X-Message-Number: 14613
From: "Igor Artyuhov" <>
Subject: Injections of Glycerol Make Tissue Temporarily Transparent
Date: Wed, 4 Oct 2000 12:16:43 +0400

Source:
http://www.utexas.edu/admin/opa/news/00newsreleases/nr_200008/nr_tissue00082
1.html
http://www.newswise.com/articles/2000/8/TISSUE.TXA.html

Title:
Making Tissue Temporarily Transparent

University of Texas, Austin
22-Aug-00

Library: SCI
Keywords: BIOMEDICAL ENGINEERING UT AUSTIN TISSUE LASER SURGERY
Description: By manipulating the way light passes through tissue, a
biomedical engineering team at The University of Texas at Austin has made
tiny bits of flesh transparent for brief periods of time in the lab.


By manipulating the way light passes through tissue, a biomedical
engineering research team at The University of Texas at Austin has taken a
step toward what was once the realm of science fiction. The researchers have
made tiny bits of flesh transparent for brief periods of time in the lab.

In effect, the engineers temporarily can create a window of tissue, allowing
doctors to see up to five times deeper than they can at present. Although it
has not yet been tested on human skin, the engineers say the process could
have wide applications for medical diagnosis and new therapies.

Using injections of substances such as glycerol, the UT Austin researchers
have succeeded in making small areas of rat or hamster skin nearly
transparent for a period of 20 minutes or more. Glycerol is hygroscopic
alcohol, which means it pulls water out of tissue. Glycerol often is used in
cosmetics and for medical applications.

Dr. Ashley J. Welch, a professor of biomedical engineering and chief
investigator on the project, said: "When we injected glycerol into the skin
of a hamster, we could actually see a blood vessel which had not been
visible." Welch is the Marion E. Foreman Centennial Professor in
Engineering.

If the procedure works on human tissue, it has the potential to lead to
improvements in a variety of diagnostic and therapeutic medical procedures
ranging from laser surgery to the treatment of tumors, Welch said. At
present, therapeutic procedures that depend on accurately focusing lasers on
a particular area -- such as retinal surgery and the accurate targeting of
tumors and other laser surgeries -- are limited by the fact that a beam of
light cannot pass directly through overlying tissue, Welch explained.

The new process has to do with refraction -- or the fact that light is
scattered as it moves through skin.

Welch explained that the optical process could be compared to searching for
an object obscured by a dense fog. When a searchlight is directed at the
fog, the light is scattered in all directions, creating a glow about the
remnants of the light beam.

The degree of light scattering depends upon the size of the small water
droplets and their index of refraction relative to the index of refraction
of the surrounding air, Welch said.

Just as each water droplet in the fog scatters light, so small components of
tissue also scatter light. This can be demonstrated by placing a penlight
against the thin tissue between the fingers.

"This scattering prevents us from seeing blood vessels near the surface of
the skin, because none of the light passes directly through the skin to
reflect from the blood vessel back to our eyes. It is all multiply
scattered, destroying the image," Welch explained.

Light travels straight through transparent objects because they have similar
or identical degrees of refraction throughout, Welch explained. Different
components in skin and tissue scatter or refract light differently, and that
is why skin and tissue are opaque.

Glycerol briefly can change the degree of scattering through small areas of
tissue by two different mechanisms. First, glycerol shrinks tissue because
of an outflow of water. When glycerol is added to cells, the imbalance in
pressure causes water to flow from the cell. Glycerol enters at a slower
rate. Over time, the process reverses and water begins to enter the cell
again. Researchers believe the shrinkage may bring certain tissue
components, such as collagen fibers, closer together, modifying the way
light is scattered.

Secondly, it changes the optical composition of tissue because the glycerol
that replaces the water within the tissue has an index of refraction that
matches tissue components such as collagen.

The discovery was made by two graduate students at UT Austin's College of
Engineering. They are Dr. Eric Chan, currently employed by Indigo Medical in
Cleveland, Ohio, and Dr. Jennifer Barton, currently an assistant professor
of biomedical engineering at the University of Arizona.

Doctoral candidate Gracie Vargas is continuing the research. UT Austin has
applied for a patent of the process. This peer-reviewed research is
supported by grants from the National Science Foundation, the Texas Higher
Education Coordinating Board Advance Research Program, and the Albert W. and
Clemmie A. Caster Foundation.

Researchers said the next step would be to study various other agents, which
may have similar effects on tissue, looking for the safest agents to use.
The effects of glycerol and other agents will be studied on different types
of tissue. Scientists also wish to learn more details of the processes by
which tissue can become optically clear as well as medical applications of
these processes.

For more information, contact Dr. Ashley J. Welch at (512) 471-1453 or Becky
Rische at the College of Engineering at (512) 471-7272. For black and white
images, contact The University of Texas Office of Public Affairs (512)
471-3151.

# # #

I wonder what concentration of glycerol is needed to make tissues
transparent?
How do they avoid side effects?

Igor Artyuhov.

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