Initial technical and clinical evaluation of a new universal image receptor system.

The aim of this study was to evaluate the physical performance of an experimental flat-panel digital X-ray detector plate (FDXD), and to assess its clinical potential in radiographic and fluoroscopic mode. The efficiency of the detector was assessed by calculating the low-frequency detective quantum efficiency (DQE(0)), and a measure of image quality was obtained using a threshold contrast detail detectability (TCDD) test object. A range of clinical examinations were also carried out, and the results reviewed by members of the radiology staff. The DQE(0) of the system was calculated to be almost 75%, compared with a value of approximately 20 % for modern computed radiography equipment, offering the potential for increased image quality or significant dose reduction. Measurements using the TCDD test object demonstrated a corresponding advantage for the FDXD in image quality and dose efficiency. Clinical studies are producing radiographic results which are at least the equal of the best currently available digital technology, and a limited number of examinations using fluoroscopic mode at 25 frames per second have been equally encouraging. Equipment using FDXD technology could potentially fulfill all the radiographic and fluoroscopic requirements of the digital department, with improved image quality and dose efficiency.

Random walk type models for indicator-dilution studies: comparison of a local density random walk and a first passage times distribution.

The relative merits of the local density random walk and the first passage times distributions were compared with respect to their practical applicability in cardiovascular research and clinical practice. Open indicator-dilution curves of varying shape were used, and reference values for area and mean transit times were calculated numerically. Curves not perturbed by recirculation were obtained in two different ways. Thermodilution curves were obtained in an animal model at the left and the right side of the heart respectively and conductivity curves with 0.5% NaCl solution as indicator were obtained in a hydrodynamic circulation model. The fits of the two types of distribution were equally accurate for the more symmetrical curves; for very skewed curves the local density random walk fit proved to be more accurate. This result could be related to the greater difference in shape between the first passage times and local density random walk distribution for a large degree of asymmetry. For this reason the local density random walk distribution for fitting indicator-dilution curves was used in a variety of other experimental conditions.

Model studies on the influence of nonstationary flow on the mean flow estimate with the indicator-dilution technique.

The applicability of the indicator-dilution technique for the estimate of the mean flow under circumstances of nonstationary flow is investigated by model studies. The studies comprise experiments using a hydrodynamical model as well as calculations with a compartmental approach. The main conclusions are: (1) The influence of nonstationary flow on the mean flow estimate with the indicator-dilution technique can be described accurately by a mathematical model based on a mixing-chamber approach. (2) The relative error in the mean flow estimate by a single measurement is dependent on the system parameters (number and time constant of mixing chambers) and the flow parameters (relative amplitude and relative frequency of flow variation and the phase with respect to the variation at the moment of injection). (3) Errors due to cyclic nonstationarities of the flow can be reduced strongly by averaging over two measurements with injection at two points of time with phases pi radians apart.