Thermal Feedback Control during Laser-Assisted Tissue Welding

Laser assisted tissue welding (LTW) has been investigated at several institutions as a surgical tool to improve the anastomosis of severed blood vessels, nerves and a variety of hollow organs. LTW can provide immediate fluid-tight sealing and achieve successful anastomosis rates comparable to conventional suture techniques. It has also been reported to reduce foreign-body reaction associated with healing around sutures and to preserve the mechanical integrity of the "weld" site in the long run. However, extensive training is required to form reproducibly successful bonds with laser irradiation. Temporal profiles in photothermally treated tissue not only depend on laser irradiation parameters but also the optical and thermal properties of tissue being irradiated. Within the scope of this dissertation, the influences of dehydration, thermal damage and freezing on the optical properties of tissue in vitro are investigated. A well tested thermal model for laser tissue interaction is studied using measured optical properties. Temperature predictions are compared to tissue temperatures obtained through thermographic imaging. The discrepancies between predictions are examined and principles of closed loop thermal feedback control for LTW are described. The development of an experimental device for thermal feedback control during LTW is presented. A thermally/optically co-aligned experimental device is designed and tested in in vitro studies. The results with the initial design are evaluated and an improved design is implemented. The improved device is tested in in vivo studies. Finally, accomplishments and implications of the presented work are discussed.