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Related Concept Videos

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...
¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers energy to a nearby...
¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)01:20

¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)

When proton-coupled carbon-13 spectra are simplified by a broadband proton decoupling technique, structural information about the coupled protons is lost. Distortionless enhancement by polarization transfer (DEPT) is a technique that provides information on the number of hydrogens attached to each carbon in a molecule. While the DEPT experiment utilizes complex pulse sequences, the pulse delay and flip angle are specifically manipulated. The resulting signals have different phases depending on...
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...

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Meso-Scale Particle Image Velocimetry Studies of Neurovascular Flows In Vitro
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Published on: December 3, 2018

Bloch simulations with intra-voxel spin dephasing.

Peter Latta1, Marco L H Gruwel, Vladimír Jellús

  • 1Institute for Biodiagnostics, National Research Council of Canada, 435 Ellice Avenue, Winnipeg, Manitoba, Canada. peter.latta@nrc-cnrc.gc.ca

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|December 22, 2009
PubMed
Summary

Simulations of Magnetic Resonance Imaging (MRI) experiments often yield inaccurate signals due to a limited number of isochromats. This study introduces a novel method using four isochromats per voxel to significantly improve simulation accuracy.

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Computational Physics
  • Nuclear Magnetic Resonance (NMR) Spectroscopy

Background:

  • Numerical simulations of Bloch equations in MRI are crucial for predicting experimental outcomes.
  • A common limitation is the use of a finite number of isochromats, leading to signal artifacts and discrepancies.
  • These inaccuracies hinder the precise interpretation of MRI data.

Purpose of the Study:

  • To address the issue of spurious signals in Bloch equation simulations.
  • To propose and validate a new method for representing sample voxels in MRI simulations.
  • To enhance the precision and reliability of calculated NMR signals.

Main Methods:

  • Developed a technique representing each voxel with a central isochromat and three additional, orthogonally shifted isochromats.
  • This approach approximates intra-voxel dephasing linearly.
  • Algorithm details and simulation examples are provided to demonstrate efficacy.

Main Results:

  • The proposed four-isochromat method significantly reduces artifacts caused by a finite isochromat set.
  • Achieved improved precision in calculated NMR signals compared to standard methods.
  • Simulations confirmed the efficiency and effectiveness of the new technique.

Conclusions:

  • The novel four-isochromat approach offers a substantial improvement for Bloch equation simulations in MRI.
  • This method virtually eliminates problems associated with a finite number of isochromats.
  • It enhances the accuracy of NMR signal calculations, leading to more reliable MRI data interpretation.