I don't think there was. It's not like people figured out today that bad quantities of helium can be bad, and that big tanks have big quantities of helium, so M

I don't think there was. It's not like people figured out today that bad quantities of helium can be bad, and that big tanks have big quantities of helium, so MRI rooms are routinely equipped with oxygen sensors (see e.g. https://www.pureairemonitoring.com/oxygen-o2-monitor-for-mri-rooms-pureaire-sells-a-hassle-free-10-year-oxygen-monitor/ https://www.pureairemonitoring.com/oxygen-o2-monitor-for-mri... -- not affiliated, it's just the first result on Google). If the spill had been significant, these would have definitely caught it. Besides, an MRI's liquid helium tanks are big, but not that big to cause trouble if they leak over a period of a couple of hours in a ventilated room.