This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. It is typically assumed that hyperoxia substantially alters the hemodynamics of the brain, confounding attempts to measure hemodynamic quantities with hyperoxic contrast. However, studies have recently shown that cerebral blood flow (CBF) experiences only a small (<4%) reduction upon breathing low to moderate oxygen concentrations (FiO2d0.5) -- flow changes that are too low to be produce signal changes that can be detected by typical BOLD T2*-weighted EPI. Hyperoxic contrast has been shown to exhibit fast washout times, which make feasible the accurate measurements of dynamic parameters ?such as blood flow -- using hyperoxic contrast. We have recently observed substantial negative contrast enhancement in T2*-weighted images near arteries in the brain that we believe is due to excess dissolved paramagnetic molecular oxygen in the plasma. This negative contrast enhancement provides the means to infer the relative excess oxygen content in the arteries feeding the brain and thereby measure an arterial input function (AIF) necessary for quantitative flow values. In addition, hyperoxic contrast can be used to measure cerebral blood volume (CBV) using hyperoxic contrast enhancement measured during steady-state. We are currently investigating the accuracy of measurements of CBV and CBF made dynamically during the washout of hyperoxic contrast using indicator-dilution theory in a manner akin to dynamic susceptibility contrast MRI (DSC-MRI)measurements.
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