Takes more than 15sec to strangle someone. 30 shouldn't cause any serious damage beyond whatever mechanical damage there is from being tugged around. Heck, 2-3min is probably fine if the MRI is located at a hospital.
Edit: Per the article that I would like to remind everyone is well worth reading, he had time to say goodbye to his wife, that would seem to me to imply he wasn't tossed hard enough to be incapacitated.
honestly, probably, yeah, but the guy running the MRI can't know that and should have quenched immediately. You don't just go "oh well he's probably dead, nothing I can do about it now."
Causing severe head trauma or crushing the trachea can be almost instant. A lot of the more serious MRI related injuries are objects flying across the room and hitting someone, especially over the head.
With 3,200 lb/ft forces inches away from 1.2 tera-gauss magnet, all damages were already done to artery, veins, tendons, muscle, by the 20 lbs necklace, all beyond surgical repair.
Per the article, his wife claims that he had time to wave goodbye to her.
A man getting dragged by the neck and hitting an MRI machine head-first is going to make all sorts of hand movements that his grieving widow might interpret as waving goodbye in hindsight.
Edit: Per the article that I would like to remind everyone is well worth reading, he had time to say goodbye to his wife, that would seem to me to imply he wasn't tossed hard enough to be incapacitated.