Magnetic Resonance Imaging takes advantage of the fact that humans contain many hydrogen atoms, which are found in the water and fat in our body.
More often than not, these atoms are randomly spinning on their axis like a spinning top, called precessing. Since it is random, there is no order or direction to which these atoms spin.
In the MRI, magnets produce a strong magnetic field, which causes the atoms to point their axes in the same direction so they line up (similar to a compass). For every atom pointing at the patient’s head, there will be one pointing at the patient’s feet. There are a few exceptions, however, that point in the wrong direction. There may be one in a hundred thousand that are like this. It may seem like a few, but remember, our body is made of trillions of hydrogen atoms, so there are many of these anomalies (enough for the machine to work).
A radio frequency pulse is emitted. This pulse causes the abnormal atoms to slowly rotate to the right direction.
When the RF pulse is removed, the anomalies adjust back to their normal position. In this process, they release the energy absorbed from the RF pulse. The energy can be tallied by a computer and then is projected in an image, where different shades and colours mean different levels of energy.
Tissues in our bodies contain different concentrations of water and fat, meaning different levels of hydrogen. Since each tissue can be classified based on its hydrogen content, MRI allows doctors to examine the insides of a patient for different diseases and abnormal tissue growth without having to conduct any surgery whatsoever.
Magnets are placed in different parts of the MRI machine so that the patient’s body can be viewed from various angles. Some machines can produce 3D images based on the different levels of hydrogen that make up our tissues.