INFORMATION TRANSFER EFFICIENCY OF X-RAY IMAGE INTENSIFIER-BASED IMAGING SYSTEMS.

摘要

The information transfer efficiency of any quantum detection imaging system can be described by a unique measure: the detective quantum efficiency {DQE(f)}, which is a function of the statistically independent frequency channels. The DQE(f) is a combined descriptor which takes into account the signal transfer as well as noise transfer properties of a complete system. For a complicated multistage imaging system, each system component contributes noise. In this dissertation, physical and mathematical models for noise analysis are developed and verified experimentally with an x-ray image intensifier (XRII)-based imaging system. In such a system, the DQE at low frequency range is primarily determined by the x-ray detection and scintillation processes at the CsI layer of the XRII. The effects of x-ray photon energy and sensor layer thickness on DQE are measured in detail. Numerical calculations based on a physical model of x-ray interactions show a general agreement with the experimental data. At higher frequencies, the DQE behavior becomes more complicated. A mathematical model which combines the micro-image properties and noise statistics is formulated to analyze the noise power spectrum (NPS) of a linear n-stage imaging system. Measurement of NPS components of an XRII system verifies the validity of this analytical prediction. The associated image transfer properties are also measured with emphasis on the effect of signal-induced background on the image information transfer. The low frequency data derived from these image property measurements show further agreement with the numerical calculations based on the physical model. As a result of this predictability of information transfer efficiency, system gain and recording capacity are emphasized in the design consideration of a projected high performance XRII radiographic system.