Unlike X-rays and CAT scans, the MRI, or magnetic resonance imaging, does
not make use of ionizing radiation to create inside pictures. Invented by
Dr. Raymound Damadian, Dr. Larry Minkoff, and Dr. Michael Goldsmith, the MRI
uses nuclear magnetic resonance to stimulate protons inside the body to
giving off electromagnetic signals. At the MRI exam, the patient is placed
inside a large magnet, similar in shape to a CAT scanner, but larger. The
magnet spins to create its own magnetic field thirty thousand times stronger
than earth’s. Next the MRI emits radio waves to alter the
stable
orientation of the protons, when the radio waves stop the body gives off
electromagnetic transmissions. The MRI processes these signals into
internal pictures of the body. The average exam lasts between an hour and a
half to one hour, and it takes three to ten minutes to collect images for
each scan, compared to the first MRI on July 3, 1977, which took almost five
hours for one image.
The MRI has a greater contrast resolution than X-rays and CAT
scans. As it views soft tissue and emits no ionizing radiation, it is the
preferred technique for diagnosing problems in the central nervous system,
including the brain. It can also create “maps of biochemical compounds
within any cross-section of the human body”2, allowing for early
disease diagnosis. It is also very useful for looking at the structure of
the circulatory system.
What also sets the MRI apart from X-rays and CAT scans is its
safety. No radiation is involved in the making of MRI pictures. The only
risk comes from magnetic metals
inside the body, such as pacemakers, inner
ear transplants, and aneurysm clips in the brain. It is also not safe for
people who may have iron filings next to their eyes like sheet metal
workers, to get an MRI. Besides being dangerous, the metal gets in the way
of the radio waves and causes the image to be distorted. It is okay to get
a MRI if you have dental fillings, although bridgework sometimes causes
problems. Many new surgical implants are now made of non-magnetic stainless
steel. As the MRI machine spins, it makes a loud whirring noise, so
subjects are given ear plugs to protect their ears. Sometimes MRI patients
experience magnetophosphenes during the MRI exam. Magnetophosphenes are
“visual sensations of flashes of light in the retina…caused by induced
electric currents in the retina when moving through a static magnetic field,
or when stationary in any changing magnetic field.”3
Outside of the
medical field, magnetic resonance has several practical applications. It is
commonly used to study the flow and velocity of liquids and to study the
molecular structure of plastics and liquid crystals. In the pharmaceutical
industry magnetic resonance is used to analyze and identify new drugs. In
the pulp and paper industry, magnetic resonance helps to determine what
chemical treatments should be given to wood pulp samples. Dead and damaged
roots due to frost damage can be seen with the MRI weeks before the shoots
show any symptoms of damage. This application can lead to a better
understanding of root systems. Like X-rays and CAT scans, MRIs are also
useful for studying the characteristics of explosives, but on a molecular
level. Magnetic resonance is valuable to food sciences. With traditional
methods, measuring the water content-fat ratio in foods could take up to one
day; with MRIs measurements can be taken in one minute. An MRI also shows
scientists how freeze-thaw cycles affect produce. Technology is always
advancing, and in the future the MRI will become even more of a valuable
tool to these, and many more, industries.
