Biothermal Technology Laboratory

Fracture Formation Around a 2.2 mm Cryosurgical Probe

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. Fractures tend to form during cooling as well as during natural rewarming.

2. Compared with fracture formation around smaller diameter cryoprobes, the tendency to fracture increases with the increase in the diameter of the cryoprobe. Note that the cooling rate in this large diameter probe is about 800°C/min (~15 sec to -190°C!), which can explain the high tendency to fracture.

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 = 2.2 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 8:40