Complications in Equine Surgery. Группа авторов. Читать онлайн. Newlib. NEWLIB.NET

Автор: Группа авторов
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Биология
Год издания: 0
isbn: 9781119190158
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id="ulink_e2d59229-6447-5b60-b4cd-d2c574e49df0">Laser Physics and Tissue Interaction

Photo depicts wavelengths of surgical lasers. Wavelengths in common veterinary use are in gray. The surgical lasers are generally not in the visible range. graph depicts tissue absorption common surgical laser wavelengths. The visible spectrum is shown on the horizontal axis. The near-infrared GAA Diode and Nd:YAG lasers are highly absorbed by dark pigment. However, note the increased absorption of the GAA Diode laser on the water curve compared to the Nd:YAG laser. The Ho:YAG and CO2 lasers are both highly absorbed by water. equation Power density profoundly affects rate of tissue effect and collateral heating of tissue. Both water hoses transmit identical flows of water. The wider aperture of delivery in the top image produces no mechanical effect on the flower, whereas the narrower aperture in the lower image produces a jet of water that can disrupt the flower.

      Source: Kenneth E. Sullins.

Photo depicts power density decreases with the square of the increase in spot size, which in turn increases with distance from the surface. The beams depicted are all CO2 laser beams from machines set to 50 W. The power densities shown below each demonstrate the profound reduction in tissue effect by increasing spot size. Moving the handpiece away from the tissue increases spot size and decreases power density.

      Delivering identical power density values over different periods of time produces different results. If an acceptable full‐thickness skin incision could be created with a 10‐W laser beam delivered as a 0.4‐mm spot size advanced along the skin for 5 sec just penetrating the skin completely, doubling the rate of advancement (total time halved), the incision would be shallower because the total laser energy (fluence) has been halved. Conversely, if the original time were doubled (advancement slowed), the depth of the incision would increase beyond the skin and damaging collateral heating of adjacent skin would increase. Furthermore, varying spot size or increasing distance from tissue dramatically changes power density. Using a single power setting, the power density (tissue effect) can regress from focal incision/ablation (vaporization) to coagulation to negligible by simply moving the delivery device away from the tissue surface. This is described further below under Carbon Dioxide Laser [2].

Photo depicts cO2 laser handpiece with focusing lens. The stylus indicates the point of maximum focus (power density) for incision. Slight increase of distance widens the spot size and tissue can still be vaporized. More distance from the tissue further increases the spot size and reduces the effect on tissue to coagulation.