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PROFESSOR’S
ROW
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Mastering the “Light Touch”
For Sergio Fantini, lasers can illuminate
our understanding and care of the body
Interview by Laura Ferguson
The word laser has such common currency today that few probably
realize it started out as an acronym: Light Amplification by
Stimulated Emission of Radiation. Invented in 1958 by A. L.
Schawlow and C. H. Townes, it was first considered a toy for
physicists. Today, from the proverbial laser gun of science
fiction movies to more controversial scenarios, lasers continue
to provoke the imagination. At Tufts, the applications are based
solidly in resolving complex problems and diagnostic challenges
confronted in medical care. In the newly established Department
of Biomedical Engineering, Assistant Professor Sergio Fantini
explores that frontier of therapeutic and diagnostic tools—how
light emitted by lasers can be used to cure diseases and to
look inside the body to identify potential medical problems.
A native of Italy, educated in Florence, and trained as a physicist,
he brings an inventive approach to this emerging field. He holds
several patents, including one for optical mammography, which
offers a new approach to the imaging of breast tumors.
What is the basic principle
of lasers?
There are unique features of laser light that cannot be found
in nature. Laser light has one single color; it’s monochromatic.
It moves in only one direction; it’s not diffuse. With
laser light you are amplifying the number of photons that make
up light but only in one particular direction and only in one
particular color. So you have highly focused optical energy.
If you turn on a 50-watt lightbulb you can be sure that you
are safe, but if you had a 50-watt laser beam it would drill
a hole in your skin.
What are the benefits
of lasers?
The main advantage of a laser-based instrument for medical diagnostics
is practical: it’s inexpensive, it may be packaged into
portable units and the light is perfectly safe. Also, it can
be applied noninvasively. It’s not painful and there are
no probes under the skin.
How does the light actually
illuminate?
We use red and near-infrared light, which penetrates deeply
into tissue; blue and green light will not. When you hold a
flashlight up to your hand, you see that red comes out; red
is not being absorbed because water and blood, two of the main
tissue constituents, are relatively transparent to red light.
The basic idea is that this light, once it is in the tissue,
is affected by the presence of hemoglobin, a protein in the
blood responsible for oxygen transportation. The color of blood
is different depending on its level of oxygenation: red blood
indicates it’s richly oxygenated. The key aspect here
is that we will see a difference in light transmission as oxygen
is exchanged from the blood to the tissue, thus obtaining a
measure of the balance between the oxygen supply and the oxygen
consumption, which is an indicator of the tissue viability.
So X rays look at density
of tissue but laser light is looking at a metabolic process.
Right, the process of oxygenation. Blood changes in color as
it becomes deoxygenated on its course through the body. In your
veins, for instance, where there is lower oxygenation than in
the arteries, the color of the blood appears blue. When you
cut yourself, the blood that comes out picks up oxygen from
the air and turns red.
What drew you to the
field of lasers?
I still remember a conversation that I had many years ago with
a salesperson who told me that a CD player uses laser light,
which, he said, “is essentially like confining all the
light in this room to a small point.” I was fascinated
by the idea, but I thought that there must have been a more
rigorous explanation of laser light. As a result, as a physics
student, I was attracted by the physics of lasers, which is
based on a number of elegant principles. Then, I was interested
in the applications of lasers in spectroscopy, and I used a
laser to study a new kind of superconductor. When I moved to
the University of Illinois at Urbana-Champaign in 1993, I started
working on medical applications of lasers, which I felt, and
still feel, have a truly outstanding potential and significant
societal importance.
What specifically are
you doing at Tufts?
I am involved with medical optics, which is using light to collect
diagnostic information with a potential for medical applications,
just as X rays gather information by using radiation. The practical
difference is that X rays are an ionizing radiation; the energy
applied is sufficient to separate the electrons from the atoms
and molecules. When this phenomenon affects water, a major component
of most living tissues, it results in the production of free
radicals, which in turn may induce harmful chemical modifications
in organic molecules. This introduces risk or the potential
for cancer.
More specifically, we are developing imaging techniques in three
areas. We study blood flow and oxygen metabolism of muscles
so we can look at the effect of exercise. We have found significant
differences between the response to exercise in normal subjects
and in patients affected by vascular diseases.
In the case of optical mammography, we know that breast cancer
is usually associated with a high concentration of blood vessels
and with high metabolic rate. We are trying to take advantage
of these features to develop an optical imaging technique that
uses this process to tell us more subtle information about what
is going on. X-ray mammography, the gold standard today, is
very effective in detecting the presence of cancer, but is ineffective
in discriminating cancer from other benign tumors. As a result,
many women without cancer have a biopsy and endure the emotional
reaction to being told that they have a suspicious mass in their
breast. So this is the main aspect that can be improved. While
more research is needed to identify the potential clinical role
of optical mammography, its sensitivity to the oxygenation level
of breast tumors may add significant physiological information
to the structural information provided by X-ray mammography.
With lasers we could determine more precisely the nature of
the tumor or mass.
We are also looking at blood-flow changes that are associated
with brain activity. Of course, brain activation is an electrical
signal, but we would like to understand better the coupling
between that electrical activity and the blood-flow response
to it, or neurovascular coupling. Today there are a number of
techniques that look at blood-flow changes (for instance, functional
magnetic resonance imaging) and other techniques, such as EEGs,
are sensitive only to electrical signals. There are now reports
that optical methods, in addition to being sensitive to blood-flow
changes, are sensitive also to electrical signals. If this is
confirmed, this feature would render optical imaging of the
brain an ideal technology for the study of neurovascular coupling.
What are your long-range
goals?
My goal is to introduce some of these optical techniques in
hospitals. That’s why it’s so important to have
collaborations with physicians who can contribute to research
and who understand that this technology may fill some gaps in
clinical practice. In optical mammography the gap is clear:
there is a lack of specificity for mammograms. I’m also
interested in the oxygenation of muscles. Dr. Ronenn Roubenoff,
a medical doctor with whom I have collaborated at the New England
Medical Center, referred to a number of muscle disorders that
are associated with areas of restricted blood flow and currently
the only way to identify the problem areas is with a biopsy.
But there is no precise guide for where to stick the needle.
It would be great to develop and refine this clinical application.
Your office wall is dominated
by a facsimile of Raphael’s “School of Athens.”
Do you ever wonder what Plato or Aristotle would make of your
work?
Not really. But there is one thing in that painting that reminds
me of the evolution of my scientific career. Plato points up
towards the world of ideas, while Aristotle—who was Plato’s
pupil—keeps his right hand down to indicate the world
of experience. This reminds me of my own intellectual development—from
physics, where I studied basic processes in nature, to biomedical
engineering, where I try to use scientific knowledge to realize
practical devices for everyday life applications. |
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