X-ray tomography / Computer tomography
Dipl.-Ing. Andreas Szentivanyi
MSc., Dipl.-Ing. Tanja Wadouh
X-ray tomography (also called Computer tomography, abbr. CT) is one of the tomo- graphic measurement techniques which are used at and enhanced by the Institute of process engineering of the University of Hannover. At the beginning of the 1970s X-ray tomography was developed for medical diagnostics. This still is its main field of appli- cation. But meanwhile X-ray tomography is increasingly used for testing technical ma- terials and components and for reverse engineering. Process engineering is a new field of application for X-ray tomography.
X-rays are electromagnetic radiation of a short wavelength. They have the ability to penetrate materials (to a certain degree). Like conventional radiography X-ray tomo- graphy is based on irradiating the measured object and measuring the intensity of the X-rays which have been attenuated by the object.
|figure 1: principle of radiography|
In conventional radiography a projection of the measured object is taken. This projection is a 2-dimensional image of the 3-dimensional measured object. This leads to a loss of information. Objects that lie behind each other on the path of the X-rays are superim- posed in the measured projection. Their exact position cannot be determined after- wards.
X-ray tomography is based on irradiating the measured object as well. But in contrary to conventional radiography, the object is rotated and projections are measured in many directions successively. Afterwards from this multitude of projections a slice through the object is calculated using a computer. A full 3-dimensional CT-scan consists of many such slices through the measured object. As an alternative to rotating the measured object, the X-ray source and X-ray detector can be rotated around the static object. This option is mainly used in medical
X-ray tomography. X-ray tomography is a non-destructive measurement technique. The measured object is not influenced, altered or even destructed. Information is gained about details of the object which are inaccessible to other non-destructive measurement techniques (like embeddings in a material, composite materials, undercuts, voids, etc).
The following pictures show examples from various fields of application of X-ray tomo- graphy such as medicine, material and component testing and process engineering.
figures 3-5: blood vessels in brain, cylinder head, transmission housing
figures 6+7: trickle bed, structured packing
At the Institute of process engineering X-ray tomography is used as a non-intrusive measurement technique for complex multiphase flows to determine the spatial distribution of the various phases. It is used to measure the multiphase flow in packings and trickle bed reactors. Dual-energy X-ray tomography is used to measure the flow in a three-phase bubble column. This is an enhancement of the X-ray tomography described above. By using X-rays of 2 different wavelengths the local volume fractions of all 3 phases can be determined. For this purpose a specially designed X-ray tomograph is build at the institute.
Scan - Service
The Institute of process engineering owns and operates an industrial X-ray tomograph. Besides using this tomograph for the own research work, this machine is offered to customers. Service measurements can be carried out for customers from various fields of industry and research. Do you have a specific measurement task? Would you like to find out if X-ray tomo- graphy suits your application? Do you need tomographic measurements, but don't want to buy your own X-ray tomograph? Please contact:
- Cylinder head: measurement of inner and outer contours, cheching for pores, voids and embeddings
- Car axle: measuring of contour, implementing into CAD system
- Sculpture: measuring of contour with complex undercuts for rapid prototyping duplication
- Process engineering: liquid phase distribution in packings and trickle beds
- Composite, fiber reinforced materials: checking for delaminations, voids and embeddings