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Related Concept Videos

NMR Spectroscopy: Chemical Shift Overview01:15

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The position of the absorption signal of a sample is reported relative to the position of the signal of tetramethylsilane (TMS), which is added as an internal reference while recording spectra. The difference between the absorption frequencies of the sample and TMS (in Hz) is divided by the spectrometer operating frequency (in MHz) to obtain a dimensionless quantity called the chemical shift. It is reported on the δ (delta) scale and expressed in parts per million.
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¹H NMR Chemical Shift Equivalence: Enantiotopic and Diastereotopic Protons00:58

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Replacing each alpha-hydrogen in chloroethane by bromine (or a different functional group) yields a pair of enantiomers. Such protons are called prochiral or enantiotopic and are related by a mirror plane. Enantiotopic protons are chemically equivalent in an achiral environment. Because most proton NMR spectra are recorded using achiral solvents, enantiotopic hydrogens yield a single signal.
In chiral compounds such as 2-butanol, replacing the methylene hydrogens at C3 produces a pair of...
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¹H NMR: Interpreting Distorted and Overlapping Signals01:02

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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.
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Double Resonance Techniques: Overview01:12

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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...
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π Electron Effects on Chemical Shift: Overview01:27

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An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
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Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

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In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the...
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Pure Shift Nuclear Magnetic Resonance: a New Tool for Plant Metabolomics
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Chemical shift encoding using asymmetric readout waveforms.

Henric Rydén1,2, Ola Norbeck1,2, Enrico Avventi1,2

  • 1Department of Neuroradiology, Karolinska University Hospital, Stockholm, Sweden.

Magnetic Resonance in Medicine
|October 22, 2020
PubMed
Summary
This summary is machine-generated.

New asymmetric readout waveforms improve fat/water imaging by shortening scan times up to 30% or increasing signal-to-noise ratio (SNR). This method enhances chemical shift encoding for MRI applications.

Keywords:
DixonMRIchemical shift

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Medical Physics
  • Biomedical Engineering

Background:

  • Conventional MRI techniques for fat/water separation face limitations in speed and signal-to-noise ratio (SNR).
  • Optimizing chemical shift encoding is crucial for efficient and high-quality imaging.

Purpose of the Study:

  • To introduce and evaluate a novel method for chemical shift encoding using asymmetric readout waveforms.
  • To demonstrate enhanced SNR efficiency and reduced scan times in fat/water imaging.

Main Methods:

  • Asymmetric readout waveforms (triangle and spline) were developed and compared to conventional shifted trapezoid readouts.
  • The method was integrated into a fat/water separated Rapid Acquisition Relaxation Enhancement (RARE) sequence.
  • Applications in cervical spine, musculoskeletal (MSK), and optic nerve imaging at 3 Tesla were demonstrated.

Main Results:

  • Scan times were reduced by 30% with maintained SNR by eliminating dead times.
  • Shorter echo spacing led to reduced motion blurring.
  • Maintaining scan times with asymmetric waveforms resulted in improved SNR, consistent with extended sampling.

Conclusions:

  • Asymmetric readout waveforms provide greater flexibility in pulse sequence design for chemical shift encoding.
  • This technique enables significant reductions in scan time or substantial increases in SNR while maintaining scan duration.