Assessment of target recovery after TV camera saturation in X-ray fluoroscopy using a personal computer with frame-grabber

X-ray fluoroscopy images were digitized with a personal computer and frame-grabber system. This system was used to measure the recovery from saturation of the target of a TV camera by calculating the time at which contrast falls to 50% (C 1/2). This measurement was performed on images of: (a) a rotating lead disk with a slit at its side and (b) a square hole in a thick lead sheet. These images represented the moving (MOTR) and stationary (SOTR) object target recovery. The SOTR method produced much higher C 1/2 values in two mobile fluoroscopy systems used for cardiac catheterizations where waveforms permitted the application of both methods. The SOTR method was also applied to three additional fluoroscopy systems. It was found that, contrary to expectations, C 1/2 increased with exposure rate in all five machines. Target recovery characteristics of the machines tested, represented by the gradient of C 1/2 against exposure rate, were found to increase with inherent noise level measured in the vidicon camera target. The set-up used here for measuring target recovery proved to work quickly and reproducibly for both SOTR and MOTR. If initial values are calculated then the condition of any fluoroscopy system may easily be followed irrespective of the method used.