@article {269, title = {Distortion-free magnetic resonance imaging in the zero-field limit}, journal = {Journal of Magnetic Resonance}, volume = {200}, year = {2009}, note = {J Magn Reson526AWTimes Cited:6Cited References Count:29}, month = {Oct}, pages = {285-290}, abstract = {

MRI is a powerful technique for clinical diagnosis and materials characterization. Images are acquired in a homogeneous static magnetic field much higher than the fields generated across the field of view by the spatially encoding field gradients. Without such a high field, the concomitant components of the field gradient dictated by Maxwell\&$\#$39;s equations lead to severe distortions that make imaging impossible with conventional MRI encoding. In this paper, we present a distortion-free image of a phantom acquired with a fundamentally different methodology in which the applied static field approaches zero. Our technique involves encoding with pulses of uniform and gradient field, and acquiring the magnetic field signals with a SQUID. The method can be extended to weak ambient fields, potentially enabling imaging in the Earth\&$\#$39;s field without cancellation coils or shielding. Other potential applications include quantum information processing and fundamental studies of long-range ferromagnetic interactions. (C) 2009 Elsevier Inc. All rights reserved.

}, keywords = {gradients}, isbn = {1090-7807}, doi = {Doi 10.1016/J.Jmr.2009.07.016}, url = {://WOS:000272260900015}, author = {Kelso, N. and Lee, S. K. and Bouchard, L. S. and Demas, V. and M{\"u}ck, M. and Pines, A. and Clarke, J.} } @article {271, title = {{\textquoteright}Ex situ{\textquoteright} magnetic resonance volume imaging}, journal = {Chemical Physics Letters}, volume = {467}, year = {2009}, note = {Chem Phys Lett386VCTimes Cited:2Cited References Count:25}, month = {Jan 5}, pages = {398-401}, abstract = {

The portable NMR community has introduced advances that have allowed for a variety of studies. Imaging of static and moving objects has almost become standardized. The inherent static field gradients of portable systems have, however, limited such studies to imaging of slices perpendicular to the main gradient; full volume imaging in transportable, open systems has not been actively pursued. We present a true three-dimensional image of a phantom in an ex situ, electromagnet-based system. The basic concepts and designs put forth here extend in a straightforward fashion to higher fields and imaging of larger samples by ex situ methodologies. (C) 2008 Elsevier B.V. All rights reserved.

}, keywords = {array}, isbn = {0009-2614}, doi = {Doi 10.1016/J.Cplett.2008.11.069}, url = {://WOS:000261909700037}, author = {Demas, V. and Franck, J. M. and Bouchard, L. S. and Sakellariou, D. and Meriles, C. A. and Martin, R. and Prado, P. J. and Bussandri, A. and Reimer, J. A. and Pines, A.} } @article {270, title = {Shimmed matching pulses: Simultaneous control of rf and static gradients for inhomogeneity correction}, journal = {Journal of Chemical Physics}, volume = {131}, year = {2009}, note = {J Chem Phys536HUTimes Cited:4Cited References Count:30}, month = {Dec 21}, abstract = {

Portable NMR systems generally suffer from poor field homogeneity and are therefore used more commonly for imaging and relaxation measurements rather than for spectroscopy. In recent years, various approaches have been proposed to increase the sample volume that is usable for spectroscopy. These include approaches based on manual shimming and those based on clever combinations of modulated radio frequency and gradient fields. However, this volume remains small and, therefore, of limited utility. We present improved pulses designed to correct for inhomogeneous dispersion across wide ranges of frequency offsets without eliminating chemical shift or spatial encoding. This method, based on the adiabatic double passage, combines the relatively larger corrections available from spatially matched rf gradients [C. Meriles , J. Magn. Reson. 164, 177 (2003)]. with the adjustable corrections available from time-modulated static field gradients [D. Topgaard , Proc. Natl. Acad. Sci. U.S.A. 101, 17576 (2004)]. We explain the origins of these corrections with a theoretical model that simplifies and expedites the design of the pulse waveforms. We also present a generalized method for evaluating and comparing pulses designed for inhomogeneity correction. Experiments validate this method and support simulations that offer new possibilities for significantly enhanced performance in portable environments.

}, keywords = {design}, isbn = {0021-9606}, doi = {Doi 10.1063/1.3243850}, url = {://WOS:000273036300030}, author = {Franck, J. M. and Demas, V. and Martin, R. W. and Bouchard, L. S. and Pines, A.} } @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 {308, title = {High-resolution NMR spectroscopy with a portable single-sided sensor}, journal = {Science}, volume = {308}, year = {2005}, note = {Science931JTTimes Cited:89Cited References Count:7}, month = {May 27}, pages = {1279-1279}, keywords = {fields}, isbn = {0036-8075}, doi = {Doi 10.1126/Science.1108944}, url = {://WOS:000229482300037}, author = {Perlo, J. and Demas, V. and Casanova, F. and Meriles, C. A. and Reimer, J. and Pines, A. and Blumich, B.} } @article {310, title = {Zero- to low-field MRI with averaging of concomitant gradient fields}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {102}, year = {2005}, note = {P Natl Acad Sci USA898JKTimes Cited:18Cited References Count:22}, month = {Feb 8}, pages = {1840-1842}, abstract = {

Magnetic resonance imaging (MRI) encounters fundamental limits in circumstances in which the static magnetic field is not sufficiently strong to truncate unwanted, so-called concomitant components of the gradient field. This limitation affects the attainable optimal image fidelity and resolution most prominently in low-field imaging. in this article, we introduce the use of pulsed magnetic-field averaging toward relaxing these constraints. It is found that the image of an object can be retrieved by pulsed low fields in the presence of the full spatial variation of the imaging encoding gradient field even in the absence of the typical uniform high-field time-independent contribution. In addition, error-compensation schemes can be introduced through the application of symmetrized pulse sequences. Such schemes substantially mitigate artifacts related to evolution in strong magnetic-field gradients, magnetic fields that vary in direction and orientation, and imperfections of the applied field pulses.

}, keywords = {selection}, isbn = {0027-8424}, doi = {Doi 10.1073/Pnas.0409115102}, url = {://WOS:000227072900009}, author = {Meriles, C. A. and Sakellariou, D. and Trabesinger, A. H. and Demas, V. and Pines, A.} } @article {336, title = {Three-dimensional phase-encoded chemical shift MRI in the presence of inhomogeneous fields}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {101}, year = {2004}, note = {P Natl Acad Sci USA830EQTimes Cited:18Cited References Count:12}, month = {Jun 15}, pages = {8845-8847}, abstract = {

A pulse sequence consisting of an excitation pulse and two adiabatic full-passage pulses with scaled relative peak amplitudes is combined with phase encoding to recover chemical shift information within 3D images in a 1D inhomogeneous static magnetic field with a matched rf field gradient. The results are discussed in the context of ex situ magnetic resonance and imaging. The future directions of our research in implementing the ex situ technique in a real one-sided system are also discussed.

}, keywords = {pulses}, isbn = {0027-8424}, doi = {Doi 10.1073/Pnas.0403016101}, url = {://WOS:000222104900004}, author = {Demas, V. and Sakellariou, D. and Meriles, C. A. and Han, S. and Reimer, J. and Pines, A.} }