The free-electron laser's "Star Wars" legacy as a detect
and destroy system in the discarded Strategic Defense Initiative of the
1980s has been refocused on a new adversary closer to home- cancer.
"When we first proposed using the FEL this way, even the Star Wars
people thought our idea was too far out," says Frank E. Carroll,
a breast cancer specialist at the Vanderbilt University Medical Center Department
of Radiology and a researcher at the FEL Center.
"Now," Carroll says with a smile, "they think our project
may be the first medical application of the FEL to be approved for widespread
use." Carroll and his colleagues are using the FEL to develop a new
kind of x-ray they hope will vastly improve doctors' ability to detect and
treat cancer and other conditions.
Carroll's research grew out of his frustration with mammography, the technique
currently used to detect breast cancer. "I've been reading mammograms
for decades, and I still feel like I'm standing in quicksand when I do it,"
Carroll says. "We find a lot of things, but we miss a lot of them,
too."
The problem, Carroll explains, is that standard x-ray tubes bombard patients
with a wide spectrum of x-rays. At one end of that spectrum are the so-called
"soft" rays. These barely penetrate skin or tissue and thus do
not produce an image on x-ray film at all. At the other end of the spectrum
are a much "harder" variety of x-ray. During a standard mammogram,
these rays hit tissue and bounce wildly before registering on the x-ray
film, creating a fog that can obscure tumors. Between these two extremes
lies a frequency of x-ray that is perfectly suited to medical imaging, a
type of ray that passes through tissue and registers on x-ray film with
little or no scattering to fog up the image.
Using the FEL and a phenomenon known as Compton backscatter, Carroll and
his colleagues have found a way to generate an x-ray beam that can be tuned
to produce only those mid-spectrum x-rays that yield the clearest images.
Although thorough testing of this beam is not set to begin until January,
preliminary trials on tissue samples have shown great promise.
"When we use this beam, cancers absorb about 11 percent more x-rays
than normal tissues," Carroll says. "Normally in radiology, if
we can get a one percent difference we're jumping for joy. With 11 percent,
the cancers just stand out like headlights."
What's more, because the monochromatic beam uses only a fraction of the
number of x-rays produced by traditional radiology, it exposes patients
to 10 times less radiation than current x-ray technology.
But that's only the beginning. Working in collaboration with scientists
at the Lawrence Livermore, Los Alamos and Oak Ridge national laboratories,
Carroll and his colleagues are also studying ways to use the FEL to produce
two even more sophisticated types of medical imaging.
The first, known as time-of-flight imaging, would produce the same pristine
pictures achieved with the monochromatic x-ray beam, but would subject a
patient to 10 times less radiation - that's 100 times less radiation than
produced by current technology. The still more sophisticated technique of
phase imaging would use a similarly low dose of radiation to produce images
of body tissues that standard x-ray machines cannot even "see,"
offering doctors 100 to 1,000 times more information about patients than
currently available.
Although Carroll's project began with a goal of improving the safety and
effectiveness of mammography, the list of medical applications that may
be possible once the monochromatic x-ray beam is perfected continues to
grow. For example: