Cryotherapy system

1. A computer-readable storage medium having a computer-readable program embodied therein for directing operation of a cryotherapy system including a plurality of cryoprobes, each such cryoprobe having a shaft with a closed distal end adapted for insertion into a body and conduits for flowing a cryogenic fluid through the shaft to reduce a temperature of the distal end, a source of the cryogenic fluid, a plurality of flow-control metering valves in fluid communication with the conduits of the plurality of cryoprobes and with the source of the cryogenic fluid, a compressor in fluid communication with the conduits of the plurality of cryoprobes to define a self-contained fluid system, and a computer processor, wherein the computer-readable program includes:

instructions for controlling the plurality of flow-control metering valves and the compressor to provide desired flows of the cryogenic fluid through the conduits of the self-contained fluid system and

instructions to control the compressor and the plurality of flow-control metering valves to provide an initial flow of the cryogenic fluid through the conduits of the cryoprobes under physical conditions near a critical point of a liquid-vapor system for the cryogenic fluid, wherein the critical point defines a point in a phase diagram of the liquid-vapor system where molar volumes are substantially equivalent for liquid and gas,

whereby vapor lock associated with freezing of the cryoprobes is avoided.

2. The computer-readable storage medium recited in claim 1 wherein the self-contained fluid system is an open-loop system.

3. The computer-readable storage medium recited in claim 1 wherein the self-contained fluid system is a closed-loop system.

4. The computer-readable medium recited in claim 1 wherein:

the cryogenic fluid is a gas;

each such cryoprobe further has a heat exchanger disposed within the shaft in thermal communication with the conduits of such cryoprobe and has a Joule-Thomson port disposed in the distal end of the shaft in thermal communication With the heat exchanger; and

the computer-readable program further has instructions for controlling operation of each of the Joule-Thomson ports.

5. The computer-readable storage medium recited in claim 1 wherein:

the cryogenic fluid is a liquid; and

the computer-readable program further has instructions for controlling the compressor and plurality of flow-control metering valves to provide an initial flow of the liquid through the conduits of the cryoprobes under physical conditions near a critical point of a liquid-vapor system for the liquid,

whereby vapor lock associated with freezing of the cryoprobes is avoided.

6. The computer-readable storage medium recited in claim 5 wherein the computer-readable program further has instructions for controlling the compressor and plurality of flow-control metering valves to reduce a pressure of the liquid in the cryoprobes, whereby colder liquid temperatures may be maintained without vapor lock after the initial flow is established.

7. The computer-readable storage medium recited in claim 1 wherein the computer-readable program further has instructions for determining the desired flows from predefined imaging parameters.

8. The computer-readable storage medium recited in claim 1 wherein:

each of the plurality of cryoprobes further has a plurality of multifunction electrical wires; and

the computer-readable program further has instructions for monitoring the operation of the multifunction electrical wires.