Considerations during clinical operation of two commercially available cryomachines.

BACKGROUND AND OBJECTIVES: Advances in the technology of cryomachines in the last 10 years have led to the development of both liquid nitrogen and argon-based Joule-Thompson cryomachines. Theoretical and practical evaluation of the CMS Accuprobe and the ENDOcare CRYOcare was performed as respective examples of these technologies. METHODS: Thermal gradients were calculated about both probes for the best case scenario of probe surface temperature equaling that of the cryogen used. Also, experimental evaluation in gelatin phantoms was performed with five probe arrays. RESULTS: Theoretically, a liquid nitrogen-cooled probe provides only a slight advantage over one cooled with liquid argon. However, the experimental performance evaluation demonstrated that the CRYOcare system creates an iceball faster with steeper internal temperature gradients than the Accuprobe. Further, temperature outputs from the Accuprobe were shown to be in error, likely due to the position of the thermocouple within the probe. CONCLUSIONS: Cryomachine performance is determined more by technological innovations than by cryogen temperature. Thermocouple monitoring is urged for users of the Accuprobe.