X-ray imaging with amorphous selenium: theoretical feasibility of the liquid crystal light valve for radiography

A novel radiographic imaging system based on a liquid crystal light valve is described. A liquid crystal light valve is a photon addressed spatial light modulator that consists of a high resolution, solid-state electrostatic detector (photoconductor) and an electro-optic light modulator (liquid crystal cell) physically coupled in a sandwich structure. We propose a light valve with a thick, x-ray sensitive photoconductive layer and call the system under study the x-ray light valve (XLV). The image formation in the XLV is based on x-ray exposure controlled modulation of light from an external source; the XLV is essentially an x-ray image intensifier that allows the image brightness to be adjusted independently from the x-ray exposure. Thus the XLV may be coupled to an optical imager, such as a charge coupled device (CCD), for image digitization without a secondary quantum sink. A model of the XLV operation is developed to investigate its sensitivity, speed, noise, and resolution. The imaging properties of the XLV are found to be time dependent, which leads to an unusual transmission versus exposure characteristic. The feasibility of clinical use of the XLV based on amorphous selenium (a-Se) photoconductor and a twisted nematic liquid crystal cell is analyzed, and the device is shown to be adaptable to a variety of radiographic imaging tasks.