How does MRI use electromagnets?

Answer 1

• An MRI uses electromagnets to produce an super strong magnetic field. This field causes changes in the behavior of cells and when the magnet is off those cells emit a detectable wave that is picked up by sensors. A computer then interprets those signals and creates a picture of the tissue. The picture is then looked at by specialists to find things that are not normal compared to surrounding tissue.

Answer 2

In the early days of MRI research, the magnets were resistive (a big coil of wire), or permanent (like a bar magnet, but bent around into a C-shape). However, it's not possible to make a very strong permanent magnet, and resistive magnets are not very efficient (lots of energy is wasted as heat), so almost all modern MRI magnets are superconductors.

The magnet consists of a large coil of superconducting wire (something like niobium titanate). This only superconducts when it is kept close to absolute zero (-273 degrees Celcius), so it is immersed in a bath of liquid helium to keep it cold. Because the magnet windings are superconducting they have no resistance, so the magnet doesn't dissipate energy as heat.

Current clinical magnets are typically 1.5 Tesla. University research magnets are between 3 and 9.4T for human systems, with small animal magnets going up to 16T (it's easier to produce a larger magnetic field over a smaller volume). By way of comparison, the earths magnetic field is about 50uT (microTesla).

Answer 3

An MRI scanner uses several magnets depending on its design to create an even gradient of magnetic field. The magnet creates a magnetic field (BO) which lines up the hydrogen atoms in either a paralel or anti-paralele direction. A radio pulse then knocks the hydrogen atoms out of alignment radio waves act like magnets so we call this (B1). We can measure how long it takes the hydrogen atoms to go back to normal after they have been knocked and that's an MRI scan.