punctograph

Century Dictionary and Cyclopedia

1. n. An instrument used in radiography to locate a foreign body embedded in the tissues. It consists of two rods, each having a metallic ring at one end. These are placed on opposite sides of the patient under examination. When the shadow of the foreign body appears, viewed with a fluorescent screen, in the center of each ring, marks are made on the person at these points. The position of the rods is then shifted and the operation is repeated several times. The intersection of all the imaginary lines connecting the several pairs of opposite points determines the position of the foreign body. Encyc. Dict.