Department of Biochemistry, The London Hospital Medical College, Turner Street, EI 2AD, London, UK.
Biol Trace Elem Res. 1987 Aug;13(1):219-27. doi: 10.1007/BF02796634.
X-ray microradiography is a well established technique for the study of biological structures in which the projected absorption is measured, usually with photographic film or resist. If scanning X-ray microradiography with a 15-μm beam, 2-D scanning, and photon counting is used, more accurate results can be obtained and real-time experiments undertaken. Addition of a rotation axis allows computerized axial tomography to be done at a resolution of 15 μm. This technique overcomes the inherent difficulty of microradiography that all detail perpendicular to the plane of the specimen is superimposed. This method has been applied to the study of the 3-D mineral distribution in a 0.8×0.8 mm column of human cortical bone with a laboratory X-ray source. Calculation of the wavelength dependence of the linear absorption coefficient for liver and bone shows that, for a choice of wavelength in the range of 3-0.4 Å (4-30 keV), the specimen thickness can be from 100μm-2 cm and 10 μm-3 mm, respectively.Synchrotron X-radiation has the potential for better resolution because of the higher intensity, which allows the use of a narrower beam. There is also the possibility of determining individual element 3-D distributions from measurements on either side of the absorption edges because of the continuous nature of the spectrum and also the possibility of doing this from X-ray fluorescence measurements. To investigate these possibilities, a tomographic apparatus has been built based on the availability of accurately ground, tungsten carbide balls. Metrological assessment shows that the specimen remains within <1 μm of the required position during translation and rotation. Preliminary X-ray tomographic studies with a 4-μm diameter beam have been started at the Daresbury laboratory synchrotron source.
X 射线显微放射摄影术是一种成熟的技术，用于研究投影吸收的生物结构，通常使用照相胶片或抗蚀剂进行测量。如果使用 15μm 光束、二维扫描和光子计数进行扫描 X 射线显微放射摄影术，则可以获得更准确的结果并进行实时实验。添加旋转轴允许以 15μm 的分辨率进行计算机轴向断层摄影术。该技术克服了显微放射摄影术的固有困难，即所有垂直于标本平面的细节都被叠加。该方法已应用于实验室 X 射线源研究 0.8×0.8mm 人皮质骨柱中 3-D 矿物分布。计算肝脏和骨骼线性吸收系数的波长依赖性表明，对于在 3-0.4Å（4-30keV）范围内的波长选择，标本厚度可以分别为 100μm-2cm 和 10μm-3mm。由于强度较高，同步辐射具有更好分辨率的潜力，这允许使用更窄的光束。由于光谱的连续性，也有可能从吸收边两侧的测量值来确定单个元素的 3-D 分布，并且也有可能通过 X 射线荧光测量来实现。为了研究这些可能性，已经基于精确研磨的碳化钨球的可用性构建了一个层析成像仪。计量评估表明，在平移和旋转过程中，标本始终保持在所需位置的<1μm 内。已经在达雷斯顿实验室同步辐射源开始进行直径为 4μm 的初步 X 射线层析成像研究。
