The use of CT in monitoring cryosurgery

One of the main problems encountered in cryosurgery is that of controlling the amount of tissue that is irreversibly destroyed by cooling. In vitro-experiments in which the homogeneous cooling of various substances, as well as "ice-ball" propagation within different tissues of animals via a cryotip were evaluated. In vivo experiments, on an anaesthetized pig, indicate CT to be a useful continuous-monitoring technique with a high spatial resolution. Using CT simultaneous localization of pathological tissue and measurement of temperature distribution is possible. The density changes induced by cooling were visualized on CT and the corresponding temperature changes were measured using thermocouples. The greatest decrease in density was observed as a change of phase took place. The speed of ice-ball propagation as well as the diameter of the ice ball generated varied considerably depending on the type of tissue. Construction of cryoprobes of a very small diameter could facilitate the percutaneous treatment of lesions within the body.