scholarly journals Assessment of single-vessel cerebral blood velocity by phase contrast fMRI

PLoS Biology ◽  
2021 ◽  
Vol 19 (9) ◽  
pp. e3000923
Author(s):  
Xuming Chen ◽  
Yuanyuan Jiang ◽  
Sangcheon Choi ◽  
Rolf Pohmann ◽  
Klaus Scheffler ◽  
...  
Keyword(s):  
High Resolution ◽  
High Field ◽  
Phase Contrast ◽  
Cerebral Blood Volume ◽  
Blood Velocity ◽  
Blood Oxygenation ◽  
Single Vessel ◽  
Oxygenation Level ◽  
Cerebral Blood Velocity ◽  
Human Brains

Current approaches to high-field functional MRI (fMRI) provide 2 means to map hemodynamics at the level of single vessels in the brain. One is through changes in deoxyhemoglobin in venules, i.e., blood oxygenation level–dependent (BOLD) fMRI, while the second is through changes in arteriole diameter, i.e., cerebral blood volume (CBV) fMRI. Here, we introduce cerebral blood flow–related velocity-based fMRI, denoted CBFv-fMRI, which uses high-resolution phase contrast (PC) MRI to form velocity measurements of flow. We use CBFv-fMRI in measure changes in blood velocity in single penetrating microvessels across rat parietal cortex. In contrast to the venule-dominated BOLD and arteriole-dominated CBV fMRI signals, CBFv-fMRI is comparable from both arterioles and venules. A single fMRI platform is used to map changes in blood pO2 (BOLD), volume (CBV), and velocity (CBFv). This combined high-resolution single-vessel fMRI mapping scheme enables vessel-specific hemodynamic mapping in animal models of normal and diseased states and further has translational potential to map vascular dementia in diseased or injured human brains with ultra–high-field fMRI.

scholarly journals Single-vessel cerebral blood flow fMRI to map blood velocity by phase-contrast imaging

2020 ◽  
Author(s):  
Xuming Chen ◽  
Yuanyuan Jiang ◽  
Sangcheon Choi ◽  
Rolf Pohmann ◽  
Klaus Scheffler ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
High Resolution ◽  
High Field ◽  
Phase Contrast ◽  
Blood Oxygenation ◽  
Contrast Imaging ◽  
Velocity Mapping ◽  
Single Vessel ◽  
Mapping Scheme

AbstractCurrent approaches to high-field fMRI provide two means to map hemodynamics at the level of single vessels in the brain. One is through changes in deoxyhemoglobin in venules, i.e., blood oxygenation level-dependent (BOLD) fMRI, while the second is through changes in arteriole diameter, i.e., cerebral blood volume (CBV) fMRI. Here we introduce cerebral blood flow (CBF)-fMRI, which uses high-resolution phase-contrast MRI to form velocity measurements of flow and demonstrate CBF-fMRI in single penetrating microvessels across rat parietal cortex. In contrast to the venule-dominated BOLD and arteriole-dominated CBV fMRI signal, the phase-contrast -based CBF signal changes are highly comparable from both arterioles and venules. Thus, we have developed a single-vessel fMRI platform to map the BOLD, CBV, and CBF from penetrating microvessels throughout the cortex. This high-resolution single-vessel fMRI mapping scheme not only enables the vessel-specific hemodynamic mapping in diseased animal models but also presents a translational potential to map vascular dementia in diseased or injured human brains with ultra-high field fMRI.SummaryWe established a high-resolution PC-based single-vessel velocity mapping method using the high field MRI. This PC-based micro-vessel velocity measurement enables the development of the single-vessel CBF-fMRI method. In particular, in contrast to the arteriole-dominated CBV and venule-dominated BOLD responses, the CBF-fMRI shows similar velocity changes in penetrating arterioles and venules in activated brain regions. Thus, we have built a noninvasive single-vessel fMRI mapping scheme for BOLD, CBV, and CBF hemodynamic parameter measurements in animals.

scholarly journals Time-dependent spatial specificity of high-resolution fMRI: insights into mesoscopic neurovascular coupling

2020 ◽  
Vol 376 (1815) ◽  
pp. 20190623
Author(s):  
Mitsuhiro Fukuda ◽  
Alexander J. Poplawsky ◽  
Seong-Gi Kim
Keyword(s):  
High Resolution ◽  
Neuronal Activity ◽  
Cerebral Blood Volume ◽  
Functional Neuroimaging ◽  
Neurovascular Coupling ◽  
Blood Oxygenation ◽  
Non Invasive ◽  
True Location ◽  
Oxygenation Level ◽  
Spatial Specificity

High-resolution functional magnetic resonance imaging (fMRI) is becoming increasingly popular because of the growing availability of ultra-high magnetic fields which are capable of improving sensitivity and spatial resolution. However, it is debatable whether increased spatial resolutions for haemodynamic-based techniques, like fMRI, can accurately detect the true location of neuronal activity. We have addressed this issue in functional columns and layers of animals with haemoglobin-based optical imaging and different fMRI contrasts, such as blood oxygenation level-dependent, cerebral blood flow and cerebral blood volume fMRI. In this review, we describe empirical evidence primarily from our own studies on how well these fMRI signals are spatially specific to the neuronally active site and discuss insights into neurovascular coupling at the mesoscale. This article is part of the theme issue ‘Key relationships between non-invasive functional neuroimaging and the underlying neuronal activity’.

scholarly journals Physiological origin for the BOLD poststimulus undershoot in human brain: Vascular compliance versus oxygen metabolism

2011 ◽  
Vol 31 (7) ◽  
pp. 1599-1611 ◽  
Author(s):  
Jun Hua ◽  
Robert D Stevens ◽  
Alan J Huang ◽  
James J Pekar ◽  
Peter CM van Zijl
Keyword(s):  
Cerebral Blood Volume ◽  
Visual Stimulation ◽  
Oxygen Metabolism ◽  
Blood Oxygenation ◽  
Biophysical Model ◽  
Breath Hold ◽  
Signal Recovery ◽  
Vascular Compliance ◽  
Oxygenation Level ◽  
Bold Undershoot

The poststimulus blood oxygenation level-dependent (BOLD) undershoot has been attributed to two main plausible origins: delayed vascular compliance based on delayed cerebral blood volume (CBV) recovery and a sustained increased oxygen metabolism after stimulus cessation. To investigate these contributions, multimodal functional magnetic resonance imaging was employed to monitor responses of BOLD, cerebral blood flow (CBF), total CBV, and arterial CBV (CBVa) in human visual cortex after brief breath hold and visual stimulation. In visual experiments, after stimulus cessation, CBVa was restored to baseline in 7.9 ± 3.4 seconds, and CBF and CBV in 14.8 ± 5.0 seconds and 16.1 ± 5.8 seconds, respectively, all significantly faster than BOLD signal recovery after undershoot (28.1 ± 5.5 seconds). During the BOLD undershoot, postarterial CBV (CBVpa, capillaries and venules) was slightly elevated (2.4 ± 1.8%), and cerebral metabolic rate of oxygen ( CMRO2) was above baseline (10.6 ± 7.4%). Following breath hold, however, CBF, CBV, CBVa and BOLD signals all returned to baseline in ∼20 seconds. No significant BOLD undershoot, and residual CBVpa dilation were observed, and CMRO2 did not substantially differ from baseline. These data suggest that both delayed CBVpa recovery and enduring increased oxidative metabolism impact the BOLD undershoot. Using a biophysical model, their relative contributions were estimated to be 19.7 ± 15.9% and 78.7 ± 18.6%, respectively.

scholarly journals Multimodal Measurements of Blood Plasma and Red Blood Cell Volumes during Functional Brain Activation

2008 ◽  
Vol 29 (1) ◽  
pp. 19-24 ◽  
Author(s):  
Peter Herman ◽  
Basavaraju G Sanganahalli ◽  
Fahmeed Hyder
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Blood Plasma ◽  
Cerebral Blood Volume ◽  
Superparamagnetic Iron Oxide ◽  
Blood Oxygenation ◽  
Mri Contrast Agent ◽  
Resonance Imaging ◽  
Doppler Flowmetry ◽  
Oxygenation Level

As an alternative to functional magnetic resonance imaging (fMRI) with blood oxygenation level dependent (BOLD) contrast, cerebral blood volume (CBV)-weighted fMRI with intravascular contrast agents in animal models have become popular. In this study, dynamic measurements of CBV were performed by magnetic resonance imaging (MRI) and laser-Doppler flowmetry (LDF) in α-chloralose anesthetized rats during forepaw stimulation. All recordings were localized to the contralateral primary somatosensory cortex as revealed by BOLD at 11.7 T. Ultra-small superparamagnetic iron oxide (15mg/kg)—a plasma-borne MRI contrast agent with a half-life of several hours in blood circulation—was used to quantify changes in magnetic field inhomogeneity in blood plasma. The LDF backscattered laser light (805 nm), which reflects the amount of red blood cells, was used to measure alterations in the non-plasma compartment. Dynamic and layer-specific comparisons of the two CBV signals during functional hyperemia revealed excellent correlations (> 0.86). These results suggest that CBV measurements from either compartment may be used to reflect dynamic changes in total CBV. Furthermore, by assuming steady-state mass balance and negligible counter flow, these results indicate that volume hematocrit is not appreciably affected during functional activation.

scholarly journals Simultaneous Blood Oxygenation Level-Dependent and Cerebral Blood Flow Functional Magnetic Resonance Imaging during Forepaw Stimulation in the Rat

1999 ◽  
Vol 19 (8) ◽  
pp. 871-879 ◽  
Author(s):  
Afonso C. Silva ◽  
Sang-Pil Lee ◽  
Guang Yang ◽  
Costantino Iadecola ◽  
Seong-Gi Kim
Keyword(s):  
Correlation Coefficient ◽  
Cerebral Blood Volume ◽  
Blood Oxygenation Level Dependent ◽  
Blood Oxygenation ◽  
Single Shot ◽  
Bold Signal ◽  
Doppler Flowmetry ◽  
Blood Oxygenation Level ◽  
Oxygenation Level ◽  
Signal Changes

The blood oxygenation level-dependent (BOLD) contrast mechanism can be modeled as a complex interplay between CBF, cerebral blood volume (CBV), and CMRO2. Positive BOLD signal changes are presumably caused by CBF changes in excess of increases in CMRO2. Because this uncoupling between CBF and CMRO2 may not always be present, the magnitude of BOLD changes may not be a good index of CBF changes. In this study, the relation between BOLD and CBF was investigated further. Continuous arterial spin labeling was combined with a single-shot, multislice echo-planar imaging to enable simultaneous measurements of BOLD and CBF changes in a well-established model of functional brain activation, the electrical forepaw stimulation of a-chloralose-anesthetized rats. The paradigm consisted of two 18- to 30-second stimulation periods separated by a 1-minute resting interval. Stimulation parameters were optimized by laser Doppler flowmetry. For the same cross-correlation threshold, the BOLD and CBF active maps were centered within the size of one pixel (470 µm). However, the BOLD map was significantly larger than the CBF map. Measurements taken from 15 rats at 9.4 T using a 10-millisecond echo-time showed 3.7 ± 1.7% BOLD and 125.67 ± 81.7% CBF increases in the contralateral somatosensory cortex during the first stimulation, and 2.6 ± 1.2% BOLD and 79.3 ± 43.6% CBF increases during the second stimulation. The correlation coefficient between BOLD and CBF changes was 0.89. The overall temporal correlation coefficient between BOLD and CBF time-courses was 0.97. These results show that under the experimental conditions of the current study, the BOLD signal changes follow the changes in CBF.

scholarly journals Indication of BOLD-Specific Venous Flow-Volume Changes from Precisely Controlled Hyperoxic vs. Hypercapnic Calibration

2011 ◽  
Vol 32 (4) ◽  
pp. 709-719 ◽  
Author(s):  
Clarisse I Mark ◽  
G Bruce Pike
Keyword(s):  
Cerebral Blood Volume ◽  
Blood Oxygenation ◽  
Flow Volume ◽  
Volume Changes ◽  
Venous Flow ◽  
Precise Control ◽  
Volume Relationship ◽  
Oxygenation Level ◽  
Rate Of Oxygen Consumption ◽  
End Tidal

Deriving cerebral metabolic rate of oxygen consumption (CMRO2) from blood oxygenation level-dependent (BOLD) signals involves a flow-volume parameter (α), reflecting total cerebral blood volume changes, and a calibration constant ( M). Traditionally, the former is assumed a fixed value and the latter is measured under alterations in fixed inspired fractional concentrations of carbon dioxide. We recently reported on reductions in M-variability via precise control of end-tidal pressures of both hypercapnic (HC) and hyperoxic (HO) gases. In light of these findings, our aim was to apply the improved calibration alternatives to neuronal activation, making use of their distinct vasoactive natures to evaluate the α-value. Nine healthy volunteers were imaged at 3 T while simultaneously measuring BOLD and arterial spin-labeling signals during controlled, graded, HC, and HO, followed by visual (VC) and sensorimotor cortices (SMC) activation. On the basis of low M- and CMRO2-variability, the comparison of these calibration alternatives accurately highlighted a reduced venous flow—volume relationship (α = 0.16 ± 0.02, with αVC = 0.12 ± 0.04, and αSMC = 0.20 ± 0.02), as appropriate for BOLD modeling.

scholarly journals Basal Cerebral Blood Volume during the Poststimulation Undershoot in BOLD MRI of the Human Brain

2010 ◽  
Vol 31 (1) ◽  
pp. 82-89 ◽  
Author(s):  
Peter Dechent ◽  
Gunther Schütze ◽  
Gunther Helms ◽  
Klaus Dietmar Merboldt ◽  
Jens Frahm
Keyword(s):  
Contrast Agent ◽  
Blood Volume ◽  
Animal Studies ◽  
Cerebral Blood Volume ◽  
Visual Stimulation ◽  
Three Dimensional ◽  
Blood Pool ◽  
Blood Oxygenation ◽  
Bold Mri ◽  
Oxygenation Level

One of the characteristics of the blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) response to functional challenges of the brain is the poststimulation undershoot, which has been suggested to originate from a delayed recovery of either cerebral blood volume (CBV) or cerebral metabolic rate of oxygen to baseline. Using bolus-tracking MRI in humans, we recently showed that relative CBV rapidly normalizes after the end of stimulation. As this observation contradicts at least part of the blood-pool contrast agent studies performed in animals, we reinvestigated the CBV contribution by dynamic T1-weighted three-dimensional MRI (8 seconds temporal resolution) and Vasovist at 3 T (12 subjects). Initially, we determined the time constants of individual BOLD responses. After injection of Vasovist, CBV-related T1-weighted signal changes revealed a signal increase during visual stimulation (1.7%±0.4%), but no change relative to baseline in the poststimulation phase (0.2%±0.3%). This finding renders the specific nature of the contrast agent unlikely to be responsible for the discrepancy between human and animal studies. With the assumption of normalized cerebral blood flow after stimulus cessation, a normalized CBV lends support to the idea that the BOLD MRI undershoot reflects a prolonged elevation of oxidative metabolism.

scholarly journals Modelling the depth-dependent VASO and BOLD responses in human primary visual cortex

2021 ◽  
Author(s):  
Atena Akbari ◽  
Saskia Bollmann ◽  
Tonima Ali ◽  
Markus Barth
Keyword(s):  
Visual Cortex ◽  
Blood Volume ◽  
Primary Visual Cortex ◽  
Cerebral Blood Volume ◽  
Blood Oxygenation ◽  
Physiological Variables ◽  
Oxygenation Level ◽  
Signal Specificity ◽  
Experimental Findings ◽  
Spatial Specificity

Functional magnetic resonance imaging (fMRI) using blood-oxygenation-level-dependent (BOLD) contrast is a common method for studying human brain function non-invasively. Gradient-echo (GRE) BOLD is highly sensitive to the blood oxygenation change in blood vessels; however, the signal specificity can be degraded due to signal leakage from the activated lower layers to the superficial layers in depth-dependent (also called laminar or layer-specific) fMRI. Alternatively, physiological variables such as cerebral blood volume using VAscular-Space-Occupancy (VASO) measurements have shown higher spatial specificity compared to BOLD. To better understand the physiological mechanisms (e.g., blood volume and oxygenation change) and to interpret the measured depth-dependent responses we need models that reflect vascular properties at this scale. For this purpose, we adapted a cortical vascular model previously developed to predict the layer-specific BOLD signal change in human primary visual cortex to also predict layer-specific VASO response. To evaluate the model, we compared the predictions with experimental results of simultaneous VASO and BOLD measurements in a group of healthy participants. Fitting the model to our experimental findings provided an estimate of CBV change in different vascular compartments upon neural activity. We found that stimulus-evoked CBV changes mainly occur in intracortical arteries as well as small arterioles and capillaries and that the contribution from venules is small for a long stimulus (~30 sec). Our results confirm the notion that VASO contrast is less susceptible to large vessel effects compared to BOLD.

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