The preliminary finding suggest that physiologically harmful pH changes in rodent lungs after a few cryogenics-free hp gas deliveries are not likely, even with the high Rb density at 83Kr SEOP conditions and in the absence of gas filters. Although filter usage may still be prudent for ABT-263 purchase further reducing any potentially

remaining Rb contamination, a study detailing the exact quantity of the Rb carried through the gas extraction process and the effects of filtering techniques upon the spin polarization is beyond the scope of this work. Extraction scheme 2 was modified to generate hp gas mixtures with a precisely selected O2 concentration. After transfer of the hp gas into the volume Vextmax of the extraction unit, O2 was added and resulted in a carefully regulated pressure increase signaling pathway until the desired O2 concentration was

reached. The total pressure in the large volume Vextmax = 790 ml was typically between 10–20 kPa and the mixing of the gasses was sufficient within 5 s after addition of O2. The method was tested by measuring the 129Xe longitudinal relaxation rates caused by paramagnetic O2 as a function of O2 density (or corresponding oxygen concentration; shown in Fig. 7). The O2 density dependent relaxation data shown in Fig. 7a (filled triangles) demonstrated the accuracy in the preparation of the gas mixture. The data was obtained using a series of small flip angle pulses at physiologically relevant, (i.e. ambient) pressure. The resulting slope of the oxygen density dependent 129Xe relaxation rate equation(2) 1T1ρO2129Xe290K,9.4T=0.360±0.007s-1amagat-1at 9.4 T field strength and 290 K was in good agreement with that obtained by Jameson et al.

with thermally polarized 129Xe at high xenon and oxygen densities [31]: equation(3) 1T1ρO2129Xe9.4T=0.343s-1amagat1·(T/300K)-0.03where T   is the temperature of the gas mixture in Kelvin. An amagat is defined in this work as the density of an ideal gas at standard pressure and temperature of 101.325 kPa and 273.15 K and therefore 1amagat=2.6868×1025m-3. At the conditions used in this work, N2, O2, Kr, and Xe are considered to follow ideal gas laws. According to Eq. (2), a relaxation time of T1 = 14.2 s was observed for a 21% O2, 79% hp 129Xe–N2 mixture contained also in an NMR test tube at 9.4 T and ambient pressure. However, the experimental setup used in this work was also applied to relaxation measurements in lungs as shown in Fig. 7c after SEOP, hp gas extraction, mixing with a quantified amount of O2, compression, transfer into a storage container, and inhalation by the excised lungs. The average longitudinal relaxation rate for two excised lungs was found to have the following dependence: equation(4) 1T1ρO2129Xe290K,9.4T=0.361±0.020s-1amagat-1 Eq. (4) describes the oxygen dependent term of the 129Xe T  1 relaxation, however the average longitudinal relaxation rate measured in the absence of oxygen (i.e.