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. Hyperpolarized gas MR imaging in small animals (and other studies as well) have generally required a dedicated ventilator system. The use of expensive rare isotopes (such as 3He and 129Xe) present a need to miinimize cost by recycling these gases after they have been used for imaging.