A device for assisting a fluoroscope operator in orienting a fluoroscope on an object during a fluoroscope examination, and thereby reduce the time of use and exposure to radiation, which device consists of a sheet transparent to x-ray radiation, preferably disc shaped, possessing orientation indication...http://www.google.se/patents/US5189690?utm_source=gb-gplus-sharePatent US5189690 - Fluoroscopy orientation device
