[Influence of tandem optics and television tube of modern digital fluoroscopy equipment on image quality]. / Einfluss von Tandemoptik und Fernsehaufnahmeröhre moderner Durchleuchtungsanlagen auf die Bildqualität.

The influence of the tandem optics and the TV-tube to the image quality of 1k- and 2k-radiographs of a modern fluoroscopy equipment should be assessed on the basis of objective parameters and clinical requirements. Radiographs of different phantoms with 1k- and 2k-image matrix, different illumination point corrections (IPC) and signal gray levels were taken, examined and evaluated, in order to determine the objective image parameters and the clinical relevancy of these parameters. On the one hand, the digital images data could be used directly for evaluation; on the other hand, the radiographs could be visually evaluated by experienced radiologists within the framework of a blind study. The IPC is controlled by the aperture of the iris diaphragm and the insertion of a neutral gray filter in the tandem optics. The larger the aperture of the iris diaphragm (at constant image receiver dose) the higher were gradation, signal to noise ratio (SNR) and image homogeneity. Furthermore, the larger the aperture, the lower was the square wave response function (SWRF). The insertion of a gray filter in the tandem optics decreases gradation, SNR and homogeneity, and improves the SWRF.

Very-long-baseline radio interferometry (VLBI) observations of gamma-ray blazars: results from millimeter-VLBI observations.

VLBI observations of the extremely gamma-bright blazar PKS 0528+134 at 8, 22, 43, and 86 GHz reveal a strongly bent one-sided-core jet structure with at least three moving and two apparently stationary jet components. At the highest observing frequencies the brightest and most compact jet component (the VLBI core) is unresolved with an upper limit to its size of approximately 50 microarcsec corresponding to approximately 0.2 parsec [H0 = 100 km.s-1.Mpc-1 (megaparsec-1), q0 = 0.5, where H0 is Hubble constant and q0 is the deceleration parameter]. Two 86-GHz VLBI observations performed in 1993.3 and 1994.0 reveal a new jet component emerging with superluminal speed from the core. Linear back-extrapolation of its motion yields strong evidence that the ejection of this component is related to an outburst in the millimeter regime and a preceding intense flare of the gamma-flux density observed in early 1993. This and the radio/optical "light curves" and VLBI data for two other sources (S5 0836+710 and 3C 454.3) suggest that the observed gamma-radiation might be Doppler-boosted and perhaps is closely related to the physical processes acting near the "base" of the highly relativistic jets observed in quasars.