@article {285, title = {Para-hydrogen-induced polarization in heterogeneous hydrogenation reactions}, journal = {Journal of the American Chemical Society}, volume = {129}, year = {2007}, note = {J Am Chem Soc160MRTimes Cited:36Cited References Count:45}, month = {May 2}, pages = {5580-5586}, abstract = {

We demonstrate the creation and observation of para-hydrogen-induced polarization in heterogeneous hydrogenation reactions. Wilkinson\&$\#$39;s catalyst, RhCl(PPh3)(3), supported on either modified silica gel or a polymer, is shown to hydrogenate styrene into ethylbenzene and to produce enhanced spin polarizations, observed through NMR, when the reaction was performed with H-2 gas enriched in the para spin isomer. Furthermore, gaseous phase para-hydrogenation of propylene to propane with two catalysts, the Wilkinson\&$\#$39;s catalyst supported on modified silica gel and Rh(cod)(sulfos) (cod = cycloocta-1,5-diene; sulfos = -O3S(C6H4)CH2C(CH2PPh2)(3)) supported on silica gel, demonstrates heterogeneous catalytic conversion resulting in large spin polarizations. These experiments serve as a direct verification of the mechanism of heterogeneous hydrogenation reactions involving immobilized metal complexes and can be potentially developed into a practical tool for producing catalyst-free fluids with highly polarized nuclear spins for a broad range of hyperpolarized NMR and MRI applications.

}, keywords = {alignment}, isbn = {0002-7863}, doi = {Doi 10.1021/Ja068653o}, url = {://WOS:000245946400064}, author = {Koptyug, I. V. and Kovtunov, K. V. and Burt, S. R. and Anwar, M. S. and Hilty, C. and Han, S. I. and Pines, A. and Sagdeev, R. Z.} } @article {289, title = {Sensitivity enhancement by exchange mediated magnetization transfer of the xenon biosensor signal}, journal = {Journal of Magnetic Resonance}, volume = {184}, year = {2007}, note = {J Magn Reson127EUTimes Cited:7Cited References Count:18}, month = {Jan}, pages = {72-77}, abstract = {

Hyperpolarized xenon associated with ligand derivatized cryptophane-A cages has been developed as a NMR based biosensor. To optimize the detection sensitivity we describe use of xenon exchange between the caged and bulk dissolved xenon as an effective signal amplifier. This approach, somewhat analogous to \&$\#$39;remote detection\&$\#$39; described recently, uses the chemical exchange to repeatedly transfer spectroscopic information from caged to bulk xenon, effectively integrating the caged signal. After an optimized integration period, the signal is read out by observation of the bulk magnetization. The spectrum of the caged xenon is reconstructed through use of a variable evolution period before transfer and Fourier analysis of the bulk signal as a function of the evolution time. (c) 2006 Elsevier Inc. All rights reserved.

}, keywords = {resonance}, isbn = {1090-7807}, doi = {Doi 10.1016/J.Jmr.2006.09.010}, url = {://WOS:000243568900009}, author = {Garcia, S. and Chavez, L. and Lowery, T. J. and Han, S. I. and Wemmer, D. E. and Pines, A.} } @article {304, title = {Auxiliary probe design adaptable to existing probes for remote detection NMR, MRI, and time-of-flight tracing}, journal = {Journal of Magnetic Resonance}, volume = {182}, year = {2006}, note = {J Magn Reson093XPTimes Cited:7Cited References Count:21}, month = {Oct}, pages = {260-272}, abstract = {

A versatile, detection-only probe design is presented that can be adapted to any existing NMR or MRI probe with the purpose of making the remote detection concept generally applicable. Remote detection suggests freeing the NMR experiment from the confinement of using the same radio frequency (RF) coil and magnetic field for both information encoding and signal detection. Information is stored during the encoding step onto a fluid sensor medium whose magnetization is later measured in a different location. The choice of an RF probe and magnetic field for encoding can be made based solely on the size and characteristics of the sample and the desired information quality without considering detection sensitivity, as this aspect is dealt with by a separate detector. While early experiments required building probes that included two resonant circuits, one for encoding and one for detection, a modular approach with a detection-only probe as presented here can be used along with any existing NMR probe of choice for encoding. The design of two different detection-only probes is presented, one with a saddle coil for milliliter-sized detection volumes, and the other one with a microsolenoid coil for sub-microliter fluid quantities. As example applications, we present time-of-flight (TOF) tracing of hyperpolarized Xe-129 spins in a gas mixture through coiled tubing using the microsolenoid coil detector and TOF flow imaging through a nested glass container where the gas flow changes its direction twice between inlet and outlet using the saddle coil detector. (c) 2006 Elsevier Inc. All rights reserved.

}, keywords = {flow}, isbn = {1090-7807}, doi = {Doi 10.1016/J.Jmr.2006.06.024}, url = {://WOS:000241203900010}, author = {Han, S. I. and Granwehr, J. and Garcia, S. and McDonnell, E. E. and Pines, A.} } @article {303, title = {NMR velocity mapping of gas flow around solid objects}, journal = {Physical Review E}, volume = {74}, year = {2006}, note = {Phys Rev EPart 2069DJTimes Cited:4Cited References Count:31}, month = {Jul}, abstract = {

We present experimental visualizations of gas flow around solid blunt bodies by NMR imaging. NMR velocimetry is a model-free and tracer-free experimental means for quantitative and multi-dimensional flow visualization. Hyperpolarization of Xe-129 provided sufficient NMR signal to overcome the low density of the dilute gas phase, and its long coherence time allows for true velocity vector mapping. In this study, the diverging gas flow around and wake patterns immediately behind a sphere could be vectorally visualized and quantified. In a similar experiment, the flow over an aerodynamic model airplane body revealed a less disrupted flow pattern.

}, keywords = {wake}, isbn = {1539-3755}, doi = {Doi 10.1103/Physreve.74.016302}, url = {://WOS:000239425700044}, author = {Han, S. I. and Pierce, K. L. and Pines, A.} } @article {298, title = {SQUID-detected microtesla MRI in the presence of metal}, journal = {Journal of Magnetic Resonance}, volume = {179}, year = {2006}, note = {J Magn Reson035CMTimes Cited:36Cited References Count:23}, month = {Mar}, pages = {146-151}, abstract = {

In magnetic resonance imaging performed at fields of I T and above, the presence of a metal insert can distort the image because of susceptibility differences within the sample and modification of the radiofrequency fields by screening currents. Furthermore, it is not feasible to perform nuclear magnetic resonance (NMR) spectroscopy or acquire a magnetic resonance image if the sample is enclosed in a metal container. Both problems can be overcome by substantially lowering the NMR frequency. Using a microtesla imaging system operating at 2.8 kHz, with a superconducting quantum interference device as the signal detector, we have obtained distortion-free images of a phantom containing a titanium bar and three-dimensional images of an object enclosed in an aluminum can; in both cases high-field images are inaccessible. (c) 2005 Elsevier Inc. All rights reserved.

}, keywords = {nmr}, isbn = {1090-7807}, doi = {Doi 10.1016/J.Jmr.2005.11.005}, url = {://WOS:000236977600019}, author = {Mossle, M. and Han, S. I. and Myers, W. R. and Lee, S. K. and Kelso, N. and Hatridge, M. and Pines, A. and Clarke, J.} } @article {305, title = {Toward ex situ phase-encoded spectroscopic imaging}, journal = {Concepts in Magnetic Resonance Part B-Magnetic Resonance Engineering}, volume = {29B}, year = {2006}, note = {Concept Magn Reson B067JNTimes Cited:7Cited References Count:20}, month = {Aug}, pages = {137-144}, abstract = {

Spectroscopic imaging of a sample placed outside of both the radio frequency and the imaging gradient coils is presented. The sample is placed in a field with a permanent one-dimensional inhomogeneity. The imaging gradients used for phase encoding are designed to produce a static field that depends only on the transverse direction, uncoupling the effects associated with the single-sided nature of these coils. Two-dimensional imaging coupled with chemical shift information is obtained via the ex situ matching technique. Open-saddle geometry is used to match the static field profile for chemical shift information recovery. (C) 2006 Wiley Periodicals, Inc.

}, keywords = {probe}, isbn = {1552-5031}, doi = {Doi 10.1002/Cmr.B.20069}, url = {://WOS:000239298100004}, author = {Demas, V. and Meriles, C. and Sakellariou, D. and Han, S. I. and Reimer, J. and Pines, A.} } @article {315, title = {Microfluidic gas-flow profiling using remote-detection NMR}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {102}, year = {2005}, note = {P Natl Acad Sci USA977NZTimes Cited:41Cited References Count:26}, month = {Oct 18}, pages = {14960-14963}, abstract = {

We have used nuclear magnetic resonance (NMR) to obtain spatially and temporally resolved profiles of gas flow in microfluidic devices. Remote detection of the NMR signal both overcomes the sensitivity limitation of NMR and enables time-of-flight measurement in addition to spatially resolved imaging. Thus, detailed insight is gained into the effects of flow, diffusion, and mixing in specific geometries. The ability for noninvasive measurement of microfluidic flow, without the introduction of foreign tracer particles, is unique to this approach and is important for the design and operation of microfluidic devices. Although here we demonstrate an application to gas flow, extension to liquids, which have higher density, is implicit.

}, keywords = {mri}, isbn = {0027-8424}, doi = {Doi 10.1073/Pnas.0507566102}, url = {://WOS:000232811800006}, author = {Hilty, C. and McDonnell, E. E. and Granwehr, J. and Pierce, K. L. and Han, S. I. and Pines, A.} } @article {317, title = {NMR-based biosensing with optimized delivery of polarized Xe-129 to solutions}, journal = {Analytical Chemistry}, volume = {77}, year = {2005}, note = {Anal Chem942GLTimes Cited:30Cited References Count:37}, month = {Jul 1}, pages = {4008-4012}, abstract = {

Laser-enhanced (LE) Xe-129 nuclear magnetic resonance (NMR) is an exceptional tool for sensing extremely small physical and chemical changes; however, the difficult mechanics of bringing polarized xenon and samples of interest together have limited applications, particularly to biological molecules. Here we present a method for accomplishing solution Xe-129 biosensing based on flow (bubbling) of LE Xe-129 gas through a solution in situ in the NMR probe, with pauses for data acquisition. This overcomes fundamental limitations of conventional solution-state LE Xe-129 NMR, e.g., the difficulty in transferring hydrophobic xenon into aqueous environments, and the need to handle the sample to refresh LE Xe-129 after an observation pulse depletes polarization. With this new method, we gained a factor of \> 100 in sensitivity due to improved xenon transfer to the solution and the ability to signal average by renewing the polarized xenon. Polarized xenon in biosensors was detected at very low concentrations, \<= 250 nanomolar, while retaining all the usual information from NMR. This approach can be used to simultaneously detect multiple sensors with different chemical shifts and is also capable of detecting signals from opaque, heterogeneous samples, which is a unique advantage over optical methods. This general approach is adaptable for sensing minute quantities of xenon in heterogeneous in vitro samples, in miniaturized devices and should be applicable to certain in-vivo environments.

}, keywords = {blood}, isbn = {0003-2700}, doi = {Doi 10.1021/Ac0500479}, url = {://WOS:000230270800035}, author = {Han, S. I. and Garcia, S. and Lowery, T. J. and Ruiz, E. J. and Seeley, J. A. and Chavez, L. and King, D. S. and Wemmer, D. E. and Pines, A.} } @article {327, title = {Remotely detected high-field MRI of porous samples}, journal = {Journal of Magnetic Resonance}, volume = {167}, year = {2004}, note = {J Magn Reson809KKTimes Cited:26Cited References Count:28}, month = {Apr}, pages = {282-290}, abstract = {

Remote detection of NMR is a novel technique in which an NMR-active sensor surveys an environment of interest and retains memory of that environment to be recovered at a later time in a different location. The NMR or MRI information about the sensor nucleus is encoded and stored as spin polarization at the first location and subsequently moved to a different physical location for optimized detection. A dedicated probe incorporating two separate radio frequency (RF)-circuits was built for this purpose. The encoding solenoid coil was large enough to fit around the bulky sample matrix, while the smaller detection solenoid coil had not only a higher quality factor, but also an enhanced filling factor since the coil volume comprised purely the sensor nuclei. We obtained two-dimensional (2D) void space images of two model porous samples with resolution less than 1.4 mm(2). The remotely reconstructed images demonstrate the ability to determine fine structure with image quality superior to their directly detected counterparts and show the great potential of NMR remote detection for imaging applications that suffer from low sensitivity due to low concentrations and filling factor. Published by Elsevier Inc.

}, keywords = {gas}, isbn = {1090-7807}, doi = {Doi 10.1016/J.Jmr.2003.12.018}, url = {://WOS:000220635400012}, author = {Seeley, J. A. and Han, S. I. and Pines, A.} } @article {340, title = {Amplification of xenon NMR and MRI by remote detection}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {100}, year = {2003}, note = {P Natl Acad Sci USA709HPTimes Cited:65Cited References Count:28}, month = {Aug 5}, pages = {9122-9127}, abstract = {

A technique is proposed in which an NMR spectrum or MRI is encoded and stored as spin polarization and is then moved to a different physical location to be detected. Remote detection allows the separate optimization of the encoding and detection steps, permitting the independent choice of experimental conditions and excitation and detection methodologies. In the initial experimental demonstration of this technique, we show that taking dilute Xe-129 from a porous sample placed inside a large encoding coil and concentrating it into a smaller detection coil can amplify NMR signal. In general, the study of NMR active molecules at low concentration that have low physical filling factor is facilitated by remote detection. In the second experimental demonstration, MRI information encoded in a very low-field magnet (4-7 mT) is transferred to a high-field magnet (4.2 T) to be detected under optimized conditions. Furthermore, remote detection allows the utilization of ultrasensitive optical or superconducting quantum interference device detection techniques, which broadens the horizon of NMR experimentation.

}, keywords = {field}, isbn = {0027-8424}, doi = {Doi 10.1073/Pnas.1133497100}, url = {://WOS:000184620000007}, author = {Moule, A. J. and Spence, M. M. and Han, S. I. and Seeley, J. A. and Pierce, K. L. and Saxena, S. and Pines, A.} }