Beckmann F, Bonse U, Busch F, Günnewig O
Institute of Physics, University of Dortmund, Germany.
J Comput Assist Tomogr. 1997 Jul-Aug;21(4):539-53. doi: 10.1097/00004728-199707000-00006.
We show that microtomography (microCT) using synchrotron radiation (SR) can be extended to include X-ray phase contrast, which is two to three orders of magnitude more sensitive than conventional attenuation contrast and better suited for the investigation of specimens consisting chiefly of light elements for photon energies ranging at least from 1 to 100 keV.
Phase contrast is generated by placing the specimen in one of the interfering beams of an X-ray interferometer. With use of 12-keV X-rays, phase projections of the specimen are recorded at 180 or 360 angular settings equally spaced between 0 and 180 degrees. One phase projection consists of four pairs of "associated" radiograms in the sense that one is taken with and the other without the specimen in the beam. Between pairs a parallel-sided phase-shifter plate is rotated for changing the relative phase of the two interfering beams by multiples of pi/2 rad. By calculating phase-weighted sums of all associated pairs of radiograms, true phase-shift projections are obtained for all angular settings of the specimen, which are then reconstructed.
Three-dimensional images have been obtained from rat cerebrum and rat trigeminal nerve, showing cell structures at 8- to 15-micron spatial resolution. Gray and white matter of cerebrum and neurons in the trigeminal nerve are clearly visible.
X-ray phase-contrast microCT is becoming a valuable tool for studies of organic samples in medicine and biology.
我们证明，使用同步辐射（SR）的显微断层扫描（microCT）可以扩展到包括X射线相衬成像，其灵敏度比传统的衰减相衬高两到三个数量级，并且更适合于研究主要由轻元素组成的标本，光子能量范围至少为1至100keV。
通过将标本放置在X射线干涉仪的一束干涉光束中来产生相衬。使用12keV的X射线，在0到180度之间等间距的180或360个角度设置下记录标本的相投影。一个相投影由四对“相关”射线照片组成，即一对是光束中有标本时拍摄的，另一对是光束中没有标本时拍摄的。在每对之间，一个平行边的相移板旋转，以将两束干涉光束的相对相位改变π/2 rad的倍数。通过计算所有相关射线照片对的相位加权和，获得标本所有角度设置下的真实相移投影，然后进行重建。
已从大鼠大脑和大鼠三叉神经获得三维图像，显示出8至15微米空间分辨率的细胞结构。大脑的灰质和白质以及三叉神经中的神经元清晰可见。
X射线相衬显微CT正成为医学和生物学中有机样品研究的一种有价值的工具。
