Use of a quality index in threshold contrast detail detection measurements in television fluoroscopy.

The use of a single index to assist in quality control procedures of X-ray television fluoroscopy systems was investigated. A single quality index was devised incorporating a measure of threshold contrast detail detectability (TCDD) performance and taking into account image intensifier input kerma rate, field size, differences in radiation beam quality, and pulsed fluoroscopy. This was applied to a number of clinical systems to investigate changes in image quality index quantified over time. Accepted measurement protocols were used to obtain these measurements. The results show system performance for different systems and can establish the decline in performance parameters over time or assess non-optimal image quality with clinical systems in field measurements. The systems studied were assessed with a variety of performance parameters including TCDD results, low contrast sensitivity, limiting resolution, and image intensifier input kerma rate under clinical modes of operation. The TCDD quality index, and dose normalized quality index, were found to be useful image quality assessment parameters for serial testing of systems, which augment the use of graphical methods for the display of TCDD curves.