"script" is "prescription" (here in US and possibly elsewhere). Imaging techniques generally require them because medicine considers the potential harm of giving patients an inconclusive diagnosis or a conclusive diagnosis for which there's no treatment. Without a symptom to weigh against these risks, it makes some sense to consider them as not "over the counter".

But in practice I think you can show up at any imaging center and get some kind of "full body MRI" to screen for cancer or some other risk. They'll probably ask about family history and other predispositions but even if you didn't have those they'd still take your money.