Medullary vein architecture modulates the white matter BOLD cerebrovascular reactivity signal response to CO2: observations from high-resolution T2* weighted imaging at 7T

Mapping Intimacies ◽

10.1101/2021.09.03.458842 ◽

2021 ◽

Author(s):

Alex A. Bhogal

Keyword(s):

White Matter ◽

High Resolution ◽

Vascular Reactivity ◽

Blood Oxygenation ◽

Cerebrovascular Reactivity ◽

7 Tesla ◽

Hemodynamic Parameters ◽

Vascular Control ◽

Bold Imaging ◽

Anatomical Images

ABSTRACTBrain stress testing using blood oxygenation level-dependent (BOLD) MRI to evaluate changes in cerebrovascular reactivity (CVR) is of growing interest for evaluating white matter integrity. However, even under healthy conditions, the white matter BOLD-CVR response differs notably from that observed in the gray matter. In addition to actual arterial vascular control, the venous draining topology may influence the WM-CVR response leading to signal delays and dispersions. These types of alterations in hemodynamic parameters are sometimes linked with pathology, but may also arise from differences in normal venous architecture. In this work, high-resolution T2*weighted anatomical images combined with BOLD imaging during a hypercapnic breathing protocol were acquired using a 7 tesla MRI system. Hemodynamic parameters including base CVR, hemodynamic lag, lag-corrected CVR, response onset and signal dispersion, and finally ΔCVR (corrected CVR minus base CVR) were calculated in 8 subjects. Parameter maps were spatially normalized and correlated against an MNI-registered white matter medullary vein atlas. Moderate correlations (Pearson’s rho) were observed between medullary vessel frequency (MVF) and ΔCVR (0.52; 0.58 for total WM), MVF and hemodynamic lag (0.42; 0.54 for total WM), MVF and signal dispersion (0.44; 0.53 for total WM), and finally MVF and signal onset (0.43; 0.52 for total WM). Results indicate that, when assessed in the context of the WM venous architecture, changes in the response shape may only be partially reflective of the actual vascular reactivity response occurring further upstream by control vessels. This finding may have implications when attributing diseases mechanisms and/or progression to presumed impaired WM BOLD-CVR.

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The Cumulative Influence of Hyperoxia and Hypercapnia on Blood Oxygenation and R2*

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.2015.168 ◽

2015 ◽

Vol 35 (12) ◽

pp. 2032-2042 ◽

Cited By ~ 9

Author(s):

Carlos C Faraco ◽

Megan K Strother ◽

Jeroen CW Siero ◽

Daniel F Arteaga ◽

Allison O Scott ◽

...

Keyword(s):

Venous Blood ◽

Quantitative Information ◽

Blood Oxygenation ◽

Cerebrovascular Reactivity ◽

Resonance Imaging ◽

Tissue Water ◽

Bold Mri ◽

Bold Imaging ◽

Complex Interactions ◽

Oxygenation Level

Cerebrovascular reactivity (CVR)-weighted blood-oxygenation-level-dependent magnetic resonance imaging (BOLD-MRI) experiments are frequently used in conjunction with hyperoxia. Owing to complex interactions between hyperoxia and hypercapnia, quantitative effects of these gas mixtures on BOLD responses, blood and tissue R2∗, and blood oxygenation are incompletely understood. Here we performed BOLD imaging (3T; TE/TR = 35/2,000 ms; spatial resolution = 3×3×3.5 mm3) in healthy volunteers ( n = 12; age = 29±4.1 years) breathing (i) room air (RA), (ii) normocapnic-hyperoxia (95% O2/5% N2, HO), (iii) hypercapnic-normoxia (5% CO2/21% O2/74% N2, HC-NO), and (iv) hypercapnic-hyperoxia (5% CO2/95% O2, HC-HO). For HC-HO, experiments were performed with separate RA and HO baselines to control for changes in O2. T2-relaxation-under-spin-tagging MRI was used to calculate basal venous oxygenation. Signal changes were quantified and established hemodynamic models were applied to quantify vasoactive blood oxygenation, blood–water R∗2, and tissue-water R∗2. In the cortex, fractional BOLD changes (stimulus/baseline) were HO/RA = 0.011 ± 0.007; HC-NO/RA = 0.014±0.004; HC-HO/HO = 0.020±0.008; and HC-HO/RA = 0.035 ±0.010; for the measured basal venous oxygenation level of 0.632, this led to venous blood oxygenation levels of 0.660 (HO), 0.665 (HC-NO), and 0.712 (HC-HO). Interleaving a HC-HO stimulus with HO baseline provided a smaller but significantly elevated BOLD response compared with a HC-NO stimulus. Results provide an outline for how blood oxygenation differs for several gas stimuli and provides quantitative information on how hypercapnic BOLD CVR and R∗2 are altered during hyperoxia.

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White Matter Hyperintensities Subtypes in Cerebral Small Vessel Disease : 7 Tesla Ultra-high Resolution Imaging MRI

Case Medical Research ◽

10.31525/ct1-nct04298866 ◽

2020 ◽

Author(s):

Keyword(s):

White Matter ◽

High Resolution ◽

White Matter Hyperintensities ◽

Small Vessel Disease ◽

Cerebral Small Vessel Disease ◽

Small Vessel ◽

7 Tesla ◽

High Resolution Imaging ◽

Vessel Disease ◽

Resolution Imaging

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Medullary vein architecture modulates the white matter BOLD cerebrovascular reactivity signal response to CO2: observations from high-resolution T2* weighted imaging at 7T

NeuroImage ◽

10.1016/j.neuroimage.2021.118771 ◽

2021 ◽

pp. 118771

Author(s):

Alex A. Bhogal

Keyword(s):

White Matter ◽

High Resolution ◽

Cerebrovascular Reactivity ◽

Signal Response

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A High-Resolution Interactive Atlas of the Human Brainstem Using Magnetic Resonance Histology

Neurosurgery ◽

10.1093/neuros/nyaa447_644 ◽

2020 ◽

Vol 67 (Supplement_1) ◽

Author(s):

Syed M Adil ◽

Evan Calabrese ◽

Lefko T Charalambous ◽

James Cook ◽

Shervin Rahimpour ◽

...

Keyword(s):

White Matter ◽

Magnetic Resonance ◽

High Resolution ◽

Spatial Resolution ◽

7 Tesla ◽

Acquisition Time ◽

Superior Cerebellar Peduncle ◽

Corticospinal Tracts ◽

Custom Made ◽

And Diffusion

Abstract INTRODUCTION Traditional atlases of the human brainstem are limited by the inflexible, sparsely-sampled, two-dimensional nature of histology or the low spatial resolution of magnetic resonance imaging (MRI). Magnetic resonance histology (MRH) uses postmortem high-resolution MRI to circumvent the challenges associated with both modalities. METHODS A human brainstem specimen extending from the rostral diencephalon through the caudal medulla was removed from a 65-year-old male within 24 hours of death. The specimen was formalin-fixed for two weeks, then rehydrated and placed in a custom-made MRI compatible tube and immersed in buffered liquid fluorocarbon. MRI was performed in a 7-Tesla machine with 120 unique diffusion directions. Acquisition time for anatomic and diffusion images were 14 hours and 208 hours, respectively. Segmentation was performed manually. Deterministic fiber tractography was done using strategically chosen regions of interest and avoidance, with manual editing using expert knowledge of human neuroanatomy. RESULTS Anatomic and diffusion images were rendered with isotropic resolutions of 50 μm and 200 μm, respectively. Spatial resolution was high enough to visualize individual fasciculi of the descending corticospinal tracts intercalated between the transverse pontocerebellar fibers. Ninety different structures were segmented and 11 different fiber bundles were rendered with tractography. Angular resolution was high enough to visualize crossing fibers, such as those of the superior cerebellar peduncle. Both gray and white matter can be visualized in 3D simultaneously, such as the subthalamic nuclei and corticospinal tracts, as may be used in deep brain stimulation. CONCLUSION We used MRH to enable unprecedented resolution in digital imaging of the human brainstem and adjacent diencephalic structures, and we then performed comprehensive segmentation and tractography to render an interactive, three-dimensional atlas of both gray and white matter. This atlas has immediate applications in neuroanatomical study and education, with the potential for future neurosurgical applications in enhancing neurosurgical planning through “safe” zones of entry into the human brainstem. We are currently building the computer infrastructure to make this atlas publicly-available.

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Spatial specificity of the functional MRI blood oxygenation response relative to neuronal activity

10.1101/097287 ◽

2016 ◽

Cited By ~ 1

Author(s):

Denis Chaimow ◽

Essa Yacoub ◽

Kâmil Uğurbil ◽

Amir Shmuel

Keyword(s):

Functional Mri ◽

Spatial Organization ◽

Ocular Dominance ◽

Blood Oxygenation ◽

7 Tesla ◽

Published Data ◽

Model Parameters ◽

Bold Fmri ◽

Bold Imaging ◽

Spatial Specificity

AbstractPrevious attempts at characterizing the spatial specificity of the blood oxygenation level dependent functional MRI (BOLD fMRI) response by estimating its point-spread function (PSF) have conventionally relied on spatial representations of visual stimuli in area V1. Consequently, their estimates were confounded by the width and scatter of receptive fields of V1 neurons. Here, we circumvent these limits by instead using the inherent cortical spatial organization of ocular dominance columns (ODCs) to determine the PSF for both Gradient Echo (GE) and Spin Echo (SE) BOLD imaging at 7 Tesla. By applying Markov Chain Monte Carlo sampling on a probabilistic generative model of imaging ODCs, we quantified the PSFs that best predict the spatial structure and magnitude of differential ODCs’ responses. Prior distributions for the ODC model parameters were determined by analyzing published data of cytochrome oxidase patterns from post-mortem histology of human V1 and of neurophysio-logical ocular dominance indices. The most probable PSF full-widths at halfmaximum were 0.82 mm (SE) and 1.02 mm (GE). Our results provide a quantitative basis for the spatial specificity of BOLD fMRI at ultra-high fields, which can be used for planning and interpretation of high-resolution differential fMRI of fine-scale cortical organizations.

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Cerebrovascular Reactivity in the Brain White Matter: Magnitude, Temporal Characteristics, and Age Effects

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.2013.194 ◽

2013 ◽

Vol 34 (2) ◽

pp. 242-247 ◽

Cited By ~ 59

Author(s):

Binu P Thomas ◽

Peiying Liu ◽

Denise C Park ◽

Matthias JP van Osch ◽

Hanzhang Lu

Keyword(s):

White Matter ◽

Magnetic Resonance ◽

Structural Characteristics ◽

Blood Oxygenation ◽

Cerebrovascular Reactivity ◽

Tissue Ischemia ◽

Brain White Matter ◽

Oxygenation Level ◽

Magnetic Resonance Imaging Mri ◽

The Brain

White matter (WM) comprises about half of the brain and its dysfunction is implicated in many brain disorders. While structural properties in healthy and diseased WM have been extensively studied, relatively little is known about the physiology underlying these structural characteristics. Recent advances in magnetic resonance (MR) technologies provided new opportunities to better understand perfusion and microvasculature in the WM. Here, we aim to evaluate vasodilatory capacity of the WM vasculature, which is thought to be important in tissue ischemia and autoregulation. Fifteen younger and fifteen older subjects performed a CO2 inhalation task while blood-oxygenation-level-dependent (BOLD) magnetic resonance imaging (MRI) images were continuously collected. The cerebrovascular reactivity (CVR) index showed that the value of CVR in the WM (0.03±0.002%/mm Hg) was positive, but was significantly lower than that in the gray matter (GM) (0.22±0.01%/mm Hg). More strikingly, the WM response showed a temporal delay of 19±3 seconds compared with GM, which was attributed to the longer time it takes for extravascular CO2 to change. With age, WM CVR response becomes greater and faster, which is opposite to the changes seen in the GM. These data suggest that characteristics of WM CVR are different from that of GM and caution should be used when interpreting pathologic WM CVR results.

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Cerebrovascular reactivity mapping without hypercapnic challenge in patients with carotid artery stenosis

Revista Brasileira de Física Médica ◽

10.29384/rbfm.2019.v13.n2.p62-65 ◽

2019 ◽

Vol 13 (2) ◽

pp. 62

Author(s):

Kaio Felippe Secchinato ◽

Pedro Henrique Rodrigues Da Silva ◽

Ana Paula Afonso Camargo ◽

Octávio Marques Pontes-Neto ◽

Renata Ferranti Leoni

Keyword(s):

Resting State ◽

Vascular Reactivity ◽

Blood Oxygenation ◽

Cerebrovascular Reactivity ◽

Breath Holding ◽

Metabolic Demand ◽

Additional Equipment ◽

Oxygenation Level ◽

Magnetic Resonance Imaging Mri ◽

Carbon Dioxide Co2

Vascular reactivity represents the ability of the vascular smooth muscle to dilate or contract in response to changes in metabolic demand or vasoactive stimulus. More specifically, the cerebrovascular reactivity (CVR) has raised interest in several studies that point to its potential to predict stroke risk in patients with cerebrovascular disease. CVR mapping is typically performed using carbon dioxide (CO2) inhalation, breath-holding, or acetazolamide injection as vasoactive challenges, while magnetic resonance imaging (MRI) based on the blood oxygenation level-dependent (BOLD) contrast is acquired. However, such challenges of hypercapnia depend on additional equipment and cooperation of the subjects, limiting their applications, especially in elderly patients. Therefore, the objective of the present study was to map the CVR using resting-state MRI-BOLD, with no hypercapnic challenge, considering the variations in BOLD signal associated with variations in the arterial partial pressure of CO2. The CVR maps obtained with resting data showed a high correlation with those obtained by the conventional experiment with CO2 inhalation (r > 0.70). In addition, the CVR changes observed for the patients were consistent with their clinical reports. These results show that the mapping of CVR obtained with resting-state data may become a useful alternative in the detection of perfusion changes in clinical applications when the hypercapnic challenge is not feasible.

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