How lasers cut flesh
Lasers might be at the cutting edge of surgery, but scientists still don't know much about how laser lights interact with living tissue. Now, researchers at Vanderbilt University have investigated how ultraviolet lasers are cutting living tissues. As you could have guessed, 'the effect that powerful lasers have on actual flesh varies both with the wavelength, or color, of the light and the duration of the pulses that they produce.' But the real finding of these researchers is that lasers cut flesh by creating a series of overlapping micro-explosions. This might improve procedures such as LASIK eye surgery or even brain surgery.
This study has been conducted by Shane Hutson, an assistant professor of physics at Vanderbilt University with the help of post-doctoral student Xiaoyan Ma, a member of his Biophotonics Lab. You can see above a photo of Shane Huston in his laboratory (Credit: Daniel Dubois/Vanderbilt University). And here is a link to a presentation featuring other images.
Huston and Ma discovered that there were two basic ways to cut living tissues with lasers with pulse lengths of a millionth of a second or less.
- "Mid-infrared lasers with long wavelengths cut by burning. That is, they heat up the tissue to the point where the chemical bonds holding it together break down. Because they automatically cauterize the cuts that they make, infrared lasers are used frequently for surgery in areas where there is a lot of bleeding."
- "Shorter wavelength lasers in the near-infrared, visible and ultraviolet range cut by an entirely different mechanism. They create a series of micro-explosions that break the molecules apart. During each laser pulse, high-intensity light at the laser focus creates an electrically-charged gas known as a plasma. At the end of each laser pulse, the plasma collapses and the energy released produces the micro-explosions. As a result, these lasers -- particularly the ultraviolet ones -- can cut more precisely and produce less collateral damage than mid-infrared lasers. That is why they are being used for eye surgery, delicate brain surgery and microsurgery."
As said Huston, "This is the first study that looks at the plasma dynamics of ultraviolet lasers in living tissue," who added "The subject has been extensively studied in water and, because biological systems are overwhelmingly water by weight, you would expect it to behave in the same fashion. However, we found a surprising number of differences." Two of these differences involved the the elasticity, or stretchiness, of tissue, and the origination of the individual plasma "bubbles."
This research work has been published in Physical Review Letters under the name "Plasma and Cavitation Dynamics during Pulsed Laser Microsurgery in vivo" (Volume 99, Number 15, Article 158104, October 12, 2007). Here is a link to the abstract which clearly explains the differences mentioned above. "We compare the plasma and cavitation dynamics underlying pulsed laser microsurgery in water and in fruit fly embryos (in vivo) -- specifically for nanosecond pulses at 355 and 532 nm. We find two key differences. First, the plasma-formation thresholds are lower in vivo --especially at 355 nm -- due to the presence of endogenous chromophores that serve as additional sources for plasma seed electrons. Second, the biological matrix constrains the growth of laser-induced cavitation bubbles. Both effects reduce the disrupted region in vivo when compared to extrapolations from measurements in water." Finally, here is another link to the full paper (PDF format, 9 pages, 171 KB).
Sources: Vanderbilt University news release, via EurekAlert!, October 25, 2007; and various websites
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