Because x-rays can penetrate almost any object and yield information of the interior of specimens opaque to visible light,
they have been used as a powerful tool for the investigation of all kinds of materials and bodies right from their
discovery by Conrad Roentgen1 in 1895. Among the multitude of different ways such studies can be performed the
imaging methods play a predominant and most important role. The intent is to describe some interesting and relevant
ways x-ray imaging has been employed up to now. Clinical tomography will be excluded here. Recent surveys exist in
the literature, e.g.2.
Attenuation-contrast tomography with monochromatic thermal neutrons was developed and operated at guide station S18 of the institute Laue-Langevin in Grenoble. From the S18 spectrum the neutron wavelength (lambda) equals 0.18 nm was selected by employing a fore crystal with the silicon 220 reflection at a Bragg angle (Theta) equals 30 degrees. Projections were registered by a position sensitive detector (PSD) consisting of a neutron-to-visible-light converter coupled to a CCD detector. Neutron tomography and its comparison with X-ray tomography is studied. This is of special interest since the cross section for neutron attenuation ((sigma) atom) and the cross section for neutron phase shift (bc) are isotope specific and, in addition, by no means mostly monotonous functions of atomic number Z as are attenuation coefficient ((mu) x) and atomic scattering amplitude (f) in the case of X-rays. Results obtained with n-attenuation tomography will be presented. Possibilities and the setup of an instrument for neutron phase-contrast tomography based on single-crystal neutron interferometry will be described.
Synchrotron radiation and x-ray microtomography based on absorption contrast (performed at HASYLAB at DESY/Hamburg and BAM/Berlin) have been used for imaging of temporal bones and various internal components in situ at spatial resolution down to 7 micrometers with potential enhancement into the submicron range. Due to the volume imaging approach, several hidden structures (e.g., intra-ossicular channels) were revealed. Using several 3D-image processing techniques all data have been segmented into objects (e.g., bony ossicles, ligaments, fluids, air spaces) and subsequently transformed into vectorized data models. Because they are based on the original voxel resolution their content of vector primitives (e.g., polygons) is huge compared to recent models. Therefore they became polygon-reduced to fit into current computation limitations. So far individual data models of the entire hearing apparatus from tympanic membrane to cochlea out of intact specimen, including separate models of ossicles, ligaments and other components have been obtained, provided, in interchangeable data formats (e.g. vector-based: IGES, STL, VRML) and introduced into FEA for modeling of acousto-mechanic transfer characteristics of the middle ear. Their pseudo and real 3D- visualizations (rendering, autosteroscopic display, enlarged solid models) allow easy understanding of the anatomy and pathology of the human hearing organ and may support patient and student education in the field of otology and audiology.
A new set-up for high-energy micro tomography using synchrotron radiation at beamline BW5, HASYLAB at DESY, is presented. Results demonstrating the high spatial resolution by performing attenuation-contrast microtomography in the photon-energy range of 60 to 150 keV are given. The feasibility for investigation of larger samples by applying scanning techniques is demonstrated.
Microtomography using synchrotron radiation is widely used in fields of e.g. medicine, biology and material science. Using attenuation contrast at photon energies in the range of 8 to 25 keV and phase contrast at photon energies of 12 keV, 20 keV and 24 keV the method of microtomography is applied to a large number of samples. A comparison of the two different contrast mechanism is presented. Feasibility, advantage and limits of these methods are shown in theory and by experiment. New developments in high-energy microtomography using synchrotron radiation in the energy range of 60 to 100 keV are described. Using attenuation contrast, several samples are investigated. For the investigation of larger specimens with diameters on the order of 1 - 2 cm, the use of a new (mu) CT-technique based on scanning a 2-dim. X-ray detector is demonstrated. At 70 keV photon energy an X-ray LLL-interferometer is tested and used to measure phase projections. For the first time, phase- contrast microtomography could be applied to weakly and normally absorbing material at a high photon energy.
The principle and experimental l realization of x-ray phase- contrast in compute assisted microtomography ((mu) CT) at the micrometer resolution level is described. The camera used is a modification of a setup previously developed by us for attenuation-contrast (mu) CT using synchrotron x-rays. Phase detection is accomplished by employing the x-ray interferometer. By using x-ray phase contrast it is possible to image structural details in low-z biological tissues much better than with absorption contrast. The advantage of phase over attenuation contrast is not limited to light element or to low x-ray energies. Examples of applying phase contrast (mu) CT to the structural investigation of rat trigeminal nerve are given.
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