功能磁共振（fMRI）靠什么“看”大脑活动？
How does fMRI 'see' brain activity?
神经活动耗能增加局部血流，含氧与脱氧血红蛋白的磁化率不同，改变 MRI 信号（BOLD 对比）；据此间接映射哪片脑区在“加班”。
Active neurons draw more blood; oxy- and deoxy-hemoglobin differ magnetically, shifting the MRI signal (BOLD contrast), indirectly mapping which brain regions are busy.
难度 专业 · 适合 小学高段(9-12)
CC BY 4.0 · 来源待核验 · Source pending review
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出处备注：著录含书名，但缺版次 / 出版社 / 年份中的一部分，需编辑补全后才能做独立比对。
Ogawa 等，《依赖血氧的脑磁共振成像对比》，Biophysical Journal 58 (1990)
Ogawa et al., 'Brain Magnetic Resonance Imaging with Contrast Dependent on Blood Oxygenation', Biophysical Journal 58 (1990)
#fMRI #BOLD #脑功能
MRI 里的“射频”和“梯度”各自做什么？
What do the radio-frequency and gradient fields do in an MRI?
强静磁场先让体内氢核排队；射频脉冲把它们轻轻推开，松开后释放信号；梯度磁场给不同位置“贴地址”，计算机据此拼出断层图像。
A static field aligns hydrogen nuclei; a radio pulse tips them and they emit signals on release; gradient fields tag each location with an address so the computer builds a slice image.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 来源待核验 · Source pending review
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出处备注：著录仅给书名，无版次与年份；同一书名常对应多个版次，不臆测具体版本。
Hashemi、Bradley 与 Lisanti，《MRI 基础》（第3版）
Hashemi, Bradley & Lisanti, 'MRI: The Basics' (3rd ed.)
#MRI #射频 #梯度场
CT 的“断层”和 MRI 的“断层”成像原理有何区别？
How do CT and MRI slicing principles differ?
CT 用旋转 X 射线从多角度投影，靠反投影重建密度切片；MRI 用磁场加射频直接探测氢核信号并定位，对软组织对比更好、无电离辐射。
CT rotates X-ray projections and reconstructs density slices by back-projection; MRI directly detects localized hydrogen signals, giving better soft-tissue contrast without ionizing radiation.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Lauterbur，《用感应局部相互作用形成图像》，Nature 242 (1973)；Hounsfield，《计算机化断层扫描》，British Journal of Radiology 46 (1973)
Lauterbur, 'Image Formation by Induced Local Interactions', Nature 242 (1973); Hounsfield, 'Computerized Transverse Axial Scanning', British Journal of Radiology 46 (1973)
独立核验依据 · Independent verification: 核验依据 1 CROSSREF 标识 10.1038/242190a0：Image Formation by Induced
#CT #断层 #MRI对比
CT 图像里的 Hounsfield 单位(HU)是怎么规定的?水、肺组织与皮质骨大致落在哪些数值区间?
How are Hounsfield units defined in CT imaging, and where do water, lung tissue, and cortical bone fall numerically?
HU 以水的线性衰减系数为基准做线性标定:HU = 1000(μ − μ_water)/μ_water,因此水恒定为 0,空气接近 −1000。含气的肺组织大致在 −700 到 −800,脂肪约 −100,致密皮质骨可超过 +1000。统一的标度让不同机型与扫描协议下的测量可以相互比较,是定量影像诊断的前提。
HU is a linear calibration anchored on water: HU = 1000(mu − mu_water)/mu_water, so water is fixed at 0 and air lies near −1000. Aerated lung tissue falls around −700 to −800, fat near −100, and dense cortical bone can exceed +1000. One common scale makes measurements comparable across scanners and protocols, which quantitative image diagnosis depends on.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-10-04
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Russell K. Hobbie 与 Bradley J. Roth 著《Intermediate Physics for Medicine and Biology》（医学与生物学中的中级物理）
Russell K. Hobbie & Bradley J. Roth, Intermediate Physics for Medicine and Biology
独立核验依据 · Independent verification: 核验依据 1 ISBN 978-3-319-12682-1 / DOI 10.1007/978-3-319-12682-1 (
#医学物理 #CT 值与 Hounsfield 标度
CT 扫描是怎样利用 X 射线重建出人体的断层图像的？
How does a CT scan use X-rays to reconstruct cross-sectional images of the human body?
CT 设备从大量不同角度测量 X 射线穿过人体后的透射强度，每条射线服从比尔–朗伯指数衰减定律，构成一组投影数据。计算机用滤波反投影等算法把全部投影反演为体内线性衰减系数的二维分布，再标定为以水为零点的 CT 值（HU）。它把平片中相互重叠的结构分解为断层图像，密度分辨本领可达百分之零点五左右。
A CT scanner measures transmitted X-ray intensities through the body from many angles; every ray obeys Beer–Lambert exponential attenuation, producing a set of projections. Algorithms such as filtered back-projection invert these projections into a two-dimensional map of linear attenuation coefficients, calibrated into Hounsfield units referenced to water. Tomography thereby separates structures that overlap on plain radiographs, achieving density resolution of roughly half a percent.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-04
来源 · Source
Hounsfield,《Computerized transverse axial scanning (tomography): Part 1. Description of system》,The British Journal of Radiology,1973 (DOI: 10.1259/0007-1285-46-552-1016)
G. N. Hounsfield, 'Computerized transverse axial scanning (tomography): Part 1. Description of system', The British Journal of Radiology, 1973, DOI: 10.1259/0007-1285-46-552-1016
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1259/0007-1285-46-552-1016
#医学物理 #计算机断层成像
医院里的 MRI 和 CT 有什么不一样？
How are MRI and CT different in the hospital?
CT 用 X 射线看骨头和密度；MRI 用强磁场和无线电看软软的组织（如水、脂肪），而且没有辐射。
CT uses X-rays to show bone and density; MRI uses strong magnets and radio waves to image soft tissue, with no ionizing radiation.
难度 入门 · 适合 幼儿(3-6)
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
Lauterbur，《用感应局部相互作用形成图像》，Nature 242 (1973)；Hounsfield，《计算机化断层扫描》，British Journal of Radiology 46 (1973)
Lauterbur, 'Image Formation by Induced Local Interactions', Nature 242 (1973); Hounsfield, 'Computerized Transverse Axial Scanning', British Journal of Radiology 46 (1973)
独立核验依据 · Independent verification: 核验依据 1 CROSSREF 标识 10.1038/242190a0：Image Formation by Induced
#MRI #CT #医学影像
做 MRI 时为什么不能带金属进去？
Why can't you bring metal into an MRI?
机器里有很强磁铁，会吸住铁制品伤到人，也可能让金属发热或干扰图像。
The machine has a powerful magnet that can pull iron objects, hurt people, heat metal, or ruin the image.
难度 入门 · 适合 小学低段(6-8)
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：著录含书名，但缺版次 / 出版社 / 年份中的一部分，需编辑补全后才能做独立比对。
Schenck，《核磁共振成像中的磁场安全性》，Journal of Magnetic Resonance Imaging 12 (2000)
Schenck, 'Safety of Magnetic Resonance Imaging', Journal of Magnetic Resonance Imaging 12 (2000)
#MRI #磁场 #安全