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

November 1, 2019

Tatsuji TokiwaLev ZiminHiroshi IshiguroTakao InoueHiroshi KajigayaSadahiro NomuraMichiyasu SuzukiTakeshi Yamakawa

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

We have studied a palm-sized cryoprobe system and showed that cryosurgery may be an effective treatment for epilepsy. Conventional cryoprobe systems have triple coaxial tubes. Since accurate temperature measurement of the probe tip is indispensable for reliable treatment of cryosurgery, a wired thermocouple is attached externally using adhesive. However, because the adhesive creates thermal resistance between the thermocouple and the external surface, the temperature measurement accuracy deteriorates.

To cope with this problem, the outer and middle coaxial tubes are made of two different metals that are welded only at the probe tip, thereby forming a thermocouple. As a result, the proposed system has a built-in thermocouple that requires no adhesive. This concept is widely applicable to the measurement of the tip temperature of equipment composed of two or more metal pipes. Since the built-in thermocouple at the operative field is leadless, there is no concern of wear or disconnection of wiring during surgery.

To evaluate and verify the effectiveness of the proposed system, the thermoelectric properties and measurement accuracy were investigated in agar. The system was also applied in a penicillin G-induced rat brain epilepsy model.

We verified that the built-in thermocouple has appropriate thermoelectric properties and that the system more accurately and sensitively measured temperature changes at the probe tip compared to conventional systems. In the rat model, epileptiform activities disappeared on freezing and reliable cell necrosis was achieved at an end temperature of −45.2 ± 1.6 ºC. The measured temperature is the same as the temperature of the cell close to the probe tip, which gives reliable information on cell necrosis that has not been obtained with conventional systems. The system is suitable for reliable cryosurgery and is probably to be valuable for clarifying the relationship between freezing temperature and cell necrosis in vivo.

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