Echoes and imaging in solids

1990 ◽  
Vol 333 (1632) ◽  
pp. 427-439 ◽  
Keyword(s):  
Spin Echo ◽  
Three Dimensional ◽  
Two Dimensions ◽  
Spectral Lines ◽  
Line Broadening ◽  
Rf Pulses ◽  
Field Gradients ◽  
Magnetic Field Gradients ◽  
Bandwidth Limitation ◽  
Successful Approach

The broad spectral lines usually encountered in solid state NMR present considerable difficulties for imaging. One successful approach to the problem is to artificially narrow the line by multipulse or sample spinning methods. An alternative is to apply sufficiently large magnetic field gradients that they dominate the line broadening and seek ways to deal with bandwidth and power requirements thereby introduced. This paper explores the second route and demonstrates that spin-echo techniques help to solve several of the inherent problems. Gradient echoes produced by periodic reversal of the field gradients have significant advantages. The addition of synchronous RF pulses can produce an extended train of ‘solid’ echoes which overcomes, at least to some extent, the bandwidth limitation of this approach and permits rapid imaging in two dimensions. Slice selection and three-dimensional back projection have also been achieved in solid-like samples. Comparison with linenarrowing methods and relative advantages of the different approaches are addressed.

MAGNETIC FORCE MICROMANIPULATION SYSTEMS FOR THE BIOLOGICAL SCIENCES

NANO ◽  
2006 ◽  
Vol 01 (03) ◽  
pp. 191-205 ◽  
Author(s):  
J. K. FISHER ◽  
L. VICCI ◽  
J. CRIBB ◽  
E. T. O'BRIEN ◽  
R. M. TAYLOR ◽  
...  
Keyword(s):  
Biological Sciences ◽  
Magnetic Field ◽  
High Frequency ◽  
Magnetic Force ◽  
Force Feedback ◽  
Large Range ◽  
Three Dimensional ◽  
Design Considerations ◽  
Field Gradients ◽  
Magnetic Field Gradients

Manipulation systems using magnetic field gradients have the ability to apply a large range of forces noninvasively to a specific target. Depending on the requirements of a given experiment, the systems may be as simple as a single electromagnet for unidirectional manipulation or as complex as a high-frequency three-dimensional manipulator with force feedback. Here, we discuss the motivation for developing such systems, theory and design considerations, and give examples of the broad range of manipulators that has been put to use. In addition, we discuss a variety of applications demonstrating the range of experiments for which such a system is applicable.

scholarly journals Simulated basis sets for semi-LASER: the impact of including shaped RF pulses and magnetic field gradients

2020 ◽  
Author(s):  
Oscar Jalnefjord ◽  
Patrick Pettersson ◽  
Lukas Lundholm ◽  
Maria Ljungberg
Keyword(s):  
Magnetic Field ◽  
Pulse Sequence ◽  
Basis Sets ◽  
Rf Pulses ◽  
Strongly Coupled ◽  
In Vivo Measurements ◽  
Field Gradients ◽  
Magnetic Field Gradients ◽  
Metabolite Quantification

Abstract Objective To study the need for inclusion of shaped RF pulses and magnetic field gradients in simulations of basis sets for the analysis of proton MR spectra of single voxels of the brain acquired with a semi-LASER pulse sequence. Materials and methods MRS basis sets where simulated at different echo times with hard RF pulses as well as with shaped RF pulses without or with magnetic field gradients included. The influence on metabolite concentration quantification was assessed using both phantom and in vivo measurements. For comparison, simulations and measurements were performed with the PRESS pulse sequence. Results The effect of including gradients in the simulations was smaller for semi-LASER than for PRESS, however, still noticeable. The difference was larger for strongly coupled metabolites and at longer echo times. Metabolite quantification using semi-LASER was thereby less dependent on the inclusion of gradients than PRESS, which was seen in both phantom and in vivo measurements. Discussion The inclusion of the shaped RF pulses and magnetic field gradients in the simulation of basis sets for semi-LASER is only important for strongly coupled metabolites. If computational time is a limiting factor, simple simulations with hard RF pulses can provide almost as accurate metabolite quantification as those that include the chemical-shift related displacement.

Magnetically Actuable Scaffolds for Tissue Regeneration

2008 ◽  
Author(s):  
Julia J. Mack ◽  
Abigail A. Corrin ◽  
Sergio L. dos Santos e Lucato ◽  
Brian N. Cox ◽  
Jennifer S. Andrew ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Tissue Engineering ◽  
Magnetic Fields ◽  
Tissue Regeneration ◽  
Three Dimensional ◽  
Functionalized Polymers ◽  
Polymer Scaffolds ◽  
Biocompatible Polymer ◽  
Field Gradients ◽  
Magnetic Field Gradients

Presented here are methods to fabricate magnetically modified biocompatible polymer scaffolds, which can be actuated by remotely applied magnetic fields. The magnitude of the actuation is shown to be biologically useful by simple tests in known magnetic fields and magnetic field gradients. Methods of processing the functionalized polymers into three-dimensional scaffolds have been demonstrated, suggesting wide applicability in tissue engineering.

Spin Echo Self-Diffusion Measurements in Molten Salts

1988 ◽  
Vol 43 (12) ◽  
pp. 1075-1082 ◽  
Author(s):  
C. Herdlicka ◽  
J. Richter ◽  
M. D. Zeidler
Keyword(s):  
Magnetic Field ◽  
Diffusion Coefficients ◽  
Molten Salts ◽  
Spin Echo ◽  
Pulsed Magnetic Field ◽  
Self Diffusion ◽  
Field Gradients ◽  
Magnetic Field Gradients ◽  
Spin Echo Technique ◽  
Probe Head

An NMR probe head for diffusion measurements in molten salts at temperatures up to 673 K is described. The spin echo technique using pulsed magnetic field gradients was employed. Resulting self-diffusion coefficients of Na+ in molten NaNO3 in the temperature range 596-670 K are compa­red with literature data obtained by other methods.

Temperature and Pressure Dependence of Self Diffusion in Octamethylcyclotetrasiloxane and Hexamethylcyclotrisilazane

1990 ◽  
Vol 45 (11-12) ◽  
pp. 1281-1284 ◽  
Author(s):  
A. Greiner-Schmid ◽  
M. Has ◽  
H.-D. Lüdemann
Keyword(s):  
Magnetic Field ◽  
Pressure Dependence ◽  
Spin Echo ◽  
The Self ◽  
Self Diffusion ◽  
Field Gradients ◽  
Magnetic Field Gradients ◽  
Temperature And Pressure ◽  
Spin Echo Technique ◽  
Self Diffusion Coefficient

AbstractThe pressure dependence of the self diffusion coefficient D for octamethylcyclotetrasiloxane and hexamethylcyclotrisilazane has been determined by the NMR spin echo technique with pulsed magnetic field gradients at pressures up to 200 MPa and at temperatures between 490 K and 290 K. The data extend partially into the deeply supercooled range. The isobaric temperature dependence of these data is quantitatively described by the empirical Vogel-Fulcher-Tammann equation. For both substances the melting pressure curves were determined in addition.

scholarly journals The Approach to Steady State Using Homogeneous and Cartesian Coordinates

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
D. F. Gochberg ◽  
Z. Ding
Keyword(s):  
Steady State ◽  
Arbitrary Sequence ◽  
Resonance System ◽  
Rf Pulses ◽  
Steady State Condition ◽  
Homogeneous Coordinates ◽  
Field Gradients ◽  
Magnetic Field Gradients ◽  
Cartesian Coordinate ◽  
Approach To Steady State

Repeating an arbitrary sequence of RF pulses and magnetic field gradients will eventually lead to a steady-state condition in any magnetic resonance system. While numerical methods can quantify this trajectory, analytic analysis provides significantly more insight and a means for faster calculation. Recently, an analytic analysis using homogeneous coordinates was published. The current work further develops this line of thought and compares the relative merits of using a homogeneous or a Cartesian coordinate system.

Laser Scanning Confocal Microscopy and Three-Dimesnsional Reconstruction of the Mitotic Spindles of Unequally Dividing Embryonic Cells

1990 ◽  
Vol 48 (3) ◽  
pp. 166-167
Author(s):  
J. Holy ◽  
G. Schatten
Keyword(s):  
Confocal Microscopy ◽  
Mitotic Spindle ◽  
Laser Scanning ◽  
Three Dimensional ◽  
Laser Scanning Confocal Microscopy ◽  
Two Dimensions ◽  
Embryonic Cells ◽  
Mitotic Spindles ◽  
Cleavage Division ◽  
Scanning Confocal Microscopy

One of the classic limitations of light microscopy has been the fact that three dimensional biological events could only be visualized in two dimensions. Recently, this shortcoming has been overcome by combining the technologies of laser scanning confocal microscopy (LSCM) and computer processing of microscopical data by volume rendering methods. We have employed these techniques to examine morphogenetic events characterizing early development of sea urchin embryos. Specifically, the fourth cleavage division was examined because it is at this point that the first morphological signs of cell differentiation appear, manifested in the production of macromeres and micromeres by unequally dividing vegetal blastomeres.The mitotic spindle within vegetal blastomeres undergoing unequal cleavage are highly polarized and develop specialized, flattened asters toward the micromere pole. In order to reconstruct the three-dimensional features of these spindles, both isolated spindles and intact, extracted embryos were fluorescently labeled with antibodies directed against either centrosomes or tubulin.

Nuclear magnetic resonance microscopy

1989 ◽  
Vol 47 ◽  
pp. 828-829
Author(s):  
Paul C. Lauterbur
Keyword(s):  
Magnetic Field ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Fields ◽  
Signal To Noise ◽  
Field Gradients ◽  
Useful Signal ◽  
Magnetic Field Gradients ◽  
Observation Times ◽  
Nuclear Magnetic

Nuclear magnetic resonance imaging can reach microscopic resolution, as was noted many years ago, but the first serious attempt to explore the limits of the possibilities was made by Hedges. Resolution is ultimately limited under most circumstances by the signal-to-noise ratio, which is greater for small radio receiver coils, high magnetic fields and long observation times. The strongest signals in biological applications are obtained from water protons; for the usual magnetic fields used in NMR experiments (2-14 tesla), receiver coils of one to several millimeters in diameter, and observation times of a number of minutes, the volume resolution will be limited to a few hundred or thousand cubic micrometers. The proportions of voxels may be freely chosen within wide limits by varying the details of the imaging procedure. For isotropic resolution, therefore, objects of the order of (10μm) may be distinguished.Because the spatial coordinates are encoded by magnetic field gradients, the NMR resonance frequency differences, which determine the potential spatial resolution, may be made very large. As noted above, however, the corresponding volumes may become too small to give useful signal-to-noise ratios. In the presence of magnetic field gradients there will also be a loss of signal strength and resolution because molecular diffusion causes the coherence of the NMR signal to decay more rapidly than it otherwise would. This phenomenon is especially important in microscopic imaging.

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