Filtern
Erscheinungsjahr
Dokumenttyp
- Beitrag zu einem Tagungsband (12)
- Vortrag (8)
- Zeitschriftenartikel (3)
- Dissertation (1)
- Posterpräsentation (1)
- Forschungsbericht (1)
- Forschungsdatensatz (1)
Referierte Publikation
- nein (27) (entfernen)
Schlagworte
- Radiography (27) (entfernen)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (8)
Biocompatible materials such as porous bioactive calcium phosphate ceramics or titanium are regularly applied in dental surgery: ceramics are used to support the local bone regeneration in a given defect, afterwards titanium implants replace lost teeth. The current gold standard for bone reconstruction in implant dentistry is the use of autogenous bone grafts. But the concept of guided bone regeneration (GBR) has become a predictable and well documented surgical approach using biomaterials (bioactive calcium phosphate ceramics) which qualify as bone substitutes for this kind of application as well. We applied high resolution synchrotron microtomography and subsequent 3d image analysis in order to investigate bone formation and degradation of the bone substitute material in a three-dimensional manner, extending the knowledge beyond the limits of classical histology. Following the bone regeneration, titanium-based implants to replace lost teeth call for high mechanical precision, especially when two-piece concepts are used in order to guaranty leak tightness. Here, synchrotron-based radiography in comparison with classical laboratory radiography yields high spatial resolution in combination with high contrast even when exploiting micro-sized features in these kind of highly attenuating objects. Therefore, we could study micro-gap formation at interfaces in two-piece dental implants with the specimen under different mechanical load. We could prove the existence of micro-gaps for implants with conical connections as well as to study the micromechanical behavior of the mating zone of conical implants during loading. The micro-gap is a potential issue of failure, i. e. bacterial leakage which can induce an inflammatory process.
An approach is presented to construct operators for transforming the characteristics of incident radiation to transmitted radiation, as well as operators for transforming the transmitted radiation to measured values. Simu-lating the radiation transport is based on Monte Carlo modeling of the interaction of X-ray photons and electrons with matter. The proposed method permits to construct, for instance, the operator connecting the initial radiation spectrum with the absorbed photon energy penetrating a given object. The elaborated approach provides the possibility of effective mathematical modeling of radiation techniques such as radiography, treating complex multi-component objects. Moreover, the method can be used to construct the operator equation for solving in-verse problems, e.g. the reconstruction of the initial radiation spectrum using simple experimental measure-ments. Comparison with some experimental measurements is presented.
A novel approach to strongly suppress artifacts in radiography and computed tomography caused by the effect of
diffuse background signals ('backlighting') of 2D X-ray detectors is suggested. Depending on the detector
geometry the mechanism may be different, either based on the optical scattering of the fluorescent screen
materials into optical detection devices or Compton or X-ray fluorescence scattering by the detector components.
Consequently, these erroneous intensity portions result in locally different violations of Lambert Beers law in
single projections (radiographs) as function of the detector area coverage and the magnitude of the attenuation.
The absorption of multiple metal sheets is investigated by monochromatic synchrotron radiation, thus excluding
beam hardening. The proposed correction procedure simply requires the individual subtraction of one and the
same fraction of the primary and transmitted mean intensity, as a constant (non-local) scattering mechanism is
assumed.
Computer modelling of non-destructive testing methods has come a long
way from the beginnings in the mid 90s to today. Radiographic modelling for
components with higher wall thicknesses, as they are typical for nuclear
applications, must include precise predictions of scattered radiation and its impact
in terms of contrast reduction. Dedicated or general purpose Monte Carlo methods
with the ability to calculate higher order scattering events are the state of the art for
these applications. Aerospace applications, on the other hand, have stronger
requirements on the modelling code's capabilities to import complex CAD
geometries, and can benefit from faster analytical scatter models, limited to first or
second order scattering events. Similar distinctions can be made for the various
approaches proposed to accurately model geometrical and film unsharpness, film
granularity, film responses, film/foil cartridges and photon noise. This article
presents a state-of-the-art review of radiographic modelling from the perspective of
two important application domains with very different requirements, nuclear and
aerospace.