A standard dose of ionizing radiation from the scan—which creates a 3-D model of our organs—alters the molecules in the hippocampus, and starts to create patterns that are typical in an Alzheimer’s patient, say researchers from the University of Southern Denmark.

People could probably get away with having just one scan, says lead researcher Stefan Kempf, but he’s concerned about the cumulative effects of having several. Even low radiation doses, equivalent to two CT scans, could trigger molecular changes in the brain that cause cognitive dysfunction, a common symptom of Alzheimer’s disease.

The researchers exposed laboratory mice to doses of radiation that were a thousand times smaller than humans receive in a standard CT scan, and yet it altered molecules in their hippocampus.

People are also exposed to ionizing radiation in airplanes, but levels are far lower than those from CT scans.