They don't! MRI scanners work just fine with regular electromagnets, or even plain old normal magnets. However, work better with stronger magnetic fields. In p

They don't! MRI scanners work just fine with regular electromagnets, or even plain old normal magnets. However, work better with stronger magnetic fields. In practice normal magnets end up being extremely large and heavy, and electromagnets end up using massive amounts of power. Both options are also limited in their field strength because getting enough stuff close together is tricky. A superconducting magnet is an electromagnet which is way smaller and uses orders of magnitude less power. For extremely high field strength MRIs they are the only viable option, and for regular MRIs they are often the best option.