But doesn't this effectively reduce to "we don't know?" FWIW I have had one CT scan in my life (in childhood I had a seizure which was probably caused by medic

But doesn't this effectively reduce to "we don't know?" FWIW I have had one CT scan in my life (in childhood I had a seizure which was probably caused by medicines I was taking) and they did one to rule out brain tumors. Probably a reasonable choice given that all the other tests for other stuff kept coming back negative. But I wouldn't suggest doing one without either a clear immediate need or else a significant concern and no materialized alternative causes for a symptom.