04 September 2009

Nuclear magnetic resonance


The invention: 

Procedure that uses hydrogen atoms in the human
body, strong electromagnets, radio waves, and detection equipment
to produce images of sections of the brain.

The people behind the invention:

Raymond Damadian (1936- ), an American physicist and
inventor
Paul C. Lauterbur (1929- ), an American chemist
Peter Mansfield (1933- ), a scientist at the University of
Nottingham, England



Peering into the Brain

Doctors have always wanted the ability to look into the skull and
see the human brain without harming the patient who is being examined.
Over the years, various attempts were made to achieve this
ability. At one time, the use of X rays, which were first used byWilhelm
Conrad Röntgen in 1895, seemed to be an option, but it was
found that X rays are absorbed by bone, so the skull made it impossible
to use X-ray technology to view the brain. The relatively recent
use of computed tomography (CT) scanning, a computer-assisted
imaging technology, made it possible to view sections of the head
and other areas of the body, but the technique requires that the part
of the body being “imaged,” or viewed, be subjected to a small
amount of radiation, thereby putting the patient at risk. Positron
emission tomography (PET) could also be used, but it requires that
small amounts of radiation be injected into the patient, which also
puts the patient at risk. Since the early 1940’s, however, a new technology
had been developing.
This technology, which appears to pose no risk to patients, is
called “nuclear magnetic resonance spectroscopy.” It was first used
to study the molecular structures of pure samples of chemicals. This
method developed until it could be used to follow one chemical as it
changed into another, and then another, in a living cell. By 1971,
Raymond Damadian had proposed that body images that were
more vivid and more useful than X rays could be produced by
means of nuclear magnetic resonance spectroscopy. In 1978, he
founded his own company, FONAR, which manufactured the scanners
that are necessary for the technique.

Magnetic Resonance Images

The first nuclear magnetic resonance images (MRIs) were published
by Paul Lauterbur in 1973. Although there seemed to be no
possibility that MRI could be harmful to patients, everyone involved
in MRI research was very cautious. In 1976, Peter Mansfield,
at the University of Nottingham, England, obtained an MRI of his
partner’s finger. The next year, Paul Bottomley, a member ofWaldo
Hinshaw’s research group at the same university, put his left wrist
into an experimental machine that the group had developed. A
vivid cross section that showed layers of skin, muscle, bone, muscle,
and skin, in that order, appeared on the machine’s monitor. Studies
with animals showed no apparent memory or other brain problems.
In 1978, Electrical and Musical Industries (EMI), a British corporate
pioneer in electronics that merged with Thorn in 1980, obtained the
first MRI of the human head. It took six minutes.
An MRI of the brain, or any other part of the body, is made possible
by the water content of the body. The gray matter of the brain
contains more water than the white matter does. The blood vessels
and the blood itself also have water contents that are different from
those of other parts of the brain. Therefore, the different structures
and areas of the brain can be seen clearly in an MRI. Bone contains
very little water, so it does not appear on the monitor. This is why
the skull and the backbone cause no interference when the brain or
the spinal cord is viewed.
Every water molecule contains two hydrogen atoms and one
oxygen atom. A strong electromagnetic field causes the hydrogen
molecules to line up like marchers in a parade. Radio waves can be
used to change the position of these parallel hydrogen molecules.
When the radio waves are discontinued, a small radio signal is
produced as the molecules return to their marching position. This
distinct radio signal is the basis for the production of the image on
a computer screen.
Hydrogen was selected for use in MRI work because it is very
abundant in the human body, it is part of the water molecule, and it
has the proper magnetic qualities. The nucleus of the hydrogen
atom consists of a single proton, a particle with a positive charge.
The signal from the hydrogen’s proton is comparatively strong.
There are several methods by which the radio signal from the
hydrogen atom can be converted into an image. Each method
uses a computer to create first a two-dimensional, then a threedimensional,
image.
Peter Mansfield’s team at the University of Nottingham holds
the patent for the slice-selection technique that makes it possible to
excite and image selectively a specific cross section of the brain or
any other part of the body. This is the key patent in MRI technology.
Damadian was granted a patent that described the use of two coils,
one to drive and one to pick up signals across selected portions of
the human body. EMI, the company that introduced the X-ray scanner
for CT images, developed a commercial prototype for the MRI.
The British Technology Group, a state-owned company that helps to
bring innovations to the marketplace, has sixteen separate MRIrelated
patents. Ten years after EMI produced the first image of the
human brain, patents and royalties were still being sorted out.


Consequences

MRI technology has revolutionized medical diagnosis, especially
in regard to the brain and the spinal cord. For example, in multiple
sclerosis, the loss of the covering on nerve cells can be detected. Tumors
can be identified accurately. The painless and noninvasive use
of MRI has almost completely replaced the myelogram, which involves
using a needle to inject dye into the spine.
Although there is every indication that the use of MRI is very
safe, there are some people who cannot benefit from this valuable
tool. Those whose bodies contain metal cannot be placed into the
MRI machine. No one instrument can meet everyone’s needs.
The development of MRI stands as an example of the interaction
of achievements in various fields of science. Fundamental physics,
biochemistry, physiology, electronic image reconstruction, advances
in superconducting wires, the development of computers, and ad-
vancements in anatomy all contributed to the development of MRI.
Its development is also the result of international efforts. Scientists
and laboratories in England and the United States pioneered the
technology, but contributions were also made by scientists in France,
Switzerland, and Scotland. This kind of interaction and cooperation
can only lead to greater understanding of the human brain.

See also:  Amniocentesis; CAT scanner; Electrocardiogram; Electroencephalogram;
Mammography;

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