An MRI, or Magnetic Resonance Imaging, was a machine used to produce detailed pictures of a patient's innards such as the brain, skeleton, and heart. A patient would lay on a platform that was inserted into the imaging device.
An MRI at the Royal Hope Hospital was amplified to 50,000 tesla by the Plasmavore Florence Finnegan when it was transported to the Moon. This was enough to send a lethal shockwave for hundreds of thousands of miles. Such a wave would fry the brainstems of every living creature in its path. The range covered half the Earth. (TV: Smith and Jones)