Hyperpolarized 129Xe MRI:: A viable functional lung imaging modality?

The majority of researchers investigating hyperpolarized gas MRI as a candidate functional lung imaging modality have used He-3 as their imaging agent of choice rather than Xe-129. This preference has been predominantly due to, He-3 providing stronger signals due to higher levels of polarization and higher gyromagnetic ratio, as well as its being easily available to more researchers due to availability of polarizers (USA) or ease of gas transport (Europe). Most researchers agree, however, that hyperpolarized Xe-129 Will ultimately emerge as the imaging agent of choice due to its unlimited supply in nature and its falling cost. Our recent polarizer technology delivers vast improvements in hyperpolarized Xe-129 output. Using this polarizer, we have demonstrated the unique property of xenon to measure alveolar surface area noninvasively. In this article, we describe our human protocols and their safety, and our results for the measurement of the partial pressure of pulmonary oxygen (pO(2)) by observation of Xe-129 signal decay. We note that the measurement of pO(2) by observation of Xe-129 signal decay is more complex than that for He-3 because of an additional signal loss mechanism due to interphase diffusion of Xe-129 from alveolar gas spaces to septal tissue. This results in measurements of an equivalent pO(2) that accounts for both traditional T-1 decay from pO(2) and that from interphase diffusion. We also provide an update on new technological advancements that form the foundation for an improved compact design polarizer as well as improvements that provide another order-of-magnitude scale-up in xenon polarizer output. (c) 2007 Elsevier Ireland Ltd. All rights reserved.