Enhancing the Efficacy of Noncontact Laser Ablation of Weakly Absorbing Cholesteatoma Tissue Using a Blood Layer

Abstract

Objectives: The 445 nm diode lasers have already been used successfully and safely for cholesteatoma surgery. However, the ablation of low absorbing and strongly scattering anemic tissue, such as keratinizing squamous epithelium of the cholesteatoma becomes challenging with low laser power. The initiation of ablation often occurs abruptly and not reproducibly with a noticeable acceleration after the start of carbonization. This study investigates whether a thin layer of blood on an adequate tissue model can improve light absorption and ablation. Materials and Methods: Porcine aortic tissue served as a model for pale, weakly absorbing tissue. Blood volumes of 2.5–110 μL were pipetted onto punch samples with a diameter of 12 mm. Tissue ablation was performed with a 445 nm diode laser at continuous wave powers of 1 W and 4 W at working distances of 1 mm and 2 mm to the distal tip of the transmitting multimode optical fiber, being moved with a speed of 5 mm/s across the tissue. Ablation depths and blood layer thicknesses were measured using optical coherence tomography (OCT). A theoretical model was used to estimate the optimal amount of blood to achieve the deepest ablation. Results: Different blood layer thicknesses were examined, ranging from 17 μm to 1.3 mm. With the blood layer thickness of 50–100 μm the maximum ablation depth of approximately 370 μm was measured with a power of 4 W. Without blood, no ablation was achieved. However, it could be shown that the optimal blood layer thickness depended on the selected parameters, such as laser power and working distance. The experimental results closely matched model predictions, confirming the model's validity in estimating the ablation outcomes. Conclusion: A thin blood layer enhances laser ablation of low-absorbing tissue with 445 nm laser radiation, such as cholesteatoma, allowing precise tissue removal.