The matter conversion nodes were part of the holodeck technology aboard the USS Voyager. They were also identified as holodeck conversion nodes. In 2371, Tuvok suggested that the holodeck conversion nodes were contamined with photonic energy and that as a result, Harry Kim undergone the process of matter conversion. When Tuvok and Chakotay disappered like Harry Kim did, B'Elanna Torres was pretty sure that the matter conversion nodes had a malfunction. That photonic energy leaked into the subsystems and damaged the nodes. (VOY: "Heroes and Demons")