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A diffusing applicator integrated with a balloon catheter has been developed to treat various types of stenosis [1,2]. To deliver uniform laser light to the tubular tissue, the balloon was inflated by inserting water. However, the residual air trapped in the balloon can cause non-uniform ablation in the tissue due to different thermal boundary conditions between air and water. The current study aims to evaluate optical and thermal effects of the air trap on cylindrical laser treatment on the tubular tissue. A balloon-integrated diffusing applicator was fabricated to deliver 532-nm laser light and to expand an ex vivo liver ductal tissue. The balloon was deflated by using a syringe and then inflated with water. Various numbers of deflations were tested for ex vivo experiments using porcine liver duct. For each deflation condition, the 532 nm laser light was delivered to the tissue at 10 W for 45 s. The liver tissue experienced more coagulation near the air trap region than the water-filled region. In spite of a significant decrease of the air volume in the balloon, at least two deflations were required to entail uniform tissue coagulation in a tubular structure and to avoid the unpredictable optical/thermal effects from the air trap. Further in vivo experiments will be performed to evaluate the effect of the air trap on chronic tissue responses after the cylindrical laser treatment for clinical translations.
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