MRI machines cost in the six figures [0], last 10+ years and could reasonably do thousands of full-body scans a year. That's basically free by healthcare standards. Rent for the room to put it in would cost more in most cities.

MRI operators are specially trained technicians, because these are complicated machines. But like, semi trucks and photocopiers are fantastically complicated machines, and we seem to be able to keep a pipeline of people trained to operate and maintain them.

So I don't think there's an economic blocker for giving everyone a full-body MRI scan every year or two.

[0] https://www.blockimaging.com/bid/92623/mri-machine-cost-and-...