scholarly journals A frequency-domain machine learning method for dual-calibrated fMRI mapping of oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen consumption (CMRO2)

2019 ◽  
Author(s):  
Michael Germuska ◽  
Hannah Chandler ◽  
Thomas Okell ◽  
Fabrizio Fasano ◽  
Valentina Tomassini ◽  
...  
Keyword(s):  
Machine Learning ◽  
Blood Flow ◽  
Oxygen Consumption ◽  
Oxygen Metabolism ◽  
Oxygen Extraction Fraction ◽  
Oxygen Extraction ◽  
Single Subject ◽  
Extraction Fraction ◽  
Wide Range ◽  
Calibrated Fmri

AbstractMagnetic resonance imaging (MRI) offers the possibility to non-invasively map the brain’s metabolic oxygen consumption (CMRO2), which is essential for understanding and monitoring neural function in both health and disease. However, in depth study of oxygen metabolism with MRI has so far been hindered by the lack of robust methods. One MRI method of mapping CMRO2 is based on the simultaneous acquisition of cerebral blood flow (CBF) and blood oxygen level dependent (BOLD) weighted images during respiratory modulation of both oxygen and carbon dioxide. Although this dual-calibrated methodology has shown promise in the research setting, current analysis methods are unstable in the presence of noise and/or are computationally demanding. In this paper, we present a machine learning implementation for the multi-parametric assessment of dual-calibrated fMRI data. The proposed method aims to address the issues of stability, accuracy, and computational overhead, removing significant barriers to the investigation of oxygen metabolism with MRI. The method utilizes a time-frequency transformation of the acquired perfusion and BOLD-weighted data, from which appropriate feature vectors are selected for training of machine learning regressors. The implemented machine learning methods are chosen for their robustness to noise and their ability to map complex non-linear relationships (such as those that exist between BOLD signal weighting and blood oxygenation). An extremely randomized trees (ET) regressor is used to estimate resting blood flow and a multi-layer perceptron (MLP) is used to estimate CMRO2 and the oxygen extraction fraction (OEF). Synthetic data with additive noise are used to train the regressors, with data simulated to cover a wide range of physiologically plausible parameters. The performance of the implemented analysis method is compared to published methods both in simulation and with in-vivo data (n=30). The proposed method is demonstrated to significantly reduce computation time, error, and proportional bias in both CMRO2 and OEF estimates. The introduction of the proposed analysis pipeline has the potential to not only increase the detectability of metabolic difference between groups of subjects, but may also allow for single subject examinations within a clinical context.

scholarly journals Effect of ephedrine and phenylephrine on brain oxygenation and microcirculation in anaesthetised patients with cerebral tumours: study protocol for a randomised controlled trial

BMJ Open ◽  
2017 ◽  
Vol 7 (11) ◽  
pp. e018560 ◽  
Author(s):  
Klaus Ulrik Koch ◽  
Anna Tietze ◽  
Joel Aanerud ◽  
Gorm von Öettingen ◽  
Niels Juul ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Metabolic Rate ◽  
Transit Time ◽  
Oxygen Extraction Fraction ◽  
Oxygen Extraction ◽  
Brain Oxygenation ◽  
Cerebral Metabolic Rate ◽  
Arterial Blood ◽  
Extraction Fraction

IntroductionDuring brain tumour surgery, vasopressor drugs are commonly administered to increase mean arterial blood pressure with the aim of maintaining sufficient cerebral perfusion pressure. Studies of the commonly used vasopressors show that brain oxygen saturation is reduced after phenylephrine administration, but unaltered by ephedrine administration. These findings may be explained by different effects of phenylephrine and ephedrine on the cerebral microcirculation, in particular the capillary transit-time heterogeneity, which determines oxygen extraction efficacy. We hypothesised that phenylephrine is associated with an increase in capillary transit-time heterogeneity and a reduction in cerebral metabolic rate of oxygen compared with ephedrine. Using MRI and positron emission tomography (PET) as measurements in anaesthetised patients with brain tumours, this study will examine whether phenylephrine administration elevates capillary transit-time heterogeneity more than ephedrine, thereby reducing brain oxygenation.Methods and analysisThis is a double-blind, randomised clinical trial including 48 patients scheduled for surgical brain tumour removal. Prior to imaging and surgery, anaesthetised patients will be randomised to receive either phenylephrine or ephedrine infusion until mean arterial blood pressure increases to above 60 mm Hg or 20% above baseline. Twenty-four patients were allocated to MRI and another 24 patients to PET examination. MRI measurements include cerebral blood flow, capillary transit-time heterogeneity, cerebral blood volume, blood mean transit time, and calculated oxygen extraction fraction and cerebral metabolic rate of oxygen for negligible tissue oxygen extraction. PET measurements include cerebral metabolic rate of oxygen, cerebral blood flow and oxygen extraction fraction. Surgery is initiated after MRI/PET measurements and subdural intracranial pressure is measured.Ethics and disseminationThis study was approved by the Central Denmark Region Committee on Health Research Ethics (12 June 2015; 1-10-72-116-15). Results will be disseminated via peer-reviewed publication and presentation at international conferences.Trial registration numberNCT02713087; Pre-results. 2015-001359-60; Pre-results.

scholarly journals The thermodynamics of thinking: connections between neural activity, energy metabolism and blood flow

2019 ◽  
Author(s):  
Richard B. Buxton
Keyword(s):  
Blood Flow ◽  
Neural Activity ◽  
Oxidative Metabolism ◽  
Functional Neuroimaging ◽  
Cerebral Metabolism ◽  
Oxygen Metabolism ◽  
Oxygen Extraction Fraction ◽  
Neural Activation ◽  
Thermodynamic Framework ◽  
Wide Range

SummarySeveral current functional neuroimaging methods are sensitive to cerebral metabolism and cerebral blood flow (CBF) rather than the underlying neural activity itself. Empirically, the connections between metabolism, flow and neural activity are complex and somewhat counterintuitive: CBF and glycolysis increase more than seems to be needed to provide oxygen and pyruvate for oxidative metabolism, and the oxygen extraction fraction is relatively low in the brain and decreases when oxygen metabolism increases. This work lays a foundation for the idea that this unexpected pattern of physiological changes is consistent with basic thermodynamic considerations related to metabolism. In the context of this thermodynamic framework, the apparent mismatches in metabolic rates and CBF are related to preserving the entropy change of oxidative metabolism, specifically the O2/CO2 ratio in the mitochondria. However, the mechanism supporting this CBF response is likely not due to feedback from a hypothetical O2 sensor in tissue, but rather is consistent with feed-forward control by signals from both excitatory and inhibitory neural activity. Quantitative predictions of the thermodynamic framework, based on models of O2 and CO2 transport and possible neural drivers of CBF control, are in good agreement with a wide range of experimental data, including responses to neural activation, hypercapnia, hypoxia and high-altitude acclimatization.

scholarly journals Hemodynamics and oxygen extraction in chronic large artery steno-occlusive disease: Clinical applications for predicting stroke risk

2017 ◽  
Vol 38 (9) ◽  
pp. 1584-1597 ◽  
Author(s):  
Colin P Derdeyn
Keyword(s):  
Blood Flow ◽  
Ischemic Stroke ◽  
Carotid Artery ◽  
Stroke Risk ◽  
Arterial Stenosis ◽  
Oxygen Extraction Fraction ◽  
Oxygen Extraction ◽  
Large Artery ◽  
Extraction Fraction ◽  
Hemodynamic Assessment

Depending on the adequacy of collateral sources of blood flow, arterial stenosis or occlusion may lead to reduced perfusion pressure and ultimately reduced blood flow in the distal territory supplied by that vessel. There are two well-defined compensatory mechanisms to reduced pressure or flow – autoregulatory vasodilation and increased oxygen extraction fraction. Other changes, such as metabolic downregulation, are likely. The positive identification of autoregulatory vasodilation and increased oxygen extraction fraction in humans is an established risk factor for future ischemic stroke in some disease states such as atherosclerotic carotid stenosis and occlusion. The mechanisms by which ischemic stroke may occur are not clear, and may include an increased vulnerability to embolic events. The use of hemodynamic assessment to identify patients with occlusive vasculopathy at an increased risk for stroke is very appealing for several different patient populations, such as those with symptomatic intracranial atherosclerotic disease, moyamoya phenomenon, complete internal carotid artery occlusion, and asymptomatic cervical carotid artery stenosis. While there is very good data for stroke risk prediction in some of these groups, no intervention based on these tools has been proven effective yet. In this manuscript, we will review these topics above and identify areas for future research.

13.22 Effect of dobutamine on myocardial blood flow and oxygen extraction fraction

2001 ◽  
Vol 8 (1) ◽  
pp. S83-S83
Author(s):  
E TADAMURA ◽  
M MAMEDE ◽  
K MATSUMOTO ◽  
S KUBO ◽  
H IIDA ◽  
...  
Keyword(s):  
Blood Flow ◽  
Myocardial Blood Flow ◽  
Oxygen Extraction Fraction ◽  
Oxygen Extraction ◽  
Extraction Fraction
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