Measurement Of Thermal Properties Of Biological Tissue For Bipolar Electrosurgical Modality

The surgery methods that dealing with lesions using thermal energy arebecoming more widespread in clinical medicine, but the potential thermal damageto the adjacent tissue and nerve is still the problem which needs to be further solved.Vessel sealing is one of advanced surgical technique in bipolar electrosurgery,which disposes tissue using electrothermal energy. However, the existing data ofbiological tissue thermophysical property is little, and the study on vessel thermalproperties in bipolar electrosurgical mode is even more rarely reported, which leadto lacking comprehensive understanding of the heat transfer mechanism, and it isdifficult to accurately predict the temperature distribution in vascular closureoperations. To understand the heat transfer mechanism of vascular tissue in bipolarelectrosurgical modality, this work investigates the thermophysical properties ofvascular tissue utilizing self-made system for measurement thermal properties ofbiological tissue.At first, the design for the module of the system that measurement thermalproperties of biological tissue is completed based on the analysis of the biologicaltissue transfer model, testing methods and its principle, and theresistance-temperature characteristics and volt-ampere characteristics of theselected NTC thermistors are mainly analyzed; specifications of the system fortesting thermal properties of biological tissue are determined, which laying thefoundation for the design of the circuit of the test system follow-up tests.Secondly, testing system based on step-temperature approach is fabricated. Thefabricated system includes a data acquisition and control, AD/DA conversion anddata processing module, and a temperature rise≤3℃can be achieved for thefabricated thermistor probe. The effective radius and the effective thermalconductivity of the probe with the thermistor are calculated. A correction for thedesigned system is completed, which makes the measurement error of the testsystem is less than3%after correction. Finally, the thermal properties of the isolated bovine vascular tissue aremeasured using the calibration system. The thermal conductivity of0.4602W/mk,thermal diffusion rate of5.132×10-7m2/s at25℃is calculated. The effects of thedifferent water content, compression rates and different temperature on the thermalconductivity and thermal diffusivity of the blood vessels are studied. The functionsbetween various experimental parameters and thermal conductivity are fitted out. Itis found that the thermal conductivity is significantly influenced by the watercontent of vascular tissue, and then is temperature, and the compression ratio is thesmallest.This study verified the feasibility of the developed test system, laid thefoundation for further studies of thermal conduction mechanisms of the bipolarvessel sealing and temperature field simulation.