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. During the past decade, hyperpolarized (HP) 129Xe has found application in biomedical MRI with exciting results. Typically, the gas is introduced into the organism by inhalation, which is an efficient strategy for imaging the gas space of the lungs. Due to the alveolar gas exchange, a small amount of inhaled HP 129Xe enters the pulmonary blood and is delivered to other organs. This has already been exploited to study brain perfusion. More efficient methods for the local delivery of xenon to other target organs may include pre-dissolving of the HP gas in a suitable liquid or the production of microbubbles with subsequent injection into the blood stream. For initial experiments, we will use isotopically enriched 129Xe (82%), Intralipid 30% (Pharmacia, Clayton, NC) and a 'shaker'as described in M?ller et al. MRM 41, 1058 (1999) to reproduce previous experiments serving as a reference. The search for other vehicles for local delivery will include dissolving of HP 129Xe in fully oxygenated blood or plasma and dissolving of HP 129Xe in deuterated saline solution. Although the solubility of xenon in these liquids is significantly less than that of lipid emulsions, they are of interest because Xe will be released to the alveolar gas phase upon passing through the lungs, which can be exploited for perfusion imaging if RF excitation is selectively applied to the gas phase resonance. In addition, such systems may be tolerated better during prolonged infusion experiments. Experiments with deuterated saline are of further interest one may expect a drasticallyprolonged 129Xe T1. Insead of the previously used 'shaker'for dissolving HP 129Xe, another strategy will involve hollow-fiber membranes to improve the process of dissolving. This technique may also hold a potential for continuous infusion of the HP gas carrier. For comparison, experiments involving direct injection of small amounts of HP 129Xe into a vein will also be investigated. Regarding the Ostwald solubility (L) of Xe in water, roughly 0.1 mL of gas may be injected per mL of blood. If f is the venous blood flow in mL/sec, HP gas may be injected continuously at a rate of L x f provided that the dissolving process is sufficently rapid in vivo and the gas is quantitatively released to the alveoli.
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