Fracture Formation Around a 1.3 mm Cryosurgical Probe

with Thermal Insulation – Low Cooling Rate

Biothermal Technology Laboratory

Department of Mechanical Engineering

Carnegie Mellon University

Objective

To demonstrate fracture formation around a cryosurgical probe.

Methods

A prototype of a proprietary cryoprobe is applied in water. The cryoprobe is constructed as a U-shape heat exchanger with a sharp pointed tip. The cryoprobe is cooled with liquid nitrogen, supplied from a hand-held container, and pressurized with compressed air.

Observations and Comments

1.  Due to the slow cooling rate, no significant fracture formation is observed during cooling. Some minor fractures are observed during cooling, around the cryoprobe tip.

2. Fractures always form within seconds from the beginning of rewarming (natural thawing – slow rewarming rate).

3. 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 stopped at 6:10

Liquid nitrogen flow stopped at 6:10