Resolution properties of a 2048 x 2048 matrix image intensifier-TV based digital radiography system

Spatial resolution properties of a 2048 x 2048 matrix image intensifier (II) TV based real-time digital radiography (DR) system were investigated. The presampling modulation transfer function (MTF), which includes the unsharpness of the detector and the blurring effect of the sampling aperture, was measured by a slit method. Also determined was the limiting resolution using a bar pattern. It was found that, the spatial resolution in this system is substantially improved relative to previous II-TV based DR systems, and is comparable or even superior to that in a computed radiography system depending on the imaging plate employed. However, the presampling MTF for 2048 x 2048 matrix is comparable to that for 1024 x 1024 matrix in this DR system, because the same sampling aperture is assumed to be used for both matrices. Even under these conditions obtained the improved clinical image since the Nyquist frequency is doubled for 2048 x 2048 matrix. It should be noted that the resolution property in the II-TV based DR system depends on the signal current from the TV image pickup tube (level of image pixel value) and also on the size of the iris in the TV lens. We must pay attention to these parameters when acquiring clinical images and evaluating the resolution properties. Finally, it was demonstrated that smaller focus than that used in a screen-film system can be employed in the DR system due to its high sensitivity, so the geometric unsharpness can be reduced. Therefore, the image resolution of our system was found to be superior to a screen-film system at some geometric magnification factors.