How Does an MRI Machine Work?

Magnetic Resonance Imaging (MRI) exploits the fact that the human body is mostly water, and each water molecule contains hydrogen atoms with a single proton that acts like a tiny magnet. The MRI machine generates a powerful magnetic field (typically 1.5 to 3 Tesla — thousands of times stronger than Earth magnetic field) that aligns these protons. Short bursts of radio-frequency energy then knock the protons out of alignment. As they relax back, they emit radio signals whose strength and timing vary depending on tissue type. A computer processes these signals into highly detailed cross-sectional images. Unlike CT scans, MRI uses no ionising radiation.