were 287 and 488, respectively. The lesions with abnormal vascular behavior were broken up into following categories: small lesions appearing only at the vessel boundary; dilated vessels within the lesions; and developmental venous angiomas. These vessel abnormalities observed within lesions increased from 55 on pre-contrast data to 153 on post-contrast data. Finally, across all the patients, the periventricular lesional vessel density was significantly higher (p < 0.05) than that of the periventricular NAWM.

CONCLUSIONS

By inducing a super-paramagnetic susceptibility in the blood using Ferumoxytol, the vascular abnormalities in the RRMS patients were revealed and small vessel densities were obtained. This approach has the potential to monitor the venous vasculature present in MS lesions, catalogue their characteristics and compare the vascular structures spatially to the presence of lesions. These enhanced vascular features may provide new insight into the pathophysiology of MS.

Multi-Class ASD Classification Based on Functional Connectivity and Functional Correlation Tensor via Multi-Source Domain Adaptation and Multi-View Sparse Representation

The resting-state functional magnetic resonance imaging (rs-fMRI) reflects functional activity of brain regions by blood-oxygen-level dependent (BOLD) signals. Up to now, many computer-aided diagnosis methods based on rs-fMRI have been developed for Autism Spectrum Disorder (ASD). These methods are mostly the binary classification approaches to determine whether a subject is an ASD patient or not. However, the disease often consists of several sub-categories, which are complex and thus still confusing to many automatic classification methods. Besides, existing methods usually focus on the functional connectivity (FC) features in grey matter regions, which only account for a small portion of the rs-fMRI data. Recently, the possibility to reveal the connectivity information in the white matter regions of rs-fMRI has drawn high attention. To this end, we propose to use the patch-based functional correlation tensor (PBFCT) features extracted from rs-fMRI in white matter, in addition to the traditional FC features from gray matter, to develop a novel multi-class ASD diagnosis method in this work. Our method has two stages. Specifically, in the first stage of multi-source domain adaptation (MSDA), the source subjects belonging to multiple clinical centers (thus called as source domains) are all transformed into the same target feature space. Thus each subject in the target domain can be linearly reconstructed by the transformed subjects. In the second stage of multi-view sparse representation (MVSR), a multi-view classifier for multi-class ASD diagnosis is developed by jointly using both views of the FC and PBFCT features. The experimental results using the ABIDE dataset verify the effectiveness of our method, which is capable of accurately classifying each subject into a respective ASD sub-category.

Diabetic rats are more susceptible to cognitive decline in a model of microemboli-mediated vascular contributions to cognitive impairment and dementia

Vascular disease plays an important role in all kinds of cognitive impairment and dementia. Diabetes increases the risk of vascular disease and dementia. However, it is not clear how existing vascular disease in the brain accelerates the development of small vessel disease and promotes cognitive dysfunction in diabetes. We used microemboli (ME) injection model in the current study to test the hypothesis that cerebrovascular dysfunction in diabetes facilitates entrapment of ME leading to inflammation and cognitive decline. We investigated cognitive function, axonal/white matter (WM) changes, neurovascular coupling, and microglial activation in control and diabetic male and female Wistar rats subjected to sham or low/high dose ME injection. Diabetic male animals had cognitive deficits, WM demyelination and greater microglial activation than the control animals even at baseline. Functional hyperemia gradually declined in diabetic male animals after ME injection. Both low and high ME injection worsened WM damage and increased microglial activation in diabetic male and female animals. Low ME did not cause cognitive decline in controls, while promoting learning/memory deficits in diabetic female rats and no further decline in diabetic male animals. High ME led to cognitive decline in control male rats and exacerbated the deficits in diabetic cohort. These results suggest that the existing cerebrovascular dysfunction in diabetes may facilitate ME-mediated demyelination leading to cognitive decline. It is important to integrate comorbidities/sex as a biological variable into experimental models for the development of preventive or therapeutic targets.

Identification of White Matter Networks Engaged in Object (Face) Recognition Showing Differential Responses to Modulated Stimulus Strength

Blood-oxygenation-level-dependent (BOLD) signals in magnetic resonance imaging indirectly reflect neural activity in cortex, but they are also detectable in white matter (WM). BOLD signals in WM exhibit strong correlations with those in gray matter (GM) in a resting state, but their interpretation and relationship to GM activity in a task are unclear. We performed a parametric visual object recognition task designed to modulate the BOLD signal response in GM regions engaged in higher order visual processing, and measured corresponding changes in specific WM tracts. Human faces embedded in different levels of random noise have previously been shown to produce graded changes in BOLD activation in for example, the fusiform gyrus, as well as in electrophysiological (N170) evoked potentials. The magnitudes of BOLD responses in both GM regions and selected WM tracts varied monotonically with the stimulus strength (noise level). In addition, the magnitudes and temporal profiles of signals in GM and WM regions involved in the task coupled strongly across different task parameters. These findings reveal the network of WM tracts engaged in object (face) recognition and confirm that WM BOLD signals may be directly affected by neural activity in GM regions to which they connect.

Meninges: A Widespread Niche of Neural Progenitors for the Brain

Emerging evidence highlights the several roles that meninges play in relevant brain functions as they are a protective membrane for the brain, produce and release several trophic factors important for neural cell migration and survival, control cerebrospinal fluid dynamics, and embrace numerous immune interactions affecting neural parenchymal functions. Furthermore, different groups have identified subsets of neural progenitors residing in the meninges during development and in the adulthood in different mammalian species, including humans. Interestingly, these immature neural cells are able to migrate from the meninges to the neural parenchyma and differentiate into functional cortical neurons or oligodendrocytes. Immature neural cells residing in the meninges promptly react to brain disease. Injury-induced expansion and migration of meningeal neural progenitors have been observed following experimental demyelination, traumatic spinal cord and brain injury, amygdala lesion, stroke, and progressive ataxia. In this review, we summarize data on the function of meninges as stem cell niche and on the presence of immature neural cells in the meninges, and discuss their roles in brain health and disease. Furthermore, we consider the potential exploitation of meningeal neural progenitors for the regenerative medicine to treat neurological disorders.

Hemodynamic Response Function in Brain White Matter in a Resting State

The hemodynamic response function (HRF) characterizes temporal variations of blood oxygenation level-dependent (BOLD) signals. Although a variety of HRF models have been proposed for gray matter responses to functional demands, few studies have investigated HRF profiles in white matter particularly under resting conditions. In the present work we quantified the nature of the HRFs that are embedded in resting state BOLD signals in white matter, and which modulate the temporal fluctuations of baseline signals. We demonstrate that resting state HRFs in white matter could be derived by referencing to intrinsic avalanches in gray matter activities, and the derived white matter HRFs had reduced peak amplitudes and delayed peak times as compared with those in gray matter. Distributions of the time delays and correlation profiles in white matter depend on gray matter activities as well as white matter tract distributions, indicating that resting state BOLD signals in white matter encode neural activities associated with those of gray matter. This is the first investigation of derivations and characterizations of resting state HRFs in white matter and their relations to gray matter activities. Findings from this work have important implications for analysis of BOLD signals in the brain.

Demonstrating a reduced capacity for removal of fluid from cerebral white matter and hypoxia in areas of white matter hyperintensity associated with age and dementia

White matter hyperintensities (WMH) occur in association with dementia but the aetiology is unclear. Here we test the hypothesis that there is a combination of impaired elimination of interstitial fluid from the white matter together with a degree of hypoxia in WMH. One of the mechanisms for the elimination of amyloid-β (Aβ) from the brain is along the basement membranes in the walls of capillaries and arteries (Intramural Peri-Arterial Drainage – IPAD). We compared the dynamics of IPAD in the grey matter of the hippocampus and in the white matter of the corpus callosum in 10 week old C57/B16 mice by injecting soluble Aβ as a tracer. The dynamics of IPAD in the white matter were significantly slower compared with the grey matter and this was associated with a lower density of capillaries in the white matter. Exposing cultures of smooth muscle cells to hypercapnia as a model of cerebral hypoperfusion resulted in a reduction in fibronectin and an increase in laminin in the extracellular matrix. Similar changes were detected in the white matter in human WMH suggesting that hypercapnia/hypoxia may play a role in WMH. Employing therapies to enhance both IPAD and blood flow in the white matter may reduce WMH in patients with dementia.

Subvoxel vascular imaging of the midbrain using USPIO-Enhanced MRI

There is an urgent need for better detection and understanding of vascular abnormalities at the micro-level, where critical vascular nourishment and cellular metabolic changes occur. This is especially the case for structures such as the midbrain where both the feeding and draining vessels are quite small. Being able to monitor and diagnose vascular changes earlier will aid in better understanding the etiology of the disease and in the development of therapeutics. In this work, thirteen healthy volunteers were scanned with a dual echo susceptibility weighted imaging (SWI) sequence, with a resolution of 0.22 ​× ​0.44 ​× ​1 ​mm³ at 3T. Ultra-small superparamagnetic iron oxides (USPIO) were used to induce an increase in susceptibility in both arteries and veins. Although the increased vascular susceptibility enhances the visibility of small subvoxel vessels, the accompanying strong signal loss of the large vessels deteriorates the local tissue contrast. To overcome this problem, the SWI data were acquired at different time points during a gradual administration (final concentration ​= ​4 ​mg/kg) of the USPIO agent, Ferumoxytol, and the data was processed to combine the SWI data dynamically, in order to see through these blooming artifacts. The major vessels and their tributaries (such as the collicular artery, peduncular artery, peduncular vein and the lateral mesencephalic vein) were identified on the combined SWI data using arterio-venous maps. Dynamically combined SWI data was then compared with previous histological work to validate that this protocol was able to detect small vessels on the order of 50 ​μm-100 ​μm. A complex division-based phase unwrapping was also employed to improve the quality of quantitative susceptibility maps by reducing the artifacts due to aliased voxels at the vessel boundaries. The smallest detectable vessel size was then evaluated by revisiting numerical simulations, using estimated true susceptibilities for the basal vein and the posterior cerebral artery in the presence of Ferumoxytol. These simulations suggest that vessels as small as 50 ​μm should be visible with the maximum dose of 4 ​mg/kg.

Association of FLAIR vascular hyperintensity and acute MCA stroke outcome changes with the severity of leukoaraiosis

PURPOSE

The clinical significance of FLAIR vascular hyperintensity (FVH), a marker of collateral circulation in ischaemic stroke, remains controversial. We hypothesised that the association between FVH and outcomes varies with the severity of leukoaraiosis (LA), another marker of collaterals, and that their combined significance may vary with time.

METHODS

We included 459 consecutive patients with middle cerebral artery (MCA) stroke. Proximal and distal FVHs were distinguished based on location. LA was divided into two grades, according to Fazekas scores of 0-2 and 3-6. Symptom-to-MRI time was divided into two categories: ≤ 14 days and ≥ 15 days.

RESULTS

We found no difference in FVH proportion according to LA grade. Multivariate analysis revealed that LA and FVH status were independently associated with unfavourable outcomes (modified Rankin scale ≥ 2) in patients with symptom-to-MRI times ≤ 14 days (P = 0.008), but not in those with symptom-to-MRI times ≥15 days (P = 0.61). In the group with symptom-to-MRI times ≤14 days, patients with LA 3-6 and FVH(+) (OR, 3.044; 95% CI, 1.116-8.305) were more likely to have unfavourable clinical outcomes compared with patients with LA 0-2 and FVH(+) but not compared with those with LA 0-2 and FVH(-) or LA 3-6 and FVH(-). In addition, FVH location did not influence the relationship between FVH and outcomes.

CONCLUSIONS

The association between FVH and outcomes was influenced by the degree of LA in the acute but not in the subacute and chronic stages of MCA infarction. FVH predicts clinical outcomes independently only in those with more extensive LA.

Characterizing white matter fiber orientation effects on multi-parametric quantitative BOLD assessment of oxygen extraction fraction

Relative oxygen extraction fraction (rOEF) is a fundamental indicator of cerebral metabolic function. An easily applicable method for magnetic resonance imaging (MRI) based rOEF mapping is the multi-parametric quantitative blood oxygenation level dependent (mq-BOLD) approach with separate acquisitions of transverse relaxation times   T 2 * and T2 and dynamic susceptibility contrast (DSC) based relative cerebral blood volume (rCBV). Given that transverse relaxation and rCBV in white matter (WM) strongly depend on nerve fiber orientation, mq-BOLD derived rOEF is expected to be affected as well. To investigate fiber orientation related rOEF artefacts, we present a methodological study characterizing anisotropy effects of WM as measured by diffusion tensor imaging (DTI) on mq-BOLD in 30 healthy volunteers. Using a 3T clinical MRI-scanner, we performed a comprehensive correlation of all parameters (  T 2 * , T2, R 2 ' , rCBV, rOEF, where R 2 ' =1/  T 2 * -1/T2) with DTI-derived fiber orientation towards the main magnetic field (B0). Our results confirm strong dependencies of transverse relaxation and rCBV on the nerve fiber orientation towards B0, with anisotropy-driven variations up to 37%. Comparably weak orientation-dependent variations of mq-BOLD derived rOEF (3.8%) demonstrate partially counteracting influences of R 2 ' and rCBV effects, possibly suggesting applicability of rOEF as an oxygenation sensitive biomarker. However, unresolved issues warrant caution when applying mq-BOLD to WM.

White Matter fMRI Activation Cannot Be Treated as a Nuisance Regressor: Overcoming a Historical Blind Spot

Despite past controversies, increasing evidence has led to acceptance that white matter activity is detectable using functional magnetic resonance imaging (fMRI). In spite of this, advanced analytic methods continue to be published that reinforce a historic bias against white matter activation by using it as a nuisance regressor. It is important that contemporary analyses overcome this blind spot in whole brain functional imaging, both to ensure that newly developed noise regression techniques are accurate, and to ensure that white matter, a vital and understudied part of the brain, is not ignored in functional neuroimaging studies.

Altered Resting State Functional Activity and Microstructure of the White Matter in Migraine With Aura

Introduction: Brain structure and function were reported to be altered in migraine. Importantly our earlier results showed that white matter diffusion abnormalities and resting state functional activity were affected differently in the two subtypes of the disease, migraine with and without aura. Resting fluctuation of the BOLD signal in the white matter was reported recently. The question arising whether the white matter activity, that is strongly coupled with gray matter activity is also perturbed differentially in the two subtypes of the disease and if so, is it related to the microstructural alterations of the white matter.

Methods: Resting state fMRI, 60 directional DTI images and high-resolution T1 images were obtained from 51 migraine patients and 32 healthy volunteers. The images were pre-processed and the white matter was extracted. Independent component analysis was performed to obtain white matter functional networks. The differential expression of the white matter functional networks in the two subtypes of the disease was investigated with dual-regression approach. The Fourier spectrum of the resting fMRI fluctuations were compared between groups. Voxel-wise correlation was calculated between the resting state functional activity fluctuations and white matter microstructural measures.

Results: Three white matter networks were identified that were expressed differently in migraine with and without aura. Migraineurs with aura showed increased functional connectivity and amplitude of BOLD fluctuation. Fractional anisotropy and radial diffusivity showed strong correlation with the expression of the frontal white matter network in patients with aura.

Discussion: Our study is the first to describe changes in white matter resting state functional activity in migraine with aura, showing correlation with the underlying microstructure. Functional and structural differences between disease subtypes suggest at least partially different pathomechanism, which may necessitate handling of these subtypes as separate entities in further studies.

Cerebral perfusion and compensatory blood supply in patients with recent small subcortical infarcts

Hypoperfusion is the typical perfusion pattern associated with recent small subcortical infarcts of the brain, but other perfusion patterns may be present in patients with these infarcts. Using CT perfusion, we studied 67 consecutive patients who had a small subcortical infarct at a follow-up MRI study to investigate the correlation between the perfusion pattern and the clinical and radiological course. On CT perfusion map analysis, 51 patients (76%) had focal hypoperfusion, 4 patients (6%) had hyperperfusion and the remaining 12 patients (18%) showed no abnormalities. On dynamic sequential imaging analysis obtained from the source perfusion images, 32 patients (48%) had a sustained hypoperfusion pattern, 11 patients (16%) had a reperfusion pattern, and 18 patients (27%) had a delayed compensation pattern. Systolic blood pressure was higher in patients with sustained hypoperfusion although the perfusion pattern was independent of the final volume of infarction. These results reinforce the notion that mechanisms other than hypoperfusion are at play in patients with small subcortical infarcts including the intervention of compensatory sources of blood flow. The ultimate clinical significance of these perfusion patterns remains to be determined in larger series of patients assessed longitudinally.