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NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

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.

Atomic Nuclei: Magnetic Resonance

Atomic Nuclei: Magnetic Resonance

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...

Atomic Nuclei: Nuclear Relaxation Processes

Atomic Nuclei: Nuclear Relaxation Processes

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.

Double Resonance Techniques: Overview

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 Correction

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: Distortionless Enhancement by Polarization Transfer (DEPT)

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...

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相关实验视频

Updated: Jan 15, 2026

Author Spotlight: Using Hyperpolarized Xenon-129 MRI to Study Lung Diseases

Author Spotlight: Using Hyperpolarized Xenon-129 MRI to Study Lung Diseases

Published on: January 5, 2024

超极化MR动力学建模的最佳可变翻转角度方案坚固对射频场变化.

Marie Frederikke Garnæs¹, Rie Beck Olin¹, Pernille R Jensen¹

¹Department of Health Technology, Technical University of Denmark, Kongens Lyngby, Denmark.

NMR in biomedicine

|October 11, 2025

概括

此摘要是机器生成的。

在超极化碳-13磁共振中优化的可变翻转角度 (VFA) 方案通过减少参数估计的不确定性来改善代谢途径分析. 包括B1场强度作为一个合适的参数对于准确的结果至关重要.

关键词:

超极化的碳-13磁共振磁共振.最优的实验设计最优的实验设计药物动力学建模药物动力学建模

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Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease

Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease

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Last Updated: Jan 15, 2026

Author Spotlight: Using Hyperpolarized Xenon-129 MRI to Study Lung Diseases

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Measuring the Spin-Lattice Relaxation Magnetic Field Dependence of Hyperpolarized [1-13C]pyruvate

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Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease

Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease

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科学领域:

磁共振成像是一种磁共振成像技术.
生物医学工程生物医学工程
代谢途径分析

背景情况:

超极化碳-13磁共振允许实时观察生物化学途径 in vivo.
药物动力学建模估计了代谢物转化率,有助于区分健康和患病的组织.
准确的参数估计对于可靠地解释超极化NMR数据至关重要.

研究的目的:

开发时间变化的翻转角度方案,以尽量减少药理动力学模型参数估计的不确定性.
通过最大限度地利用费舍尔信息来优化这些方案,同时考虑B1场强度变化.
为了比较优化可变翻转角度 (VFA) 方案与优化常量翻转角度 (CFA) 方案的性能.

主要方法:

利用蒙特卡洛模拟来评估优化的VFA和CFA方案.
将B1场强度变化的先前分布纳入优化过程中.
使用体外实验验证实了酶驱动的转化模型.

主要成果:

与优化的CFA方案相比,优化的VFA方案在模型参数估计中的不确定性显著降低.
在各种基本模型参数中,VFA计划的绩效改进是强大的.
准确估计B1场强度被证明是避免不准确的参数估计至关重要的.

结论:

优化的VFA方案在超极化NMR中为药代动力学建模提供了卓越的性能.
包括B1场强度作为适配参数提高了代谢参数估计的精度.
这种方法提高了使用超极化NMR区分健康和患病组织的可靠性.