Browsing by Subject "Oxygen tension"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Novel optical techniques for imaging oxygen and other hemodynamic parameters during physiological events(2010-12) Ponticorvo, Adrien; Dunn, Andrew Kenneth, 1970-; Jones, Theresa; Ress, David; Rylander, Grady; Tunnell, JamesThis dissertation presents the development and use of a novel optical imaging system capable of monitoring changes in blood flow, oxygenated hemoglobin, deoxygenated hemoglobin, and absolute pO₂ in the brain. There are several imaging modalities capable of monitoring these parameters separately. Laser speckle contrast imaging (LSCI) and multi-spectral reflectance imaging (MSRI) have been used to monitor relative blood flow and hemoglobin changes respectively. Phosphorescence quenching, while not typically used for imaging, is capable of noninvasive measurements of pO₂. Combining these three techniques has led to the development of an imaging system that could ultimately lead to a better understanding of brain physiology. By combining techniques such as LSCI and MSRI, it becomes possible to estimate the cerebral metabolic rate of oxygen (CMRO₂), an important indicator of neuronal function. It is equally important to understand absolute pO₂ levels so that oxygen metabolism can be examined in context. Integrating phosphorescence quenching and a spatial light modulator into the imaging system allowed absolute pO₂ to be simultaneously measured in distinct regions. This new combined system was used to investigate pathophysiological conditions such as cortical spreading depression (CSD) and ischemia. The observed hemodynamic changes associated with these events were largely dictated by baseline oxygen levels and varied significantly in different regions. This finding highlighted the importance of having a system capable of monitoring hemodynamic changes and absolute pO₂ simultaneously while maintaining enough spatial resolution to distinguish the changes in different regions. It was found that animals with low baseline pO₂ were unable to deliver enough oxygen to the brain during events like CSD because of the high metabolic demand. In order for this technique to become more prevalent among researchers, it is essential to make it cost effective and simple to use. This was accomplished by replacing the expensive excitation sources with cheaper light emitting diodes (LEDs) and redesigning the software interface so that it was easier to control the entire device. The final system shows the potential to become a key tool for researchers studying the role of absolute pO₂ and other hemodynamic parameters during pathophysiological conditions such as CSD and ischemia.Item Quantitative optical imaging of hemodynamics as platforms for studying neuro-vascular physiology and disease(2014-08) Kazmi, Syed Mohammad Shams; Dunn, Andrew Kenneth, 1970-; Milner, Thomas E; Tunnell, James W; Rylander, H. Grady; Jones, Theresa ABlood flow and its payload of molecular oxygen are two parameters of most physiological interest. Systemic tissue health is routinely gauged through measurements of vitals and oxygen saturation to estimate the state of these physiological parameters. We design, develop, and deploy optical imaging systems for examining perfusion and oxygenation at the local tissue level and apply these techniques for elucidating the normal and pathological processes associated with neurovascular disease. Specifically, we develop and validate the ability to use Multi-Exposure Speckle Imaging (MESI) to estimate microvascular flow dynamics in rodents over acute and chronic periods. Next, we pose significant optimizations to improve the efficacy of the widefield imaging technique for adoption by bench-side and clinical perfusion studies. We also introduce re-interpretations of the underlying physics to advance the theory that quantifies motion from the imaged speckle patterns. Finally, the technique is deployed for chronic monitoring of cortical flow dynamics before after focal ischemia of the motor cortex as part of a behavioral study in rodents. At the microscale, we develop and validate Two Photon Phosphorescence Lifetime Microscopy (2PLM) to examine dissolved oxygen concentration in microvasculature in three dimensions. We examine the technique’s ability for functional mapping of the rodent cortical microvascular network by quantifying the partial pressure of oxygen (pO₂) before and after occlusion of critical arterioles. Automation of acquisitions and processing for robust oxygen mapping within the micro-vascular network are developed and evaluated. The in vivo results are presented in light of those from studies utilizing more invasive mapping electrodes to provide independent corroboration of the observed neurovascular oxygen distributions. The technique is deployed for examining high resolution functional and structural remodeling after focal cerebral ischemia.