Improved Medical X-Ray Imaging Device Employing a CdZnTe Detector Array.

The goal of this program is to develop a new method of x-ray imaging in which room temperature semiconductor arrays provide direct, digitized detection. The objectives of Phase I have been achieved, and a Phase II program to develop a practical instrument for medical radiography has been outlined. The approach of Phase I was to experimentally determine the achievable spatial resolution of monolithic cadmium zinc telluride CZT arrays, and to evaluate the feasibility of CZT-based imaging systems for medical radiography. For low x-ray energies useful for imaging soft tissue such as the breast, 50 um spatial resolution with virtually 100 detection efficiency was demonstrated, while for higher energy x- rays used for more general radiography 100 - 200 um spatial resolution was demonstrated. Calculated dynamic range of systems using existing commercial multiplexer readouts is 100 times that of film-screen systems. The Phase I results provide a basis for design of Cd1-xZnxTe instruments for x-ray radiography. The data support electron trapping rather than lateral charge diffusion as the chief mechanism for signal spreading within the semiconductor under conditions of low bias. A model was developed to design Cd1-xZnxTe imaging arrays for radiography. Available readout technologies have been surveyed and, example detectors have been designed for current-mode imaging using a commercial readout. It is concluded that CZT imagers are presently both technically and economically feasible in scanning or focusing systems, similar to existing systems for breast imaging and fluoroscopy.