A mechanism for cooling the anode of an x-ray tube using a phase change material to transfer heat away from the anode. The x-ray tube is joined to a sealed heat exchange chamber which contains a liquid metal as a liquid to vapor phase change material (L-V PCM). The back side of the anode is exposed to an interior of the heat exchange chamber, and a jet sprayer inside the heat exchange chamber sprays a liquid of the metal onto the back side of the heated anode. The L-C PCM evaporates on that surface to carry away the heat, and the vapor then condenses back into the liquid on the cool surfaces of the heat exchange chamber. The surfaces of the heat exchange chamber may be cooled by convection cooling. Optionally, pipes containing a circulating cooling fluid may be provide inside the heat exchange chamber.