The Trolley problem is only a problem because there is perfect information in the hypothetical about the consequences of your actions. In real life, you have far less information to go on, which often leads to a more obvious right answer. Shutting down the machine to try to save the one person right in front of you that you know is in immediate danger is the right answer, versus the far less knowable hypothetical future where some number of people may or may not have delayed or relocated scans which may or may not have delayed treatment that may or may not have been immediately necessary as a life-saving matter. As a private MRI operator, you are not morally responsible for keeping your machine functional in order to help keep (figurative) passers-by alive. But you are morally responsible for the health and safety of the patients and visitors on your premises.

It'll need to be shut down anyway to pull the giant metal chain out. You might as well do it right away. Patients can and will be rescheduled to other MRI facilities.

I'm not sure how this is a Trolley problem?

It's a logistics and legislation problem. Hospitals need to be adequately prepared for emergencies and handle backups.

I think a death machine that can't be stopped is an issue.

You're not exactly going to be running many scans with a human corpse stuck in the MRI machine...