A Palm-Sized Cryoprobe System With a Built-In Thermocouple and Its Application in an Animal Model of Epilepsy

Objective: The purpose of this study is to propose a palm-sized cryoprobe system with a built-in thermocouple (TC) for highly accurate and sensitive temperature measurements, and to verify the effectiveness of the system. Methods: Conventional cryoprobe systems based on the boiling effect of a refrigerant have triple coaxial tubes. In the proposed system, the outer and middle coaxial tubes are made of two different metals that are welded only at the probe tip, thereby forming a TC. The thermoelectric properties of the built-in TC and measurement accuracy were investigated in agar in a constant-temperature chamber. The system was also applied in a penicillin G-induced rat brain epilepsy model. Results: We verified that the built-in TC has appropriate thermoelectric properties and that the system more accurately and sensitively measured transient temperature changes at the probe tip wall compared to conventional systems, showing the cooling performance of the system. In the rat model, epileptiform activities disappeared on freezing, and reliable cell necrosis was achieved at an end temperature of -45.2 ± 1.6 °C. Conclusions: The proposed system is suitable for reliable cryosurgery. Significance: The system is probably to be valuable for clarifying the relationship between freezing temperature and cell necrosis in vivo.

I. Introduction

Cryosurgery is an alternative surgical technique for resection and is mainly applied to tumors [2]. Compared with conventional resection, cryosurgery has advantages of being a less-invasive and simple procedure [2], [3]. Since Arnott's initial study [4], numerous cryoprobe systems and techniques have been described [5]. In terms of the extreme freezing power, most cryosurgeons prefer the boiling effect to the powerful freezing technique [6].