Die Zielsetzung dieser Studie war es, für digitale Panoramaschichtaufnahmen die Relation der subjektiven Bildqualität zur Exposition zu bestimmen. An Hand von Humanpräparataufnahmen konnten bei Standardwerten sowie experimentellen Variationen der Expositionsdaten weiterhin Effekte der intentionellen Unterexposition sowie der Strahlenaufhärtung auf die subjektive Bildqualität quantifiziert werden. Die Herstellung der Aufnahmen erfolgte auf einem Sirona Orthophos DS. Dabei wurden 37 Aufnahmen mit Expositionswerten von 60 kV/9 mA - 84 kV/13 mA aus dem Herstellerprogramm erzeugt und mit Hilfe einer modifizierten Steuerungssoftware zusätzliche PSA mit experimentellen Einstellungen von 60 kV/3 mA - 90 kV/11 mA hergestellt. Für die Beurteilung und Auswertung der subjektiven Bildqualität wurde eine individuelle Software (Eldoredo V2.2) entwickelt. 39 Zahnärzte und 5 MTRA beurteilten die Aufnahmen damit an einem Monitor unter standardisierten Bedingungen. Ein iterativer Beurteilungsprozess erlaubte, eine Serie von 1369 (37 x 37) PSA-Abbildungspaaren darzustellen. Für jedes Paar entschieden die Untersucher an Hand definierter Kriterien, ob eine PSA hinsichtlich der subjektiv beurteilten Bildqualität vorzuziehen oder Äquivalenz gegeben sei. Nach statistischer Aufarbeitung der Einzelentscheidungen ließ sich damit für jede Expositionsstufe ein Index der Bildqualität berechnen. Bei Expositionswerten in einem Bereich von 60 kV/9 mA - 69 kV/15 mA der Herstellersoftware und 60 kV/5 - 15 mA sowie 70 kV/5 - 15mA der experimentellen Software fanden sich dabei keine signifikanten Verteilungsunterschiede der Bildqualität. Eine intentionelle Unterexposition bei digitalen PSA-Geräten, etwa bei Kindern oder häufigen Wiederholungsaufnahmen, kann nach den vorliegenden Ergebnissen vertreten werden, ohne dass es dabei zu einer signifikanten Verschlechterung der Bildqualität kommt. Damit ist im Gegensatz dazu bei einer Strahlenaufhärtung in dem untersuchten digitalen System stets zu rechnen. Insgesamt zeigen die Ergebnisse, dass auch digitale PSA-Systeme beachtliche Reserven hinsichtlich der Dosisminimierung aufweisen können. / The aim of this study was to describe the relation of the subjective image quality of digital panoramic radiographs in relation to exposure. In addition, variations of exposure were compared to standard settings, thus evaluating the effects of intentional underexposure on the achievable image quality. A Sirona Orthophos DS unit was used to produce 37 digital panoramic images of a human skull. Exposure values ranged from 60 kV/9 mA to 84 kV/13 mA in the conventional and 60 kV/3 mA to 90 kV/11 mA in the experimental setting. Assessment and evaluation of the subjective image quality were performed with an HTML-based protocol. 39 dentists and 5 radiographic assistants had to assign their preference of an image or equality in 1,369 (37x37) image pairs. The decisions were computed to a quality index for each exposure setting. Statistical analysis demonstrated no significant differences of image quality between 60 kV/9 mA - 69 kV/15 mA in the conventional and 60 kV/5 to15 mA as well as 70 kV/5 to 15 mA in the experimental setting. Following these results, a considerable dose reduction by the means of intentional underexposure can be achieved without any loss of image quality. By reducing the absorbed doses, an increase of kV values up to 80 kV and more is also correlated with dose reduction. However, those images showed high significant loss of quality. In summary, the results demonstrate an equivalent image quality of digital panoramic images over a very wide range of exposure values. The feasible dose reduction might be of interest not only in individuals (minors, repeated images), but also in defining general principles of panoramic imaging.

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Non-destructive testing (NDT) combines the application of the sciences of phys-ics, mathematics, chemistry, and biology to create a comprehensive process, that can be used for inspection, examination, and testing of materials or components to find flaws, defects or discontinuities at the surface, subsurface areas, or inner volume of the component under test. NDT maintains the serviceability of the component after inspection, without causing any damage to its original form or usefulness. In addition to the need for safety, NDT is used to ensure the efficiency and durability of the equipment. NDT is carried out to ascertain that the compo-nents or materials being used are not damaged or faulty and are fit to be used by any personnel. The result of testing can show whether the components need to be repaired or if they are safe for operation. The first NDT method to evolve in the industrial age was X-ray testing (RT). This innovation was discovered by German physicist Wilhelm Conrad Röntgen in 1895. His experiments involved cathode rays which led to not only the discovery of X-ray but to the first Nobel Prize. Among all NDT methods, RT is no exception, so there are still many issues for optimizations even today. One of them is the measurement of the focal spot of X-ray tubes. The size of the focal spot is critical for imaging because it deter-mines the spatial resolution in the X-ray image. The classical way to image focal spots of X-ray tubes is by pinhole imaging using a camera obscura. This is caused by the fact, that X-ray radiation cannot be imaged by lenses like optical wavelengths. This pinhole imaging has been standardized since a long time, e.g., by EN 12543:1999, ASTM E 1165:1992, IEC 336:1982, and DIN 6823:1962. But this method has a natural lower limit, which is defined by the diameter of the pin-hole (today min. 10 µm). Focal spot sizes lower than this diameter cannot be im-aged and measured correctly. Meanwhile, the development of algorithms of Computed Tomography allows a similar approach for focal spot imaging but using pinholes with a much larger diameter than the focal spot size to be imaged. In such a large hole the edge unsharpness of the hole rim by the focal spot size can be measured in different directions, and a first derivative following a CT recon-struction will deliver a nearly identical focal spot image compared to classical pin-hole imaging. There is principal no lower focal spot size limit anymore. Computa-tional problems must be analyzed and application and parameter range for practi-cal focal spot measurements have to be determined.