The Doctor utilizes a cellular regenerator on Ensign Kim
A cellular regenerator was a medical device utilized by Starfleet in the 24th century.
In 2373, The Doctor utilized a cellular regenerator, along with a bio-electric field generator and a subdermal scalpel, to perform a spinal shunt on Ensign Harry Kim, who had been severely injured in an alien attack. Although The Doctor was successful in saving Kim's life, he failed to save the life of Ensign Ahni Jetal, who had also been injured in the attack. (VOY: "Latent Image")