Apparatus, consisting of a probe having a distal end that is configured to be inserted into contact with tissue. An electrode is attached to the distal end, and there is a temperature sensor incorporated in the distal end and configured to output a temperature signal. A radiofrequency (RF) signal generator is configured to apply a pulse of RF electrical energy via the electrode to the tissue, so as to heat the tissue. The apparatus includes processing circuitry that is configured to compute, based on the temperature signal, a rate of temperature change of the distal end following termination of the pulse, and to estimate a thickness of the tissue in response to the rate of temperature change.
