Star Wars Laser Makes Its Move Into Biomedical Research

THE VANDERBILT FREE ELECTRON LASER CENTER Vanderbilt University's Free Electron Laser Center was dedicated on April 16, 1992, with a commemorative lecture delivered by noted physicist Edward Teller, an outspoken proponent of the Strategic Defense Initiative. The FEL facility is a 13,000-square-foot building, which includes a subsurface vault with seven-foot-thick concrete walls for housing the radiation-producing laser. The laser light is sent upstairs to the research laboratories through a series of pipes and mirrors, according to university officials. In addition to a sterile surgical suite, the university has made tissue culture and animal care facilities available. By adjusting the energy of the electrons used to generate the laser light, the wavelength can be tuned between 2 and 10 micrometers, in the infrared part of the electromagnetic spectrum. In the future the center expects to have a far-infrared FEL, tunable between 50 and 200 micrometers. Vanderbilt was selected as the location for this center in competition against five rivals—a Harvard University-Massachusetts Institute of Technology consortium, Columbia University, Northwestern University, Baylor University, and the University of Utah. The free-electron laser itself was purchased as part of an $8.9 million contract from the Office of Naval Research, which administers the Medical Free Electron Laser program established by Congress in 1985. Vanderbilt also received a subsequent $5.7 million contract from Naval Research to support FEL research projects. The university paid for and supervised construction of the $2.6 million building, which houses the center. —SV With a new research program in the works—and a brand-new facility to house it—scientists at Vanderbilt University intend to see the free-electron laser (FEL), studied primarily in the past for its potential as a space-based defense against nuclear missiles, applied here on Earth as an effective tool in biomedical treatment and research. The site for the program—whose results could benefit investigators in both physical and life sciences—is the Free Electron Laser Center, dedicated in April at the Nashville, Tenn., school. By launching the new center, Vanderbilt joins three other United States institutions—Duke University, Stanford University, and the University of California, Santa Barbara—in possessing one of the complex and expensive lasers. In addition to the free-electron laser itself—housed underground to shield users from the radiation it emits—the Vanderbilt facility includes a medical suite for experimental surgery and laser target rooms for experiments in biology and materials science. The idea is to take the FEL out of the gritty world of physics research and make it available to researchers who require clean, sterile surroundings, say those who will be involved in the program. Charles Brau, director of the Vanderbilt center, says that the work on biomedical applications of FELs is just getting off the ground. But he is excited about the interesting cross-disciplinary collaborations this research is engendering. "The thing [about FEL research] that makes me the most optimistic is the research going on between disciplines," he says. One such interdisciplinary project involves development of monochromatic X-rays, which could deliver 50 times less radiation to a patient while producing the same image. Conventional X-ray machines emit a broad spectrum of photons, with many of the frequencies emitted increasing the dose of radiation while contributing nothing to the image. An FEL-driven X-ray beam would be a single wavelength; or, for greater detail, a combination of the most useful pure wavelengths could be used, says Brau. The basic free-electron laser beam is produced by accelerating electrons at 45 million electron volts and then passing them through a magnetic field designed to make them "wiggle." Because these highly energetic electrons are traveling at close to the speed of light, this oscillation forces them to emit photons at a specific wavelength—determined by the adjustable energy of the electron beam. To produce monochromatic X-rays, the laser beam is then directed to collide with the same high-energy electron beam, yielding monochromatic X-rays. This process is called backscatter doppler, according to Brau. Another application requiring cross-disciplinary cooperation is the work on computer-image-guided laser surgery, which has brought together researchers from Vanderbilt's neurosurgery and medical imaging departments, Brau says. Free-electron lasers have a couple of advantages over the standard chemical lasers used widely by physicians, physicists, and chemists—tunability over a broad range of wavelengths and variability of the strength and pulse shape of the beam, says Michael Marron, manager of the Medical Free Electron Laser (MFEL) program, a $20 million-a-year project within the Office of Naval Research, The MFEL program was established in 1985 by Congress as a way of spinning off a down-to-earth application of the FEL research being conducted under the Strategic Defense Initiative. The hundreds of millions of dollars spent on SDI re, search helped scientists develop an FEL that's more reliable than earlier versions. The Department of Defense is still spending $23 million per year on FEL development. But, because FELs require massive power sources, chemical lasers are closest to possible deployment as a space-based defense against ballistic missiles, according to SDI officials. But FELs still have a few significant drawbacks that have held up applications outside of defense and physical science research, says Marron. FELs are finicky, requiring a group of physicists to operate them; and they are expensive, at $5 million to build. "And it takes $2 million a year for the care and feeding before you get a single photon," Marron says. The FEL power source also emits quite a bit of radiation that requires extensive shielding, such as concrete-lined underground vaults. Marron says the MFEL budget has, in the past, gone toward building free-electron lasers at centers that are well shielded from radiation and that have the sort of biological research, animal care, and surgical facilities that provide an environment conducive to biomedical investigations. For the most part, the centers at Duke, Vanderbilt, Stanford, and UCSB have only recently become readily available to biomedical researchers. The next few years" will tell which applications of the FEL will really pay off in the biomedical arena, he says. Marron agrees with Vanderbilt's Brau that, so far, one of the big benefits of the MFEL program is the development of interdisciplinary teams. "Just by the nature of this program, there's no way a physician can deal with a free-electron laser without a competent physicist." However, that same physicist won't stand for being just a bright pair of hands for the physician, he says. Physicians are therapy- and application-oriented, says Marron. "The notion of investing years of research aimed at some of the basic biology is really foreign to them. But physicists are very much oriented to basic research," he says. The challenge comes in marrying these two divergent-paradigms. FEL centers bring them together, he says. Physicist John Madey, considered the father of the free-electron laser, developed the FEL back in the late 1960s when he was at Stanford. Madey continued to work at Stanford but recently moved himself and much of his equipment to Duke. While Madey regrets leaving his friends and colleagues out West, the reason for the move was simple economics, he says: Stanford wanted to raise the overhead charge for his center by $1.5 million a year, while Duke was offering to build him a new $6 million building—similar to the Vanderbilt facility—to house his lasers. Although he began his move in 1988, it's been only since January that his complex lasers have reliably been providing FEL beams for use by biomedical investigators. Among FEL projects at Duke are research in ophthalmic surgery and the use of a tightly focused X-ray beam to provide higher image resolution in sectioned tissue samples. Other work has focused on biochemistry, such as the studies into energy transport in proteins, taking advantage of the FEL's precise tunability in terms of wavelength and pulse duration (W. Fann et al., Physical Review Letters, 64:607-610, 1990). But Madey would like to expand the biomedical research at the Duke facility: "We're always happy to receive proposals from qualified users of the facility." With FEL centers just now becoming readily accessible to medical and biological researchers, Madey says it will be at least a couple of years before it becomes clear which applications of this laser will ultimately bear fruit. It may end up being an excellent tool for brain surgery, say, or it may wind up finding its widest applications as a basic research tool. "But for widespread applications you need to have a well-documented track record," he says. "Few people will be in the position to speculate on the prospects until the initial results roll in."

Star Wars Laser Makes Its Move Into Biomedical Research

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Scott Veggeberg

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July 1992

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