Use Of Magnetic Field Gradients Research Articles

Discovery of magnetic resonance imaging: Paul Lauterbur and Peter Mansfield. The Nobel Prize in Physiology or Medicine 2003

The 2003 Nobel Prize in Physiology or Medicine was awarded to two researchers, Paul Lauterbur and Peter Mansfield, for their discovery of magnetic resonance imaging. This discovery enabled the creation of two-dimensional images of structures that could not be visualized by other methods. Paul Lauterbur found a way to generate two-dimensional images using magnetic field gradients. By analyzing­ the characteristics of the emitted radio waves, he could determine their origin. Peter Mansfield further developed the use of magnetic field gradients and demonstrated how the signals could be mathematically analyzed, which allowed the development of new effective imaging equipment. In modern medicine, magnetic resonance imaging is of great importance in diagnosing and finding the best treatment for many diseases. Keywords: MRI, Nobel Prize in Physiology or Medicine, Paul Lauterbur, Peter Mansfield

A novel synthetic strategy for bioinspired functionally graded nanocomposites employing magnetic field gradients

In order to mimic the complex architecture of many bio-materials and synthesize composites characterized by continuously graded composition and mechanical properties, an innovative synthetic strategy making use of magnetic field gradients and based on the motion of superparamagnetic Fe3O4@SiO2 core–shell nanoparticles is adopted. It is demonstrated that by lowering the viscosity of the system through particle functionalization, and increasing the magnetic force acting on the nanoparticles upon optimization of a simple set-up composed of two permanent magnets in repulsion configuration, the magnephoretic process can be considerably accelerated. Thus, owing to the magnetic responsiveness of the Fe3O4 core and the remarkable mechanical properties of the SiO2 shell, approximately 150 μm thick polymeric films with continuous gradients in composition and characterized by considerable increments in elastic modulus (up to ≈70%) and hardness (up to ≈150%) when going from particle-depleted to particle-enriched regions can be synthesized, even in times as short as 1 hour. The present methods are highly promising for a more efficient magnetic force-based synthesis of inhomogeneous soft materials whose composition is required to be locally tuned to meet the specific mechanical demands arising from non-uniform external loads.

Spectrally resolved flow imaging of fluids inside a microfluidic chip with ultrahigh time resolution

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 ‘slicing’ 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.

Introduction to diffusion tensor imaging mathematics: Part II. Anisotropy, diffusion‐weighting factors, and gradient encoding schemes

AbstractThe mathematical aspects of diffusion tensor magnetic resonance imaging (DTMRI, or DTI), the measurement of the diffusion tensor by magnetic resonance imaging (MRI), are discussed in this three‐part series. In part II, different formulas for measuring diffusion anisotropy are compared in two and three dimensions. The use of magnetic field gradients to measure diffusion is explained, including calculation of the diffusion‐weighting b factor. Selection of gradient directions is discussed, with the focus on directions defined by the regular polyhedra (Platonic solids). © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 123–154, 2006.

Field Gradients in Early MRI

Bertram Schwarzschild described the important contributions made by the 2003 Nobel laureates Paul Lauterbur and Peter Mansfield during the 1970s (Physics Today, December 2003, page 24). They extended magnetic resonance imaging for applications in medicine into two and three dimensions and to faster speeds. Schwarzschild refers to an article by Felix Wehrli (Physics Today, Physics Today 0031-9228 45 6 1992 34 https://doi.org/10.1063/1.881310. June 1992, page 34 ), but Wehrli makes no mention of the earlier use of magnetic field gradients and MRI during the 1950s and 1960s (see Physics Today, January 1993, page 94).Schwarzschild does mention the early use of magnetic field gradients to correlate the nuclear signal (usually proton) with spatial coordinates. He cites work by Erwin Harm and by Edward Purcell and me, 1 1. E. L. Hahn, Phys. Rev. 80, 580 (1950); https://doi.org/10.1103/PhysRev.80.580 H. Y. Carr, E. M. Purcell, Phys Rev. 94, 630 (1954). https://doi.org/10.1103/PhysRev.94.630 but that work is not directly related to internal macroscopic imaging. Hahn used existing gradients to observe diffusion, while Purcell and I intentionally applied additional gradients to study diffusion. For modern internal MRI, another component in addition to the applied gradient is necessary. Unlike for diffusion or flow studies, the object being observed must have spatially inhomogeneous internal structure. To the best of my knowledge, the first time such a field gradient was applied to a nuclear magnetic resonance (NMR) sample having an inhomogeneously distributed internal spin system was during a demonstration I conducted for my PhD thesis. 2 2. H. Y. Carr, “Free Precession Techniques in Nuclear Magnetic Resonance,” PhD thesis, Harvard U., Cambridge, MA (1952); Encyclopedia of Nuclear Magnetic Resonance, vol. 1, Wiley and Sons, Hoboken, NJ (1996), p. 253. My motivation in that demonstration was to help faculty and other graduate students understand the recently discovered and rather complicated NMR fine structure in ethyl alcohol. A special object, built for the demonstration, consisted initially of two and later three small separated groups of protons having numbers of protons in the ratios of 3:2:1. The groups were placed in a straight line parallel to the direction of the magnetic field gradient. Thus that first MRI image or spin map was one-dimensional. Although medical applications for 1D imaging are very few, in physics there are several; the most notable was in the discovery of superfluid helium-3. The 1952 demonstration used the new and faster pulsed NMR technique 3 3. D. D. Stark, W. G. Bradley, Magnetic Resonance Imaging, C. V. Mosby, St. Louis, MO (1988), p. 9. rather than the simpler and slower continuous-wave frequency (or field) sweep technique. 4 4. C. Leon Partain et al. , Nuclear Magnetic Resonance (NMR) Imaging, W. B. Saunders, Philadelphia (1983), chap. 17. The visual observation of the three separated groups of protons provided confidence in the pulsed MRI technique with its spatial image coming from the Fourier transform of the complicated time-dependent free-induction decay. That first MRI demonstration was not reported in the 1954 paper, which concentrated on the basic techniques of the new pulsed NMR used with internally homogeneous samples. Other topics, including gradient echoes, electric shims, and the spinning of the samples to obtain narrower lines for observing very fine structure, were left for later papers.My thesis received significant distribution. In particular, Nuclear Magnetic Resonance Specialties near Pittsburgh, Pennsylvania, where Lauterbur and Raymond Damadian did their initial MRI work, received a copy in 1967. Shortly thereafter, the president of the company requested additional copies for some of the purchasers of the company’s pulsed NMR spectrometers.REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. E. L. Hahn, Phys. Rev. 80, 580 (1950); https://doi.org/10.1103/PhysRev.80.580 , Google ScholarCrossref, ISI H. Y. Carr, E. M. Purcell, Phys Rev. 94, 630 (1954). https://doi.org/10.1103/PhysRev.94.630 , , Google ScholarCrossref, ISI2. H. Y. Carr, “Free Precession Techniques in Nuclear Magnetic Resonance,” PhD thesis, Harvard U., Cambridge, MA (1952); Google Scholar Encyclopedia of Nuclear Magnetic Resonance, vol. 1, Wiley and Sons, Hoboken, NJ (1996), p. 253. Google Scholar3. D. D. Stark, W. G. Bradley, Magnetic Resonance Imaging, C. V. Mosby, St. Louis, MO (1988), p. 9. Google Scholar4. C. Leon Partain et al. , Nuclear Magnetic Resonance (NMR) Imaging, W. B. Saunders, Philadelphia (1983), chap. 17. Google Scholar© 2004 American Institute of Physics.

The 2003 Nobel Prize for MRI: significance and impact.

The 2003 Nobel Prize for MRI: significance and impact.

An NMR technique for measurement of magnetic field gradient waveforms

Almost all NMR imaging and localized spectroscopic methods fundamentally rely on the use of magnetic field gradients. It follows that precise information on gradient waveform shape and rise-times is often most useful in experimental MRI. We present a very simple and robust method for measuring the time evolution of a magnetic field gradient. The method is based on the analysis of the NMR signal in the time domain, and requires no specialized field measurement probes for its implementation. The technique makes use of the principal that for small flip angles the excitation profile is a good approximation to the Fourier transform of the radio frequency pulse shape. Creation of the NMR signal can be considered as an inverse Fourier transform and thus variation of the gradient strength during the excitation pulse influences the shape of the NMR signal. Although originally designed for measurement of the rise time only, we have now extended the technique to measure the exact time course of the gradient. The theory is confirmed by experimental results for gradient waveform field measurements in a high-field vertical bore system.

Motion correction in MRI using an apparatus for dynamic angular position tracking (ADAPT).

Motion during MRI examinations is a serious problem that degrades the quality of the data (images) acquired. Motion can be corrected during the postprocessing of the data; however, this approach is suboptimal and is typically limited to in-plane or translational motion. An apparatus for dynamic angular position tracking (ADAPT) for prospective angular motion correction has been developed. This application is capable of "tracking" the scanned region of interest by performing dynamic adjustments of orientation of the scanning plane. The operation of the apparatus is based on deuterium MR spectroscopy and does not rely on the use of magnetic field gradients. Orientation-sensitive deuterium quadrupolar interaction in a single crystal attached to a subject is used to monitor the angular position in magnetic fields. Measurements are performed with an independent spectrometer channel in the background of the MRI scans. This apparatus is very cost- and time-efficient because it utilizes the hardware already available on many spectrometers and can be used in parallel with MRI scans. Potentially, rotations by a fraction of one degree can be easily corrected and the angular position information can be rapidly updated.

Functional magnetic resonance imaging with intermolecular multiple-quantum coherences

For the first time, we demonstrate here functional magnetic resonance imaging (fMRI) using intermolecular multiple-quantum coherences (iMQCs). iMQCs are normally not observed in liquid-state NMR because dipolar interactions between spins average to zero. If the magnetic isotropy of the sample is broken through the use of magnetic field gradients, dipolar couplings can reappear, and hence iMQCs can be observed. Conventional (BOLD) fMRI measures susceptibility variations averaged over each voxel. In the experiment performed here, the sensitivity of iMQCs to frequency variations over mesoscopic and well-defined distances is exploited. We show that iMQC contrast is qualitatively and quantitatively different from BOLD contrast in a visual stimulation task. While the number of activated pixels is smaller in iMQC contrast, the intensity change in some pixels exceeds that of BOLD contrast severalfold.

Triple resonance isotope-edited (TRIED): a powerful new NMR technique for studying metabolism

A powerful new technique for studying metabolism, Triple-Resonance Isotope-Edited (TRIED) NMR, is described and demonstrated experimentally. The experiment uses through-bond (scalar) coupling between spins to select NMR signals from molecules having 1 H- 13 C- 15 N labeled triples. Natural-abundance background signal from molecules not containing such labeled triples (e.g., signal from 1 H- 12 C and 1 H- 13 C fragments) is effectively suppressed, with a suppression ratio of approximately 10 4 :1. This effective filtering of signal from labeled molecules allows these species and their metabolites to be detected and characterized without requiring extensive, time-consuming sample purification. Results are presented for 13 C, 15 N-aminomethylphosphonate (AMPA) in soybean and pigweed plant matrices. The potential use of TRIED for studying the pharmacokinetics of drugs and extension of the experiment to include the use of magnetic-field gradients for selecting signal from labeled fragments are also described.

Elimination of high-flux signals near surface coils and field gradient sample localization using depth pulses

The previously described depth pulse sequences, 2 θ; θ[± x]; (2 θ;[± x, ± y]) n ; acquire signal (M. R. Bendall and R. E. Gordon, J. Magn. Reson. 53, 365 (1983)) for use in in vivo spectroscopy discriminate against sample regions where the sequence pulse angle, Φ, differs markedly from mπ 2 ( m an odd integer). It is shown theoretically and experimentally that high-flux signals close to the coil wire where θ; is close to 270 or 450°, may be eliminated efficiently by varying the θ; pulse length relative to the 2θ; pulse length in the depth pulses. The generality of use of depth pulses is further extended by showing experimentally that at low pulse power the depth pulses are cleanly selective with respect to chemical shift. This selectivity is improved by use of a spin-locked period subsequent to the depth pulses but prior to signal acquisition, and may be converted to spatial selectivity by applying the depth pulses in the presence of a magnetic field gradient. Application of the spin-locking field enables the field gradient to be switched off and a fully localized high-resolution spectrum may be acquired. The elimination of high-flux signals and/or the use of magnetic field gradients, in relation to various known and prospective methods for complete sample localization, is discussed.

Application of zeugmatography to study kinetics of physical adsorption

Spatial resolution of nuclear magnetic resonance signals may be achieved by use of magnetic field gradients. This new technique, called “zeugmatography”, has been applied in the present work to study dynamic processes, especially the kinetics of physical adsorption in microporous systems. The method provides information similar to the results of Dubinin's X-ray technique, but is not limited to X-ray contrast adsorbates. After a general discussion, examples of application of “dynamic zeugmatography” are given. Mass transfer for sorption of butane in NaCa A zeolites of different shape and of water in Na X zeolites could be observed directly.