Performance characteristics of a real-time digital x-ray fluoroscopic system using an intensified charge injection device camera and CsI:Na crystal.

A digital x-ray photoelectronic imaging system has been constructed using an optically flat 152-mm-diam, 2.5-mm-thick CsI:Na scintillating crystal. X-ray images formed by the scintillator are viewed by a single microchannel plate intensified charge injection device (ICID) camera and digitized at a real-time rate by a computerized frame-grabbing system. Video images are recorded and selected image frames are subjected to image processing and analysis schemes. Parameters governing the performance characteristics of the system are determined accordingly. For a 152-mm field size at the crystal plane, a spatial resolution limit of 1.50 +/- 0.10 1p/mm (1 sigma) measured at the 4% level of the modulation transfer function of the system has been obtained. This result is consistent with the measurements of the full width at half-maximum of the line spread function which is found to be 645 +/- 35 microns (1 sigma). Similarly, the intrinsic resolution of the CsI:Na scintillator only was found to be 6.5 +/- 0.5 1p/mm (1 sigma). Contrast ratio measurements, which are mainly determined by the quality of phosphor, have indicated a value of 12.1 +/- 0.6, whereas minimum visible details are observed at radiation exposure rates of 100 microR/s. This limit has been reduced to 10 microR/s using the single-scan integrating option provided by the ICID camera. A maximum contrast resolution of 1% corresponding to 100 statistically significant meaningful gray levels is achieved at a maximum exposure rate of 1000 microR/s. Consequently, although the imaging capability of the present system compares favorably with that of conventional x-ray video-fluoroscopic systems, a better performance may be achieved by using a higher resolution cooled dual-microchannel intensified CID camera in conjunction with a thinner CsI:Na crystal and a real-time digital image processing subsystem.