Last time I checked neither x-ray machines nor CT scanners are considered food or drug so why is the FDA involved? I could see the FCC or OSHA but not FDA.
In addition to drugs, the FDA is also responsible for clearing medical products and devices.
Here's this year's list of newly-approved devices so far. If you're going to stick it in your coronary artery, your cardiologist probably wants to know that people smarter than him have spent a lot of time asking a lot of hard questions about it.
Not every device gets the full treatment. But even if you're coming up with a minor tweak to something that's comparatively low risk, it must be cleared under section 510(k): last month's cleared devices. The paperwork's simple compared to a new device approval, but even the 510(k) clearance process means that something as simple as "STERILE LUBRICATING JELLY" is sterile, biocompatible, made in a factory that follows good manufacturing processes, etc.
If it sounds like a horrendous amount of paperwork, well, it is. But the alternative - random uncleared devices without even the practicioner knowing what's in them - is far, far worse. There's a reason that both prescription and over-the-counter medications have standard packaging and labeling requirements, undergo multiyear-long clinical studies, and take the better part of a billion dollars and a decade to bring to market, and why quack 'supplements' advertised on TV and in your email's spam filter have a big disclaimer that "this product is not intended for the diagnosis and treatment of any disease".
If it sounds like TSA used the loophole of "these backscatter X-ray machines aren't intended for the diagnosis and treatment of any disease" in order to circumvent FDA scrutiny, well, I'd have to agree with you there, too. But what's more important: the health of the traveling public, or securing cushy careers for HomeSec bureaucrats?