Mid-infrared lasers for endoscopic surgery. A new class of surgical lasers

Unlike the Nd:YAG, the CO2 laser produces well circumscribed tissue removal with little unwanted damage because of its high absorption coefficient relative to tissue water. Unfortunately, conventional quartz fibers cannot transmit wavelengths greater than three microns, well below the ten micron wavelength of the CO2 laser. Thus, fiberoptic transmission of CO2 laser requires use of exotic materials that lack the excellent properties of quartz fibers and that, in some cases, are toxic or chemically unstable. However, there are large peaks in the infrared absorption curve of water in the two to three micron region. Lasers that operate in this mid-infrared region should permit CO2-like precision of cutting, along with excellent transmission through quartz fiberoptics. Two mid-infrared lasers with a fiberoptic delivery system, the Er:YAG (2.94 micron) and the Tm-Ho-Cr:YAG (2.15 micron) have been evaluated with human colon tissue in vitro and with rabbit gastric tissue in vivo. Histologic sections reveal excellently well localized lesions with minimal underlying thermal damage. Depth of penetration is controllable and occurs in very small increments. There is little spreading of the lesions at the 24 hour mark resulting from secondary thermal damage. Based on these facts, the authors think that these lasers will be of benefit to endoscopic surgeons.