Cryoprobe

Abstract

Apparatus, consisting of a probe with a probe distal end having an external surface that contacts tissue when the distal end is inserted into a patient. A heater and a temperature sensor are in the distal end, and a gas inlet is coupled to the distal end to provide gas. While the heater is activated, a controller registers a first time when a temperature measured by the sensor equals or exceeds a preset temperature, and, in response to the temperature equaling or exceeding the preset temperature, delivers a gas pulse through the gas inlet so as to cool the probe distal end. The controller then registers a second time when the temperature measured by the sensor equals or exceeds the preset temperature, and, in response to a time difference between the second and first times, estimates a temperature of the external surface of the probe distal end.