This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The metabolic demands of the brain are met almost exclusively through metabolism of glucose. Under normal conditions, the brain consistently extracts about 50% of the oxygen in the blood. The changes in metabolic demand are matched by changes in blood flow rather than by changes in oxygen extraction. Regional variations in oxidative metabolism typically correlate well with regional variations in blood flow. The correlation is the rationale for substituting blood flow maps for oxygen consumption maps. There are no clinically used methods for detection of oxidative metabolism in-vivo though metabolic disturbances in many diseases are important. In the past, in order to have a suitable model, 17O MRI techniques are modeled in swine to measure hemispheric cerebral metabolic rate of oxygen consumption (CMRO2) by detection of metabolically produced H217O by rapid T1?-wieghted proton magnetic resonance imaging on a 1.5 T clinical scanner. The 17O is delivered as oxygen gas by a custom built, minimal-loss, precision delivery breathing circuit and converted to H217O by oxidative metabolism. A high temporal resolution pulse sequence is employed to measure CMRO2. Proton measurements of signal change due to metabolically produced water are correlated with 17O in-vivo measurements. Using these techniques, the hemispheric CMRO2 in swine is estimated to be 1.23 ?0.26 ?mol/g/min;consistent with existing literature values. In the present study, we employed diffuse reflectance and correlation spectroscopy to monitor the response of cerebral oxygenation and blood flow to hypercapnia in swine and to compare oxygen consumption optically estimated with17O MRI measurements. Currently, both optical and indirect detection of 17O by T1?-wieghted proton magnetic resonance imaging studies are in progress to correlate the data. All the technology used to perform these CMRO2 estimates can easily be adapted to clinical MR scanners and it is expected that this work will lead to future studies on human diseases.
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