Preface

Since the first report of the NMR detection of ¹²⁹Xe in 1954 by Brun et al., an amazingly broad scope of research efforts in xenon magnetic resonance has kept generations of scientists captivated with this apparently simple nuclear spin I=1/2 system. Indeed, it is the simplicity of this mono-atomic probe that enables investigations of complex porous structures and the processes that take place within these porous systems ranging from materials science to the study of the complex nature of gas exchange in mammalian lungs. Many of the sophisticated applications have become feasible with the advent of hyperpolarized (hp) ¹²⁹Xe but also build on previous research with thermally polarized ¹²⁹Xe NMR spectroscopy. The experiments are of an inherently interdisciplinary nature and many of the key scientists who lead the way in the various aspects of ¹²⁹Xe magnetic resonance have contributed to this book.

The first two chapters, written by two of the pioneers of ¹²⁹Xe NMR spectroscopy, will shed light to the historical context but also explain in detail the one of most valuable assets of these methods – i.e. the ¹²⁹Xe chemical shift. Chapter 1 by Jacques Fraissard reviews the usage of the ¹²⁹Xe chemical shift in porous materials, while Chapter 2 by Cynthia Jameson explains the theoretical treatment of xenon chemical shift.

Chapters 3–7 review the methods of hyperpolarization starting with an introduction of some of the concepts and practicalities of spin exchange optical pumping (SEOP), to date the most important method to generate hyperpolarized (hp) ¹²⁹Xe. Chapter 4 describes the simulation of the processes in an SEOP cell, and William Hersman and co-workers review in Chapter 5 the most sophisticated design of a continuous flow SEOP apparatus available to date. Boyd Goodson and co-workers describe in Chapter 6 a batch mode (i.e. stopped flow) SEOP system. Long relaxation T₁ times are generally very important for all work with hyperpolarized spin systems as the hp state is generated outside the NMR or MRI magnet and then transferred into the sample or target organ. Brian Saam details the physical phenomena that cause ¹²⁹Xe T₁ relaxation in the gas phase but also on cell surfaces in Chapter 7. Very slow T₁ relaxation, for example, enables storage of the hp ¹²⁹Xe for some duration in between SEOP and actual usage of the gas.

Chapters 8–12 are highlighting recent applications of xenon to materials investigations, mainly with respect to porosity. Li-Qiong Wang describes in Chapter 8 how hp ¹²⁹Xe helps to study the pore structure and interconnectivity, e.g., of ordered mesoporous compounds and electrode materials. In Chapter 9, Piero Sozzani and co-workers review ¹²⁹Xe NMR studies especially with respect to porous organic and hybrid materials. The fundamental concepts and applications of xenon cryoporology are explained in Chapter 10 by Jukka Jokisaari and co-workers. The usage of hp ¹²⁹Xe for the investigation of single-file diffusion – i.e. a diffusion phenomenon characteristic for narrow, elongated channels that exhibits a very different time dependence than unilateral diffusion in wider channels – is described by Russ Bowers in Chapter 11. Finally, Chapter 12 is devoted to the use of xenon to characterize adsorption-induced breathing transitions in flexible, i.e., switchable metal–organic frameworks.

A fascinating development, pioneered by the groups of Alexander Pines and David Wemmer at UC Berkeley, is the use of hp ¹²⁹Xe entrapped in functionalized cage compounds for molecular imaging. Since the first conceptual studies in the late 1990’s a number of groups have further advanced this xenon biosensor methodology. David Wemmer provides an introductory report about some of these developments in Chapter 13. In the following three chapters (Chapter 14–16), further key researchers, Patrick Berthault, Ivan Dmochowski, Leif Schroeder, and their respective co-workers, report about the amazing recent developments in this emerging area including biological cell studies.

Due to the limited supply of ³He, pulmonary researchers are increasingly turning to ¹²⁹Xe for MRI of the lungs. Xenon’s chemical shift, that is not available with ³He, provides an additional incentive as it enables new insights in to pulmonary physiology in health and disease. Chapter 17 by Hideaki Fujiwara and co-workers describes how hp ¹²⁹Xe, administered for breathing in continuous flow mode, can be used for dissolved phase studies in animal lungs. Kai Ruppert and co-workers describe xenon uptake studies in human lungs in Chapter 18. Xenon septal uptake is reviewed from a different viewpoint focusing on different protocols by Samuel Patz and co-worker in Chapter 19. Xenon uptake in the lung leads to dissolved xenon in the blood. The ¹²⁹Xe chemical shift and relaxation behavior in blood is detailed by Jim Wild and co-worker in Chapter 20. Knowledge about transverse relaxation of xenon in lungs is crucial for MRI protocol development and is described by Giles Santyr and his co-workers in Chapter 21. Finally, dissolved phase xenon can also be used for MRI of the brain as Mitch Albert and co-workers explain in Chapter 22.

The final three Chapter belong to the ‘Exotica’ group as Chapter 23 introduces the reader to hyperpolarized noble gases with nuclear spin I>1/2, namely another xenon isotope, ¹³¹Xe and the only MR active krypton isotope, ⁸³Kr. Arnaud Comment explains in Chapter 24 why DNP may very well be the future methodology to produce hp ¹²⁹Xe. Finally, Joseph Granwehr illustrates in Chapter 25 that NMR and MRI detection of hp ¹²⁹Xe does not have to take place at the same location as radio frequency excitation and spatial encoding with pulsed field gradients.

The topics have been selected to provide the reader with a thorough, although not exhaustive, overview of current topics in hyperpolarized noble gas magnetic resonance. This book focuses on techniques and applications that utilize the ¹²⁹Xe chemical shift. Methods and applications that are more in line with hp ³He methodology, such as apparent diffusion coefficient (ADC) measurement, are mostly left to the extensive literature in this field. We hope you will enjoy this book dedicated to magnetic resonance with ¹²⁹Xe – and, of course, with the occasional quadrupolar noble gas isotope.

Thomas Meersmann

Eike Brunner

Nottingham and Dresden