Holographic organ replacement

From Memory Alpha, the free Star Trek reference

Holographic organ replacement was a medical procedure developed by The Doctor onboard the USS Voyager in 2371, creating a holographic duplicate of a missing organ to keep a patient alive.

The procedure requires the patient to be completely motionless in an isotropic restraint to allow for the organ to always be in the correct location to operate properly. The holographic organ is then created through file records on the computer and projected into the patient.

This method was used as a holographic lung replacement for Neelix. When Neelix's lungs were removed by a Vidiian. The Doctor's idea worked, but Neelix was confined to an isotropic restraint. The Doctor was later able to transplant one of Kes' lungs into Neelix with help from the Vidiians. (VOY: "Phage")