Perhaps this is my failure to truly understand the scope of the problem, but where is the real motivation for hackers to compromise MRI machines and CAT scanners? Seriously. Why would somebody go to any level of effort and for that matter risk the felony charges that would come as a result?
I am not questioning that such a thing would be a violation of privacy. I am also not questioning that there is potential for serious harm to be maliciously done to or against somebody. I merely question the scope of the threat in terms of motivating factors. It is clear to me the motivating factor of compromising email. Serious hackers are motivated by Nationalism/Activism, financial gain, or sexual thrill/lulz. Hack the email account of important people or enemies and use private information to damage them or their cause. This can also get you closer to hacking their bank account for money, or possibly finding lewd or compromising content that can be used to blackmail them for money. Or maybe you are just doing it for the thrill of potentially finding sexual content that others are not supposed to see.
Beyond just the occasional script kiddie doing it for the lulz, I don't see many motivating factors to go through the trouble. Even if you leave the door to your house wide open, the vast majority of people won't risk walking in, especially if they know there is little of value in the house, and especially if they know the danger of being caught. It is still trespassing even if your door is open because of the fact that you weren't invited.