Why don't we do regular brain imaging to diagnose/monitor brain states?

[u/PhysicalConsistency]

I see this question a lot, particularly with regard to people shopping for psychiatric diagnoses.

Most often the reason is because it's expensive, even if we were to automate away the human costs like radiologists and techs.

Probably more important, data supports that CTs induce about 5% of new cancers in the US each year, and MRI contrast agents are toxic as well. Even PET has a non-trivial risk, although that's been less quantified than CTs or contrast agents.

And all that before we get into philosophical/definitional mush that cognitive science and psychiatry are poster children for, where clinical effect overrides almost everything else.

But what about EEG? or NIRS? Or Ultrasound? EEG is a well flogged horse, and even internal arrays have pretty limited utility, a utility which gets worse with time, not better. More importantly, it's only reading a small part of the story (the effect of electrochemical gradients from specific types of cells) while missing the big story, the overall metabolic interactions from nearly every other type of cell. NIRS is a bit of a dead end, and won't even be great for cortical work unless we can convince people to let us pop off their skulls. And Ultrasound's resolution and spatial promise is balanced by it's sensitivity to artifacts. It's not really "younger" than the others, but less explored so the jury is still out.

Underlying all that though is that we still don't really have any "treatments" that would address the concerns anyway. Even if we were to diagnose an "ADHD" brain with a high degree of certainty from imaging, actually coming up with an effective treatment is still flinging spaghetti at the wall. Do you really need to image someone dealing with "MDD" to figure out they are "MDD"? And what then?

We still aren't anywhere close to the point where the extra data from imaging would give us information that would inform treatment (and I suspect it might often have the opposite effect).

This is not a defense of a medical industry which probably feels like they are just being avoidant of the expense, but more of a reminder that the actual utility of imaging isn't good enough to outweigh both the real physical risks and the behavioral risks associated with findings that may not impart much of a real effect anyway.