High Xe density, high photon flux, stopped-flow spin-exchange optical pumping: Simulations versus experiments

Abstract

Spin-exchange optical pumping (SEOP) can enhance the NMR sensitivity of noble gases by up to five orders of magnitude at Tesla-strength magnetic fields. SEOP-generated hyperpolarised (HP) 129 Xe is a promising contrast agent for lung imaging but an ongoing barrier to widespread clinical usage has been eco-

Enabling Clinical Technologies for Hyperpolarized 129Xenon Magnetic Resonance Imaging and Spectroscopy

“…[80] FEM models also have had success reproducing the behavior of CF-SEOP hyperpolarizers.F ink et al [82] examined small-cell systems and reported relatively good agreement with data from Shah et al, [89] who used aSEOP cell with ac ross-section of 13 cm 2 and am odest laser power of 50 W. More recent FEM models of CF-SEOP created by Burant and Schrank [83][84][85] are currently under development with the goal of better capturing all phenomena of CF-SEOP hyperpolarizers,i ncluding complexities of mass and thermal transport within different regions of CF-SEOP cells. [65]…”

“…[74] Angewandte Chemie Aufsätze 22310 www.angewandte.de Rb clusters (which, if relevant, are thought to occur only in certain CF regimes). [90] Tw os uch simulations of SF-SEOP were implemented by Skinner et al [65] and validated against two experimental datasets [75,91] from the high-Xe-density,high resonant-photon-flux regime.B oth simulations provided excellent qualitative and quantitative reproduction of the Xe-rich SF-SEOP datasets,including the inverse relationship between the optimal cell temperature (T opt )a nd [Xe]. Furthermore,u nder certain conditions the simulations trended towards a" universally optimal" laser absorption when P Xe is maximized-which may help provide 1) an explanation for the experimentally observed interplay of laser linewidth, T opt ,and [Xe],inthe context of optimizing the photon-to-[Rb] ratio (mentioned above), and 2) anew way to optimize SF hyperpolarizer operation.…”

“…Thes imulations also studied the design and operation of such hyperpolarizers, considering cell temperature,c ell geometry,l aser linewidth, laser power, gas mixture,a nd gas pressure,t oh elp further improve performance,including the prediction that reduction of laser linewidth improves P Xe disproportionately at higher [Xe],a nd the potential utility of ternary gas mixtures containing 4 He (for improved temperature stability owing to higher thermal conductivity), which was recently realized in asecond-generation clinical-scale hyperpolarizer. [65] Finally,v ery recently Branca and co-workers [92,93] published simulation work that aimed to improve previous efforts by going against assumptions that may lead to underestimation of Rb/Xe spin-exchange cross-sections but significant overestimatation of Rb vapor densities (particularly in CF polarizers) and Xe cell residence times (exclusively in CF polarizers). Ther esulting simulations showed good quantitative reproduction of experimental polarization values and dynamics in both CF-SEOP and SF-SEOP,w ithout considerations of contributions to spin exchange or relaxation beyond those considered in established theory.…”

Hyperpolarized 129Xe Time-of-Flight MR Imaging of Perfusion and Brain Function

“…Hyperpolarized (HP) xenon-129 ( 129 Xe) MRI is a powerful MRI approach used mainly for lung imaging and for the study of lung disorders [27,28]. A hyperpolarized (HP) metastable state is produced by spin exchange optical pumping [29][30][31], and is characterized by up to 10 5 larger longitudinal magnetization compared to thermal polarization [27]. Therefore, the magnetic resonance signal of HP nuclei can be up to 10 5 times stronger than at thermal equilibrium.…”

A semi-empirical model to optimize continuous-flow hyperpolarized 129Xe production under practical cryogenic-accumulation conditions

“…Ignoring these minor thermal variations, it was possible to examine P Xe simulations for higher laser powers against various 129 Xe blends -a useful design consideration as laser power, P l , in clinical-scale SEOP polarizers currently ranges from 29 W [55] to 1.5 kW (XeBox-E10, XeMed LLC, Durham, NH). While higher P l is expected to generate higher P Xe , Figure 6 demonstrates that for each gas blend there is a point at which increasing P l delivers no significant enhancement in polarization.…”