A thermally polarized, dissolved-phase 129Xe phantom for quality-control and multisite comparisons of gas-exchange imaging

Abstract

Harmonizing and validating ¹²⁹Xe gas exchange imaging across multiple sites is hampered by a lack of a quantitative standard that 1) displays the unique spectral properties of ¹²⁹Xe observed from human subjects in vivo and 2) has short enough $T_1$ times to enable practical imaging. This work describes and demonstrates the development of two dissolved-phase, thermally polarized phantoms that mimic the in-vivo, red blood cell and membrane resonances of ¹²⁹Xe dissolved in human lungs. Following optimization, combinations of two common organic solvents, acetone and dimethyl sulfoxide, resulted in two in-vivo-like dissolved-phase ¹²⁹Xe phantoms yielding chemical shifts of 212.4 ppm and 193.9 ppm. By doping the solutions with iron(iii) acetylacetonate, the longitudinal relaxation time was reduced $T_1$ = 1.2 s for both phantoms at 3 T and 7 T. There was minimal change in chemical shift (+1.58 ppm) and $T_1$ (+1.2 %) over 1 year. In a 2D Dixon-type acquisition with 3 mm² in-plane resolution, ¹²⁹Xe dissolved-phase images yielded signal-to-noise ratios 6 and 12 for the RBC and membrane phantoms, respectively. A simple scaling of these phantoms to clinically relevant volumes of several liters would result in an SNR of 7 for the RBC phantom acquired in less than one minute. These findings demonstrate the ability to fabricate robust, quantitative, thermally polarized dissolved-phase phantoms, which will be needed to validate and harmonize gas exchange imaging in multi-site clinical trials.