A new cryosurgical device for controlled freezing.

A new cryosurgical device was developed in this study to facilitate examination of factors affecting the outcome of cryotreatment. Special emphasis was placed on the control of the cooling rate at the freezing front. In the new computer-controlled cryosurgical device, the controlling variable is the cryoprobe temperature, which is calculated to ensure prespecified cooling rates at the freezing front. Details of the new cryodevice, results of a validation test, and the system characteristics are presented in Part I of this study. In this part of the study initial results of 13 in vivo experimental cryotreatments, including histological observations, are presented. The in vivo pilot investigations include the normal, healthy skin and the underlying skeletal muscle of the thighs in rabbits. Using low cooling rate-controlled freezing, the new cryosurgical device is demonstrated here as an effective surgical tool. An in vivo temperature measurement technique is employed based on miniature thermocouples and X-ray images. Thermal analysis of the heat transfer in the cryotreated tissue is presented, based on the temperature measurements and on numerical heat transfer simulations. Cryotreated tissue was extracted either immediately or 4 or 7 days following the procedure. The histological observations on the skeletal muscle of the 4- and 7-day postcryoinjury were not substantially different. The effective penetration depth of the cryolesion was in the range of 5-15 mm, possibly extending up to 25 mm, depending on the specific area treated and operating parameters. The cryotreatment resulted in complete destruction of cells in the skin followed by rapid replacement by epithelial cells. Histological responses to cryotreatment of skeletal muscle were similar to those resulting from a range of traumatic episodes, e.g., crush damage. It was also found that most of the blood vessels in the cryotreated region remained intact without histological evidence of extravasation of erythrocytes.