The children’s game “I spy with my little eye …” is the everyday experience at the airport luggage control, for the dentist starting a root channel therapy, and for the radiologist examining CT-images. With X-rays one can view non-destructively inside objects or patients.
Today, there are about 1500 computer tomographs in German hospitals with which physicians obtain three-dimensional images of the inside of a person’s body. The spatial resolution is in the range of 0.5 mm to 1 mm. While this resolution is sufficient for most medical applications, the fields of non-destructive testing and biomedical research require a significantly higher resolution.
For this purpose, the X-ray laboratory of MIBE hosts two commercial microCT devices (“versaXRM 500” of the company ZEISS and “v|tome|x s 240” of GE as well as a nanoCT setup for extreme spatial resolution developed by the Chair of Biomedical Physics. Together, these devices cover a range of spatial resolution from about 0.1 µm (nanoCT) to 3 µm.
The high spatial resolution is achieved by geometric magnification with a divergent X-ray beam. To achieve this, a sample is positioned as close as possible to a very small focal spot of an X-ray tube.
The X-ray beam is attenuated within a sample depending on the spatially varying composition of its material. The X-ray light thus generates a projection image of the sample onto a two dimensional detector. About 1500 projection images are collected during a 360° rotation of the sample. These images are then combined to generate three-dimensional images.
The total time of data collection depends on the size of the sample, its material, and the required spatial resolution. A measurement can take between some minutes and a few days.
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