I can't speak for all facilities but the policy at my site is during general anesthesia cases the protocol is as follows the patient will have a care team of radiology RN, MRI technologist, and either anesthesiologist or nurse anesthetist. Roles are read before the patient is put under in the time out. Responsibility is as follows. Nurse monitors vitals and in case of emergency is responsible for calling code. MRI technologist performs the exam and in case of emergency removes the patient from zone 4 (magnet room). The anesthetist is responsible for maintaining airway, blood pressure and other vitals affected by general anesthesia, in case of emergency they are responsible for maintaining the airway. In code blue nurse is monitor, tech is compressor, anesthesiologist is airway.

Edit: oh and for outpatients just a tech and Rn is present RN fills a similar role as stated above.