Feasibility test of a sapphire cryoprobe with optical monitoring of tissue freezing

This article describes a sapphire cryoprobe as a promising solution to the significant problem of modern cryosurgery that is the monitoring of tissue freezing. This probe consists of a sapphire rod manufactured by the edge‐defined film‐fed growth technique from Al2O3 melt and optical fibers accommodated inside the rod and connected to the source and the detector. The probe's design enables detection of spatially resolved diffuse reflected intensities of tissue optical response, which are used for the estimation of tissue freezing depth. The current type of the 12.5‐mm diameter sapphire probe cooled down by the liquid nitrogen assumes a superficial cryoablation. The experimental test made by using a gelatin‐intralipid tissue phantom shows the feasibility of such concept, revealing the capabilities of monitoring the freezing depth up to 10 mm by the particular instrumentation realization of the probe. This justifies a potential of sapphire‐based instruments aided by optical diagnosis in modern cryosurgery. We propose a sapphire cryoprobe that enables cryoablation and monitoring of tissue freezing. The design of the probe allows combining it with optically based methods of tissue state analysis. The reconstruction of the freezing depth is provided by the detection of spatially resolved diffuse reflected intensities of tissue optical response. The feasibility test shows the possibility of the sapphire probe to reconstruct the freezing depth in a gelatin‐intralipid phantom up to 10 mm.