An electromagnetic lens is designed to focus the electron beam by using a suitable shaped magnetic field. The lens is a symmetric electromagnet consisting of wire coil, magnetic iron yoke and iron pole pieces. A strong magnetic field is produced by passing a current through the windings. This field acts as a convex lens; converge off axis rays back to focus. Like an optical lens, a magnetic lens is characterized by focal length and can be altered by changing the strength of the current.

An embolization can occur by movement of a blood clot, piece of tissue, or pocket of air or gas through the bloodstream until it stops in place, cutting off the flow of blood.
An embolization during a medical procedure is the insertion of material such as gelatin sponge or metal coils through a catheter into a blood vessel to stop hemorrhaging, excessive bleeding or cut off blood flowing to a tumor or arteriovenous malformation.