Dissolution of pulmonary carcinoma via argon-laser bronchoscopy. First clinical use of fiberoptic metal cautery cap heated by laser radiation

Determination of temperature and residual laser energy on film fiber-optic thermal converter for diode laser surgery

BACKGROUND

The diode laser was utilized in soft tissue incision of oral surgery based on the photothermic effect. The contradiction between the ablation efficiency and the thermal damage has always been in diode laser surgery, due to low absorption of its radiation in the near infrared region by biological tissues. Fiber-optic thermal converters (FOTCs) were used to improve efficiency for diode laser surgery. The purpose of this study was to determine the photothermic effect by the temperature and residual laser energy on film FOTCs.

METHODS

The film FOTC was made by a distal end of optical fiber impacting on paper. The external surface of the converter is covered by a film contained amorphous carbon. The diode laser with 810 nm worked at the different rated power of 1.0 W, 1.5 W, 2.0 W, 3.0 W, 4.0 W, 5.0 W, 6.0 W, 7.0 W, 8.0 W in continuous wave (CW)and pulse mode. The temperature of the distal end of optical fiber was recorded and the power of the residual laser energy from the film FOTC was measured synchronously. The temperature, residual power and the output power were analyzed by linear or exponential regression model and Pearson correlations analysis.

RESULTS

The residual power has good linearity versus output power in CW and pulse modes (R² = 0.963, P < 0.01 for both). The temperature on film FOTCs increases exponentially with adjusted R² = 0.959 in continuous wave mode, while in pulsed mode with adjusted R² = 0.934. The temperature was elevated up to about 210 °C and eventually to be a stable state. Film FOTCs centralized approximately 50% of laser energy on the fiber tip both in CW and pulsed mode while limiting the ability of the laser light to interact directly with target tissue.

CONCLUSIONS

Film FOTCs can concentrate part of laser energy transferred to heat on distal end of optical fiber, which have the feasibility of improving efficiency and reducing thermal damage of deep tissue.

Highly Nd3+-doped Y3Al5O12 crystal fiber tip for laser thermotherapy

Based on phonon relaxation, a 12-at. % neodymium-doped YAG (Y3AlrO12) crystal fiber tip has been developed for photothermal conversion. The near-cylindrical tip, with an average diameter of 0.68 mm and a length of 1.8 mm, is fabricated on a 0.65-mm-thick 220-mm-long pure YAG single-crystal fiber by laser-heated growth. Pumped by an 810-nm wavelength diode laser with a pump power of less than 2 W, the temperatures of the tip reach 725 degrees C in air, 78 degrees C in egg white, and 79 degrees C in porcine liver, with acceptable reproducibilities and thermal response times. The photothermal conversion efficiency of the doped tip is approximately 89%, and the high stability of the tip is also proved. Experimental results show that the doped fiber tip is promising for laser thermotherapy applications.

Laser applications in the trachea and bronchi: a comparative study of the soft tissue effects using contact and noncontact delivery systems

A comparative study of laser soft tissue effects using carbon dioxide (CO2) and neodymium-yttrium aluminum garnet (Nd-YAG) lasers in contact and noncontact endoscopic delivery systems was done in the canine tracheobronchial tree to determine the best laser system for the specific disease. The CO2 laser bronchoscopic coupler, CO2 laser waveguide, Nd-YAG laser fiber, and Nd-YAG laser contact probe were used. A 5 mm diameter soft tissue injury exposing tracheal cartilage was made, and the power density for each laser modality was measured. Soft tissue effects were documented histologically using routine techniques and scanning electron microscopy acutely and at 1 week and 2 weeks after injury. The effects were similar with the CO2 laser coupler and the CO2 laser waveguide with comparable power densities. Compared with the CO2 laser, the Nd-YAG laser fiber caused more extensive and more difficult to control thermal damage in tissue. The Nd-YAG laser contact probe was capable of precise soft tissue ablation with minimal surrounding tissue damage and was associated with the most rapid healing. This study concluded that high power density with short exposures is desirable when treating benign disorders, such as tracheal stenosis, making the CO2 laser or Nd-YAG laser contact probe application a good choice. On the other hand, malignant tumors with a potential for hemorrhage are best treated with the Nd-YAG laser noncontact fiber system because of its superior coagulative effects.