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Using
light under your skin
The days of the scalpel may soon
be numbered – at least when it comes to examining areas in the
upper layers of the skin.
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Physicist
Trude Støren tests OCT light waves on lumps of jelly
to find out how she can produce the best images of real skin
tissue later.
Contact: Trude Støren,
Department of Physics, NTNU
Tel: +47 73 59 34 26
Email:trude.storen@phys.ntnu.no |
| Photo: Rune Petter Ness |
You have a tiny wound on your hand that
doesn’t heal, a bad burn on your chest – or an injured
retina. Your doctor cannot tell how serious the injuries are below
the surface. He needs tissue samples. That means using a scalpel,
which again equals pain, perhaps even a risk. Soon there may be
hope for an improved and totally harmless method to peer under the
surface of the skin: light.
LIGHT’S ANSWER TO ULTRASOUND
For some time, doctors have had good techniques for seeing what
goes on inside our bodies. Xrays, magnetic fields and sound waves
are terrific techniques on their separate fields. However, they
all have their weaknesses – especially when it comes to creating
a satisfying image of what is happening right below the skin.
X-rays cannot reveal the early stages of
skin cancer. Magnetic fields do not show how deep the injuries are
under a burn. And sound wave measurement of our eyes cannot reproduce
the structures because the resolution is too poor. But light waves
may offer an alternative approach. The body contains a number of
structures that offer good contrasts when photographed with light.
For a long time, researchers have wondered
how light waves can enter the body and exit again in a functional
way. Now they appear to on the verge of a solution: a new imaging
technique in medical diagnostics, called Optical Coherence Tomography
(OCT).
PAINLESS AND HARMLESS
Say you have a wound on your arm that needs a more detailed examination.
With an OCT device, you would put your arm under the machine and
a beam of white light would be emitted towards your wound. The light
is reflected and collected by a detector that translates the information
into images. The images are displayed on a computer screen. They
show the structure of your skin, and a trained eye will be able
to distinguish damaged tissue from healthy tissue. This scenario
still lies in the future.
The device exists, but it is not yet ready
for clinical use. Most of our knowledge about OCT is still confined
to research laboratories worldwide. Several researchers are focusing
on measuring tissue structures, while Trude Støren, a research
fellow at NTNU, is working on collecting information about the tissues’
special characteristics.
“In Trondheim we are researching the
use of OCT in photodynamic cancer therapy. This method is already
being used. Our technology could improve this method,” says
the physicist.
Photodynamic therapy has yielded good results
in the treatment of skin cancer. First, an ointment containing light-sensitive
substances is rubbed on the skin, and after a while a lamp is directed
towards the area. When the substance is exposed to light, oxygen
is released and kills all cancer cells in the area. One of the challenges
thus far has been to determine exactly when to illuminate the substances.
The substances are gradually absorbed by
the skin, and they must be in the right location with respect to
the cancer tumour to be effective. This is where OCT comes into
the picture. Ms Støren is in her laboratory sending rays
of white light down into lumps of jelly with added colour. This
allows her to test how the light rays should be set, the quality
of images they provide at varying depths and the strength of the
radiation needed to provide the images she wants. However, skin
layers diffuse light differently, making them far more complicated
to photograph. But Trude Støren will not stop before she
succeeds.
NEW RANGES OF APPLICATION
OCT does not provide sharp and detailed images deeper than a few
millimetres, and is therefore best suited to photograph tissues
in the upper layers of the skin. However, the technique holds a
trump card in its hand: Light can easily be transmitted to clinical
imaging devices such as microscopes, fibre optic endoscopes, catheters
and needles. This quality presents a whole new world in which doctors
can examine everything from blood veins to bladders. Trude Støren
concludes: “The excitement of researching new methods is that
totally new application may appear.”
| OPTICAL
COHERENCE TOMOGRAPHY: |
| A focused beam
of white light is sent through a beam splitter. The light
is divided into two beams, with one beam directed to a reference
mirror and the other to the sample being studied – such
as your skin. Both are reflected back to the beam splitter,
which sends them to a detector where they interfere with each
other. The detector signal is collected by a computer, which
then translates the information into pictures that can be
interpreted.
Skin layers have different thicknesses. When light waves
are sent through the skin, they are reflected differently,
depending upon the tissue type. The reference mirror acts
to control how deeply into the tissue the light travels. When
the light wave has traveled to a depth equivalent to the depth
set by the reference mirror, the detector reacts and sends
a signal to the computer. The computer collects signals from
different depths and combines them to make a two-dimensional
image of the skin.
OCT technology was adapted from a technique originally used
to find faults in optical fibres. Medical research began studying
OCT in the early 1990s. SINTEF Trondheim has conducted research
with OCT since 1995, and Trude Støren, a PhD student
at NTNU, has worked with it since 1997. |
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