the scalpel with a beam of purest light
David F. Salisbury
Oct. 9, 2001
Trek's doctor, Leonard McCoy, would approve. In the popular science
fiction series McCoy routinely used lasers for surgery and would
shudder at the thought of using something as crude and unhygienic
as a scalpel. So the good doctor would no doubt applaud the fact
that researchers and surgeons at Vanderbilt's Keck Free-Electron
Laser Center are laying the groundwork for eventually replacing
the scalpel with laser light in both brain and eye surgery.
course, not just any laser light will do. Conventional lasers are
finding growing applications in medical practice. Researchers have
tried to use them for brain surgery in the past, but they largely
abandoned the effort because the amount of collateral damage to
surrounding tissue is too great and in neurosurgery a fraction of
a millimeter can spell the difference between success and failure.
At the same time, the extreme delicacy of the eye has kept it one
of the least accessible areas of the body.
the existence of a radically new kind of laser, called a free-electron
laser (FEL), promises to transform both brain and eye surgery. Unlike
conventional lasers that produce light at set wavelengths, the FEL
beam can be tuned through a wide spectrum of colors. That has allowed
researchers to find the optimal wavelength for cutting cleanly through
living tissue. In addition, the FEL is extremely powerful. Although
some conventional lasers produce light in the 1 to 10 micron
range, as does the Vanderbilt FEL, they do not produce light intense
enough for surgery. In addition, the FEL produces laser light in
a series of billionth-of-a-second pulses. In the case of surgery,
these pulses act something like the teeth on a saw to cut through
tissue particularly cleanly and effectively.
the past seven years Vanderbilt researchers have discovered that
an FEL beam with a precise wavelength of 6.45 microns can slice
through soft tissue with less collateral damage than the sharpest
steel scalpel. The scientists still don't know exactly why infrared
light of this specific wavelength works so well, but its effectiveness
has been well documented in a series of experiments with animal
and human tissue that culminated in the free-electron laser's first
use in a human surgery in December 1999.
brain tumors with a beam of light
Copeland-a former Vanderbilt neurosurgeon now in private practice
in Kansas City, Missouri-was the first doctor to use the FEL beam
on a patient, Virginia Whitaker, 78, who is also from Kansas City.
The operation was conducted according to a protocol
designed to be the safest possible test of the FEL beam's capabilities.
Whitaker had a tumor of a type that can be removed using traditional
methods with a high success rate. Copeland
opened the skull using traditional techniques. He only used the
laser to remove
a sugar-cube-sized amount of tissue from the center of the tumor
mass. The rest of the golf-ball-sized tumor was removed using conventional
methods. Examination of the tumor showed that the laser beam removed
tissue with only one to three cell layers of collateral damage.
efforts to use the FEL beam as a surgical scalpel centered on a
shorter wavelength near 3 microns, but they failed. The researchers
picked 3 microns because it was one that is absorbed readily by
water molecules, but they discovered that it worked too well, creating
microscopic steam explosions and excessive heat that damaged surrounding
1993 Vanderbilt biophysicist Glenn Edwards
got the idea of trying wavelengths around 6.4 microns, a wavelength
absorbed both by water and many protein molecules. A number of his
colleagues didn't think the idea had much merit, but Edwards persisted.
"It seemed more relevant to focus on the absorption of laser
light by the proteins in soft tissue
rather than water," he said.
making some basic measurements and doing some back-of-the-envelope
calculations, Edwards and Vanderbilt ophthalmologist Regan Logan
tried the beam on some corneal tissue. It drilled a perfect hole.
"We looked at it in disbelief. I had never before had an experiment
work the first time," he said.
and Logan invited a number of other scientists to test the technique,
including Michael Copeland. They conducted a number of experiments
on a variety of tissues and found that wavelengths near 6.45 microns
were optimal for cutting all soft tissues. Since then other researchers
have found two wavelengths7.5 and 7.7 micronsthat cut
through bone particularly cleanly.
led a research effort that confirmed that 6.45 microns worked just
as well with brain tissue as it does with other kinds of soft tissue.
His goal is to use the laser beam to vaporize brain tumors completely
while minimizing the damage to healthy brain tissue. In the operation
on Mrs. Whitaker and two follow-up operations over the following
year and a half, he found that the laser beam worked "beautifully,
just the way that we expected."
the future, neurosurgeons working with the laser hope to use it
with a computer-assisted guidance system that will allow them to
safely remove small brain tumors near vital nerves and arteries
that are too risky to cut out with conventional techniques.
the hidden area behind the eye
after the second brain surgery, another team of surgeons began testing
the FEL beam's usefulness for eye surgery. Here the issues are slightly
different. The extreme delicacy of the eye makes the area behind
it one of the most difficult parts of the body to treat. "It
is one place we haven't visited yet," says Denis O'Day ,
who was involved in early studies that applied the FEL to ophthalmology,
"and this approach has the potential to take us there."
of the experimental nature of the procedure, the initial eye surgery
on a human was performed on a patient
with end-stage traumatic glaucoma who was having the eye removed.
The operation was performed by Assistant Professors of Ophthalmology
Karen Joos and Louise Mawn. First, the surgeons rotated the eye
in the socket to expose the optic nerve using the well-established
procedure of detaching a muscle on one side of the eye .
Second, they cut a tiny flap in the optic nerve sheath using the
laser beam. Finally, they removed the entire eye.
cutting the optic nerve sheath is used to treat a condition called
pseudotumor cerebri, a relatively common neurological illness among
young, obese women. A build-up of cerebral-spinal fluid in the optic
nerve causes blurred vision, headaches and even loss of vision.
Because pseudotumor cerebri occurs eight times more frequently in
young women than in young men, scientists suspect that hormones
play a role, but little is known about its cause. Surgery is called
for when the condition does not respond to dietetic and medical
treatment. Cutting a small opening in the sheath surrounding the
optic nerve relieves the pressure build-up, preventing further vision
loss and, in some cases, even restoring lost vision.
a traditional surgeon, so I was very skeptical when I was first
confronted with the idea of using a laser for this kind of an operation,"
admits Mawn." After trying it out several times on animals,
however, I became convinced that this is a better, safer and more
is particularly impressed by the fact that the laser beam can be
focused to a much smaller size than a scalpel or scissors, allowing
it to be handled more precisely. In the case of the operation on
the optic nerve sheath, the FEL has an additional advantage: a microscopic
layer of fluid between the nerve and sheath dissipates the heat
of the laser and so provides an extra layer of protection for the
delicate nerve fibers.
operation was performed with a special, curved probe that was designed
by research assistant professor Jin H. Shen. The procedure was based
on several years of basic scientific research. As part of this effort,
Joos worked closely with Vivien Casagrande, professor of cell biology,
psychology and ophthalmology. They compared the cutting characteristics
of the FEL beam with those of conventional surgical methods on a
number of different animal species. The studies included a detailed
analysis of the biological response of the nerve cells to these
injuries and their effects on visual function. This preliminary
research has now been confirmed by six operations following the
same basic protocol.
process of rotating the eye in the socket is technically difficult
and carries a high degree of risk. The eye surgeons think that they
can avoid these complications by combining the FEL probe with an
endoscope, a slender optical instrument that allows the user to
see parts of the body that are ordinarily hidden from view. According
to Joos, they have developed such a combined probe, which is only
1.5 millimeters thick ,
and have been using it in animals to evaluate its effectiveness
for treating conditions like congenital glaucoma. In a paper published
in the Journal of Glaucoma, for example, they report using this
method to treat congenital glaucoma. The combination endoscope/laser
allowed them to locate and cut open the eye's natural drainage areas
located around the outside rim of the iris even when they were hidden
beneath an opaque cornea.
effort to develop an orbital endoscope was made in the 1970s, but
was abandoned because there was no way to control bleeding if it
started behind the eye, the researchers say. Combining the instrument
with an FEL beam, however, could overcome this obstacle. For one
thing, the laser beam does not appear to cause as much bleeding
as mechanical cutting. Also, its smaller size and precise handling
allows surgeons to avoid disrupting even very small blood vessels.
surprising thing about these operations," summarizes center
director David Piston ,
"is that there have been absolutely no surprises. The laser
beam has performed exactly as predicted."
of their size, cost and complexity, no one expects free-electron
lasers to begin showing up in hospitals in the foreseeable future.
But once researchers have identified the specific characteristics
that make the FEL so effective at cutting tissue and bone, it should
be possible to design special purpose lasers that replicate these
characteristics. These devices would be much smaller, simpler and
less expensive and so could ultimately replace the steel scalpel
with beams of pure light.