I wonder if the relative rate and effect of false alarms is constant or if it increases as a function of how frequently scans are done. This is related to what studies are finding about cancer screenings. The more screenings you have, the time at which potential tumors are spotted is pushed back, and more non-dangerous tumors are caught. These benign tumors are mistakenly treated as malignant tumors because they were detected too early. I would imagine something similar would happen if people went for all out CT-scans.