Microcellular scan

A microcellular scan is a medical procedure in which an individual's brain is examined for irregularities.

In 2153 of an alternate timeline, after Captain Jonathan Archer was struck by a spatial anomaly, a microcellular scan performed by Doctor Phlox revealed that Archer's hippocampus had been infected by parasites which were preventing his formation of long-term memories. Many years later, when one cluster of parasites were eradicated from Archer's brain, that same cluster also disappeared from microcellular scans taken in the past. Theorizing that eradicating the parasites in the present also annihilated them in the past, Archer, Phlox, and T'Pol successfully destroyed the remaining parasites, creating another timeline in which the parasites did not infect Archer. (ENT: "Twilight")

In 2371, Doctor Bashir performed a microcellular scan on Chief O'Brien when the latter was experiencing shifts in time. The results of the scan revealed that the temporal shifts were causing damage to the chief's cerebrospinal nerve cells, which would only get worse if the shifts continue and could ultimately lead to death. (DS9: "Visionary")

In 2372, while trapped in an alternate timeline in which he was not aboard the USS Voyager when it was stranded in the Delta Quadrant, Harry Kim suggested that Lasca and Admiral Strickler run a microcellular scan on his cerebral cortex to prove that his memories were not altered and that he really was Harry Kim. (VOY: "Non Sequitur")

In 2373, in a hallucination caused by a non-corporeal lifeform, Kathryn Janeway saw the Doctor perform a microcellular scan to determine that she had been infected with the Phage virus. (VOY: "Coda")

Later that year, Voyager's EMH ran a microcellular scan on Dammar to search for residual energy traces after the Nyrian claimed his mysterious appearance on the ship involved a number of physical discomforts. (VOY: "Displaced")