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Fracture Formation Around Three 2.2 mm Cryosurgical Probes
Biothermal Technology Laboratory Department of Mechanical Engineering Carnegie Mellon University
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To demonstrate fracture formation around three cryosurgical probes.
Methods A setup of three prototype cryoprobes is applied in water. Each cryoprobe is constructed as a U-shape heat exchanger with a sharp pointed tip. The cryoprobes are simultaneously cooled with liquid nitrogen, supplied from a hand-held container, and pressurized with compressed air.
Observations and Comments 1. Fractures tend to form during cooling as well as during natural rewarming, however the rate of fracture formation is much more dramatic during rewarming – fractures always form within seconds from the beginning of rewarming. 2. During cryosurgery, results may differ from the current demonstration in water due to the fact that tissue freezing occurs over a significant temperature range, while pure water freezes at a unique temperature. Nevertheless, fracture formation in biological tissues is expected to be qualitatively consistent with the current demonstration.
Cryoprobe tube diameter = 1.3 mm Beaker diameter = 85 mm Two freezing periods separated by a 10 seconds interval of no liquid nitrogen flow. Elapsed time in is shown on each photo (min:sec).
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Period I: Liquid nitrogen flow started at 00:00
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Period I: Liquid nitrogen flow continues
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Period I: Liquid nitrogen flow stopped at 10:00
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Period I: Liquid nitrogen flow stopped at 10:00
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Period II: Liquid nitrogen flow restarted at 10:10
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Period II: Liquid nitrogen flow stopped at 15:00
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Period II: Liquid nitrogen flow stopped at 15:00
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Period II: Liquid nitrogen flow stopped at 15:00
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