Magnetic resonance imaging: Making protons scream

Humans are made of atoms and molecules, which are made of hydrogen.  Hydrogen nucleus is like a magnetic dipole, which is like a small magnet in the body.  When strong magnets are placed next to the patient it creates a uniform magnetic field so these hydrogen nuclei align themselves in a uniform direction of the body. If we send a pulse in the body, the protons will 'scream', eventually the protons in calcium, soft tissue, and fat will go away. If you wait long enough, you will only see protons 'scream' from the water. If we listen at this exact moment, we get images that are virtually only of water.  Liver and muscles have very little water, but the gallbladder, inside of the bowel, kidneys, and tumors are composed of water. Radiologists can look at water maps by magnetic resonance imaging.