Imaging of a mixture of hyperpolarized 3 He and 129 Xe R.H. Acosta a , P. Blqmler a, * , S. Han a,b , S. Appelt c , F.W. H7sing c , J. Schmiedeskamp d , W. Heil d , H.W. Spiess a a Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany b Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106, USA c Central Laboratory for Electronics, Research Centre Ju ¨lich, 52428 Ju ¨lich, Germany d Department of Physics, University of Mainz, 55099 Mainz, Germany Received 14 July 2004; accepted 1 August 2004 Abstract With the use of hyperpolarized gases, a great number of experiments have been carried out in order to improve the diagnostics of the lung, both from a structural and a functional point of view. 3 He is best suited for structural studies, whereas 129 Xe gives more detailed information about the functionality of the lung because it enters the bloodstream. In this work, we propose the use of a gas mixture to perform consecutive analysis of lung structure and functionality upon the delivery of a single bolus of gas. We show images of a helium– xenon gas mixture in the presence of a small amount of liquid toluene in order to demonstrate how both nuclei can be detected independently, extracting the spectroscopic information provided by the 129 Xe spectra and obtaining an image with high sensitivity for 3 He. A second experiment performed on a dissected mouse lung was used to demonstrate how the mixture of gases can enhance sensitivity in the larger airways of the lung. D 2004 Elsevier Inc. All rights reserved. Keywords: MRI; Hyperpolarized gases; Xe; He; Lungs 1. Introduction In the last years, the application of laser-polarized (LP) noble gases received growing interest in clinical imaging, particularly for the study of the otherwise binvisibleQ air spaces in the lung. Through such developments, an organ that previously would not have been easily detected because the low concentration of protons in the lung tissue renders a very weak nuclear magnetic resonance (NMR) signal and the large number of air–tissue interfaces causes large susceptibility differences, resulting in rapid decaying proton signals, became accessible. The use of LP 3 He or LP 129 Xe vastly overcame the problem of low sensitivity, where low density was compensated for by an artificial increase of the polarization by five orders of magnitude and longer living signal was dealt with. It was demonstrated by several authors that both nuclei are suitable for lung imaging [1,2]; however, these possess unique characteristics that make them very different in their physical and physiological behavior. 3 He has a high gyromagnetic ratio, and polariza- tion levels of over 70% can be achieved, thus providing high sensitivity. In addition, 3 He is a perfectly inert noble gas with no physiological effects. Therefore, from a clinical point of view 3 He is ideal for detailed observation of the anatomy of the lung’s air spaces, detection of pathological changes of the microscopic morphology via restricted self- diffusion maps [3–5] and that of O 2 concentration via paramagnetic relaxation [6,7]. 129 Xe, on the other hand, has a lower gyromagnetic ratio and, typically, a polarization level of 30% can be achieved. 129 Xe is physiologically more active and lipophilic; it passes the air–blood barrier, dissolves in the blood [8–10] and even acts as an anesthetic. Because of the large and therefore very polarizable electron cloud, 129 Xe reveals a large chemical shift range [11]. So, in contrast to 3 He, 129 Xe is suited for functionality and perfusion studies [10]; the gas dissolves in blood, a process that can be accurately monitored through its chemical shift. Recently, xenon was used for the study of gas exchange between the xenon dissolved in the lung tissue and the gas in the alveoli [12,13]. 0730-725X/$ – see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.mri.2004.08.003 * Corresponding author. Tel.: +49 1 6131 379126; fax: +49 6131 379100. E-mail address: bluemler@mpip-mainz.mpg.de (P. Blqmler). Magnetic Resonance Imaging 22 (2004) 1077 – 1083