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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

790
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.
790
Aliasing01:18

Aliasing

128
Accurate signal sampling and reconstruction are crucial in various signal-processing applications. A time-domain signal's spectrum can be revealed using its Fourier transform. When this signal is sampled at a specific frequency, it results in multiple scaled replicas of the original spectrum in the frequency domain. The spacing of these replicas is determined by the sampling frequency.
If the sampling frequency is below the Nyquist rate, these replicas overlap, preventing the original...
128
Upsampling01:22

Upsampling

225
Managing signal sampling rates is essential in digital signal processing to maintain signal integrity. A decimated signal, characterized by a reduced frequency range due to its lower sampling rate, can be upsampled by inserting zeros between each sample. This upsampling process expands the original spectrum and introduces repeated spectral replicas at intervals dictated by the new Nyquist frequency. To refine this zero-inserted sequence, it is passed through a lowpass filter with a cutoff...
225
Downsampling01:20

Downsampling

149
When considering a sampled sequence with zero values between sampling instants, one can replace it by taking every N-th value of the sequence. At these integer multiples of N, the original and sampled sequences coincide. This process, known as decimation, involves extracting every N-th sample from a sequence, thereby creating a more efficient sequence.
The Fourier transform of the decimated sequence reveals a combination of scaled and shifted versions of the original spectrum. This...
149
Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

197
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...
197
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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相关实验视频

Updated: Jun 23, 2025

Quantitative Magnetic Resonance Imaging of Skeletal Muscle Disease
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使用频率扫描射频和和代重建的脂肪抑制.

Ruoxun Zi1, Thomas Benkert1, Hersh Chandarana1

  • 1The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, New York, USA.

Magnetic resonance in medicine
|June 18, 2024
PubMed
概括

这项研究提出了一种新的脂肪抑制技术,它在低场MRI中有效,并且可以适应具有B0不均性的高场成像. 该方法确保了可靠的脂肪抑制,并为定量脂肪/水分析提供了潜力.

关键词:
脂肪抑制 脂肪抑制代的重建重建的重建这是一个低地低地.

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科学领域:

  • 磁共振成像 (MRI) 是一种磁共振成像技术.
  • 医学物理 医学物理
  • 放射学 放射学是一门学科.

背景情况:

  • 传统的MRI脂肪抑制方法在低磁场下通常是无效的,因为光谱分离狭窄.
  • 高场MRI中强烈的B0异质性也可能损害标准脂肪抑制技术的性能.

研究的目的:

  • 引入一种替代脂肪抑制技术,适用于低场MRI和高场MRI应用,具有B0不均性.
  • 在具有挑战性的成像场景中解决当前脂肪抑制方法的局限性.

主要方法:

  • 脂肪和水的分离是通过在连续的辐射采集过程中扫射射频 (RF) 和脉冲频率来实现的.
  • 使用规范化的代方法重建频率分辨率图像,使得可用于脂肪/水分类的voxel-wise信号响应曲线提取.
  • 仅用水生成复合图像,并使用3D平衡的SSFP和0.55T和3T的梯度回忆回声序来演示该原理.

主要成果:

  • 使用质子密度脂肪分数 (PDFF) 幻影的实验验证了脂肪/水分离的可靠性.
  • 该方法在0.55T的腹部成像中证明了没有水信号损失的均脂肪抑制和改善的CSF-to-fat信号比.
  • 在3T部检查中实现了一致的脂肪抑制,即使传统方法由于B0不均而失败. 证明了同时脂肪/水量化的可行性.

结论:

  • 拟议的原理为低场MRI提供可靠的脂肪抑制,并适应高场MRI与B0不均性.
  • 这种技术为开发用于定量脂肪/水 (PDFF) 测量的替代方法提供了基础.