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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...
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
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...
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...
NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

A pulse is a short burst of radio waves distributed over a range of frequencies that simultaneously excites all the nuclei in the sample. Upon passing a radio frequency pulse along the x-axis, the nuclei absorb energy corresponding to their Larmor frequencies and achieve resonance. This shifts the net magnetization vector from the z-axis toward the transverse plane. This angle of rotation of the magnetization vector, or the flip angle, is proportional to the duration and intensity of the pulse.
¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.

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Related Experiment Video

Updated: Jul 9, 2026

Measuring Interactions of Globular and Filamentous Proteins by Nuclear Magnetic Resonance Spectroscopy (NMR) and Microscale Thermophoresis (MST)
10:28

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Echo combination to reduce proton resonance frequency (PRF) thermometry errors from fat.

Viola Rieke1, Kim Butts Pauly

  • 1Department of Radiology, Stanford University, Stanford, CA 94305-5488, USA. vrieke@stanford.edu

Journal of Magnetic Resonance Imaging : JMRI
|December 8, 2007
PubMed
Summary

Echo combination significantly reduces temperature measurement errors from fat using the proton resonance frequency (PRF) shift method. This technique eliminates the need for fat suppression in MRI, improving accuracy in tissues like the liver.

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Area of Science:

  • Medical Imaging
  • Biophysics
  • Magnetic Resonance Imaging

Background:

  • Fat presence introduces significant errors in temperature measurements using the proton resonance frequency (PRF) shift method.
  • Accurate temperature monitoring is crucial for various medical applications, including thermal therapies.

Purpose of the Study:

  • To validate echo combination as a method to mitigate fat-induced errors in PRF shift temperature measurements.
  • To assess the effectiveness of echo combination in improving temperature measurement accuracy in the presence of fat.

Main Methods:

  • Computer simulations and MR experiments were conducted to analyze temperature errors as a function of echo time.
  • Temperature images were reconstructed using the PRF shift method and combined via a weighted average from multiple echo times.
  • Errors in combined images were compared to individual echo images in water and fat-containing phantoms.

Main Results:

  • Fat presence caused substantial temperature under- or overestimation in individual echo images.
  • Echo combination significantly reduced these temperature measurement errors.
  • Residual errors were approximately 0.3°C for 10% fat and 1°C for 20% fat.

Conclusions:

  • Echo combination effectively minimizes temperature measurement errors caused by small fat fractions.
  • This method negates the requirement for fat suppression in MRI, particularly beneficial for tissues like the liver.