Hp 83Kr applications in pulmonary research were thus far limited to low resolution MRI [13] and [14] and to spatially unresolved relaxation measurements in rat lungs [15]. The objective of this work was to omit cryogenic separation in the hp noble gas production process for pulmonary MRI. The ‘cryogenics-free’ concept [16] is beneficial for reducing the complexity, and therefore the costs, of the hp 129Xe production. Furthermore, this concept is crucial for biomedical hp 83Kr MRI since quadrupolar relaxation causes Selleckchem AZD8055 the loss of the hyperpolarized spin state during cryogenic separation. The streamlined
hp 129Xe and hp 83Kr production procedure without cryogenic gas separation was tested in applications for MRI of excised rat lungs. The developmental work utilized ex vivo lungs in order to simplify experimental and regulatory procedures but the general concepts will be extendible to in vivo MRI. Low xenon concentrations are typically used for 129Xe SEOP because a high density of this noble gas is detrimental to the process. The noble gas is usually diluted to 1–5% in mixtures with molecular nitrogen or helium (i.e. 4He). In the case of helium as the diluting gas, approximately 2–5% N2 are added in the mixture to ensure radiation quenching [10] and [17]. The low xenon density in the SEOP gas mixture NVP-BKM120 ic50 enables high spin polarization to be generated and values with P > 60% have been
reported [6], [7] and [8]. However, the method necessitates cryogenic separation after SEOP with hp xenon accumulation in the frozen state at cryogenic temperatures (typically 77 K) and the removal of all other gases of the mixture through evacuation [18]. In analogy L-gulonolactone oxidase to 129Xe SEOP, a low concentration of krypton is crucial for efficient SEOP of 83Kr. Despite the quadrupolar driven 83Kr T1 relaxation, a high spin polarization of P = 26% in
a gas mixture of 5% krypton and 95% N2 was obtained in stopped flow SEOP [10]. Unfortunately for hp 83Kr MRI, there is currently no practical method to separate or concentrate hp 83Kr from the gas mixture without substantial depolarization of its nuclear spin state. Fast quadrupolar driven T1 relaxation in the condensed state [19] and [20] prevents cryogenic separation of this isotope and the production process has to be realized without gas separation. The need for cryogenic separation is diminished if concentrated noble gas mixtures are used in low pressure SEOP. The associated detrimental effects of high xenon or krypton densities can partially be alleviated by low SEOP gas pressure [10], [21] and [22]. However, the pressure broadening of the alkali metal D1 transition is also reduced with lower SEOP pressures and therefore narrow laser linewidth are beneficial. Note that line narrowed diode array lasers with high power output are becoming increasingly available at affordable costs [23], [24] and [25].