Image quality evaluation and patient dose assessment of medical fluoroscopic X-ray systems: a national study.

This study presents the results from a survey conducted by the Greek Atomic Energy Commission (GAEC), during the period 1998-2003, in 530 public and private owned fluoroscopic X-ray systems in Greece. Certain operational parameters for conventional and remote control systems were assessed, according to a quality control protocol developed by GAEC on the basis of the current literature. Public (91.5%) and private (81.5%) owned fluoroscopic units exhibit high-contrast resolution values over 1 lp mm(-1). Moreover, 88.5 and 87.1% of the fluoroscopic units installed in the public and private sector, respectively, present Maximum Patient Entrance Kerma Rate values lower than 100 mGy min(-1). Additionally, 68.3% of the units assessed were found to perform within the acceptance limits. Finally, the third quartile of the Entrance Surface Dose Rate distribution was estimated according to the Dose Reference Level definition and found equal to 35 mGy min(-1).

Performance of medical radiographic X-ray systems in Greece for the time period 1998-2004.

This study presents the results of the on-site inspections performed by the Greek Atomic Energy Commission (GAEC) on conventional X-ray systems, both in public and private medical radiology departments. A part of the inspection concerns the assessment of important radiographic parameters obtained according to a specified quality control protocol and the comparison of the measured parameter values with the corresponding acceptance limits. A total number of 1011 radiographic systems were inspected by the GAEC during the period 1998-2004, with 63.4% of them being privately owned. Analysis of 8 different operational parameters is carried out providing information on the overall performance, as well as on each parameter of the inspected X-ray systems. Tube voltage reproducibility values show the highest percentage of acceptability (98.9%, 99.5% for private and public owned radiographic systems respectively), while linearity of radiation output for private systems (72.5%) and time accuracy for public ones (72.7%) show the worst results. The comparison of the results for the private sector to those of a similar study carried out during the period 1995-1997 indicates a substantial improvement in X-ray systems performance. Higher level of improvement shows exposure time accuracy (12.2% percentile increase) and linearity of radiation output (12.5% percentile increase). Nevertheless, the situation can be further optimized if maintenance and quality control of the radiographic systems are carried out on a more regular basis.

A theoretical model evaluating the angular distribution of luminescence emission in X-ray scintillating screens.

The aim of this study was to examine the angular distribution of the light emitted from radiation-excited scintillators in medical imaging detectors. This distribution diverges from Lambert's cosine law and affects the light emission efficiency of scintillators, hence it also affects the dose burden to the patient. In the present study, the angular distribution was theoretically modeled and was used to fit experimental data on various scintillator materials. Results of calculations revealed that the angular distribution is more directional than that predicted by Lambert's law. Divergence from this law is more pronounced for high values of light attenuation coefficient and thick scintillator layers (screens). This type of divergence reduces light emission efficiency and hence it increases the incident X-ray flux required for a given level of image brightness.