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相关概念视频

Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

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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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Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

675
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...
675
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

1.0K
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...
1.0K
Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

882
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...
882
Atomic Nuclei: Magnetic Resonance01:05

Atomic Nuclei: Magnetic Resonance

1.1K
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...
1.1K
¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

1.7K
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...
1.7K

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Quantifying Mixing using Magnetic Resonance Imaging
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MC BTS:同时解决多个组件的磁化转移效应和放松.

Albert Jang, Hyungseok Jang, Nian Wang

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    此摘要是机器生成的。

    这项研究引入了一种新的MRI方法,用于精确的组织量化,同时测量放松和磁化转移效应,同时纠正传输场不均性. 这种技术在复杂的生物环境中增强了多组分组织参数表征.

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    Author Spotlight: Exploring Intrinsically Disordered Protein Dynamics Through NMR Relaxation Experiments
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    科学领域:

    • 磁共振成像 (MRI) 是一种磁共振成像技术.
    • 生物物理建模 生物物理建模
    • 医学物理 医学物理

    背景情况:

    • 准确的多组分组织量化对于理解生物系统至关重要.
    • 现有的MRI方法往往难以同时评估放松,磁化转移 (MT) 和传输场 ($B_1^+$) 的不均性.
    • 富含巨分子的组织对定量MRI具有独特的挑战.

    研究的目的:

    • 开发和验证一个新的信号采集和建模框架,用于全面的多组分组织量化.
    • 为了同时考虑发射场不均性,多元件放松和磁化转移 (MT) 效应.
    • 为了能够在体内进行可靠的参数估计.

    主要方法:

    • 采用了RF破坏的梯度回声序列与非共振辐射和多个回声时间采集.
    • 在放松和旋转交换期间同时诱导布洛赫-西格特转移和MT效应.
    • 使用三池模型进行参数估计,并通过模拟和蒙特卡洛分析进行验证.
    • 在体内人类大脑和膝盖数据上进行了多参数拟合.

    主要成果:

    • 模拟结果显示,拟议方法与分析信号方程之间有很好的一致性.
    • 蒙特卡洛分析证实了在各种信号噪声比条件下强的性能.
    • 在体内研究中,多个参数的匹配结果与现有的文献值一致.

    结论:

    • 拟议的框架可靠地描述了宏分子丰富环境中的多组分组织参数.
    • 该方法有效地弥补了$B_1^+$的不均性,提高了定量准确性.
    • 这种方法为生物组织分析的定量MRI提供了显著的进步.