What is "perfluorobutane"

n. A colourless gas used in fire extinguishers and in ultrasound imaging.

Perfluorobutane (PFB) is a colorless gas. It is a simple fluorocarbon with a n-butane skeleton and all the hydrogen atoms replaced with fluorine atoms. It is used as a replacement for Halon 1301 fire extinguishers, as well as the gas component for newer generation microbubble ultrasound contrast agents. Sonazoid is one such microbubble formulation developed by Amersham Health that uses perfluorobutane for the gas core.