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Related Concept Videos

Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

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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...
306
Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

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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...
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Atomic Nuclei: Magnetic Resonance01:05

Atomic Nuclei: Magnetic Resonance

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The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
764
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

784
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...
784
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

1.6K
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...
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Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

728
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
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Updated: Sep 17, 2025

High-Temperature and High-Pressure In situ Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy
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Quadruple-refocused spin-locking: A robust method for high-amplitude T1ρ imaging.

Cai Wan1,2,3, Maximilian Gram4,5, Wei He1

  • 1School of Electrical Engineering, Chongqing University, Chongqing, China.

Magnetic Resonance in Medicine
|June 28, 2025
PubMed
Summary
This summary is machine-generated.

A new quadruple-refocused spin-locking (QR-SL) technique improves magnetic field homogeneity for more accurate T1ρ quantification. This method enhances early disease detection in medical imaging, particularly at lower magnetic field strengths.

Keywords:
T1ρ relaxationartifacts compensationfield inhomogeneityquantitative MRIspin locking

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Area of Science:

  • Magnetic Resonance Imaging (MRI)
  • Quantitative Imaging
  • Biomedical Engineering

Background:

  • Longitudinal relaxation time in the rotating frame (T1ρ) provides tissue-specific contrast for detecting fibrosis and osteoarthritis.
  • T1ρ measurements are susceptible to static (B0) and radiofrequency (B1) magnetic field inhomogeneities, impacting accuracy.
  • Accurate T1ρ quantification is crucial for early pathological change detection and intervention.

Purpose of the Study:

  • To develop an improved quadruple-refocused spin-locking (QR-SL) technique for robust compensation of B0 and B1 field inhomogeneities.
  • To enhance the accuracy and reliability of T1ρ quantification in MRI.
  • To enable earlier and more dependable detection of pathological changes using T1ρ imaging.

Main Methods:

  • The QR-SL module incorporates four 180° refocusing pulses and five spin-locking (SL) pulses with phase cycling.
  • Performance was evaluated using numerical simulations and experimental validation.
  • Compared QR-SL against composite-SL (C-SL), balanced-SL (B-SL), and triple-refocused-SL (TR-SL) preparation modules.

Main Results:

  • Numerical simulations showed QR-SL has superior tolerance to B0 and B1 field inhomogeneities compared to other modules.
  • Experimental results demonstrated a significant reduction in the residual sum of squares for QR-SL in vivo knee cartilage.
  • QR-SL achieved decreases of 24.3% (vs. C-SL), 68.9% (vs. B-SL), and 12.5% (vs. TR-SL) in residual sum of squares.

Conclusions:

  • The QR-SL module offers potential for producing more accurate T1ρ maps with minimized artifacts.
  • QR-SL is more favorable for T1ρ quantification, especially in low-field and ultralow-field MRI settings.
  • This technique can improve diagnostic capabilities for conditions like myocardial fibrosis, liver fibrosis, and osteoarthritis.