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相关概念视频

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

735
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.
735
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

654
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...
654
Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

185
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...
185
¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

1.0K
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...
1.0K
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

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

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

1.0K
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

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Author Spotlight: Using Hyperpolarized Xenon-129 MRI to Study Lung Diseases
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对于加速相循环23Na多量子一致性MRI的噪声强的后处理管道.

Christian Licht1, Efe Ilicak2, Fernando E Boada3

  • 1Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany; Mannheim Institute for Intelligent Systems in Medicine, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany; Radiological Sciences Laboratory, School of Medicine, Stanford University, Stanford, California, USA.

Zeitschrift fur medizinische Physik
|January 22, 2025
PubMed
概括

这项研究引入了 (Na) 多量子一致性 (MQC) MRI 的新管道,提高了图像质量并减少了扫描时间. 该方法提高了信号与噪声的比率,并强大地分离信号,以获得更好的大脑成像7特斯拉.

关键词:
动态模式分解分解这是一个低级别的低级别.神经成像是一种神经成像.单个和三重量子成像技术核磁共振成像 (MRI) 的使用方法的多量子连贯性是一种多量子连贯性.

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科学领域:

  • 医疗成像医学成像
  • 生物物理学的生物物理.
  • 神经成像是一种神经成像.

背景情况:

  • (Na23) 多量子连贯性 (MQC) 核磁共振是有价值的体内人类大脑成像在7特斯拉.
  • 目前的MQCMRI技术面临的挑战是低信号噪声比 (SNR) 和漫长的射频 (RF) 阶段循环.
  • 单量子 (SQ) 和三量子 (TQ) 信号的准确分离对于计算TQ/SQ比率至关重要,这是一个关键的诊断参数.

研究的目的:

  • 开发一个先进的后处理管道,以对抗噪声,加速NaMQCMRI的体内人类大脑在7T.
  • 为了增强SNR和改善SQ和TQ信号组件的分离在Na MQCMRI.
  • 为了减少采集时间,同时保持高图像质量.

主要方法:

  • 结合低级 k 空间无声化用于 SNR 增强与动态模式分解 (DMD) 进行强大的 SQ 和 TQ 信号分离.
  • 验证了 in silico, in vitro 和 in vivo 的管道,并将其与传统的消极化和富里埃转换 (FT) 方法进行比较.
  • 通过模拟受损的射频相循环步骤的废弃实验来评估管道的稳定性.

主要成果:

  • 与未被拒绝的图像相比,拒绝算法增加了SNR的两倍,并且在波形拒绝上提高了SNR高达29%.
  • 与FT方法相比,DMD有效地分离了SQ和TQ信号,即使没有完整的RF相循环,也实现了优越的SSIM (0.89±0.024) 和较低的RMSE (0.055±0.008).
  • 启用了高质量的8x8x15mm3 in vivo23Na MQC MRI,采集时间从48分钟缩短到10分钟.

结论:

  • 拟议的管道通过低级别的无声化和基于DMD的信号分离,显著提高了Na MQCMRI的稳定性.
  • 对于SQ和TQ组件,即使在加速和不完整的RF相循环条件下,也可以获得高质量的MR图像.
  • 这种方法为人类大脑的先进Na MQCMRI提供了更有效和可靠的方法.