Magnetic Resonance Imaging
Although magnetic resonance imaging (MRI) dates back to 1946, it was used primarily to study atoms and molecules and to identify their properties. In 1978, the first commercial MRI scanner was available, but it was not until the 1980s that MRI became a useful tool for looking into the human body. MRI works by using a huge magnet to create a magnetic field around the patient. This field causes protons in the patient's body to "line up" in a uniform formation. A radio pulse is then sent through the patient, which results in the protons being knocked out of alignment. When the radio pulse is turned off, the protons create a faint but recordable pulse as they spin or spiral back into position. A computer is used to turn these signals into images.
This nonradiological technique has many benefits. It does not use ionizing radiation, which can be harmful to humans. In addition, it has superb low-contrast resolution, allowing radiologists to view and diagnose a wider range of diseases and injuries within the patient, including brain tumors and carotid artery obstructions. More recent advances in MRI technology are allowing scientists to look into how the brain actually functions.