%0 Journal Article %J Journal of Magnetic Resonance %D 2005 %T NMR detection using laser-polarized xenon as a dipolar sensor %A Granwehr, J. %A Urban, J. T. %A Trabesinger, A. H. %A Pines, A. %K dynamics %X

Hyperpolarized Xe-129 can be used as a sensor to indirectly detect NMR spectra of heteronuclei that are neither covalently bound nor necessarily in direct contact with the Xe atoms, but coupled through long-range intermolecular dipole-dipole interactions. To reintroduce long-range dipolar couplings the sample symmetry has to be broken. This can be done either by using an asymmetric sample arrangement, or by breaking the symmetry of the spin magnetization with field gradient pulses. Experiments are performed where only a small fraction of the available Xe-129 magnetization is used for each point, so that a single batch of xenon suffices for the point-by-point acquisition of a heteronuclear NMR spectrum. Examples with H-1 as the analyte nucleus show that these methods have the potential to obtain spectra with a resolution that is high enough to determine homonuclear J couplings. The applicability of this technique with remote detection is discussed. Published by Elsevier Inc.

%B Journal of Magnetic Resonance %V 176 %P 125-139 %8 Oct %@ 1090-7807 %G English %U ://WOS:000232425800001 %N 2 %M WOS:000232425800001 %! NMR detection using laser-polarized xenon as a dipolar sensor %R Doi 10.1016/J.Jmr.2005.05.013 %0 Journal Article %J Magnetic Resonance in Medicine %D 2005 %T SQUID-detected MRI at 132 mu T with T(1)-weighted contrast established at 10 mu T-300 mT %A Lee, S. K. %A Mossle, M. %A Myers, W. %A Kelso, N. %A Trabesinger, A. H. %A Pines, A. %A Clarke, J. %K dispersion %X

T(1)-weighted contrast MRI with prepolarization was detected with a superconducting quantum interference device (SQUID). A spin evolution period in a variable field between prepolarization and detection enabled the measurement of T(1) in fields between 1.7 muT and 300 mT; T, dispersion curves of agarose gel samples over five decades in frequency were obtained. SQUID detection at 5.6 kHz drastically reduces the field homogeneity requirements compared to conventional field-cycling methods using Faraday coil detection. This allows T(1) dispersion measurements to be easily combined with MRI, so that T(1) in a wide range of fields can be used for tissue contrast. Images of gel phantoms with T(1)-weighted contrast at four different fields between 10 muT and 300 mT demonstrated dramatic contrast enhancement in low fields. A modified inversion recovery technique further enhanced the contrast by selectively suppressing the signal contribution for a specific value of the low-field T(1). Published 2004 Wiley-Liss, Inc.

%B Magnetic Resonance in Medicine %V 53 %P 9-14 %8 Jan %@ 0740-3194 %G English %U ://WOS:000226380700003 %N 1 %M WOS:000226380700003 %! SQUID-detected MRI at 132 mu T with T(1)-weighted contrast established at 10 mu T-300 mT %R Doi 10.1002/Mrm.20316 %0 Journal Article %J Proceedings of the National Academy of Sciences of the United States of America %D 2005 %T Zero- to low-field MRI with averaging of concomitant gradient fields %A Meriles, C. A. %A Sakellariou, D. %A Trabesinger, A. H. %A Demas, V. %A Pines, A. %K selection %X

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.

%B Proceedings of the National Academy of Sciences of the United States of America %V 102 %P 1840-1842 %8 Feb 8 %@ 0027-8424 %G English %U ://WOS:000227072900009 %N 6 %M WOS:000227072900009 %! Zero- to low-field MRI with averaging of concomitant gradient fields %R Doi 10.1073/Pnas.0409115102 %0 Journal Article %J Physical Review Letters %D 2004 %T Hyperpolarized xenon nuclear spins detected by optical atomic magnetometry %A Yashchuk, V. V. %A Granwehr, J. %A Kimball, D. F. %A Rochester, S. M. %A Trabesinger, A. H. %A Urban, J. T. %A Budker, D. %A Pines, A. %K mri %X

We report the use of an atomic magnetometer based on nonlinear magneto-optical rotation with frequency-modulated light to detect nuclear magnetization of xenon gas. The magnetization of a spin-exchange-polarized xenon sample (1.7 cm(3) at a pressure of 5 bars, natural isotopic abundance, polarization 1%), prepared remotely to the detection apparatus, is measured with an atomic sensor. An average magnetic field of similar to10 nG induced by the xenon sample on the 10 cm diameter atomic sensor is detected with signal-to-noise ratio similar to10, limited by residual noise in the magnetic environment. The possibility of using modern atomic magnetometers as detectors of nuclear magnetic resonance and in magnetic resonance imaging is discussed. Atomic magnetometers appear to be ideally suited for emerging low-field and remote-detection magnetic resonance applications.

%B Physical Review Letters %V 93 %8 Oct 15 %@ 0031-9007 %G English %U ://WOS:000224533300012 %N 16 %M WOS:000224533300012 %! Hyperpolarized xenon nuclear spins detected by optical atomic magnetometry %R Doi 10.1103/Physrevlett.93.160801 %0 Journal Article %J Proceedings of the National Academy of Sciences of the United States of America %D 2004 %T Microtesla MRI with a superconducting quantum interference device %A McDermott, R. %A Lee, S. K. %A ten Haken, B. %A Trabesinger, A. H. %A Pines, A. %A Clarke, J. %K system %X

MRI scanners enable fast, noninvasive, and high-resolution imaging of organs and soft tissue. The images are reconstructed from NMR signals generated by nuclear spins that precess in a static magnetic field B(0) in the presence of magnetic field gradients. Most clinical MRI scanners operate at a magnetic field B(0) = 1.5 T, corresponding to a proton resonance frequency of 64 MHz. Because these systems rely on large superconducting magnets, they are costly and demanding of infrastructure. On the other hand, low-field imagers have the potential to be less expensive, less confining, and more mobile. The major obstacle is the intrinsically low sensitivity of the low-field NMR experiment. Here, we show that prepolarization of the nuclear spins and detection with a superconducting quantum interference device (SQUID) yield a signal that is independent of B(0), allowing acquisition of high-resolution MRIs in microtesla fields. Reduction of the strength of the measurement field eliminates inhomogeneous broadening of the NMR lines, resulting in enhanced signal-to-noise ratio and spatial resolution for a fixed strength of the magnetic field gradients used to encode the image. We present high-resolution images of phantoms and other samples and T(1)-weighted contrast images acquired in highly inhomogeneous magnetic fields of 132 muT; here, T, is the spin-lattice relaxation time. These techniques could readily be adapted to existing multichannel SQUID systems used for magnetic source imaging of brain signals. Further potential applications include low-cost systems for tumor screening and imaging peripheral regions of the body.

%B Proceedings of the National Academy of Sciences of the United States of America %V 101 %P 7857-7861 %8 May 25 %@ 0027-8424 %G English %U ://WOS:000221652000005 %N 21 %M WOS:000221652000005 %! Microtesla MRI with a superconducting quantum interference device %R Doi 10.1073/Pnas.0402382101 %0 Journal Article %J Journal of Physical Chemistry A %D 2004 %T SQUID-detected liquid state NMR in microtesla fields %A Trabesinger, A. H. %A McDermott, R. %A Lee, S. K. %A Mück, M. %A Clarke, J. %A Pines, A. %K water %X

Nuclear magnetic resonance (NMR) experiments performed in magnetic fields on the order of microtesla yield line widths comparable to the lifetime limit even in grossly inhomogeneous magnets. The potential loss in sensitivity is overcome by combining prepolarization in fields on the order of millitesla and signal detection with a Superconducting Quantum Interference Device (SQUID). The enhanced spectral resolution attainable in microtesla fields enables NMR studies of pure liquids and solutions without the need for strong magnets. We have investigated a variety of heteronuclear systems in both the weak and strong J-coupling regimes. Six different nuclear species have been detected with the same experimental apparatus. NMR signals of thermally polarized protons were obtained in fields as low as 554 nT.

%B Journal of Physical Chemistry A %V 108 %P 957-963 %8 Feb 12 %@ 1089-5639 %G English %U ://WOS:000188831500005 %N 6 %M WOS:000188831500005 %! SQUID-detected liquid state NMR in microtesla fields %R Doi 10.1021/Jp035181g %0 Journal Article %J Journal of Low Temperature Physics %D 2004 %T SQUID-detected magnetic resonance imaging in microtesla magnetic fields %A McDermott, R. %A Kelso, N. %A Lee, S. K. %A Mossle, M. %A Mück, M. %A Myers, W. %A ten Haken, B. %A Seton, H. C. %A Trabesinger, A. H. %A Pines, A. %A Clarke, J. %K mri %X

We describe studies of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) of liquid samples at room temperature in microtesla magnetic fields. The nuclear spins are prepolarized in a strong transient field. The magnetic signals generated by the precessing spins, which range in frequency from tens of Hz to several kHz, are detected by a low-transition temperature dc SQUID (Superconducting QUantum Interference Device) coupled to an untuned, superconducting flux transformer configured as an axial gradiometer. The combination of prepolarization and frequency-independent detector sensitivity results in a high signal-to-noise ratio and high spectral resolution (similar to 1 Hz) even in grossly inhomogeneous magnetic fields. In the NMR experiments, the high spectral resolution enables us to detect the 10-Hz splitting of the spectrum of protons due to their scalar coupling to a P-31 nucleus. Furthermore, the broadband detection scheme combined with a non-resonant field-reversal spin echo allows the simultaneous observation of signals from protons and P-31 nuclei, even though their NMR resonance frequencies differ by a factor of 2.5. We extend our methodology to MRI in microtesla fields, where the high spectral resolution translates into high spatial resolution. We demonstrate two-dimensional images of a mineral oil phantom and slices of peppers, with a spatial resolution of about 1 mm. We also image an intact pepper using slice selection, again with 1-mm, resolution. A further experiments we demonstrate T-1-contrast imaging of a water phantom, some parts of which were doped with a paramagnetic salt to reduce the longitudinal relaxation time T-1. Possible applications of this MRI technique include screening for tumors and integration with existing multichannel SQUID systems for brain imaging.

%B Journal of Low Temperature Physics %V 135 %P 793-821 %8 Jun %@ 0022-2291 %G English %U ://WOS:000221710600023 %N 5-6 %M WOS:000221710600023 %! SQUID-detected magnetic resonance imaging in microtesla magnetic fields %R Doi 10.1023/B:Jolt.0000029519.09286.C5 %0 Journal Article %J Science %D 2002 %T Liquid-state NMR and scalar couplings in microtesla magnetic fields %A McDermott, R. %A Trabesinger, A. H. %A Mück, M. %A Hahn, E. L. %A Pines, A. %A Clarke, J. %K resonance %X

We obtained nuclear magnetic resonance (NMR) spectra of liquids in fields of a few microtesla, using prepolarization in fields of a few millitesta and detection with a dc superconducting quantum interference device (SQUID). Because the sensitivity of the SQUID is frequency independent, we enhanced both signal-to-noise ratio and spectral resolution by detecting the NMR signal in extremely tow magnetic fields, where the NMR tines become very narrow even for grossly inhomogeneous measurement fields. In the absence of chemical shifts, proton-phosphorous scalar (J) couplings have been detected, indicating the presence of specific covalent bonds. This observation opens the possibility for "pure J spectroscopy" as a diagnostic tool, for the detection of molecules in low magnetic fields.

%B Science %V 295 %P 2247-2249 %8 Mar 22 %@ 0036-8075 %G English %U ://WOS:000174561700039 %N 5563 %M WOS:000174561700039 %! Liquid-state NMR and scalar couplings in microtesla magnetic fields %R Doi 10.1126/Science.1069280