@article {266, title = {Zooming In on Microscopic Flow by Remotely Detected MRI}, journal = {Science}, volume = {330}, year = {2010}, note = {Science682BUTimes Cited:12Cited References Count:27}, month = {Nov 19}, pages = {1078-1081}, abstract = {

Magnetic resonance imaging (MRI) can elucidate the interior structure of an optically opaque object in unparalleled detail but is ultimately limited by the need to enclose the object within a detection coil; acquiring the image with increasingly smaller pixels reduces the sensitivity, because each pixel occupies a proportionately smaller fraction of the detector\&$\#$39;s volume. We developed a technique that overcomes this limitation by means of remotely detected MRI. Images of fluids flowing in channel assemblies are encoded into the phase and intensity of the constituent molecules\&$\#$39; nuclear magnetic resonance signals and then decoded by a volume-matched detector after the fluids flow out of the sample. In combination with compressive sampling, we thus obtain microscopic images of flow and velocity distributions similar to 10(6) times faster than is possible with conventional MRI on this hardware. Our results illustrate the facile integration of MRI with microfluidic assays and suggest generalizations to other systems involving microscopic flow.

}, keywords = {biosensor}, isbn = {0036-8075}, doi = {Doi 10.1126/Science.1192313}, url = {://WOS:000284374700036}, author = {Bajaj, V. S. and Paulsen, J. and Harel, E. and Pines, A.} } @article {273, title = {Flow in Porous Metallic Materials: A Magnetic Resonance Imaging Study}, journal = {Journal of Magnetic Resonance Imaging}, volume = {28}, year = {2008}, note = {J Magn Reson Imaging367QCTimes Cited:5Cited References Count:22}, month = {Nov}, pages = {1299-1302}, abstract = {

Purpose: To visualize flow dynamics of analytes inside porous metallic materials with laser-detected magnetic resonance imaging (MRI).Materials and Methods: We examine the flow of nuclear-polarized water in a porous stainless steel cylinder. Laser-detected MRI utilizes a sensitive optical atomic magnetometer as the detector. Imaging was performed in a remote-detection mode: the encoding was conducted in the Earth\&$\#$39;s magnetic field, and detection is conducted downstream of the encoding location. Conventional MRI (7T) was also performed for comparison.Results: Laser-detected MRI clearly showed MR images of water flowing through the sample, whereas conventional MRI provided no image.Conclusion: We demonstrated the viability of laser-detected MRI at low-field for studying porous metallic materials, extending MRI techniques to a new group of systems that is normally not accessible to conventional MRI.

}, keywords = {mri}, isbn = {1053-1807}, doi = {Doi 10.1002/Jmri.21532}, url = {://WOS:000260566100033}, author = {Xu, S. J. and Harel, E. and Michalak, D. J. and Crawford, C. W. and Budker, D. and Pines, A.} } @article {280, title = {Spectrally resolved flow imaging of fluids inside a microfluidic chip with ultrahigh time resolution}, journal = {Journal of Magnetic Resonance}, volume = {193}, year = {2008}, note = {J Magn Reson336INTimes Cited:14Cited References Count:19}, month = {Aug}, pages = {199-206}, abstract = {

Microfluidics has advanced to become a complete lab-on-a-chip platform with applications across Many disciplines of scientific research. While optical techniques are primarily used as modes of detection, magnetic resonance (MR) is emerging as a potentially powerful and complementary tool because of its non-invasive operation and analytical fidelity. Two prevailing limitations Currently inhibit MR techniques on microfluidic devices: poor sensitivity and the relatively slow time scale of dynamics that can be probed. it is commonly assumed that the time scale of observation of one variable limits the certainty with which one can measure the complementary variable. For example, short observation times imply poor spectral resolution. In this article, we demonstrate a new methodology that overcomes this fundamental limit, allowing in principle for arbitrarily high temporal resolution with a sensitivity across the entire microfluidic device several Orders of magnitude greater than is possible by direct MR measurement. The enhancement is evidenced by recording chemically resolved fluid mixing through a complex 3D microfluidic device at 500 frames per second, the highest recorded in a magnetic resonance imaging experiment. The key to this development is combining remote detection with a time \&$\#$39;slicing\&$\#$39; of its spatially encoded counterpart. Remote detection circumvents the problem of insensitive direct MR detection on a microfluidic device where the direct sensitivity is less than 10(-5) relative to traditional NMR, while the time slicing eliminates the constraints of the limited observation time by converting the time variable into a spatial variable through the use of magnetic field gradients. This method has implications for observing fast processes, Such as fluid mixing, rapid binding, and certain classes of chemical reactions with sub millisecond time resolution and as a new modality for on-chip chromatography. Published by Elsevier Inc.

}, keywords = {probes}, isbn = {1090-7807}, doi = {Doi 10.1016/J.Jmr.2008.04.037}, url = {://WOS:000258357600005}, author = {Harel, E. and Pines, A.} } @article {288, title = {Dispersion measurements using time-of-flight remote detection MRI}, journal = {Magnetic Resonance Imaging}, volume = {25}, year = {2007}, note = {Magn Reson Imaging167BHTimes Cited:5Cited References Count:10}, month = {May}, pages = {449-452}, abstract = {

Remote detection nuclear magnetic resonance and magnetic resonance imaging can be used to study fluid flow and dispersion in a porous medium from a purely Eulerian point of view (i.e., in a laboratory frame of reference). Information about fluid displacement is obtained on a macroscopic scale in a long-time regime, while local velocity distributions are averaged out. It is shown how these experiments can be described using the common flow propagator formalism and how experimental data can be analyzed to obtain effective porosity, flow velocity inside the porous medium, fluid dispersion and flow tracing of fluid. (C) 2007 Elsevier Inc. All rights reserved.

}, keywords = {flow}, isbn = {0730-725X}, doi = {Doi 10.1016/J.Mri.2006.11.011}, url = {://WOS:000246425100004}, author = {Granwehr, J. and Harel, E. and Hilty, C. and Garcia, S. and Chavez, L. and Pines, A. and Sen, P. N. and Song, Y. Q.} } @article {283, title = {Quantifying the diffusion of a fluid through membranes by double phase encoded remote detection magnetic resonance imaging}, journal = {Journal of Physical Chemistry B}, volume = {111}, year = {2007}, note = {J Phys Chem B240VDTimes Cited:11Cited References Count:31}, month = {Dec 20}, pages = {13929-13936}, abstract = {

We demonstrate that a position correlation magnetic resonance imaging (MRI) experiment based on two phase encoding steps separated by a delay can be used for quantifying diffusion across a membrane. This method is noninvasive, and no tracer substance or concentration gradient across the membrane is required. Because, in typical membranes, the T-1 relaxation time of the fluid spins is usually much longer than the T-2 time, we developed and implemented a new position correlation experiment based on a stimulated spin-echo, in which the relaxation attenuation of the signal is dominated by T-1 instead of T-2. This enables using relatively long delays needed in the diffusion measurements. The sensitivity of the double encoded experiment detected in a conventional way is still low because of the low filling factor of the fluid inside the NMR coil around the sample. We circumvent this problem by using the remote detection technique, which significantly increases the sensitivity, making it possible to do the measurements with gaseous fluids that have a low spin-density compared to liquids. We derive a model that enables us to extract a diffusion constant characterizing the diffusion rate through the membrane from the obtained correlation images. The double phase encoded MRI method is advantageous in any kind of diffusion studies, because the propagator of fluid molecules can directly be seen from the correlation image.

}, keywords = {mri}, isbn = {1520-6106}, doi = {Doi 10.1021/Jp076760e}, url = {://WOS:000251615400011}, author = {Telkki, V. V. and Hilty, C. and Garcia, S. and Harel, E. and Pines, A.} } @article {287, title = {Time-of-flight flow imaging of two-component flow inside a microfluidic chip}, journal = {Physical Review Letters}, volume = {98}, year = {2007}, note = {Phys Rev Lett124OYTimes Cited:21Cited References Count:16}, month = {Jan 5}, abstract = {

Here we report on using NMR imaging and spectroscopy in conjunction with time-of-flight tracking to noninvasively tag and monitor nuclear spins as they flow through the channels of a microfluidic chip. Any species with resolvable chemical-shift signatures can be separately monitored in a single experiment, irrespective of the optical properties of the fluids, thereby eliminating the need for foreign tracers. This is demonstrated on a chip with a mixing geometry in which two fluids converge from separate channels, and is generally applicable to any microfluidic device through which fluid flows within the nuclear spin-lattice relaxation time.

}, keywords = {microchannels}, isbn = {0031-9007}, doi = {Doi 10.1103/Physrevlett.98.017601}, url = {://WOS:000243379700050}, author = {Harel, E. and Hilty, C. and Koen, K. and McDonnell, E. E. and Pines, A.} } @article {302, title = {Multiphase imaging of gas flow in a nanoporous material using remote-detection NMR}, journal = {Nature Materials}, volume = {5}, year = {2006}, note = {Nat Mater029AOTimes Cited:25Cited References Count:40}, month = {Apr}, pages = {321-327}, abstract = {

Pore structure and connectivity determine how microstructured materials perform in applications such as catalysis, fluid storage and transport, filtering or as reactors. We report a model study on silica aerogel using a time-of-flight magnetic resonance imaging technique to characterize the flow field and explain the effects of heterogeneities in the pore structure on gas flow and dispersion with Xe-129 as the gas-phase sensor. The observed chemical shift allows the separate visualization of unrestricted xenon and xenon confined in the pores of the aerogel. The asymmetrical nature of the dispersion pattern alludes to the existence of a stationary and a flow regime in the aerogel. An exchange time constant is determined to characterize the gas transfer between them. As a general methodology, this technique provides insights into the dynamics of flow in porous media where several phases or chemical species may be present.

}, keywords = {visualization}, isbn = {1476-1122}, doi = {Doi 10.1038/Nmat1598}, url = {://WOS:000236530400024}, author = {Harel, E. and Granwehr, J. and Seeley, J. A. and Pines, A.} } @article {319, title = {Time-of-flight flow imaging using NMR remote detection}, journal = {Physical Review Letters}, volume = {95}, year = {2005}, note = {Phys Rev Lett955SGTimes Cited:35Cited References Count:29}, month = {Aug 12}, abstract = {

A time-of-flight imaging technique is introduced to visualize fluid flow and dispersion through porous media using NMR. As the fluid flows through a sample, the nuclear spin magnetization is modulated by rf pulses and magnetic field gradients to encode the spatial coordinates of the fluid. When the fluid leaves the sample, its magnetization is recorded by a second rf coil. This scheme not only facilitates a time-dependent imaging of fluid flow, it also allows a separate optimization of encoding and detection subsystems to enhance overall sensitivity. The technique is demonstrated by imaging gas flow through a porous rock.

}, keywords = {mri}, isbn = {0031-9007}, doi = {Doi 10.1103/Physrevlett.95.075503}, url = {://WOS:000231247300028}, author = {Granwehr, J. and Harel, E. and Han, S. and Garcia, S. and Pines, A. and Sen, P. N. and Song, Y. Q.} }