- Radiation. This is why people shouldn't get these scans several times a year, but 1-2 are very unlikely to move the needle. The average radiation from a full chest CT is just under the average dose for ~2 years of normal background radiation. (I don't know if a CTA uses less than average.)
- Acting on something you would otherwise have ignored, where ignoring it might have been the right answer. The main problem here is that it's hard to get a medical opinion saying "you should ignore this" because of perverse incentives: there's an aversion to recommending doing nothing because that could lead to a lawsuit, whereas "overtreatment" will not get a doctor sued. However, you can make a deliberate decision to do this anyway even after getting the scan; seek second and third opinions, consider alternatives, weigh risk versus reward, make a considered decision.
There are two known harms from scans:
- Radiation. This is why people shouldn't get these scans several times a year, but 1-2 are very unlikely to move the needle. The average radiation from a full chest CT is just under the average dose for ~2 years of normal background radiation. (I don't know if a CTA uses less than average.)
- Acting on something you would otherwise have ignored, where ignoring it might have been the right answer. The main problem here is that it's hard to get a medical opinion saying "you should ignore this" because of perverse incentives: there's an aversion to recommending doing nothing because that could lead to a lawsuit, whereas "overtreatment" will not get a doctor sued. However, you can make a deliberate decision to do this anyway even after getting the scan; seek second and third opinions, consider alternatives, weigh risk versus reward, make a considered decision.