How an MRI Works
A patient lies flat on their back on a platform that slides inside the MRI, or magnetic resonance imaging, machine. The MRI machine is shaped like a large circle with the platform sliding into the centre. The patient is only inserted far enough to cover the body part that is being examined. The MRI is made up of magnets that create a magnetic field stronger than that of the earth itself. This strong magnetic field causes the nuclei in the atoms inside the patient's body to line up. A short burst of radio waves then hit them, causing them to flip over and return to their original position. As they do this, they briefly send back their own radio waves that the machine reads and translates into an image. The magnetic field continues to affect the body while in the machine, giving it time to capture an image of the entire area under examination.
Types of MRI Magnets
There are three main types of magnets used in an MRI machine: resistive magnets, the permanent magnet and superconducting magnets. Resistive magnets are wound around a cylinder and create a magnetic field when electricity runs through them. They are cheaper but use more energy to create the required strength for the magnetic field. The permanent magnet is very large and heavy, and always is always charged. Electricity is not needed to generate the magnetic field in the permanent magnetic. Finally, superconducting magnets resemble the resistive magnets but are covered in liquid helium during the MRI scan. This lowers the amount of electricity needed to create the magnetic field. This is the most commonly used type of magnet in an MRI.
How MRI Magnets Work
The magnets work together in a very controlled environment to make sure the magnetic field is equal throughout the machine. The amount of electricity and the number and strength of the magnets control how strong or weak the field is. There are also three gradient magnets used in the MRI machine to help this process. They are very weak magnets, unlike the others in the machine. It creates a variable field after the other magnets have been activated to create a stable field first. The gradient magnets are turned off and on quickly to create different pictures, or "slices", for a more thorough examination of the patient.