scholarly journals A statistical 3D model of the human cortical vasculature to compute the hemodynamic fingerprint of the BOLD fMRI signal

2020 ◽  
Author(s):  
Mario Gilberto Báez-Yáñez ◽  
Jeroen C.W. Siero ◽  
Natalia Petridou
Keyword(s):  
Brain Activity ◽  
Indirect Measurement ◽  
Blood Oxygenation ◽  
Biophysical Model ◽  
Local Magnetic Field ◽  
Hemodynamic Changes ◽  
Bold Fmri ◽  
Fmri Signal ◽  
Signal Response ◽  
Biophysical Interactions

ABSTRACTBOLD fMRI is a commonly used technique to map brain activity; nevertheless, BOLD fMRI is an indirect measurement of brain function triggered by neurometabolic and neurovascular coupling. Hence, the origin of the BOLD fMRI signal is quite complex, and the signal formation depends, among others, on the geometry of the cortical vasculature and the associated hemodynamic behavior. To characterize and quantify the hemodynamic contributions to the BOLD signal response in humans, it is necessary to adopt a computational model that resembles the human cortical vascular architecture and mimics realistic hemodynamic changes. To this end, we have developed a statistically defined 3D vascular model that resembles the human cortical vasculature. Using this model, we simulated hemodynamic changes triggered by a neuronal activation and local magnetic field disturbances created by the vascular topology and the blood oxygenation changes. The proposed model considers also the biophysical interactions and the intrinsic magnetic properties of the nearby tissue in order to compute a dynamic BOLD fMRI signal response. This computational pipeline results in an integrated biophysical model that can provide a better insight on the understanding and quantification of the hemodynamic fingerprint of the BOLD fMRI signal evolution.

scholarly journals Physiological and pathological brain activation in the anesthetized rat produces hemodynamic-dependent cortical temperature increases that can confound the BOLD fMRI signal

2017 ◽  
Author(s):  
Samuel S. Harris ◽  
Luke W. Boorman ◽  
Devashish Das ◽  
Aneurin J. Kennerley ◽  
Paul S. Sharp ◽  
...  
Keyword(s):  
Core Temperature ◽  
Hemoglobin Concentration ◽  
Sensory Stimulation ◽  
Blood Oxygenation ◽  
Experimental Methodology ◽  
Temperature Changes ◽  
Bold Fmri ◽  
Fmri Signal ◽  
Acute Seizures ◽  
Cortical Temperature

AbstractAnesthetized rodent models are ubiquitous in pre-clinical neuroimaging studies. However, because the associated cerebral morphology and experimental methodology results in a profound negative brain-core temperature differential, cerebral temperature changes during functional activation are likely to be principally driven by local inflow of fresh, core-temperature, blood. This presents a confound to the interpretation of blood-oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) data acquired from such models, since this signal is also critically temperature-dependent. Nevertheless, previous investigation on the subject is surprisingly sparse. Here, we address this issue through use of a novel multi-modal methodology in the urethane anesthetized rat. We reveal that sensory stimulation, hypercapnia and recurrent acute seizures induce significant increases in cortical temperature that are preferentially correlated to changes in total hemoglobin concentration, relative to cerebral blood flow and oxidative metabolism. Furthermore, using a phantom-based evaluation of the effect of such temperature changes on the BOLD fMRI signal, we demonstrate a robust inverse relationship between the two. These findings indicate that temperature increases, due to functional hyperemia, should be accounted for to ensure accurate interpretation of BOLD fMRI signals in pre-clinical neuroimaging studies.

scholarly journals Perception affects the brain's metabolic response to sensory stimulation

2021 ◽  
Author(s):  
Mauro DiNuzzo ◽  
Silvia Mangia ◽  
Marta Moraschi ◽  
Daniele Mascali ◽  
Gisela E. Hagberg ◽  
...  
Keyword(s):  
Metabolic Response ◽  
Visual Stimulation ◽  
Aerobic Glycolysis ◽  
Sensory Stimulation ◽  
Blood Oxygenation ◽  
Bold Fmri ◽  
Physiological Variables ◽  
Fmri Signal ◽  
Oxygenation Level ◽  
Neurochemical Profile

Processing of incoming sensory stimulation triggers an increase of cerebral perfusion and blood oxygenation (neurovascular response) as well as an alteration of the metabolic neurochemical profile (neurometabolic response). Here we show that perceived and unperceived isoluminant chromatic flickering stimuli designed to have similar neurovascular responses as measured by blood oxygenation level dependent functional MRI (BOLD-fMRI) in primary visual cortex (V1) have markedly different neurometabolic responses as measured by functional MRS. In particular, a significant regional buildup of lactate, an index of aerobic glycolysis, and glutamate, an index of malate-aspartate shuttle, occurred in V1 only when the flickering is perceived, without any relation with behavioral or physiological variables. Wheras the BOLD-fMRI signal in V1, a proxy for input to V1, was insensitive to flickering perception by design, the BOLD-fMRI signal in secondary visual areas was larger during perceived than unperceived flickering indicating increased output from V1. These results indicate that the upregulation of energy metabolism induced by visual stimulation depends on the type of information processing taking place in V1, and that 1H-fMRS provides unique information about local input/output balance that is not measured by BOLD-fMRI.

scholarly journals Genetically defined cellular correlates of the baseline brain MRI signal

2018 ◽  
Vol 115 (41) ◽  
pp. E9727-E9736 ◽  
Author(s):  
Jie Wen ◽  
Manu S. Goyal ◽  
Serguei V. Astafiev ◽  
Marcus E. Raichle ◽  
Dmitriy A. Yablonskiy
Keyword(s):  
Functional Connectivity ◽  
Human Brain ◽  
Brain Activity ◽  
Brain Mri ◽  
Blood Oxygenation ◽  
Brain Atlas ◽  
Functional Connections ◽  
Fmri Signal ◽  
Useful Signal

fMRI revolutionized neuroscience by allowing in vivo real-time detection of human brain activity. While the nature of the fMRI signal is understood as resulting from variations in the MRI signal due to brain-activity-induced changes in the blood oxygenation level (BOLD effect), these variations constitute a very minor part of a baseline MRI signal. Hence, the fundamental (and not addressed) questions are how underlying brain cellular composition defines this baseline MRI signal and how a baseline MRI signal relates to fMRI. Herein we investigate these questions by using a multimodality approach that includes quantitative gradient recalled echo (qGRE), volumetric and functional connectivity MRI, and gene expression data from the Allen Human Brain Atlas. We demonstrate that in vivo measurement of the major baseline component of a GRE signal decay rate parameter (R2t*) provides a unique genetic perspective into the cellular constituents of the human cortex and serves as a previously unidentified link between cortical tissue composition and fMRI signal. Data show that areas of the brain cortex characterized by higher R2t* have high neuronal density and have stronger functional connections to other brain areas. Interestingly, these areas have a relatively smaller concentration of synapses and glial cells, suggesting that myelinated cortical axons are likely key cortical structures that contribute to functional connectivity. Given these associations, R2t* is expected to be a useful signal in assessing microstructural changes in the human brain during development and aging in health and disease.

scholarly journals Large Enhancement of Perfusion Contribution on fMRI Signal

2012 ◽  
Vol 32 (5) ◽  
pp. 907-918 ◽  
Author(s):  
Xiao Wang ◽  
Xiao-Hong Zhu ◽  
Yi Zhang ◽  
Wei Chen
Keyword(s):  
Visual Stimulation ◽  
Human Subjects ◽  
Brain Activity ◽  
Human Study ◽  
Blood Oxygenation ◽  
Calibration Model ◽  
Linear Superposition ◽  
Fmri Signal ◽  
Oxygenation Level ◽  
True Blood

The perfusion contribution to the total functional magnetic resonance imaging (fMRI) signal was investigated using a rat model with mild hypercapnia at 9.4 T, and human subjects with visual stimulation at 4 T. It was found that the total fMRI signal change could be approximated as a linear superposition of ‘true’ blood oxygenation level-dependent (BOLD; T2/T2*) effect and the blood flow-related ( T1) effect. The latter effect was significantly enhanced by using short repetition time and large radiofrequency pulse flip angle and became comparable to the ‘true’ BOLD signal in response to a mild hypercapnia in the rat brain, resulting in an improved contrast-to-noise ratio (CNR). Bipolar diffusion gradients suppressed the intravascular signals but had no significant effect on the flow-related signal. Similar results of enhanced fMRI signal were observed in the human study. The overall results suggest that the observed flow-related signal enhancement is likely originated from perfusion, and this enhancement can improve CNR and the spatial specificity for mapping brain activity and physiology changes. The nature of mixed BOLD and perfusion-related contributions in the total fMRI signal also has implication on BOLD quantification, in particular, the BOLD calibration model commonly used to estimate the change of cerebral metabolic rate of oxygen.

The Effects of CCRC on Cognition and Brain Activity in aMCI Patients: A Pilot Placebo Controlled BOLD fMRI Study

2014 ◽  
Vol 11 (5) ◽  
pp. 484-493 ◽  
Author(s):  
Junying Zhang ◽  
Zijing Wang ◽  
Shijun Xu ◽  
Yaojing Chen ◽  
Kewei Chen ◽  
...  
Keyword(s):  
Brain Activity ◽  
Bold Fmri ◽  
Fmri Study

Within-subject variation in BOLD-fMRI signal changes across repeated measurements: Quantification and implications for sample size

NeuroImage ◽  
2008 ◽  
Vol 42 (1) ◽  
pp. 196-206 ◽  
Author(s):  
Bram B. Zandbelt ◽  
Thomas E. Gladwin ◽  
Mathijs Raemaekers ◽  
Mariët van Buuren ◽  
Sebastiaan F. Neggers ◽  
...  
Keyword(s):  
Sample Size ◽  
Repeated Measurements ◽  
Bold Fmri ◽  
Fmri Signal ◽  
Signal Changes

scholarly journals Roles of Ventromedial Prefrontal Cortex and Anterior Cingulate in Subjective Valuation of Prospective Effort

2018 ◽  
Vol 29 (10) ◽  
pp. 4277-4290 ◽  
Author(s):  
Patrick S Hogan ◽  
Joseph K Galaro ◽  
Vikram S Chib
Keyword(s):  
Decision Making ◽  
Prefrontal Cortex ◽  
Brain Activity ◽  
Blood Oxygenation ◽  
Ventromedial Prefrontal Cortex ◽  
Anterior Cingulate ◽  
Effort Level ◽  
Perceived Effort ◽  
Trade Offs ◽  
Subjective Valuation

Abstract The perceived effort level of an action shapes everyday decisions. Despite the importance of these perceptions for decision-making, the behavioral and neural representations of the subjective cost of effort are not well understood. While a number of studies have implicated anterior cingulate cortex (ACC) in decisions about effort/reward trade-offs, none have experimentally isolated effort valuation from reward and choice difficulty, a function that is commonly ascribed to this region. We used functional magnetic resonance imaging to monitor brain activity while human participants engaged in uncertain choices for prospective physical effort. Our task was designed to examine effort-based decision-making in the absence of reward and separated from choice difficulty—allowing us to investigate the brain’s role in effort valuation, independent of these other factors. Participants exhibited subjectivity in their decision-making, displaying increased sensitivity to changes in subjective effort as objective effort levels increased. Analysis of blood-oxygenation-level dependent activity revealed that the ventromedial prefrontal cortex (vmPFC) encoded the subjective valuation of prospective effort, and ACC activity was best described by choice difficulty. These results provide insight into the processes responsible for decision-making regarding effort, partly dissociating the roles of vmPFC and ACC in prospective valuation of effort and choice difficulty.

scholarly journals Functional Near-Infrared Spectroscopy for the Classification of Motor-Related Brain Activity on the Sensor-Level

Sensors ◽  
2020 ◽  
Vol 20 (8) ◽  
pp. 2362 ◽  
Author(s):  
Alexander E. Hramov ◽  
Vadim Grubov ◽  
Artem Badarin ◽  
Vladimir A. Maksimenko ◽  
Alexander N. Pisarchik
Keyword(s):  
Infrared Spectroscopy ◽  
Near Infrared Spectroscopy ◽  
Near Infrared ◽  
High Efficiency ◽  
Brain Activity ◽  
Blood Oxygenation ◽  
Hemispheric Lateralization ◽  
Motor Execution ◽  
Functional Near Infrared Spectroscopy

Sensor-level human brain activity is studied during real and imaginary motor execution using functional near-infrared spectroscopy (fNIRS). Blood oxygenation and deoxygenation spatial dynamics exhibit pronounced hemispheric lateralization when performing motor tasks with the left and right hands. This fact allowed us to reveal biomarkers of hemodynamical response of the motor cortex on the motor execution, and use them for designing a sensing method for classification of the type of movement. The recognition accuracy of real movements is close to 100%, while the classification accuracy of imaginary movements is lower but quite high (at the level of 90%). The advantage of the proposed method is its ability to classify real and imaginary movements with sufficiently high efficiency without the need for recalculating parameters. The proposed system can serve as a sensor of motor activity to be used for neurorehabilitation after severe brain injuries, including traumas and strokes.

scholarly journals Beyond BOLD: in search of genuine diffusion fMRI contrast in human brain

2021 ◽  
Author(s):  
Wiktor Olszowy ◽  
Yujian Diao ◽  
Ileana O Jelescu
Keyword(s):  
Human Brain ◽  
Brain Activity ◽  
Blood Oxygenation ◽  
Alternative Methods ◽  
Functional Responses ◽  
Spatiotemporal Resolution ◽  
Apparent Diffusion ◽  
Oxygenation Level ◽  
Vascular Origin ◽  
Positive Correlations

Functional Magnetic Resonance Imaging (fMRI) is an essential method to measure brain activity non-invasively. While fMRI almost systematically relies on the blood oxygenation level-dependent (BOLD) contrast, there is an increasing interest in alternative methods that would not rely on neurovascular coupling. A promising but controversial such alternative is diffusion fMRI (dfMRI), which relies instead on dynamic fluctuations in apparent diffusion coefficient (ADC) due to microstructural changes underlying neuronal activity. However, it is unclear whether genuine dfMRI contrast, distinct from BOLD contamination, can be detected in the human brain in physiological conditions. Here, we present the first dfMRI study in humans attempting to minimize all BOLD contamination sources and comparing functional responses at two field strengths (3T and 7T), both for task and resting-state (RS) fMRI. Our study benefits from unprecedented high spatiotemporal resolution and harnesses novel denoising strategies. We report task-induced decrease in ADC with temporal and spatial features distinct from the BOLD response and yielding more specific activation maps. Furthermore, we report dfMRI RS connectivity which, compared to its BOLD counterpart, is essentially free from physiological artifacts and preserves positive correlations but preferentially suppresses anti-correlations, which are likely of vascular origin. A careful acquisition and processing design thus enable the detection of genuine dfMRI contrast on clinical MRI systems. As opposed to BOLD, diffusion functional contrast could be particularly well suited for low-field MRI.

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