title: Influence of fibers and wavelengths on the mechanism of action of endovenous laser ablation.
abstract: OBJECTIVE
  This study aimed to investigate the different mechanisms involved in the use of bare, radial, and two-ring fibers, operating at 980- or 1470-nm wavelengths, by analyzing the histological changes caused to irradiated human great saphenous veins (GSVs).
  
  
  METHODS
  GSVs were removed by invaginated stripping and were prepared for irradiation. Irradiation was performed using bare, radial, and two-ring fibers, combined with 980- and 1470-nm laser wavelengths, operating at powers of 6 to 12 W. The fibers moved through the GSVs at a speed of 1 mm/s. The circumferences of the irradiated veins were measured, and the histological changes were examined.
  
  
  RESULTS
  The use of the bare fibers resulted in an average shrinkage ratio that increased with increasing laser power, regardless of the wavelength. Microscopic changes were heterogeneous and included carbonization and ulceration at the side where the heated fiber tip contacted the vessel wall, and sparse low-temperature changes were evident more distant from the fiber, regardless of the wavelength of the laser used. Using radial or two-ring fibers, the thermal changes were circumferentially uniform, but the shrinkage ratio and microscopic changes varied according to the laser wavelength combined. With the 1470-nm laser, the average shrinkage ratio did not vary significantly between different outputs. Mid-temperature changes were spread across the intima and superficial layer of the media, without causing carbonization. With the 980-nm laser, the average shrinkage ratio increased depending on the output. Conducted heat caused carbonization of the superficial part of the intima, with a thin layer of additional mid-temperature changes. Although adhesion of the hot fiber to the vessel wall was an annoying phenomenon during endovenous laser ablation and occurred frequently in the radial-1470 experiments, it rarely occurred in the two-ring-1470 experiments.
  
  
  CONCLUSIONS
  Using bare fibers, direct contact between the unevenly placed heated tip and the vessel wall results in heterogeneous heating of the vein. Radial and two-ring fibers, combined with 1470-nm light, can heat vessel walls circumferentially and uniformly with the laser light emitted radially penetrating into the vessel wall. Regarding the longitudinal uniformity, two-ring fibers provide a greater uniformity with a reduced incidence of sticking.
authors.affiliation: Sakata Vein Clinic, Osaka City, Japan. Electronic address: takashiyamamoto@hotmail.com.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: Sakata Vein Clinic, Osaka City, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Sakata