Slit camera focal spot measurement errors in mammography.
Slit camera focal spot measurement errors in mammography.
复制标题
乳房 X 线摄影中的狭缝相机焦点测量误差。
DOI：
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
R. L. Tanner
中科院分区：
文献类型：
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作者：
S. Tang;G. Barnes;R. L. Tanner
在验收测试和年度性能审核期间，常规测量乳腺X射线管焦斑尺寸。美国国家电气制造商协会（NEMA）推荐狭缝相机用于此目的。研究了狭缝旋转错位，倾斜错位，图像胶片密度，电影和屏幕电影的图像受体，显微镜放大倍率和分划板的准确性，观察员的变化对狭缝相机焦斑测量的影响。我们的研究结果表明，小的旋转失准（< 5度）和倾斜失准（< 3度）引入的误差微不足道。测得的焦斑尺寸随图像光密度略有增加，这表明为了获得一致的结果，图像光密度变化应最小化。对于精确的现场测量，还需要一个高倍显微镜（25- 50倍）和一个分度≤ 0.02 mm的分划板。屏幕胶片成像始终导致比直接胶片稍小的测量焦斑尺寸。最大的误差来源是由于观察者的变化。感兴趣的是，读者的变异性表现出一致的模式和两个测量之间的变化由同一个观察员是远远小于观察员之间的变化，这表明，应建立标准化的标准和方法的读者培训的发展。焦点的长度由乳房X线摄影装置制造商规定的参考轴角度定义。提供了目前和最近在北美销售的大多数乳腺X射线摄影装置的焦斑几何形状和参考轴角度的表格。
Mammography x-ray tube focal spot sizes are routinely measured during acceptance testing and annual performance audits. The National Electrical Manufactures Association (NEMA) recommends the slit camera for this purpose. Investigated were the effect of slit rotational misalignment, tilt misalignment, image film density, film and screen-film image receptors, microscope magnification and reticule accuracy, and observer variation on slit camera focal spot measurements. Our results indicate that small rotational misalignment (< 5 degrees) and tilt misalignment (< 3 degrees) introduce insignificant error. Measured focal spot size increased slightly with image optical density, indicating that for consistent results the image optical density variations should be minimized. Also desirable for accurate field measurements is a high power microscope (25-50x) and a reticule with divisions of < or = 0.02 mm. Screen-film imaging consistently resulted in a slightly smaller measured focal spot size than direct film. The greatest source of error was due to observer variation. Of interest is that reader variability showed a consistent pattern and variation between two measurements by the same observer was much smaller than between observer variation, suggesting that standardized criteria should be established and a method of reader training developed. The length of the focal spot is defined at a reference axis angle specified by the mammography unit manufacturer. Presented is a tabulation of the focal spot geometry and reference axis angles for the majority of mammography units currently and recently marketed in North America.