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相关概念视频

¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

1.1K
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...
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NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

698
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...
698
¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)01:20

¹³C NMR: Distortionless Enhancement by Polarization Transfer (DEPT)

1.1K
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...
1.1K
Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

210
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...
210
NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

805
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.
805
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

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在CEST MR中侧带 - 如何识别和避免它们

Jan-Rüdiger Schüre1, Simon Weinmüller1, Lukas Kamm1

  • 1Institute of Neuroradiology, University Clinic Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.

Magnetic resonance in medicine
|February 6, 2024
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概括
此摘要是机器生成的。

脉冲化学交换和转移 (CEST) 序列可能会由于相位积累而导致工件. 在和列车期间的梯度破坏至关重要,以防止误解这些侧带作为实际的CEST效应,特别是在液态环境中.

关键词:
在CEST中,CEST是CEST.艺术品的文物.梯度破坏破坏的破坏一个阶段循环循环.脉冲式 CEST 成像采集pulseq-CEST 这是一个很好的方法.侧带 侧带 侧带

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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
  • 频谱学是一种光谱学.

背景情况:

  • 脉冲化学交换和转移 (CEST) 序列对于临床MRI来管理放大器功率和特定吸收率 (SAR) 是必不可少的.
  • 磁化可以在非共振射频 (RF) 辐射和脉冲延迟中在脉冲CEST序列中积累相对相位.
  • 这些累积的相可以导致人工物,如果不适当地管理,特别是没有间脉冲梯度破坏.

研究的目的:

  • 调查脉冲CEST序列中侧带工件的性质和影响.
  • 为了证明在脉冲CEST采集过程中考虑磁化相积的重要性.
  • 要突出梯度破坏在脉冲CEST中减轻文物中的作用.

主要方法:

  • 在3特斯拉利用CEST-3D快照梯度回声序进行文物调查.
  • 使用Pulseq-CEST进行了Bloch-McConnell模拟.
  • 进行了体外和体内实验,以验证模拟结果.

主要成果:

  • 在Z光谱中识别了侧带,通常需要高采样才能清晰可视化.
  • 观察到B0不均性和RF相循环影响侧带结构.
  • 在体内发现侧带主要存在于像脑脊液 (CSF) 这样的液体区.
  • 证明了间脉冲梯度破坏有效地抑制了多脉冲侧带.

结论:

  • 脉冲CEST实验容易受到侧带工件的影响,受到梯度和射频破坏的影响,类似于成像序列.
  • 梯度破坏对于防止误解侧带作为真正的CEST效应至关重要,特别是在液态环境,病态组织或水附近的共振中.
  • 建议提前模拟脉冲CEST序列,以避免潜在的工件并确保准确的结果.