A quantitative estimate of cerebral blood oxygen saturation is of critical importance in the investigation of cerebrovascular disease. While positron emission tomography can map in vivo the oxygen level in blood, it has limited availability and requires ionizing radiation. Magnetic resonance imaging (MRI) offers an alternative through the blood oxygen level-dependent contrast. Here, we describe an in vivo and non-invasive approach to map brain tissue oxygen saturation (StO 2 ) with high spatial resolution. StO 2 obtained with MRI correlated well with results from blood gas analyses for various oxygen and hematocrit challenges. In a stroke model, the hypoxic areas delineated in vivo by MRI spatially matched those observed ex vivo by pimonidazole staining. In a model of diffuse traumatic brain injury, MRI was able to detect even a reduction in StO 2 that was too small to be detected by histology. In a F98 glioma model, MRI was able to map oxygenation heterogeneity. Thus, the MRI technique may improve our understanding of the pathophysiology of several brain diseases involving impaired oxygenation.
Journal of Cerebral Blood
INTRODUCTIONThe sensitivity of magnetic resonance imaging (MRI) to changes in oxygenation through the blood oxygen level-dependent (BOLD) effect 1 is the basis of functional MRI. This technique allows a noninvasive exploration of the functions and dysfunctions of the human brain and has revolutionized cognitive neuroscience over the last 20 years. Less appreciated is the potential of BOLD MRI to study baseline brain oxygenation. In a clinical environment, MRI oximetry would offer definitive advantages over brain oxygenation mapping with positron emission tomography (PET), 2 a technique not widely available and that requires ionizing radiations.Several authors have laid out the foundations of a theoretical framework named quantitative BOLD (qBOLD) imaging that aims to extract quantitative vascular information from baseline scans.
We provide new evidence for the differential effect of MRT on tumor vasculature, an effect that leads to tumor hypoxia. As hypothesized formerly, the vasculature of the normal brain exposed to MRT remains sufficiently perfused to prevent any hypoxia.
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