The newly developed method measures not only the overall beam intensity absorbed by the object under examination at each angle, but also those parts of the X-ray beam that are deflected in different directions "diffracted" in the language of physics. Such a diffraction pattern is generated for every point in the sample. This supplies additional information about the exact nanostructure, as X-ray radiation is particularly sensitive to the tiniest of structural changes. "Because we have to take and process so many individual pictures with extreme precision, it was particularly important during the implementation of the method to use high-brilliance X-ray radiation and fast, low-noise pixel detectors both available at the Swiss Light Source (SLS)," says Oliver Bunk, who was responsible for the requisite experimental setup at the PSI synchrotron facilities in Switzerland.
The diffraction patterns are then processed using an algorithm developed by the team. TUM researcher Martin Dierolf, lead author of the Nature article, explains: "We developed an image reconstruction algorithm that generates a high-resolution, three-dimensional image of the sample using over one hundred thousand diffraction patterns. This algorithm takes into account not only classical X-ray absorption, but also the significantly more sensitive phase shift of the X-rays." A showcase example of the new technique was the examination of a 25-micrometer, superfine bone specimen of a laboratory mouse with surprisingly exact results. The so-called phase contrast CT pictures show even smallest variations in the specimen's bone density with extremely high precision: Cross-sections of cavities where bone cells reside and their roughly 100 nanometer-fine interconnection network are clearly visible.
"Although the new nano-CT procedure does not achieve the spatial resolutio
|Contact: Dr. Andreas Battenberg|
Technische Universitaet Muenchen