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相关概念视频

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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Atomic Nuclei: Magnetic Resonance01:05

Atomic Nuclei: Magnetic Resonance

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The number of nuclear spins aligned in the lower energy state is slightly greater than those in the higher energy state. In the presence of an external magnetic field, as the spins precess at the Larmor frequency, the excess population results in a net magnetization oriented along the z axis. When a pulse or a short burst of radio waves at the Larmor frequency is applied along the x axis, the coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the...
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Magnetic Resonance Imaging01:24

Magnetic Resonance Imaging

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Magnetic resonance imaging (MRI) is a noninvasive medical imaging technique based on a phenomenon of nuclear physics discovered in the 1930s, in which matter exposed to magnetic fields and radio waves was found to emit radio signals. In 1970, a physician and researcher named Raymond Damadian noticed that malignant (cancerous) tissue gave off different signals than normal body tissue. He applied for a patent for the first MRI scanning device in clinical use by the early 1980s. The early MRI...
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NMR Spectrometers: Resolution and Error Correction01:14

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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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Atomic Nuclei: Larmor Precession Frequency01:11

Atomic Nuclei: Larmor Precession Frequency

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The earth's gravitational field produces a 'twisting force' perpendicular to the angular momentum of a spinning mass (such as a spinning top) that causes the mass to 'wobble' around the gravitational field axis in a phenomenon called precession. Similarly, the magnetic moment (μ) of a spinning nucleus precesses due to an external magnetic field directed along the z-axis. The precession of the magnetic moment vector about the magnetic field is called Larmor precession,...
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Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

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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.
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Updated: Sep 19, 2025

Author Spotlight: Optimized Lung MRI Protocol with Computationally Efficient Reconstruction Methods
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超低电场平衡稳定状态自由前行MRI在0.05特斯拉.

Ye Ding, Varut Vardhanabhuti, Fan Huang

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    这项研究表明,平衡的稳定状态自由前行 (bSSFP) 成像在低成本,超低场 (ULF) 0.05特斯拉MRI扫描仪上是可行的. 这种ULF bSSFP方法为软组织成像在服务不足的临床环境中提供了具有成本效益的替代方案.

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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.
    • 磁共振成像是一种磁共振成像技术.

    背景情况:

    • 核磁共振扫描仪的高成本和有限的可访问性阻碍了其广泛的临床采用.
    • 超低场 (ULF) 核磁共振为经济高效的成像提供了一个潜在的解决方案.
    • 平衡稳定状态自由前行 (bSSFP) 是对T2/T1对比度敏感的脉冲序列.

    研究的目的:

    • 为了证明bSSFP成像在ULF的可行性,在一个简化的,低成本的0.05特斯拉MRI扫描仪上.
    • 在健康志愿者中优化bSSFP协议,用于全身成像.
    • 为了评估组织对比度对激发翻转角度的依赖性.

    主要方法:

    • 使用了一种新的0.05特斯拉全身MRI扫描仪与永久磁铁.
    • 针对大脑,脊柱,胸部,腹部,骨盆和膝盖的优化bSSFP成像协议.
    • 通过调整激发翻转角度来研究组织对比差异.

    主要成果:

    • 在0.05特斯拉实现了合理的图像质量和解剖结构的可视化.
    • 获得了 2×2×6 mm3 的空间分辨率,每个协议的扫描时间大约为 5 分钟.
    • 具有良好的软组织对比度,可通过翻转角度调节,主要显示T2/T1对比度.

    结论:

    • 由于减少了组织T1值,bSSFP成像在ULF (0.05特斯拉) 上是有效和可行的.
    • 与CT和超声波相比,ULF bSSFP方法提供了优越的软组织对比.
    • 这种方法为临床软组织成像提供了一个具有成本效益的替代方案,传统MRI无法使用.