Evaluation of afterglow response in irradiated intensifying screens

A simple method is presented for the calculation of the duration of afterglow in intensifying screens using a personal computer and frame-grabber system connected to a CCD television camera. The camera was set to face one of the screens and x-ray fluoroscopy images of a rotating lead disc with a slit at its side were digitized with the system and were used to measure the time at which the contrast on phantom slit images falls to 50%. This time was taken to represent afterglow. The method was applied on three representative types of intensifying screen: a Dupont-Cronex III plus, a Kodak Mini screen used for mammography, an AFGA-Curix Ortho Regular and one fluoroscopic screen made by Laboratorio DLFISICA. The time taken by afterglow to fall to 50% was calculated to be 19, 21, 9 and 52 ms respectively, demonstrating the advantage of the rare earth screen.