A Cryostat is a vessel, similar in construction to a vacuum flask used to maintain cold cryogenic temperatures. Three common types of cryostat exist, the MRI (Magnetic Resonance Imaging for Clinical imaging) magnet type, the MR research magnet type and a biological microtome type. Cryostats used in MRI machines are designed to hold a liquid cryogen typically liquid Helium in a liquid state with minimal boil off (evaporation). The liquid helium bath is designed to keep the superconducting magnets bobbin of superconductive wire in its superconductive state. Typically cryostats are manufactured with two vessels, one inside the other. Those used in MRI are built with an outer evacuated vessel, and an inner or, liquid helium vessel. The outer vessel serves as a thermal insulator as well as a thermal sink or heat removal device. The use of a coldhead and a cryocooler combination, removes thermal energy away from the outer vessel, thereby presenting an even cooler stage to the inner vessel maintaining the cryogenic stability of the inner vessel. In biology, cryostats are used for freezing specimens for sectioning and staining for microscopical examination, a type of Microtome. Specimens that are soft at room temperature need to be frozen before sectioning.