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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

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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.
766
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

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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...
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Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

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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...
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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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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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Reconstruction of Signal using Interpolation01:10

Reconstruction of Signal using Interpolation

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Signal processing techniques are essential for accurately converting continuous signals to digital formats and vice versa. When a continuous signal is sampled with a period T, the resulting sampled signal exhibits replicas of the original spectrum in the frequency domain, spaced at intervals equal to the sampling frequency. To handle this sampled signal, a zero-order hold method can be applied, which creates a piecewise constant signal by retaining each sample's value until the next...
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Updated: Jun 10, 2025

Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease
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在高度不均的场中零回声时间序列.

Jose Borreguero1,2, Fernando Galve1, José M Algarín1

  • 1MRILab, Institute for Molecular Imaging and Instrumentation (i3M), Spanish National Research Council (CSIC), Universitat Politècnica de València (UPV), Valencia, Spain.

Magnetic resonance in medicine
|October 21, 2024
PubMed
概括
此摘要是机器生成的。

这项研究引入了一种新的磁共振成像 (MRI) 方法,在高度不均的磁场中使用零回声时间 (ZTE) 序列. 该技术可以纠正文物,使得在低场MRI系统上的牙扫描等应用中能够清晰成像.

关键词:
伪造的纠正 伪造的纠正在同质性领域的同质性.这是一个低地低地.超短的 超短的零回声时间零回声时间

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科学领域:

  • 磁共振成像 (MRI) 是一种磁共振成像技术.
  • 生物医学工程 生物医学工程
  • 医学物理 医学物理

背景情况:

  • 零回声时间 (ZTE) 序列对于成像超短T2组织是有效的.
  • 强烈的磁场不均质 (高达14000ppm) 会导致ZTEMRI中的显著工件.
  • 在这种高度不均的环境中,标准的场地绘图技术失败了.

研究的目的:

  • 开发和评估一种用于纠正非卡特西安ZTEMRI采集中的重建文物的新方法.
  • 为了应对严重的磁场不均质所带来的挑战,在传统方法不足的情况下.

主要方法:

  • 使用了从两个无几何扭曲的点智能 (SPRITE) 采集中获得的磁场地图.
  • 采用了使用代代数技术 (ART) 的基于模型的图像重建.
  • 将新方法与广泛使用的结合相 (CP) 算法进行比较.

主要成果:

  • 拟议的方法有效地扭转了严重的现场不均质造成的扭曲和人工物.
  • 即使当声内带宽 (高达1.2 kHz) 接近声间带宽 (625 Hz) 时,性能也保持不变.
  • 在文物纠正方面显著优于CP重建.

结论:

  • 在高度不均的磁场中采用ZTE成像的新方法成功进行了基准测试.
  • 这种技术适用于负担得起的低场MRI系统,使牙科成像等应用成为可能.
  • 该方法有可能扩展到任意脉冲序列和极端磁体几何形状 (例如单面MRI).