Your body is composed of atoms. Water and hydrogen atoms make up 95% of the human body. Usually the hydrogen atoms within the body spin at random. When you have an MRI, you are placed in a strong magnetic field that is up to 8,000 times stronger than that of the earth, which causes these atoms to realign and spin all in the same direction. Like CT, MRI acquires images that are a “slice” of anatomy. Using the magnetic fields and radio waves, remarkably detailed cross-sectional images of the body can be obtained. A computer processes these images to produce detailed pictures of the anatomy.