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相关概念视频

Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

203
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...
203
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

695
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...
695
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

1.0K
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.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
1.0K
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

654
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.
654
Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

300
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...
300
Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

979
Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
979

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相关实验视频

Updated: Jul 1, 2025

In Situ Monitoring of Diffusion of Guest Molecules in Porous Media Using Electron Paramagnetic Resonance Imaging
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在振荡梯度旋转回声中的受限制的扩散特征与介光镜幻影回声.

Hinako Oshiro1,2, Junichi Hata1,2,3,4, Daisuke Nakashima3

  • 1Graduate School of Human Health Sciences, Tokyo Metropolitan University, Tokyo, Japan.

Heliyon
|March 4, 2024
PubMed
概括
此摘要是机器生成的。

振荡梯度旋转回声 (OGSE) 与运动探测梯度 (MPG) 揭示了微观结构细节. 在OGSEMRI中的cosine波形检测到更高频率的更快的扩散,独立于结构大小或b值.

关键词:
B值的依赖性 B值的依赖性扩散式核磁共振成像 (MRI)扩散光谱的扩散光谱一个中镜的幻影.振荡梯度旋转回声回声振荡梯度旋转回声回声有限制的扩散.

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科学领域:

  • 磁共振成像是一种磁共振成像技术.
  • 扩散式核磁共振成像 (MRI)
  • 生物物理技术 生物物理技术

背景情况:

  • 振荡梯度旋转回声 (OGSE) 能够在扩散MRI中减少扩散时间.
  • 在OGSE中,运动探测梯度 (MPG) 改变了对旋转位移速度的灵敏度.
  • OGSE可以潜在地检测微结构特异性.

研究的目的:

  • 为了研究OGSE波形的受限扩散特征.
  • 用毛细管幻影来评估正弦和正弦OGSE波形.
  • 分析b值,频率和MPG相对扩散测量的影响.

主要方法:

  • 用不同b值 (300-2000秒/毫米2) 的OGSE序列应用于毛细血管幻体 (6-100微米) 和自由水.
  • 在9.4-TMRI系统上使用正弦和正弦波形.
  • 计算了轴向和辐射扩散率 (AD,RD);MPG输出通过FT.分析.

主要成果:

  • 弦波形显示频率增加侧叶球谱,检测RD在6和12μm的差异,但没有更大的结构.
  • 随着频率的增加,Cosine波形表现出增强的扩散光谱和减少的中心光谱.
  • 同位数波形显示了频率依赖的AD和RD,在所有结构大小的频率上都增加.
  • 对于任何波形都没有观察到显著的b值依赖.

结论:

  • OGSE测量提供了与脉冲梯度旋转回声相比较的扩散信息.
  • 高频率的Cosine OGSE波形对于捕捉更快的扩散现象是有效的.
  • OGSE参数,特别是频率和波形类型,影响对微观结构特征的灵敏度.