Cryoprobe

A method, comprising:

• providing a probe comprising a probe distal end having an external surface configured to contact tissue of a patient when the probe distal end is inserted therein;
• locating a heater in the probe distal end;
• locating a temperature sensor in the probe distal end;
• coupling a gas inlet to the probe distal end, wherein the gas inlet is configured to provide gas to the probe distal end;
• activating the heater, and, while the heater is activated:
• registering a first time when a temperature measured by the sensor equals or exceeds a preset temperature,
• in response to the temperature equaling or exceeding the preset temperature, delivering a pulse of gas through the gas inlet so as to cool the probe distal end,
• registering a second time, subsequent to the first time, when the temperature measured by the sensor equals or exceeds the preset temperature, and
• in response to a time difference between the second time and the first time, estimating a temperature of the external surface of the probe distal end.