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Chen JJ, Uthayakumar B, Hyder F. Mapping oxidative metabolism in the human brain with calibrated fMRI in health and disease. J Cereb Blood Flow Metab 2022; 42:1139-1162. [PMID: 35296177 PMCID: PMC9207484 DOI: 10.1177/0271678x221077338] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Conventional functional MRI (fMRI) with blood-oxygenation level dependent (BOLD) contrast is an important tool for mapping human brain activity non-invasively. Recent interest in quantitative fMRI has renewed the importance of oxidative neuroenergetics as reflected by cerebral metabolic rate of oxygen consumption (CMRO2) to support brain function. Dynamic CMRO2 mapping by calibrated fMRI require multi-modal measurements of BOLD signal along with cerebral blood flow (CBF) and/or volume (CBV). In human subjects this "calibration" is typically performed using a gas mixture containing small amounts of carbon dioxide and/or oxygen-enriched medical air, which are thought to produce changes in CBF (and CBV) and BOLD signal with minimal or no CMRO2 changes. However non-human studies have demonstrated that the "calibration" can also be achieved without gases, revealing good agreement between CMRO2 changes and underlying neuronal activity (e.g., multi-unit activity and local field potential). Given the simpler set-up of gas-free calibrated fMRI, there is evidence of recent clinical applications for this less intrusive direction. This up-to-date review emphasizes technological advances for such translational gas-free calibrated fMRI experiments, also covering historical progression of the calibrated fMRI field that is impacting neurological and neurodegenerative investigations of the human brain.
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Affiliation(s)
- J Jean Chen
- Medical Biophysics, University of Toronto, Toronto, Canada.,Rotman Research Institute, Baycrest, Toronto, Canada
| | - Biranavan Uthayakumar
- Medical Biophysics, University of Toronto, Toronto, Canada.,Sunnybrook Research Institute, Toronto, Canada
| | - Fahmeed Hyder
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, Connecticut, USA.,Department of Radiology, Yale University, New Haven, Connecticut, USA.,Quantitative Neuroscience with Magnetic Resonance (QNMR) Research Program, Yale University, New Haven, Connecticut, USA.,Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA
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2
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Hyder F, Coman D. Imaging Extracellular Acidification and Immune Activation in Cancer. CURRENT OPINION IN BIOMEDICAL ENGINEERING 2021; 18. [PMID: 33997581 DOI: 10.1016/j.cobme.2021.100278] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Metabolism reveals pathways by which cells, in healthy and disease tissues, use nutrients to fuel their function and (re)growth. However, gene-centric views have dominated cancer hallmarks, relegating metabolic reprogramming that all cells in the tumor niche undergo as an incidental phenomenon. Aerobic glycolysis in cancer is well known, but recent evidence suggests that diverse symbolic traits of cancer cells are derived from oncogene-directed metabolism required for their sustenance and evolution. Cells in the tumor milieu actively metabolize different nutrients, but proficiently secrete acidic by-products using diverse mechanisms to create a hostile ecosystem for host cells, and where local immune cells suffer collateral damage. Since metabolic interactions between cancer and immune cells hold promise for future cancer therapies, here we focus on translational magnetic resonance methods enabling in vivo and simultaneous detection of tumor habitat acidification and immune activation - innovations for monitoring personalized treatments.
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Affiliation(s)
- Fahmeed Hyder
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA
- Department of Radiology & Biomedical Imaging, Yale University, New Haven, CT, USA
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA
- Quantitative Neuroimaging with Magnetic Resonance (QNMR) Research Program, Yale University, New Haven, CT, USA
| | - Daniel Coman
- Department of Radiology & Biomedical Imaging, Yale University, New Haven, CT, USA
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA
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3
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Buxton RB. The thermodynamics of thinking: connections between neural activity, energy metabolism and blood flow. Philos Trans R Soc Lond B Biol Sci 2020; 376:20190624. [PMID: 33190604 DOI: 10.1098/rstb.2019.0624] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Several 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 owing 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. This article is part of the theme issue 'Key relationships between non-invasive functional neuroimaging and the underlying neuronal activity'.
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Affiliation(s)
- Richard B Buxton
- Department of Radiology, University of California San Diego, 9500 Gilman Drive, MC 0677, La Jolla, CA 92093-0677, USA
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4
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Borde T, Laage Gaupp F, Geschwind JF, Savic LJ, Miszczuk M, Rexha I, Adam L, Walsh JJ, Huber S, Duncan JS, Peters DC, Sinusas A, Schlachter T, Gebauer B, Hyder F, Coman D, van Breugel JMM, Chapiro J. Idarubicin-Loaded ONCOZENE Drug-Eluting Bead Chemoembolization in a Rabbit Liver Tumor Model: Investigating Safety, Therapeutic Efficacy, and Effects on Tumor Microenvironment. J Vasc Interv Radiol 2020; 31:1706-1716.e1. [PMID: 32684417 DOI: 10.1016/j.jvir.2020.04.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Revised: 04/06/2020] [Accepted: 04/13/2020] [Indexed: 02/07/2023] Open
Abstract
PURPOSE To investigate toxicity, efficacy, and microenvironmental effects of idarubicin-loaded 40-μm and 100-μm drug-eluting embolic (DEE) transarterial chemoembolization in a rabbit liver tumor model. MATERIALS AND METHODS Twelve male New Zealand White rabbits with orthotopically implanted VX2 liver tumors were assigned to DEE chemoembolization with 40-μm (n = 5) or 100-μm (n = 4) ONCOZENE microspheres or no treatment (control; n = 3). At 24-72 hours postprocedurally, multiparametric magnetic resonance (MR) imaging including dynamic contrast-enhanced (DCE), diffusion-weighted imaging (DWI), and biosensor imaging of redundant deviation in shifts (BIRDS) was performed to assess extracellular pH (pHe), followed by immediate euthanasia. Laboratory parameters and histopathologic ex vivo analysis included fluorescence confocal microscopy and immunohistochemistry. RESULTS DCE MR imaging demonstrated a similar degree of devascularization of embolized tumors for both microsphere sizes (mean arterial enhancement, 8% ± 12 vs 36% ± 51 in controls; P = .07). Similarly, DWI showed postprocedural increases in diffusion across the entire lesion (apparent diffusion coefficient, 1.89 × 10-3 mm2/s ± 0.18 vs 2.34 × 10-3 mm2/s ± 0.18 in liver; P = .002). BIRDS demonstrated profound tumor acidosis at baseline (mean pHe, 6.79 ± 0.08 in tumor vs 7.13 ± 0.08 in liver; P = .02) and after chemoembolization (6.8 ± 0.06 in tumor vs 7.1 ± 0.04 in liver; P = .007). Laboratory and ex vivo analyses showed central tumor core penetration and greater increase in liver enzymes for 40-μm vs 100-μm microspheres. Inhibition of cell proliferation, intratumoral hypoxia, and limited idarubicin elution were equally observed with both sphere sizes. CONCLUSIONS Noninvasive multiparametric MR imaging visualized chemoembolic effects in tumor and tumor microenvironment following DEE chemoembolization. Devascularization, increased hypoxia, coagulative necrosis, tumor acidosis, and limited idarubicin elution suggest ischemia as the predominant therapeutic mechanism. Substantial size-dependent differences indicate greater toxicity with the smaller microsphere diameter.
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Affiliation(s)
- Tabea Borde
- Department of Radiology and Biomedical Imaging, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510; Institute of Radiology, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Fabian Laage Gaupp
- Department of Radiology and Biomedical Imaging, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510
| | | | - Lynn J Savic
- Department of Radiology and Biomedical Imaging, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510; Institute of Radiology, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Milena Miszczuk
- Institute of Radiology, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Irvin Rexha
- Institute of Radiology, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Lucas Adam
- Institute of Radiology, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - John J Walsh
- Department of Biomedical Engineering, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510
| | - Steffen Huber
- Department of Radiology and Biomedical Imaging, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510
| | - James S Duncan
- Department of Radiology and Biomedical Imaging, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510; Department of Biomedical Engineering, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510
| | - Dana C Peters
- Department of Radiology and Biomedical Imaging, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510
| | - Albert Sinusas
- Department of Cardiology, Yale Translational Research Imaging Center, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510
| | - Todd Schlachter
- Department of Radiology and Biomedical Imaging, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510
| | - Bernhard Gebauer
- Institute of Radiology, Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Berlin, Germany
| | - Fahmeed Hyder
- Department of Radiology and Biomedical Imaging, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510
| | - Daniel Coman
- Department of Radiology and Biomedical Imaging, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510
| | - Johanna M M van Breugel
- Department of Radiology and Biomedical Imaging, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510; Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Julius Chapiro
- Department of Radiology and Biomedical Imaging, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510.
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5
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Kaczmarz S, Hyder F, Preibisch C. Oxygen extraction fraction mapping with multi-parametric quantitative BOLD MRI: Reduced transverse relaxation bias using 3D-GraSE imaging. Neuroimage 2020; 220:117095. [PMID: 32599265 PMCID: PMC7730517 DOI: 10.1016/j.neuroimage.2020.117095] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Revised: 06/11/2020] [Accepted: 06/18/2020] [Indexed: 01/22/2023] Open
Abstract
Magnetic resonance imaging (MRI)-based quantification of the blood-oxygenation-level-dependent (BOLD) effect allows oxygen extraction fraction (OEF) mapping. The multi-parametric quantitative BOLD (mq-BOLD) technique facilitates relative OEF (rOEF) measurements with whole brain coverage in clinically applicable scan times. Mq-BOLD requires three separate scans of cerebral blood volume and transverse relaxation rates measured by gradient-echo (1/T2*) and spin-echo (1/T2). Although the current method is of clinical merit in patients with stroke, glioma and internal carotid artery stenosis (ICAS), there are relaxation measurement artefacts that impede the sensitivity of mq-BOLD and artificially elevate reported rOEF values. We posited that T2-related biases caused by slice refocusing imperfections during rapid 2D-GraSE (Gradient and Spin Echo) imaging can be reduced by applying 3D-GraSE imaging sequences, because the latter requires no slice selective pulses. The removal of T2-related biases would decrease overestimated rOEF values measured by mq-BOLD. We characterized effects of T2-related bias in mq-BOLD by comparing the initially employed 2D-GraSE and two proposed 3D-GraSE sequences to multiple single spin-echo reference measurements, both in vitro and in vivo. A phantom and 25 participants, including young and elderly healthy controls as well as ICAS-patients, were scanned. We additionally proposed a procedure to reliably identify and exclude artefact affected voxels. In the phantom, 3D-GraSE derived T2 values had 57% lower deviation from the reference. For in vivo scans, the formerly overestimated rOEF was reduced by −27% (p < 0.001). We obtained rOEF = 0.51, which is much closer to literature values from positron emission tomography (PET) measurements. Furthermore, increased sensitivity to a focal rOEF elevation in an ICAS-patient was demonstrated. In summary, the application of 3D-GraSE improves the mq-BOLD-based rOEF quantification while maintaining clinically feasible scan times. Thus, mq-BOLD with non-slice selective T2 imaging is highly promising to improve clinical diagnostics of cerebrovascular diseases such as ICAS.
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Affiliation(s)
- Stephan Kaczmarz
- Technical University of Munich, School of Medicine, Klinikum rechts der Isar, Department of Diagnostic and Interventional Neuroradiology, Munich, Germany; Departments of Radiology & Biomedical Imaging and of Biomedical Engineering, Magnetic Resonance Research Center, Yale University, New Haven, CT, 06520, USA; Technical University of Munich, School of Medicine, Klinikum rechts der Isar, TUM Neuroimaging Center, Munich, Germany.
| | - Fahmeed Hyder
- Departments of Radiology & Biomedical Imaging and of Biomedical Engineering, Magnetic Resonance Research Center, Yale University, New Haven, CT, 06520, USA
| | - Christine Preibisch
- Technical University of Munich, School of Medicine, Klinikum rechts der Isar, Department of Diagnostic and Interventional Neuroradiology, Munich, Germany; Technical University of Munich, School of Medicine, Klinikum rechts der Isar, TUM Neuroimaging Center, Munich, Germany; Technical University of Munich, School of Medicine, Klinikum rechts der Isar, Clinic for Neurology, Munich, Germany
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6
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Hendrikx D, Smits A, Lavanga M, De Wel O, Thewissen L, Jansen K, Caicedo A, Van Huffel S, Naulaers G. Measurement of Neurovascular Coupling in Neonates. Front Physiol 2019; 10:65. [PMID: 30833901 PMCID: PMC6387909 DOI: 10.3389/fphys.2019.00065] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2018] [Accepted: 01/21/2019] [Indexed: 01/01/2023] Open
Abstract
Neurovascular coupling refers to the mechanism that links the transient neural activity to the subsequent change in cerebral blood flow, which is regulated by both chemical signals and mechanical effects. Recent studies suggest that neurovascular coupling in neonates and preterm born infants is different compared to adults. The hemodynamic response after a stimulus is later and less pronounced and the stimulus might even result in a negative (hypoxic) signal. In addition, studies both in animals and neonates confirm the presence of a short hypoxic period after a stimulus in preterm infants. In clinical practice, different methodologies exist to study neurovascular coupling. The combination of functional magnetic resonance imaging or functional near-infrared spectroscopy (brain hemodynamics) with EEG (brain function) is most commonly used in neonates. Especially near-infrared spectroscopy is of interest, since it is a non-invasive method that can be integrated easily in clinical care and is able to provide results concerning longer periods of time. Therefore, near-infrared spectroscopy can be used to develop a continuous non-invasive measurement system, that could be used to study neonates in different clinical settings, or neonates with different pathologies. The main challenge for the development of a continuous marker for neurovascular coupling is how the coupling between the signals can be described. In practice, a wide range of signal interaction measures exist. Moreover, biomedical signals often operate on different time scales. In a more general setting, other variables also have to be taken into account, such as oxygen saturation, carbon dioxide and blood pressure in order to describe neurovascular coupling in a concise manner. Recently, new mathematical techniques were developed to give an answer to these questions. This review discusses these recent developments.
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Affiliation(s)
- Dries Hendrikx
- Department of Electrical Engineering, KU Leuven, Leuven, Belgium
- imec, Leuven, Belgium
| | - Anne Smits
- Department of Development and Regeneration, KU Leuven, Leuven, Belgium
- Neonatal Intensive Care Unit, University Hospitals Leuven, Leuven, Belgium
| | - Mario Lavanga
- Department of Electrical Engineering, KU Leuven, Leuven, Belgium
- imec, Leuven, Belgium
| | - Ofelie De Wel
- Department of Electrical Engineering, KU Leuven, Leuven, Belgium
- imec, Leuven, Belgium
| | - Liesbeth Thewissen
- Department of Development and Regeneration, KU Leuven, Leuven, Belgium
- Neonatal Intensive Care Unit, University Hospitals Leuven, Leuven, Belgium
| | - Katrien Jansen
- Department of Development and Regeneration, KU Leuven, Leuven, Belgium
- Neonatal Intensive Care Unit, University Hospitals Leuven, Leuven, Belgium
- Child Neurology, University Hospitals Leuven, Leuven, Belgium
| | - Alexander Caicedo
- Facultad de Ciencias Naturales y Matemáticas, Universidad del Rosario, Bogotá, Colombia
| | - Sabine Van Huffel
- Department of Electrical Engineering, KU Leuven, Leuven, Belgium
- imec, Leuven, Belgium
| | - Gunnar Naulaers
- Department of Development and Regeneration, KU Leuven, Leuven, Belgium
- Neonatal Intensive Care Unit, University Hospitals Leuven, Leuven, Belgium
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7
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Orfanos S, Toygar T, Berthold-Losleben M, Chechko N, Durst A, Laoutidis ZG, Vocke S, Weidenfeld C, Schneider F, Karges W, Beckmann CF, Habel U, Kohn N. Investigating the impact of overnight fasting on intrinsic functional connectivity: a double-blind fMRI study. Brain Imaging Behav 2019; 12:1150-1159. [PMID: 29071464 PMCID: PMC6063348 DOI: 10.1007/s11682-017-9777-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The human brain depends mainly on glucose supply from circulating blood as an energy substrate for its metabolism. Most of the energy produced by glucose catabolism in the brain is used to support intrinsic communication purposes in the absence of goal-directed activity. This intrinsic brain function can be detected with fMRI as synchronized fluctuations of the BOLD signal forming functional networks. Here, we report results from a double-blind, placebo controlled, cross-over study addressing changes in intrinsic brain activity in the context of very low, yet physiological, blood glucose levels after overnight fasting. Comparison of four major resting state networks in a fasting state and a state of elevated blood glucose levels after glucagon infusion revealed altered patterns of functional connectivity only in a small region of the posterior default mode network, while the rest of the networks appeared unaffected. Furthermore, low blood glucose was associated with changes in the right frontoparietal network after cognitive effort. Our results suggest that fasting has only limited impact on intrinsic brain activity, while a detrimental impact on a network related to attention is only observable following cognitive effort, which is in line with ego depletion and its reliance on glucose.
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Affiliation(s)
- Stelios Orfanos
- Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University, Aachen, Germany. .,Jülich Aachen Research Alliance (JARA) - BRAIN Institute Brain Structure-Function Relationships: Decoding the Human Brain at systemic levels, Forschungszentrum Jülich GmbH and RWTH Aachen University, Jülich, Germany.
| | - Timur Toygar
- Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University, Aachen, Germany.,Department of Biology, RWTH Aachen University, 52074, Aachen, Germany
| | - Mark Berthold-Losleben
- Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University, Aachen, Germany.,Jülich Aachen Research Alliance (JARA) - BRAIN Institute Brain Structure-Function Relationships: Decoding the Human Brain at systemic levels, Forschungszentrum Jülich GmbH and RWTH Aachen University, Jülich, Germany
| | - Natalya Chechko
- Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University, Aachen, Germany.,Jülich Aachen Research Alliance (JARA) - BRAIN Institute Brain Structure-Function Relationships: Decoding the Human Brain at systemic levels, Forschungszentrum Jülich GmbH and RWTH Aachen University, Jülich, Germany
| | - Annette Durst
- Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University, Aachen, Germany.,Jülich Aachen Research Alliance (JARA) - BRAIN Institute Brain Structure-Function Relationships: Decoding the Human Brain at systemic levels, Forschungszentrum Jülich GmbH and RWTH Aachen University, Jülich, Germany
| | - Zacharias G Laoutidis
- Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University, Aachen, Germany.,Department of Psychiatry and Psychotherapy, University of Düsseldorf, Bergische Landstrasse 2, 40629, Düsseldorf, Germany
| | - Sebastian Vocke
- Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University, Aachen, Germany.,Jülich Aachen Research Alliance (JARA) - BRAIN Institute Brain Structure-Function Relationships: Decoding the Human Brain at systemic levels, Forschungszentrum Jülich GmbH and RWTH Aachen University, Jülich, Germany
| | - Caren Weidenfeld
- Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University, Aachen, Germany.,Jülich Aachen Research Alliance (JARA) - BRAIN Institute Brain Structure-Function Relationships: Decoding the Human Brain at systemic levels, Forschungszentrum Jülich GmbH and RWTH Aachen University, Jülich, Germany
| | - Frank Schneider
- Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University, Aachen, Germany.,Jülich Aachen Research Alliance (JARA) - BRAIN Institute Brain Structure-Function Relationships: Decoding the Human Brain at systemic levels, Forschungszentrum Jülich GmbH and RWTH Aachen University, Jülich, Germany
| | - Wolfram Karges
- Division of Endocrinology and Diabetes, Medical Faculty, RWTH Aachen University, 52074, Aachen, Germany
| | - Christian F Beckmann
- Department of Cognitive Neuroscience, Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands.,Centre for Functional MRI of the Brain (FMRIB), University of Oxford, Oxford, UK
| | - Ute Habel
- Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University, Aachen, Germany.,Jülich Aachen Research Alliance (JARA) - BRAIN Institute Brain Structure-Function Relationships: Decoding the Human Brain at systemic levels, Forschungszentrum Jülich GmbH and RWTH Aachen University, Jülich, Germany
| | - Nils Kohn
- Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University, Aachen, Germany.,Department of Cognitive Neuroscience, Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands
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8
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How reliable is cerebral blood flow to map changes in neuronal activity? Auton Neurosci 2019; 217:71-79. [PMID: 30744905 DOI: 10.1016/j.autneu.2019.01.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Revised: 12/17/2018] [Accepted: 01/27/2019] [Indexed: 02/06/2023]
Abstract
Neuroimaging techniques, such as functional MRI, map brain activity through hemodynamic-based signals, and are invaluable diagnostic tools in several neurological disorders such as stroke and dementia. Hemodynamic signals are normally precisely related to the underlying neuronal activity through neurovascular coupling mechanisms that ensure the supply of blood, glucose and oxygen to neurons at work. The knowledge of neurovascular coupling has greatly advanced over the last 30 years, it involves multifaceted interactions between excitatory and inhibitory neurons, astrocytes, and the microvessels. While the tight relationship between blood flow and neuronal activity forms a fundamental brain function, whether neurovascular coupling mechanisms are reliable across physiological and pathological conditions has been questioned. In this review, we interrogate the relationship between blood flow and neuronal activity during activation of different brain pathways: a sensory stimulation driven by glutamate, and stimulation of neuromodulatory pathways driven by acetylcholine or noradrenaline, and we compare the underlying neurovascular coupling mechanisms. We further question if neurovascular coupling mechanisms are affected by changing brain states, as seen in behavioral conditions of sleep, wakefulness, attention and in pathological conditions. Finally, we provide a short overview of how alterations of the brain vasculature could compromise the reliability of neurovascular coupling. Overall, while neurovascular coupling requires activation of common signalling pathways, alternate unique cascades exist depending on the activated pathways. Further studies are needed to fully elucidate the alterations in neurovascular coupling across brain states and pathological conditions.
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9
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Abstract
Metabolism is central to neuroimaging because it can reveal pathways by which neuronal and glial cells use nutrients to fuel their growth and function. We focus on advanced magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) methods used in brain metabolic studies. 17O-MRS and 31P-MRS, respectively, provide rates of oxygen use and ATP synthesis inside mitochondria, whereas 19F-MRS enables measurement of cytosolic glucose metabolism. Calibrated functional MRI (fMRI), an advanced form of fMRI that uses contrast generated by deoxyhemoglobin, provides maps of oxygen use that track neuronal firing across brain regions. 13C-MRS is the only noninvasive method of measuring both glutamatergic neurotransmission and cell-specific energetics with signaling and nonsignaling purposes. Novel MRI contrasts, arising from endogenous diamagnetic agents and exogenous paramagnetic agents, permit pH imaging of glioma. Overall, these magnetic resonance methods for imaging brain metabolism demonstrate translational potential to better understand brain disorders and guide diagnosis and treatment.
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Affiliation(s)
- Fahmeed Hyder
- Department of Biomedical Engineering, Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, and Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, Connecticut 06520;
| | - Douglas L Rothman
- Department of Biomedical Engineering, Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, and Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, Connecticut 06520;
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10
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Kannurpatti SS. Mitochondrial calcium homeostasis: Implications for neurovascular and neurometabolic coupling. J Cereb Blood Flow Metab 2017; 37:381-395. [PMID: 27879386 PMCID: PMC5381466 DOI: 10.1177/0271678x16680637] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Mitochondrial function is critical to maintain high rates of oxidative metabolism supporting energy demands of both spontaneous and evoked neuronal activity in the brain. Mitochondria not only regulate energy metabolism, but also influence neuronal signaling. Regulation of "energy metabolism" and "neuronal signaling" (i.e. neurometabolic coupling), which are coupled rather than independent can be understood through mitochondria's integrative functions of calcium ion (Ca2+) uptake and cycling. While mitochondrial Ca2+ do not affect hemodynamics directly, neuronal activity changes are mechanistically linked to functional hyperemic responses (i.e. neurovascular coupling). Early in vitro studies lay the foundation of mitochondrial Ca2+ homeostasis and its functional roles within cells. However, recent in vivo approaches indicate mitochondrial Ca2+ homeostasis as maintained by the role of mitochondrial Ca2+ uniporter (mCU) influences system-level brain activity as measured by a variety of techniques. Based on earlier evidence of subcellular cytoplasmic Ca2+ microdomains and cellular bioenergetic states, a mechanistic model of Ca2+ mobilization is presented to understand systems-level neurovascular and neurometabolic coupling. This integrated view from molecular and cellular to the systems level, where mCU plays a major role in mitochondrial and cellular Ca2+ homeostasis, may explain the wide range of activation-induced coupling across neuronal activity, hemodynamic, and metabolic responses.
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11
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Hyder F, Herman P, Bailey CJ, Møller A, Globinsky R, Fulbright RK, Rothman DL, Gjedde A. Uniform distributions of glucose oxidation and oxygen extraction in gray matter of normal human brain: No evidence of regional differences of aerobic glycolysis. J Cereb Blood Flow Metab 2016; 36:903-16. [PMID: 26755443 PMCID: PMC4853838 DOI: 10.1177/0271678x15625349] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2015] [Accepted: 12/03/2015] [Indexed: 11/17/2022]
Abstract
Regionally variable rates of aerobic glycolysis in brain networks identified by resting-state functional magnetic resonance imaging (R-fMRI) imply regionally variable adenosine triphosphate (ATP) regeneration. When regional glucose utilization is not matched to oxygen delivery, affected regions have correspondingly variable rates of ATP and lactate production. We tested the extent to which aerobic glycolysis and oxidative phosphorylation power R-fMRI networks by measuring quantitative differences between the oxygen to glucose index (OGI) and the oxygen extraction fraction (OEF) as measured by positron emission tomography (PET) in normal human brain (resting awake, eyes closed). Regionally uniform and correlated OEF and OGI estimates prevailed, with network values that matched the gray matter means, regardless of size, location, and origin. The spatial agreement between oxygen delivery (OEF≈0.4) and glucose oxidation (OGI ≈ 5.3) suggests that no specific regions have preferentially high aerobic glycolysis and low oxidative phosphorylation rates, with globally optimal maximum ATP turnover rates (VATP ≈ 9.4 µmol/g/min), in good agreement with (31)P and (13)C magnetic resonance spectroscopy measurements. These results imply that the intrinsic network activity in healthy human brain powers the entire gray matter with ubiquitously high rates of glucose oxidation. Reports of departures from normal brain-wide homogeny of oxygen extraction fraction and oxygen to glucose index may be due to normalization artefacts from relative PET measurements.
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Affiliation(s)
- Fahmeed Hyder
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA Department of Radiology & Biomedical Imaging, Yale University, New Haven, CT, USA Department of Biomedical Engineering, Yale University, New Haven, CT, USA
| | - Peter Herman
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA Department of Radiology & Biomedical Imaging, Yale University, New Haven, CT, USA
| | - Christopher J Bailey
- Center of Functionally Integrative Neuroscience, Aarhus University, Aarhus, Denmark
| | - Arne Møller
- Center of Functionally Integrative Neuroscience, Aarhus University, Aarhus, Denmark Department of Nuclear Medicine and PET, Aarhus University Hospital, Aarhus, Denmark
| | - Ronen Globinsky
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA Department of Radiology & Biomedical Imaging, Yale University, New Haven, CT, USA
| | - Robert K Fulbright
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA Department of Radiology & Biomedical Imaging, Yale University, New Haven, CT, USA
| | - Douglas L Rothman
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA Department of Radiology & Biomedical Imaging, Yale University, New Haven, CT, USA Department of Biomedical Engineering, Yale University, New Haven, CT, USA
| | - Albert Gjedde
- Center of Functionally Integrative Neuroscience, Aarhus University, Aarhus, Denmark Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark
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12
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Broek JA, Guest PC, Rahmoune H, Bahn S. Proteomic analysis of post mortem brain tissue from autism patients: evidence for opposite changes in prefrontal cortex and cerebellum in synaptic connectivity-related proteins. Mol Autism 2014; 5:41. [PMID: 25126406 PMCID: PMC4131484 DOI: 10.1186/2040-2392-5-41] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Accepted: 06/27/2014] [Indexed: 12/22/2022] Open
Abstract
Background Autism is a neurodevelopmental disorder characterized by impaired language, communication and social skills. Although genetic studies have been carried out in this field, none of the genes identified have led to an explanation of the underlying causes. Here, we have investigated molecular alterations by proteomic profiling of post mortem brain samples from autism patients and controls. The analysis focussed on prefrontal cortex and cerebellum as previous studies have found that these two brain regions are structurally and functionally connected, and they have been implicated in autism. Methods Post mortem prefrontal cortex and cerebellum samples from autism patients and matched controls were analysed using selected reaction monitoring mass spectrometry (SRM-MS). The main objective was to identify significantly altered proteins and biological pathways and to compare these across these two brain regions. Results Targeted SRM-MS resulted in identification of altered levels of proteins related to myelination, synaptic vesicle regulation and energy metabolism. This showed decreased levels of the immature astrocyte marker vimentin in both brain regions, suggesting a decrease in astrocyte precursor cells. Also, decreased levels of proteins associated with myelination and increased synaptic and energy-related proteins were found in the prefrontal cortex, indicative of increased synaptic connectivity. Finally, opposite directional changes were found for myelination and synaptic proteins in the cerebellum. Conclusion These findings suggest altered structural and/or functional connectivity in the prefrontal cortex and cerebellum in autism patients, as shown by opposite effects on proteins involved in myelination and synaptic function. Further investigation of these findings could help to increase our understanding of the mechanisms underlying autism relating to brain connectivity, with the ultimate aim of facilitating novel therapeutic approaches.
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Affiliation(s)
- Jantine Ac Broek
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Tennis Court Road, CB2 1QT Cambridge, UK
| | - Paul C Guest
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Tennis Court Road, CB2 1QT Cambridge, UK
| | - Hassan Rahmoune
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Tennis Court Road, CB2 1QT Cambridge, UK
| | - Sabine Bahn
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Tennis Court Road, CB2 1QT Cambridge, UK ; Department of Neuroscience, Erasmus Medical Centre, Dr. Molenwaterplein 50, 3015 GE Rotterdam, The Netherlands
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13
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Fabjan A, Musizza B, Bajrović FF, Zaletel M, Strucl M. The effect of the cold pressor test on a visually evoked cerebral blood flow velocity response. ULTRASOUND IN MEDICINE & BIOLOGY 2012; 38:13-20. [PMID: 22104537 DOI: 10.1016/j.ultrasmedbio.2011.10.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2011] [Revised: 08/17/2011] [Accepted: 10/12/2011] [Indexed: 05/31/2023]
Abstract
We investigated the hypothesis that during tonic pain stimulus, neurovascular coupling (NVC) decreases, measuring visually evoked cerebral blood flow velocity response (VEFR) during cold pressor test (CPT) in healthy human subjects as a test. VEFR was calculated as a relative increase in blood flow velocity in the posterior cerebral artery from average values during the last 5 s of the stimulus-OFF period to average values during the last 10 s of the stimulus-ON period. Three consecutive experimental phases were compared: basal, CPT and recovery. During CPT, end-diastolic and mean VEFR increased from 20.2 to 23.6% (p < 0.05) and from 17.5 to 20.0% (p < 0.05), respectively. In recovery phase, end-diastolic and mean VEFR decreased to 17.7% and 15.5%, respectively. Both values were statistically significantly different from CPT phase (p < 0.05). Compared with the basal phase, only end-diastolic VEFR was statistically significantly different in the recovery phase (p < 0.05). Our results are consistent with the assumption that there is a change in the activity of NVC during CPT because of the modulatory influence of subcortical structures activated during tonic pain. Contrary to our expectations, the combined effect of such influences increases rather than decreases NVC.
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Affiliation(s)
- Andrej Fabjan
- Institute of Physiology, Medical Faculty, University of Ljubljana, Ljubljana, Slovenia.
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14
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Abstract
Neurovascular coupling, or functional hyperaemia, refers to complex mechanisms of communication between neurons, astrocytes and cerebral vessels which form the neurovascular unit that spatially and temporally adjusts blood supply to the needs in energy and oxygen of activated neurons. Neurovascular coupling is so precise that it underlies neuroimaging techniques to map changes in neuronal activity. Therefore, understanding its basis is indispensable for the proper interpretation of imaging signals from functional magnetic resonance imaging and positron emission tomography, routinely used in humans. Although neurovascular coupling mechanisms are not yet fully understood, considerable progress has been made over the last decade. In this review, we present recent knowledge from in vivo studies on the cortical cellular network involved in neurovascular coupling responses and the mediators implicated in these haemodynamic changes. Recent findings have emphasized the intricate interplay between both excitatory and inhibitory neurons in neurovascular coupling, together with an intermediary role of astrocytes, which are ideally positioned between neurons and microvessels. Finally, we describe latest findings on the alterations of neurovascular function encountered in neurodegenerative conditions such as Alzheimer's disease.
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Affiliation(s)
- C Lecrux
- Laboratory of Cerebrovascular Research, Montreal Neurological Institute, McGill University, Montréal, QC, Canada
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15
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Serotonergic neurotransmission plays a major role in the action of the glycogenic convulsant methionine sulfoximine. Neurosci Res 2011; 70:313-20. [DOI: 10.1016/j.neures.2011.03.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2010] [Revised: 01/31/2011] [Accepted: 03/02/2011] [Indexed: 11/21/2022]
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16
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Yaseen MA, Srinivasan VJ, Sakadžić S, Radhakrishnan H, Gorczynska I, Wu W, Fujimoto JG, Boas DA. Microvascular oxygen tension and flow measurements in rodent cerebral cortex during baseline conditions and functional activation. J Cereb Blood Flow Metab 2011; 31:1051-63. [PMID: 21179069 PMCID: PMC3070982 DOI: 10.1038/jcbfm.2010.227] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Revised: 11/17/2010] [Accepted: 11/26/2010] [Indexed: 12/13/2022]
Abstract
Measuring cerebral oxygen delivery and metabolism microscopically is important for interpreting macroscopic functional magnetic resonance imaging (fMRI) data and identifying pathological changes associated with stroke, Alzheimer's disease, and brain injury. Here, we present simultaneous, microscopic measurements of cerebral blood flow (CBF) and oxygen partial pressure (pO(2)) in cortical microvessels of anesthetized rats under baseline conditions and during somatosensory stimulation. Using a custom-built imaging system, we measured CBF with Fourier-domain optical coherence tomography (OCT), and vascular pO(2) with confocal phosphorescence lifetime microscopy. Cerebral blood flow and pO(2) measurements displayed heterogeneity over distances irresolvable with fMRI and positron emission tomography. Baseline measurements indicate O(2) extraction from pial arterioles and homogeneity of ascending venule pO(2) despite large variation in microvessel flows. Oxygen extraction is linearly related to flow in ascending venules, suggesting that flow in ascending venules closely matches oxygen demand of the drained territory. Oxygen partial pressure and relative CBF transients during somatosensory stimulation further indicate arteriolar O(2) extraction and suggest that arterioles contribute to the fMRI blood oxygen level dependent response. Understanding O(2) supply on a microscopic level will yield better insight into brain function and the underlying mechanisms of various neuropathologies.
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Affiliation(s)
- Mohammad A Yaseen
- Department of Radiology, MGH/MIT/HMS Athinuola A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, USA
| | - Vivek J Srinivasan
- Department of Radiology, MGH/MIT/HMS Athinuola A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, USA
| | - Sava Sakadžić
- Department of Radiology, MGH/MIT/HMS Athinuola A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, USA
| | - Harsha Radhakrishnan
- Department of Radiology, MGH/MIT/HMS Athinuola A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, USA
| | - Iwona Gorczynska
- Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Weicheng Wu
- Department of Radiology, MGH/MIT/HMS Athinuola A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, USA
| | - James G Fujimoto
- Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - David A Boas
- Department of Radiology, MGH/MIT/HMS Athinuola A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, USA
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17
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Magnetic resonance spectroscopic methods for the assessment of metabolic functions in the diseased brain. Curr Top Behav Neurosci 2011; 11:169-98. [PMID: 22076698 DOI: 10.1007/7854_2011_166] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Magnetic resonance spectroscopy (MRS) is a non-invasive technique that can be used to detect and quantify multiple metabolites. This chapter will review some of the applications of MRS to the study of brain functions. Typically, (1)H-MRS can detect metabolites reflecting neuronal density and integrity, markers of energy metabolism or inflammation, as well as neurotransmitters. The complexity of the proton spectrum has however led to the development of other nuclei-based methods, such as (31)P- and (13)C-MRS, which offer a broader chemical shift range and therefore can provide more detailed information at the level of single metabolites. The versatility of MRS allows for a wide range of clinical applications, of which neurodegeneration is an interesting target for spectroscopy-based studies. In particular, MRS can identify patterns of altered brain chemistry in Alzheimer's patients and can help establish differential diagnosis in Alzheimer's and Parkinson's diseases. Using MRS to follow less abundant neurotransmitters is currently out of reach and will most likely depend on the development of methods such as hyperpolarization that can increase the sensitivity of detection. In particular, dynamic nuclear polarization has opened up a new and exciting area of medical research, with developments that could greatly impact on the real-time monitoring of in vivo metabolic processes in the brain.
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Hyder F, Sanganahalli BG, Herman P, Coman D, Maandag NJG, Behar KL, Blumenfeld H, Rothman DL. Neurovascular and Neurometabolic Couplings in Dynamic Calibrated fMRI: Transient Oxidative Neuroenergetics for Block-Design and Event-Related Paradigms. FRONTIERS IN NEUROENERGETICS 2010; 2. [PMID: 20838476 PMCID: PMC2936934 DOI: 10.3389/fnene.2010.00018] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/04/2010] [Accepted: 07/02/2010] [Indexed: 11/13/2022]
Abstract
Functional magnetic resonance imaging (fMRI) with blood-oxygenation level dependent (BOLD) contrast is an important tool for mapping brain activity. Interest in quantitative fMRI has renewed awareness in importance of oxidative neuroenergetics, as reflected by cerebral metabolic rate of oxygen consumption(CMRO2), for supporting brain function. Relationships between BOLD signal and the underlying neurophysiological parameters have been elucidated to allow determination of dynamic changes inCMRO2 by "calibrated fMRI," which require multi-modal measurements of BOLD signal along with cerebral blood flow (CBF) and volume (CBV). But how doCMRO2 changes, steady-state or transient, derived from calibrated fMRI compare with neural activity recordings of local field potential (LFP) and/or multi-unit activity (MUA)? Here we discuss recent findings primarily from animal studies which allow high magnetic fields studies for superior BOLD sensitivity as well as multi-modal CBV and CBF measurements in conjunction with LFP and MUA recordings from activated sites. A key observation is that while relationships between neural activity and sensory stimulus features range from linear to non-linear, associations between hyperemic components (BOLD, CBF, CBV) and neural activity (LFP, MUA) are almost always linear. More importantly, the results demonstrate good agreement between the changes inCMRO2 and independent measures of LFP or MUA. The tight neurovascular and neurometabolic couplings, observed from steady-state conditions to events separated by <200 ms, suggest rapid oxygen equilibration between blood and tissue pools and thus calibrated fMRI at high magnetic fields can provide high spatiotemporal mapping ofCMRO2 changes.
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Affiliation(s)
- Fahmeed Hyder
- Magnetic Resonance Research Center, School of Medicine, Yale University New Haven, CT, USA
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19
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Abstract
An individual, human or animal, is defined to be in a conscious state empirically by the behavioral ability to respond meaningfully to stimuli, whereas the loss of consciousness is defined by unresponsiveness. PET measurements of glucose or oxygen consumption show a widespread approximately 45% reduction in cerebral energy consumption with anesthesia-induced loss of consciousness. Because baseline brain energy consumption has been shown by (13)C magnetic resonance spectroscopy to be almost exclusively dedicated to neuronal signaling, we propose that the high level of brain energy is a necessary property of the conscious state. Two additional neuronal properties of the conscious state change with anesthesia. The delocalized fMRI activity patterns in rat brain during sensory stimulation at a higher energy state (close to the awake) collapse to a contralateral somatosensory response at lower energy state (deep anesthesia). Firing rates of an ensemble of neurons in the rat somatosensory cortex shift from the gamma-band range (20-40 Hz) at higher energy state to <10 Hz at lower energy state. With the conscious state defined by the individual's behavior and maintained by high cerebral energy, measurable properties of that state are the widespread fMRI patterns and high frequency neuronal activity, both of which support the extensive interregional communication characteristic of consciousness. This usage of high brain energies when the person is in the "state" of consciousness differs from most studies, which attend the smaller energy increments observed during the stimulations that form the "contents" of that state.
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20
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Herman P, Sanganahalli BG, Blumenfeld H, Hyder F. Cerebral oxygen demand for short-lived and steady-state events. J Neurochem 2009; 109 Suppl 1:73-9. [PMID: 19393011 DOI: 10.1111/j.1471-4159.2009.05844.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Because of the importance of oxidative energetics for cerebral function, extraction of oxygen consumption (CMR(O2)) from blood oxygenation level-dependent (BOLD) signal using multi-modal measurements of blood flow (CBF) and volume (CBV) has become an accepted functional magnetic resonance imaging (fMRI) technique. This approach, termed calibrated fMRI, is based on a biophysical model which describes tissue oxygen extraction at steady-state. A problem encountered for calculating dynamic CMR(O2) relates to concerns whether the conventional BOLD model can be applied transiently. In particular, it is unclear whether calculation of CMR(O2) differs between short and long stimuli. Linearity was experimentally demonstrated between BOLD-related components and neural activity, thereby making it possible to use calibrated fMRI in a dynamic manner. We used multi-modal fMRI and electrophysiology, in alpha-chloralose anesthetized rats during forepaw stimulation to show that respective transfer functions (of BOLD, CBV, CBF) generated by deconvolution with neural activity are time invariant, for events in the millisecond to minute range. These results allowed extraction of a significant component of the BOLD signal that can be ascribed to CMR(O2) transients. We discuss the importance of minimizing residual signal, represented by the difference between modeled and raw signals, in convolution analysis of multi-modal signals.
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Affiliation(s)
- Peter Herman
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, Connecticut 06520, USA.
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