Oxygen advection and diffusion in a three-dimensional vascular anatomical network

Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts 02129, USA.
Optics Express (Impact Factor: 3.49). 11/2008; 16(22):17530-41. DOI: 10.1364/OE.16.017530
Source: PubMed


There is an increasing need for quantitative and computationally affordable models for analyzing tissue metabolism and hemodynamics in microvascular networks. In this work, we develop a hybrid model to solve for the time-varying oxygen advection-diffusion equation in the vessels and tissue. To obtain a three-dimensional temporal evolution of tissue oxygen concentration for realistic complex vessel networks, we used a graph-based advection model combined with a finite-element based diffusion model and an implicit time-advancing scheme. We validated this algorithm for both static and dynamic conditions. We also applied it to a complex vascular network obtained from a rodent somatosensory cortex. Qualitative agreement was found with in-vivo experiments.

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Available from: Sava Sakadzic, Dec 20, 2013
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    • "The distribution of dissolved oxygen in the brain has proven difficult to examine at the microvascular level under baseline conditions let alone after selective flow alterations due to methodological shortcomings of classical oximetry techniques. Empirical measurements are often still made outside the vascular lumen of large vessels through invasive Clark electrodes [1,2] from which mathematical models of oxygen delivery have been developed following the theory of advection-diffusion [3,4]. More recently, three-dimensional optical imaging techniques have been shown to provide hemodynamic characterization of microvascular beds with greater sensitivity and accessibility without significant physiological perturbation [5]. "
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    ABSTRACT: Occlusions in single cortical microvessels lead to a reduction in oxygen supply, but this decrement has not been able to be quantified in three dimensions at the level of individual vessels using a single instrument. We demonstrate a combined optical system using two-photon phosphorescence lifetime and fluorescence microscopy (2PLM) to characterize the partial pressure of oxygen (pO2) in single descending cortical arterioles in the mouse brain before and after generating a targeted photothrombotic occlusion. Integrated real-time Laser Speckle Contrast Imaging (LSCI) provides wide-field perfusion maps that are used to monitor and guide the occlusion process while 2PLM maps changes in intravascular oxygen tension. We present the technique’s utility in highlighting the effects of vascular networking on the residual intravascular oxygen tensions measured after occlusion in three dimensions.
    Biomedical Optics Express 07/2013; 4(7):1061-1073. DOI:10.1364/BOE.4.001061 · 3.65 Impact Factor
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    • "In animals, the emergence of new optical imaging techniques has provided unprecedented access to vascular anatomy and tissue perfusion [5]. Two photon microscopy (TPM) using labelled markers allows high resolution imaging of vascular networks. "
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    ABSTRACT: Optical coherence tomography (OCT) has recently been used to produce 3D angiography of microvasculature and blood flow maps of large vessels in the rodent brain in-vivo. However, use of this optical method for the study of cerebrovascular disease has not been fully explored. Recent developments in neurodegenerative diseases has linked common cardiovascular risk factors to neurodegenerative risk factors hinting at a vascular hypothesis for the development of the latter. Tools for studying cerebral blood flow and the myogenic tone of cerebral vasculature have thus far been either highly invasive or required ex-vivo preparations therefore not preserving the delicate in-vivo conditions. We propose a novel technique for reconstructing the flow profile over a single cardiac cycle in order to evaluate flow pulsatility and vessel compliance. A vascular model is used to simulate changes in vascular compliance and interpret OCT results. Comparison between atherosclerotic and wild type mice show a trend towards increased compliance in the smaller arterioles of the brain (diameter < 80μm) in the disease model. These results are consistent with previously published ex-vivo work confirming the ability of OCT to investigate vascular dysfunction.
    Biomedical Optics Express 11/2011; 2(11):3079-93. DOI:10.1364/BOE.2.003079 · 3.65 Impact Factor
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    • "Note, though, that the relevant question is not whether pO 2 is uniform in tissue, which would be a possible assumption that could be used to derive Eq. 3. Instead, the question is whether a much more detailed microscopic description leads to predictions for the macroscopic variables that differ significantly from the predictions of the simpler macroscopic models. A promising avenue for addressing questions like these is to construct detailed models of the vascular tree from animal imaging data and use such realistic geometries to calculate oxygen transport (Fang et al., 2008). These simulations also should include known effects of blood transport, such as the shift of p 50 , and so need to model CO 2 production and clearance simultaneously with O 2 transport and consumption. "
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    ABSTRACT: Functional magnetic resonance imaging is widely used to map patterns of brain activation based on blood oxygenation level dependent (BOLD) signal changes associated with changes in neural activity. However, because oxygenation changes depend on the relative changes in cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO(2)), a quantitative interpretation of BOLD signals, and also other functional neuroimaging signals related to blood or tissue oxygenation, is fundamentally limited until we better understand brain oxygen metabolism and how it is related to blood flow. However, the positive side of the complexity of oxygenation signals is that when combined with dynamic CBF measurements they potentially provide the best tool currently available for investigating the dynamics of CMRO(2). This review focuses on the problem of interpreting oxygenation-based signals, the challenges involved in measuring CMRO(2) in general, and what is needed to put oxygenation-based estimates of CMRO(2) on a firm foundation. The importance of developing a solid theoretical framework is emphasized, both as an essential tool for analyzing oxygenation-based multimodal measurements, and also potentially as a way to better understand the physiological phenomena themselves. The existing data, integrated within a simple theoretical framework of O(2) transport, suggests the hypothesis that an important functional role of the mismatch of CBF and CMRO(2) changes with neural activation is to prevent a fall of tissue pO(2). Future directions for better understanding brain oxygen metabolism are discussed.
    Frontiers in Neuroenergetics 06/2010; 2:8. DOI:10.3389/fnene.2010.00008
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