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

Abstract

The majority of researchers investigating hyperpolarized gas MRI as a candidate functional lung imaging modality have used 3 He as their imaging agent of choice rather than 129 Xe. This preference has been predominantly due to, 3 He 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 129 Xe 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 129 Xe 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 129 Xe signal decay. We note that the measurement of pO 2 by observation of 129 Xe signal decay is more complex than that for 3 He because of an additional signal loss mechanism due to interphase diffusion of 129 Xe 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.

Small Animal Imaging with Hyperpolarized 129Xe Magnetic Resonance

“…It has been reported that several physiological quantities related to these processes were globally evaluated from measurements of alveolar gas uptake dynamics using CSSR in animals 30,[42][43][44][45] and humans. 39,46,47 Whole-lung spectroscopy, however, limits the assessments to be accepted as global measures without any information about the spatial distribution in the lung. An extension of spectroscopybased methods to imaging-based methods is an important step toward identifying a region with impaired function with higher sensitivity and evaluation of its variation in the whole lung.…”

Functional Imaging: CT and MRI

“…(156) However, improvement in hyperpolarization systems has meant that 129-Xenon MR imaging is making rapid strides forward, giving new insight in lung function. (160)(161)(162).One of the main features of hyperpolarized gas imaging is that the signal introduced in the system is so high that imaging is less dependent on field strength than is the case for proton imaging, and this has advantages as lower field-strength magnets may result in fewer artifacts. (163)(164)(165) A main disadvantage to this technique is that the contrast is exogenous, and is non-renewable.…”

Measurement of alveolar oxygen partial pressure in the rat lung using Carr‐Purcell‐Meiboom‐Gill spin–spin relaxation times of hyperpolarized 3He and 129Xe at 74 mT

“…Measurement of p A O 2 has previously been reported using spin-lattice relaxation rates, R 1 , of both hyperpolarized 3 He (13)(14)(15)(16)(17) and 129 Xe (5). Although most previous studies have employed 3 He due to its higher signal-to-noise ratio (SNR), 3 He has a very low natural abundance, making it a poor candidate for widespread clinical use.…”