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関連する概念動画

Diffusion01:12

Diffusion

222.3K
Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...
222.3K
Diffusion01:21

Diffusion

6.7K
Diffusion is a type of passive transport. In passive transport, a substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across the space. For example, take the diffusion of substances through the air. When someone opens a perfume bottle in a room filled with people, the perfume is at its highest concentration in the bottle and is at its lowest at the edges of the room. The perfume vapor will diffuse, or spread away, from the...
6.7K
Water and Mineral Acquisition02:34

Water and Mineral Acquisition

35.9K
Specialized tissues in plant roots have evolved to capture water, minerals, and some ions from the soil. Roots exhibit a variety of branching patterns that facilitate this process. The outermost root cells have specialized structures called root hairs that increase the root surface, thus increasing soil contact. Water can passively cross into roots, as the concentration of water in the soil is higher than that of the root tissue. Minerals, in contrast, are actively transported into root cells.
35.9K
Nervous Tissue: Myelin01:25

Nervous Tissue: Myelin

6.0K
The myelin sheath is a multilayered lipid and protein covering that insulates the axon of a neuron, enhancing the speed of nerve impulse conduction. Axons without this sheath are referred to as unmyelinated. Two types of neuroglia, Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS) are responsible for producing myelin sheaths.
Schwann cells begin to form myelin sheaths around axons during fetal development. They wrap around a small...
6.0K
Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion03:48

Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion

31.4K
Although gaseous molecules travel at tremendous speeds (hundreds of meters per second), they collide with other gaseous molecules and travel in many different directions before reaching the desired target. At room temperature, a gaseous molecule will experience billions of collisions per second. The mean free path is the average distance a molecule travels between collisions. The mean free path increases with decreasing pressure; in general, the mean free path for a gaseous molecule will be...
31.4K
States of Water01:23

States of Water

57.5K
Water exists in any one of the three classical states: solid (ice), liquid (water), and gas (steam or water vapor). The state of water depends on i) the intermolecular forces that draw molecules together and ii) the kinetic energy that leads to movements that pull them apart.
Water freezes when the intermolecular forces are greater than the kinetic energy. Unlike most other substances, water is less dense in its solid state than in its liquid state. This is because each water molecule can form...
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関連する実験動画

Updated: Feb 15, 2026

Spectral Reflectometric Microscopy on Myelinated Axons In Situ
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Spectral Reflectometric Microscopy on Myelinated Axons In Situ

Published on: July 2, 2018

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ミエリン・ウォーター・ディフュージョン・MRIによる軸索直径マッピング

Hong-Hsi Lee, Kwok-Shing Chan, Dmitry S Novikov

    IEEE transactions on medical imaging
    |February 13, 2026
    PubMed
    まとめ

    この研究は,ミエリン化アクソン直径を非侵襲的に測定するための新しい拡散MRI方法を導入しています. シミュレーションにより,in vivoアプリケーションにおける精度が確認され,臨床使用への道が開けています.

    科学分野:

    • 神経画像は,神経イメージングによるものです.
    • バイオフィジックス 生物物理学
    • 医学物理 医学物理学

    背景:

    • 拡散MRIは,組織内の水分拡散を測定する.
    • ミエリン水拡散は,ミエリン状の軸索の微細構造環境に対して敏感である.
    • アクソン直径の正確なin vivo測定は,神経学的状態を理解するために重要です.

    研究 の 目的:

    • ミエリン化アクソン直径の非侵襲的な測定のための拡散MRI方法を開発し,検証する.
    • 特定のMRIパルスシーケンスの下でミエリン水拡散の理論的枠組みを確立する.
    • 数学的シミュレーションを使用してin vivoアプリケーションの実現可能性を評価する.

    主な方法:

    • 幅のグラデントパルスによる拡散MRIとガウスの相近似を用いたミエリン水拡散の理論を提唱した.
    • ミエリン膜を模倣する円筒型モデルにモンテカルロシミュレーションを使用した.
    • 球状平均拡散を用いた拡散信号の評価と,さまざまな信号対ノイズ比率 (SNR) で評価された性能.

    主要な成果:

    • 開発された理論は,外部の口径に重点を置いた軸索直径を正確に推定しています.
    • シミュレーションにより,高性能MRIスキャナー (Connectome 2.0) でSNR>20でのメソッドの適用性が実証されました.

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  • この技術では,ミエリン水の拡散を制限してアクソン直径を推論する.

    • 結論:

    • 提案された拡散MRIプロトコルは,ミエリン化アクソン直径の非侵襲的インビボ測定を可能にします.
    • この方法は,臨床的に利用可能な高梯度MRIスキャナーに適応する見通しを示しています.
    • この技術は,健康と病気における白質の微細構造を研究するための新しいツールを提供します.