Gamanit,
Brain death isnt determined by scans. It is (theoretically) possible there is some brain function that is irrelevant. I have news for you btw “regular” death isnt determined by scans either it is done by listening and feeling for breaths/heartbeat. No scans whatsoever are required nor routinely done
You do not remember correctly. A heart can pump on its own modified for younger audiences even with a spinal cord injury if on a ventilator (provided blood loss is prevented)