A new paper in the unconventional journal Medical Hypotheses raises concerns that MRI brain scans could be harmful. E. Z. Meilikhov of the Moscow Institute of Physics and Technology proposes that the powerful static magnetic fields inside an MRI scanner could exert force on tiny particles of the iron-containing mineral magnetite within the brain. These nanoparticles, being magnetic, could move and rotate in the MRI's magnetic field and even be forced inside neurons, he says: