Magnetic Resonance Imaging (MRI)

An MRI instrument is specially useful for visualizing soft tissues. In 2002, 60 million MRI procedures were performed. The 2003 Nobel Prize in Physiology or Medicine was awarded to chemist Paul C. Lauterbur and physicist Sir Peter Mansfield for their contributions in developing magnetic resonance imaging. MRI, NMR spectroscopy in medicine, is a powerful diagnostic technique. The “sample” is the patient, who is placed in a large cavity in a magnetic field, and then irradiated with RF energy. Because RF energy has very low frequency and low energy, the method is safer than X-rays or computed tomography (CT) scans that employ high-frequency, high-energy radiation that is known to damage living cells. Living tissue contains protons in different concentrations and environments. When irradiated with RF energy, these protons are excited to a higher energy spin state, and then fall back to the lower energy spin state. These data are analyzed by a computer that generates a plot that delineates tissues of different proton density. MRIs can be recorded in any plane. Moreover, because the calcium present in bones is not NMR active, an MRI instrument can “see through” bones such as the skull and visualize the soft tissue underneath.