Maybe it would end up fine “in the long run” but you cannot ignore the significant issues arising at the beginning (and at each release of a more performant tool): what do you do if you find something that “shouldn't be there".

Without clear hypotheses you will have a lot of false positives. Which are quite costly in healthcare.

The fundamental problem is that you generally can't diagnose simply from shapes. Scans show shapes, shapes cause concern, concern leads to invasive procedures, results are negative.

How do you measure the body regularly without potentially introducing problems just by measuring it?

> If the whole population had a full body scan every quarter, the “weird” things would feel more like the noise they are.

That's a tautology. We already have quite robust methods for detecting developed anomalies, treating every anomaly below standard human-to-human variation effectively raises the noise floor to already developed anomalies, defeating the purpose of population wide routine scans.