Fluoroscopic imaging: quantitation of image lag or smearing

Image lag (smearing or persistence of the image) is a characteristic of video imaging systems that is exhibited when rapidly moving objects are blurred due to motion. Video pick-up tubes can exhibit differing amounts of image lag depending on the age of the tube, the amount of light reaching the tube, the set-up parameters used (e.g., beam current and target voltages, etc.), and the tube type. We describe a new quantitative method for measuring image lag that requires only a storage oscilloscope and an inexpensive shutter. Examples of lag measurements on different systems under varying clinical conditions are given. Suggested limits for clinically acceptable amounts of image lag range from 10% to 50% depending on the particular application.