We compare diffusion activation energy measurements in a hydrated perfluorosulfonate ionomer and aqueous solutions of triflic acid. These measurements provide insight into water transport dynamics on sub-nm length scales, and gauge the contribution of the polymer sidechain terminal group. Future membrane materials design will hinge on detailed understanding of transport dynamics.

Pure water in a highly 1 H spin-polarized state is proposed as a contrast-agent-free contrast agent to visualize its macroscopic evolution in aqueous media by MRI. Remotely enhanced liquids for image contrast (RELIC) utilizes a 1 H signal of water that is enhanced outside the sample in continuous-flow mode and immediately delivered to the sample to obtain maximum contrast between entering and bulk fluids. Hyperpolarization suggests an ideal contrast mechanism to highlight the ubiquitous and specific function of water in physiology, biology, and materials because the physiological, chemical, and macroscopic function of water is not altered by the degree of magnetization. We present an approach that is capable of instantaneously enhancing the 1 H MRI signal by up to 2 orders of magnitude through the Overhauser effect under ambient conditions at 0.35 tesla by using highly spin-polarized unpaired electrons that are covalently immobilized onto a porous, water-saturated gel matrix. The continuous polarization of radicalfree flowing water allowed us to distinctively visualize vortices in model reactors and dispersion patterns through porous media. A 1 H signal enhancement of water by a factor of ؊10 and ؊100 provides for an observation time of >4 and 7 s, respectively, upon its injection into fluids with a T1 relaxation time of >1.5 s. The implications for chemical engineering or biomedical applications of using hyperpolarized solvents or physiological fluids to visualize mass transport and perfusion with high and authentic MRI contrast originating from water itself, and not from foreign contrast agents, are immediate.Water is the driver of nature.Leonardo da Vinci I n a world where water is so ubiquitous and vital, the exchange and transport characteristics of water are fundamental for the function of an endless range of biological and industrial processes: blood physiology, protein folding, plant metabolism, biomaterial function, and oil recovery from reservoir rocks are only drops in the bucket. However, there exists a paucity of analytical tools capable of directly tracing and quantifying the transport and function of water through these already-watersaturated materials in a chemically selective and noninvasive manner. Although NMR and MRI are the best tools for this purpose, they face two main challenges. One is the lack of sensitivity inherent to all NMR experiments, especially for in vivo NMR studies of transport in biological and biomedical samples. A general approach to this sensitivity issue is the employment of high magnetic fields and cryoprobes, which is not only expensive technology but also is limited to Ͻ1 order of magnitude improvement in sensitivity. The other challenge is the lack of contrast, e.g., between the flowing water molecules being traced and the bulk water or water contained in the specimen. Current perfusion MRI techniques that address this contrast issue are dynamic susceptibility contrast-enhanced imaging (1, 2) and proton electron double-resonance imaging (PEDRI), also known as Overhaus...

Purpose:To assess the feasibility of a perfusion magnetic resonance (MR) imaging technique that uses Overhauser dynamic nuclear polarization (DNP) to provide contrast during the continuous delivery of hyperpolarized water in rats. Materials and Methods:Protocols approved by the local institutional animal care and use committees were followed. Twelve male Wistar rats were anesthetized and prepared by placing injection tubing in the subcutaneous layer (n = 3), peritoneum (n = 3), aorta (n = 3), or carotid artery (n = 3). Water was hyperpolarized by means of Overhauser DNP in the 0.35-T fringe field of a 1.5-T MR imaging magnet by using a custom-built system to continuously deliver radical-free hyperpolarized water to the subject. Fast gradient-echo and spoiled gradient-recalled-echo MR imaging sequences were used. The signal-to-noise ratio (SNR) of the images was calculated and compared. Results:Images showed greatly altered SNR and enhanced flow contrast at all injection locations. For subcutaneous and intraperitoneal injections, the water perfusion trajectory was observed for approximately 5 seconds after injection. Flow through a 4.2-cm length of artery was seen during intra-aortic injection. The right hemisphere of the brain was seen during injection into the right carotid artery. Images with hyperpolarized water had greatly altered SNR compared with images without injection or with the injection of nonhyperpolarized water, with a range of 13%-27% for the carotid and 444%-2900% for the other regions. Conclusion:Perfusion contrast for MR imaging can be obtained by continuously infusing hyperpolarized water, providing localized angiography or brain perfusion information in vivo for rat models.q RSNA, 2012Supplemental material: http://radiology.rsna.org/lookup /suppl