Davalos, Arnulfo Martinez; (1995) An investigation of the imaging performance of new digital x-ray detectors. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Recent advances in detector technology have made possible to develop imaging detectors with enhanced x-ray response and fast readout electronics. In this project a quantitative evaluation of the imaging performance of two of these new x-ray detectors has been made and their possible application in the field of medical imaging has been studied. The systems investigated are based on position sensitive detectors, and produce digital output in real time. Gaseous and semiconductor detectors that use different modes of x-ray detection (counting mode and integrating mode) and different irradiation geometries (scanned projection and area projection) were considered. An experimental procedure for the assessment of the imaging characteristics of digital x-ray detectors was set up. The evaluation process was based on widely accepted image assessment and dosimetry techniques. It included both subjective and objective measurements of image quality, and took into account the effect that various digital parameters - such as sampling aperture, sampling distance and quantization - have in the imaging characteristics of the digital radiography system. Subjective measurements were based on phantom studies, and consisted in the determination of the threshold-contrast detail-detectability properties of the imaging systems under investigation at different exposure levels. Objective measurements included the study of spatial transfer characteristics and resolution using modulation transfer function analysis, and of system noise characteristics such as noise power spectrum and detective quantum efficiency. The results of the experimental measurements have been compared with equivalent figures of system performance obtained with conventional film-screen combinations. Computer models were used to investigate the parameters that alter the performance of the detectors, and to study the effect that exposure conditions (e.g. filtration and kVp) and photon statistics have upon image quality.

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