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Related Concept Videos

Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
Magnetic Damping01:17

Magnetic Damping

Eddy currents can produce significant drag on motion, called magnetic damping. For instance, when a metallic pendulum bob swings between the poles of a strong magnet, significant drag acts on the bob as it enters and leaves the field, quickly damping the motion.
If, however, the bob is a slotted metal plate, the magnet produces a much smaller effect. When a slotted metal plate enters the field, an emf is induced by the change in flux; however, it is less effective because the slots limit the...
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Eddy Currents01:25

Eddy Currents

Since eddy currents occur only in conductors, magnets can separate metals from other materials. For example, in a recycling center, trash is dumped in batches down a ramp, beneath which lies a powerful magnet. Conductors in the trash are slowed by eddy currents, while nonmetals in the trash move on, separating from the metals. This works for all metals, not just ferromagnetic ones.
Other major applications of eddy currents appear in metal detectors and the braking systems of trains and roller...
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
Nuclear Overhauser Enhancement (NOE)01:06

Nuclear Overhauser Enhancement (NOE)

Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling. This phenomenon, called the nuclear Overhauser enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring spin-active...

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Related Experiment Video

Updated: Jun 17, 2026

In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging
06:34

In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging

Published on: September 2, 2016

Double-spin-echo diffusion weighting with a modified eddy current adjustment.

Jürgen Finsterbusch1

  • 1Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany. j.finsterbusch@uke.uni-hamburg.de

Magnetic Resonance Imaging
|January 15, 2010
PubMed
Summary
This summary is machine-generated.

Eddy currents in echo-planar imaging cause geometric distortions, affecting diffusion imaging. A new method independently adjusts gradient pairs to reduce these distortions, improving diffusion-weighted imaging reliability.

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Area of Science:

  • Magnetic Resonance Imaging
  • Diffusion-Weighted Imaging

Background:

  • Magnetic field inhomogeneities, particularly eddy currents, induce geometric distortions in echo-planar imaging (EPI).
  • These distortions are problematic for diffusion-weighted imaging (DWI), as they vary with diffusion weighting direction and impede accurate diffusion parameter calculation.
  • Current double-spin-echo preparation methods partially mitigate eddy current effects but may not address all time constants, leaving residual distortions.

Purpose of the Study:

  • To propose and evaluate a modified double-spin-echo preparation technique for reducing eddy current-induced geometric distortions in DWI.
  • To investigate the efficacy of independently adjusting the two bipolar gradient pairs in the preparation sequence to different time constants.

Main Methods:

  • A modified double-spin-echo preparation sequence was developed where bipolar gradient pairs are adjusted independently to distinct eddy current time constants.
  • The proposed method was tested using phantom experiments and in vivo human brain imaging.
  • Geometric distortions and diffusion anisotropy values were assessed.

Main Results:

  • The modified preparation successfully reduced residual geometric distortions in echo-planar imaging.
  • Correspondingly, increased values of diffusion anisotropy, often caused by distortions, were reduced.
  • These improvements were observed in both phantom and human brain data.

Conclusions:

  • Independent adjustment of bipolar gradient pairs in the double-spin-echo preparation can effectively minimize residual eddy current effects.
  • This technique offers a means to enhance the accuracy and reliability of diffusion-weighted echo-planar imaging.
  • The proposed method shows promise for improving quantitative diffusion MRI analysis.