A compact cryosurgical apparatus for minimally invasive procedures

A new liquid-nitrogen-based apparatus for minimally invasive cryosurgery is presented. The cryoprobe was designed for application to breast tumors; however, it can be used for the treatment of other tumors. The cryoprobe has three major components, a cryoneedle, a thermal insulation shell, and a protective tube, which may be assembled as part of the operation. This special assembly keeps destruction to surrounding tissues due to cryoprobe penetration minimal, and allows accurate localization of the cryoprobe tip by means of stereotactic or needle-localization techniques. An alternative cryoprobe consists of a cryoneedle and a thermal insulation shell, which are rigidly connected. The liquid nitrogen supply system has two major components, an air-pressure source and a liquid nitrogen container, which are physically separated. This special configuration allows placement of the liquid nitrogen container adjacent to the cryotreated tissue and decreases the length of the cryoprobe feeding tube. In turn, heat losses to the surroundings are reduced, and therefore coolant consumption is reduced. The short feeding tube allows safe operation at low pressures. The small size of the apparatus makes it attractive for cryosurgical operations. It has been evaluated in gelatin solutions and in porcine skeletal muscle and liver. In-vivo results do not differ significantly from those obtained in gelatin solutions with regard to the dimensions of frozen regions. Using a three cryoprobe configuration, a frozen region with an average diameter of 50 mm and a length of 75 mm was obtained within 11 minutes. The thermal efficiency of that procedure was found to be 43%.