Biothermal Technology Laboratory

Fracture Formation Around Three 1.3 mm

Cryosurgical Probes

Department of Mechanical Engineering

Carnegie Mellon University

Objective

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. Due to the large size of the frozen region, the latter effect has not been demonstrated visually. However, audio recording of fracture formation indicates a high rate of fractures at 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 = 65 mm

One freeze\thaw cycle.

Elapsed time in is shown on each photo (min:sec).

Liquid nitrogen flow started

Liquid nitrogen flow continues

Liquid nitrogen flow stopped at 14:55