Others have answered part of this well so I won't repeat, but there are some other factors that aren't obvious so I'll mention them. The idea that radiation ==

Others have answered part of this well so I won't repeat, but there are some other factors that aren't obvious so I'll mention them. The idea that radiation == bad, magnetism == good is overly simplistic. It's not true that an MRI can't damage you, so much as that the design is careful to avoid the damage. Principal mechanisms here are SAR (specific absorbtion) and PNS (peripheral nerve stimulation). Basically you are dumping a bunch of energy into the body; if it gets to high you start to heat tissue too much, and/or induced currents can cause nerves to fire off aggressively. As a patient you don't need to worry much about this - when you design an MRI you have safety systems in place to limit things like this to safe levels. But your point about high field MRI being "the future" also runs into trouble with the pulse sequences having tighter tolerances, for lack of a better term, than at lower fields, before things like SAR become an issue. So you gain some resolution but some things are harder to do. Also, from a clinical view, higher cost higher resolution scans aren't always what you want. High speed, low cost, lower resolution would be great for a lot of situations. Another issue that is sometimes a problem is that MRI images are not stereotactically accurate (cf CT). Also the somewhat confusingly used "contrast" in this context. It is used both to refer to the natural differentiation of tissues by a modality (e.g. bone is bright white and easy to discern in x-ray, but some soft tissues just "look the same") but also for the introduction of a "contrast agents". The latter case is when you introduce a chemical that will highlight certain anatomical structures. There are different ways to do this but for the most part a) the contrast agents are not particularly safe and b) there are different ones for both imaging modality and for type of contrast. So there are tradeoffs there also. See for a common example, angiography. Finally, siting high field magnets is no joke, which keeps the costs high for capex, and the operational costs are high too.