A new echographic cryoprobe for in vivo ultrasonic monitoring of skin cryosurgery

One of the main difficulties encountered in cryosurgery is the uncertainty in the extent and depth of the tissue effectively treated during the freezing process. Our objective was to evaluate ultrasonic control of skin cryosurgery using a new echographic cryoprobe in vivo. The echographic cryoprobe, developed specifically for dermatology applications, combines a high-frequency (20 MHz) miniature ultrasonic transducer and a N2O-driven closed-cryoprobe. The operation of the echographic cryoprobe was assessed, under in vivo conditions similar to those used in human therapeutics, on normal skin of 3 females "Large-White" pigs under anesthesia. The edge of the growing ice layer was successfully and reproducibly detected and located during the freezing process. The average rate of growth (10(-2) mm/s) of the iceball was found to be 12.2+/-1.0 (pig N-o 1), 9.0+/-1.0 (pig N-o 2), 8.4+/-0.9 (pig N-o 3). The echographic cryoprobe had a built-in high-frequency ultrasonic transducer that served two functions. It enabled in vivo real-time monitoring of depth penetration of the iceball: and gives important feedback to the operator or to the console relating to the sate of growth of the iceball. Automatic (i.e., operator-independent) detection of the echo signal from the freezing front and calculation of the depth penetration of the iceball was possible.